ShipCo Notes - Phase 1 MMD

Phase-1 – SHIP CONSTRUCTION

Brackets: Brackets: A triangular plate, commonly with a reinforcing flange, used to connect two members; used to stiffen stiff en or tie beam angles to bulkheads, frames to longitudinals, etc. Girders: A Girders: A girder is a longitudinal member used in the construction of the bottom or the deck of a ship. They can be solid or not and can be placed above the keel (centre girder) or spaced equal distances from it (side girders). They can be continuous or divided by floor sections (intercostal side girders). The centre girder is always one continuous piece and must be fastened to the keel with a continuous weld. Girders must extend as far as possible from the forward to the aft end of a ship. The frames, frames, which are the ribs of the ship, serve to give the ship its form and at the same time support and stiffen the shell plating. They are fastened at the bottom to the outer ends of the floors fl oors by brackets and at the top to the deck beams. Floor – – A vertical athwartships athwartships member in way of the double-bottom. double-bottom. It will run from the center girder out to t he margin plate on either side of the vessel. There are two types of floors – solid floors and open / bracket floors.

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Compiled by: prodyut mukherji

Margin plate – plate – a fore and aft plate sited at the turn of the bilge. The upper edge is normally flanged to allow connection to the tank top plating, while the opposite end is secured to the inside of the shell plate by an angle-bar connection. Strake: A Strake: A for & aft row of shell or other plating. Sheer strake – strake – the continuous row of shell plates on a level with the uppermost continuous deck on both port and stbd sides. Breast hook hook - A triangular shaped plate fitted parallel to and between decks or side stringers, in the bow, for rigidly fastening together the peak frames, stem and shell plating; also used in conjunction with abov e duties to fasten the ends of side stringers firmly together. Bulkhead (longitudinal) (longitudinal) - A partition wall of plating running in a fore and aft direction. Bulkhead (transverse) (transverse) - A partition wall of plating running in an athwartship direction across the whole breadth of a ship. Intercostals Intercostals - Plates which fit between floors, frames, or beams, as stiffeners. Stringer A fore & aft aft member used to give longitudinal strength, made m ade of angle bar, bulb angle angle channel or plates, etc. Depending upon their locations, stringers are known as bilge stringers, side stringers, hole stringers, etc. Beam: An Beam: An athwartship member supporting a portion of a deck. Stiffener: An Stiffener: An angle bar, T – bar, channel etc, used to stiffen plating of a bulkhead or other member. Stealer Plate:- to reduce the number of strakes at the bow, two strakes are tapered and joined at their ends by a single plate known as a stealer plate.[ strakes that exist amidships (where the ship has greater girth) but have been eliminated at the bow and stern to reduce the amount of plating] Pillar: A Pillar: A vertical memberor column which provides support to a deck girder. Coaming: The Coaming: The vertical boundary of a hatch or skylight.

PLAIN OR FLAT W ATER-TIGHT BULKHEADS: BULKHEADS: The plating of a flat transverse bulkhead is generally welded in horizontal strakes. It has always been the practice to use horizontal strakes of plating since the plate thickness increases with depth below the top of the bulkhead. The reason for this is that the plate thickness is directly related to the pressure exerted by the head of water when a compartment on one side of the bulkhead is flooded. Apart from the depth, the plate thickness is also influenced by the supporting stiffener spacing.   

Vertical stiffeners are fitted to the transverse watertight bulkheads of a ship; the stiffeners stiffeners are generally vertical bulb bulb plates spaced 760mm apart. in case of collision collisi on bulkheads and oil tight bulkheads it is spaced 610mm apart.

Stiffening is usually in the form of welded inverted ordinary angle bars, or offset bulb plates, the size of the stiffener being dependent on the unsupported length, stiffener spacing, and rigidity of the end connections. Rigidity of the end connections will depend on the form of end connection, stiffeners in holds being bracketed or simply directly welded to the tank top or underside of deck, whilst upper tween stiffeners need not have any connection at all.

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PLAIN BULKHEAD

CORRUGATED BULKHEAD

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b/t : b/t : not to exceed 70 at bottom, 85 at top

Swedged and corrugated bulkheads - the swedges like the troughs of a corrugated bulkhead being so designed and spaced as to provide sufficient rigidity to the plate bulkhead in order that conventional stiffeners may be dispensed with - A corrugated plate is stronger than a flat plate if subject to a bending moment or pillar load along the corrugations. Both swedges and corrugations are arranged in the vertical direction like the stiffeners on transverse and short l ongitudinal ongitudinal pillar bulkheads. Since the plating is swedged or corrugated prior to i ts fabrication, the bulkhead will be plated vertically with a uniform thickness equivalent to that required at the base of the bulkhead. This implies that the actual plating will be somewhat heavier than that for a conventional bulkhead, and this will to a large extent offset any saving in weight gained by not fitting stiffeners. The angle of corrugation is normally about 45 degrees. The troughs are vertical on transverse bulkheads but must be horizontal on continuous longitudinal bulkheads, which form part of the longitudinal strength of the ship. Diaphragm plates or horizontal stringers are fitted on the bulkhead to keep the corrugation in place. At the lower end of transverse hold bulkheads in bulk carriers a bulkhead stool is generally fitted (see Figure beside) at the lower end of the bulkhead. This provides a shedder surface for cargo removal rather than a tight corner at the bulkhead/tank top interface. . Diaphragm plates or horizontal stringers are fitted on the bulkhead to keep the corrugation in place and prevent a concertina style collapse collapse of the corrugation.

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Following are the types of bulkheads: bulkheads: Flat Bulkhead Corrugated Bulkhead Bulkh ead Longitudinal Bulkhead Transverse Bulkhead. Watertight Waterti ght Bulkhead Non-Watertight Non-Waterti ght Bulkhead Fire Class A Bulkhead Fire Class B Bulkhead Fire Class C Bulkhead Collision Collisi on Bulkhead. Insulated bulkhead

FUNCTIONS OF BULKHEADS 1. Bulkheads divide the main hull into different compartments and in the event of a damage to the shell plating bulkheads limit the extend of flooding a nd hence of loss of bu oyancy.

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2. Bulkheads also prevent spread of fire from one compartment to another. 3. Transverse bulkhead prevents racking and torsional distortion on a ship. 4. Longitudinal bulkheads contribute to the longitudinal strength of the ship. 5. Bulkheads divide the main hull of a ship i nto different compartments such as the aft peak t ank,engine room, cargo holds, deep tanks, cofferdam space, and the fore peak ta nk.

Transverse watertight bulkheads divide the main hull into many different watertight compartments. Watertight bulkheads are attached to the shell, the deck, and the bottom or tank top by welding. Non watertight bulkheads are any other types of bulkhead which are non water tight such as centreline wash bulkhead in the peak tanks, partial bulkheads in the accommodation spaces, stores and cargo holds. The minimum number of transverse watertight bulkheads that must be fitted in a dry cargo ship are stipulated: o

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a collision or fore peak tank bulkhead - Classifi Classification cation societies require the location for ships whose length does not exceed 200 m as not less than 5% and not greater than 8% of the ship’s length (Lloyd’s length) from the fore end of the load waterline. A minimum distance of 10 meters may also be specified to ensure that the bulkhead is effective. Where there is a bulbous bow or any other structure extending forward of the forward perpendicular, the above distance shall be measured from a position: 1. at the midlength of such extension, or 2. at a distance of 1.5 % of the ship’s length forward of the forward perpendicular, or 3. at a distance of 3 mtrs forward of the forward perpendicular, whichever from the above is aft. As a rule this bulkhead bulkhead is fitted at the minimum minimum distance in order to gain gain the maximum length for cargo cargo stowage. The collision bulkhead is 12% thicker than other watertight bulkheads. an aft peak tank bulkhead - The aft peak bulkhead is intended to enclose the stern tubes in a watertight watertig ht compartment, preventing any emergency from leakage where the propeller shafts pierce the hull. It is located well aft so that the peak when flooded would not cause excessive trim by the stern. a bulkhead bulkhead at each end of the engine room - Machinery bulkheads provide a self-contained self-co ntained compartment compartment for engines and boilers, preventing damage to these vital components of the ship by flooding in an adjacent hold. They also localize any fire originating originating in these spaces.

As the size increases increases the classification society will recommend recommend additional additional bulkheads, bulkheads, partly to provide provide greater greater transverse strength, and also to increase the amount of subdivision. The table below indicates the number of watertight bulkheads recommended by Lloyd’s Register for any cargo ship. These should be spaced at uniform intervals, but the shipowner may require for a certain trade a longer hold, which is permitted if additional approved transverse stiffening is provided.

Number of Bulkheads for a cargo ship Length of ship Engine room mid-ship <90 m 4 90 – 105 m 5 105 – 115 m 6 115 – 125 m 6 125 – 140 m 7 140 – 165 m 8 165 – 190 m 9 > 190 m = to be considered on a case to case basis.

Engine room aft 3 4 5 5 6 7 8

TESTING OF BULKHEADS Both the collision bulkhead, as the fore peak bulkhead, and the aft peak bulkhead, provided they do not form the boundaries of tanks, are to be tested by filling the peaks with water to the level of the load waterline. All bulkheads, unless they form the boundaries of a tank that is regularly subject to a head of liquid, are hose tested to 2.0 bar

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pressure at a distance of not less than 1.5 m. Oiltight and tank bulkheads must be tested by a head of water not less than 2.45 m above the highest point of the tank. Piercings through watertight bulkheads: Where plate insert pads are used, bolted connections shall have threads tapped into the plate to a depth of not less than the diameter of the bolt. If welded, the pipe or flange shall be welded to both sides of the plating. Openings in structure through which pipes pass shall be reinforced where necessary. Flanges shall not be bolted to bulkheads so that the plate forms a part of the joint. Wash Bulkheads: It Bulkheads: It is a longitudinal non-water tight bulkhead installed in the liquid tanks of a ship. It is a nonwatertight, longitudinal, divisional bulkhead usually erected on the centre line of deep tanks and peak tanks, to prevent the fuel/water etc, from sloshing from side to side and thus reduce free surface effect. The peak tanks are generally really narrow at the bottom and the wash bulkheads installed in them need not be constructed but a few feet down from the tank top. They should be strongly built to withstand the flow of liquid caused by the motion of the ship. Racking stresses: When stresses: When a ship is rolling, the deck tends to move laterally relative to the bottom structure, and the shell on one side t o move vertically relative to the other side. This t ype of deformation is referred to as ‘racking’. Transverse bulkheads primarily resist such transverse deformation, the side frames’ contribution being insignificant provided the transverse bulkheads are at their usual regular spacings. Where transverse bulkheads are widely spaced, deep web frames and beams may be introduced to compensate.

Water tight doors: In order to maintain the efficiency of a watertight bulkhead bulkhead it is desirable that it remains intact. However, in some instances it becomes necessary to provide access between compartments on either side of a watertight bulkhead and watertight doors are fitted for this purpose. A particular example of this in cargo ships is the direct means of access required between the engine room and the shaft tunnel. In passenger ships watertight doors are more frequently found where they allow passengers to pass between one point of the accommodation and another. Requirements: Where a doorway is cut in the lower part of a watertight bulkhead care must be taken to maintain maintai n the strength of the bulkhead. The opening is to be framed and reinforced if the vertical stiffeners are cut in way of of the opening. If the stiffener stiffe ner spacing is increased to accommodate the opening, the scantlings of the stiff stiffeners eners on either side of the opening are increased to give an equivalent strength to that of an unpierced bulkhead. The actual opening is kept as small as possible, the access to the shaft tunnel being about 1000–1250 mm high and about 700 mm wide.( In passenger accommodation the openings would obviously be somewhat larger.) Mild steel or cast steel watertight watertight doors fitted fit ted below below the waterline waterlin e are either of the vertical or horizontal sliding type.( A swinging hinged type of door could prove impossible to close in the event of flooding and is not permitted.) The sliding sliding door must be capable of of operation when the ship is listed 15°. 

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To be opened or closed from the vicinity of the door as well well as from a remote position above the bulkhead deck. At the remote control position an indicator must be provided to show whether whether the door is open or closed. Vertical sliding doors may be closed by a vertical vertic al screw thread, which is turned by a shaft extending above above the bulkhead and fitted with a crank handle. (This screw thread turns in a gunmetal nut attached to the top of the door,) . A crank handle is also provided at the door to allow it to be closed from this position. positi on. Often horizontal sliding doors are fitted, and these may have a vertical vertic al shaft extending above the bulkhead deck, which may be operated by hand from above the deck or at the door. The doors can also be power driven driv en by an electric motor and worm gear, the vertical verti cal shaft shaft working through bevel wheels, and horizontal screwed shafts turning in bronze nuts on the door. The horizontal sliding door may also be opened and closed by a hydraulic ram with a hydraulic hand pump and with control at the door and above the bulkhead deck (see Figure). With the larger number of watertight doors fitted fitt ed in passenger ships the doors may be closed by means of of hydraulic power actuated by remote control from a central position above the bulkhead deck.

Doors which are normally closed at sea but are not provided with remote operation shall be marked “to be kept closed at sea” on both sides of the door. Doors which are to be permanently kept closed at sea should be marked “not to be opened at sea”. Hinged watertight doors may be fitted to watertight bulkheads in passenger ships, above decks which are 2.2 m or more above the load waterline. Simil ar doors are fitted in cargo ships to weather deck openings, which are required to be watertight. The doors are secured by clips which may be fitted to the door or to the frame. The clips are f orced against brass wedges. The hinges must be fitted with gunmetal pins. Some suitable packing is fitted round the door to ensure that it is watertight. The figure shows the hinge and clip for a hinged door, six clips being fitted to the frame.

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A watertight door preven prevents ts the passage passage of water when when exposed, exposed, for a prolonged prolonged period of tim e, to a head of water. A typical head of water for a ship could range from 3-10 metres. This refers to structures that must withstand hydrostatic loading for extended periods of time; They are meant to contain the spread of water that enters the hull as a result of hull breach due to collision, grounding, etc. Watertight doors are tested using a pressure tank where a hydrostatic pressure can be applied to the door. The door is generally pressurised form the inside as this is worst case scenario. A weathertight weathertight door is designed designed to be located located on the deck deck of a ship/boat ship/boat above the waterline, waterline, where where they can be subject to the adverse weather conditions experienced offshore. Weathertight doors are also designed to withstand brief submersion experienced from green seas. This means a weathertight door can withstand a small head of water (generally no higher than the height of the door). A weathertight door is generally tested with a high pressure hose, which is directed at the seal. Watertight doors drills on ships 1. Drills for the operation of watertight doors shall take place every week. Also the doors should be checked before leaving the port. 2. All watertight doors, both hinged and power operated should be operated daily during the rounds. 3. The door should be able to operate from both local and remote places. I.e. bridge and ship control centre. 4. If door is operated from remote location, there should be an audio and visual alarm during closing, 5. There should be indication of both open and close on the remote place of operation.

Solas Regulations Regarding Closure of Watertight Doors (As per Solas regulation, SOLAS chapter II-1, watertight doors from regulation 14 to regulation 25) 1.All the power operated doors must be capable of closing simultaneously from bridge and Ship Control Center (SCC) in not more than 60 seconds when the ship is in upright condition. 2.The door shall have an approximate uniform rate of closure under power. The closure time, from the time the door begins to close to the time it closes completely shall be in no case less than 20 seconds or more than 40 seconds with the ship in upright condition. 3.In case of hand operation of the door, during power failure, the door must be closed within 90 seconds. Doors in watertight bulkheads:   

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The opening must be framed, and thicker thick er plating used around the opening. The opening must be as small as possible. Below the load waterline, doors must be of the sliding type Sliding doors must be capable of of operating with a 15° list. Doors must be able to be operated both remotely and locally. Hydraulically Hydrauli cally operated doors must be fitted fitte d with local alarms at each door to warn of closing/opening by remote control Doors are tested by hose testing, testi ng, except for passenger vessels where the doors are required to be tested under a head of water, equal to the height of the bulkhead in which the door is to be fitted. Hose testing simply means that a jet of water is directed at the door in the closed position, at a specified pressure, and the door sealing arrangement arrangement is checked for leaks. Above the load waterline, hinged doors are permitted, provided that the hinges are made of suitabl suitable e noncorrosive material.

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Watertight doors, except doors between cargo spaces, are classed as follows: TYPE A - This type of doors may be left open and are to be closed only during an emergency. TYPE B - This type of watertight doors should be closed and are made to remain open only when personnel are working in the adjacent compartment. TYPE C - This type of watertight doors is to be kept closed all the time. It may be opened only for sufficient time when personnel are passing through the door compartment.

COFFERDAM In cargo ships where various liquid cargoes are carried, cofferdams or simply void spaces between two bulkheads are fitted fitt ed between tanks to arrest contamination of liquid of different density. Cofferdams are also fitted fitte d between tanks carrying fresh water and oil. Pump rooms rooms and ballast tanks can be designed to take the place of a cofferdam. coff erdam. The spacing of adjourning bulkheads of a cofferdam can be 760 mm, a generally accepted space through which a person can pass through. WELDING

Types of weld joints:

Welding is a f usion process process for joining j oining metals. By applying intense heat, the metal, at t he joint between two parts is melted and caused to intermix directly or more commonly, with an intermediate molten filler metal. Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the base metal.

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In electric arc welding, welding , the intense heat needed to melt metal is produced by an electric arc. The arc is formed between the actual work(metal piece) and an electrode(stick or wire). The electrode can either be a rod, with the purpose of simply carrying the current between the tip and the work piece, or it may be a specially prepared rod or wire that not only conducts the electricity but also itself melts and supplies the filler metal to the j oint. Most welding in the manufacture of steel products uses the second type of electrode. An AC or DC power power source, fitted with with whatever controls controls may be needed needed is connected connected by a welding welding cable to the the work piece and by a hot(or live) cable to an electrode holder which makes an electrical contact with the welding electrode. An arc is created across the small gap between between the electrode electrode tip and the work piece, piece, when the circuit circuit is energized. energized. The arc produces a temperature of about 3590 °C at the tip. This heat melts both the base metal and the electrode, producing a pool of molten metal. The molten metal solidifies behind the electrode as it is moved along the joint. The result is a fusion bond. The consumable welding rod has a flux coating which provides inert gas shielding for the mol ten metal and the electrodes. This gas shield consumes the surrounding atmospheric gas which would otherwise be absorbed by the molten metal. The flux also stabilizes the arc and provides a protective slag for the molten metal.

In gas welding , welding , the heat needed to melt the metal comes from a fuel gas( normally acetylene) burning with oxygen in a torch. The flame is applied to the base metal and held until a small puddle of molten metal is formed. The puddle is moved along the path where the weld bead is desired. Usually, more metal is added to the puddle as it is moved along, by means of dripping metal from a wire (welding rod or filler rod) into the molten metal puddle. The force of the jet of flame, issuing issuing from the torch tip helps to manipulate manipulate the puddle. puddle. The amount amount of heat can be be controlled controlled by the distance of the fl ame from the metal as well as the gas flow-rate and the type of nozzle.

Comparison of electric arc & gas welding Electric Arc Electric arc is the source of heat.

Gas Gas is the source of heat.

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The arc temperature is about 4000 C. Filler rod functions as electrodes. Risk due to electric shock. Arc welded joints have very high strength. Brazing and soldering can not be done using electric arc. Filler metal should be same as or an alloy of parent metal.

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The gas temperature is about 3200 3200 C. Filler rod is introduced separately. Risk due to gas pressure. Gas welded joints have not much strength. Brazing and soldering are done using gas. Filler metal need not be same as the parent metal.

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Types of Welding:

Submerged Arc Welding(SAW): This is an arc welding process in which the arc is maintained within a blan ket of granulated flux (see Figure below). below). A consumable filler wire is employed and the arc is maintained between this wire and the parent plate. Around the arc the granulated flux breaks down and provides some gases, and a highly protective thermally insulating molten container for the arc. This allows a high concentration of heat, making the process very efficient and suitable for heavy deposits at fast speeds. speeds. After welding the molten metal is protected by a layer of f used flux, which together with the unfused flux may be recovered before cooling. This is the most commonly used process for downhand mechanical welding in the shipbuilding industry, in particular for joining plates for ship shell, decks, and bulkheads. Metal powder additions that result in a 30– 50% increase in metal deposition rate without incurring an increase in arc energy input may be used for the welding of joint thicknesses of 25 mm or more. Submerged arc multi-wire and twin-arc systems are also used to give high productivity. With shipyards worldwide adopting one-side welding in their ship panel lines for improved productivity, the submerged arc process is commonly used with a fusible backing, using either flux or glass fibre materials to contain and control the weld penetration bead.

Tungsten Inert Gas(TIG) welding: Inert gas arc welding is used for welding aluminium alloys, usually with argon gas as the inerting medium and using tungsten as electrode for

manual welding of light plates or consumable metal wire for semi-automatic semi-automatic or automatic welding of heavier plates. Mild steel inert gas shielded welding is now also commonly used in automatic or semi-automatic process with CO 2 as the shielding gas. Ignition of the arc is obtained by means of a high frequency discharge across the gap since it is not advisable to strike an arc on the plate with the tungsten electrode. electrode.

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Non-consumable electrode. With or without filler metal. Shield gas usually argon. Used for thin sections of Al, Mg, Ti. Most expensive, expensive , highest quality. Tungsten has a v ery high melting point; does not burn hence it is “non-consumable”. High current is required and hence heat is generated – so the torch is air or water cooled.

Metal Inert Gas (MIG) welding [Gas Metal Arc Welding-GMAW]:

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Consumable wire electrode. electrode . Shielding provided by gas. Double productivity productiv ity of arc welding. Easily automated. All position capability. Higher deposition rates than arc welding. Less operator skill required. Long welds can be made without starts and stops. Minimal post weld cleaning is required.

Gas Metal Arc W elding (GMAW) (GMAW) is frequently referred to as MIG welding. MIG welding is a commonly used high deposition rate welding process. During the GMAW process, a solid metal wire is fed through a welding gun and becomes becomes the filler material. MIG welding is therefore referred referred to as a semiautomatic welding process. The shielding gas, forms the arc plasma, stabilizes the arc on the metal being welded, shields the arc and molten weld pool, and allows smooth transfer of metal from the weld wire to the molten weld pool. The primary shielding gases used are:

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Argon Argon - 1 to 5% Oxygen Argon - 3 to 25% CO2 Argon/Helium

Resistance Welding: Resistance Welding: Resistance welding is a welding technology widely used in manufacturing industry for joining metal sheets and components. components. The weld is made by conducting a strong current through the metal combination to heat up and finally melt the metals at localized point(s) predetermined by the design of the electrodes and/or the workpieces to be welded. A force is always applied before, during and after the application of current to confine the contact area at the weld interfaces i nterfaces.. Spot welding is a resistance welding process for joining metal sheets by directly applying opposing forces with electrodes with pointed tips. The current and the heat generation are localized by the form of the electrodes. The weld nugget size is usually defined by the electrode tip contact area. Purpose of Flux:       

Prevents oxidation of the weld metal. Provides gas shielding to the arc. Reduces cooling coolin g rate of the weld, thus reducing thermal stresses. Floats up the impurities impuriti es and levels out the wave form of of the weld. It stabilises stabilises the AC arc and and hence makes AC to be used used satisfactorily. Provides easy striking and arc stability. The gas shied consumes the surrounding surrounding oxygen and protects the molten metal.

Butt Weld:

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When two plates are in the same plane. It is simple, strongest and most efficient. For thin plates, no edge preparation is required. Plates are brought together edge to edge in closed or open square and butt joint. For thicker plates edges are to be prepared in single V or U or a double V or U to ensure full penetration and avoid distortion. A back run is recommended – this is done by welding welding on the reverse reverse side of the joint.

Fillet Weld: Fillet Weld: Fillet welding refers to the process of joining two pieces of metal together whether they be perpendicular or at an angle. Joints need not be grooved if strength is not a criteria, however more weld metal will be required. The stress carrying area of a fillet weld = throat thickness x leg length

Penetration of a Fillet Weld: A flat-faced, flat-faced, equal-legged equal-legged fillet weld weld in a 90° T-joint T-joint has a theoretical theoretical throat dimension dimension t,. This assumes fusion is i s achieved to the root of the joint, but not necessarily beyond that point. When the welding process and procedure achieve a depth of penetration beyond the root, then the effective throat dimension is increased for fillet welds with equal leg sizes. The effective throat dimension,teff, dimension,teff, is then t hen equal to the theoretical throat, tth, plus some additional value due to penetration. Therefore, if penetration beyond the root is achieved, the leg size can be reduced and the same weld strength can be achieved. This reduces the required quantity of filler metal.

Lap Weld: A Weld: A lap joint consists of one piece of metal overlapping the other, and welding the seam between the two. When welding a lap joint tack t ack welds can be used to better fixture the metal, but it is not necessary especially if the workpiece is fixtured in another way. When welding a lap joint, it is also possible to weld the overlapping seam on the opposite side of the workpiece to improve the strength.

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Advantages of lap joints include: include:  

Accommodates Accommodat es different thicknesses (thinner piece must be welded on top) Thin material such as diaphragms and foils foil s can be joined

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Some instances instanc es of lower tensile strength Less rigid than the base base materials materials since since the weld may act as a pivot Overlaps may be undesirable for mechanical or aesthetic reasons. Micro-cracks Micro-crac ks and cavity defects may occur if wrong welding speed is used. Corrosion and fatigue fati gue cracking may occur on the shielded areas due to moisture retention

Tack welding: Tack welding: Tack welding is a preliminary part of many welding techniques. It is a type of temporary weld and ensures that the parts to be welded together are secured in their places. This helps in avoiding any defects arising after welding has finally been completed. The main purpose of tack welding is to align and secure the parts to be welded till final welding is done. It helps in saving a lot of time and effort as otherwise much time would be required in assembly of parts. Several tack welds at short distance ensure that parts to be weld finally are secured in their place. One advantage of this process is that if any defect is detected before the final welding procedure, tack welds can be easily removed and parts can be reassembled and realigned and tack welded again. It is improper to think of tack welding as unimportant as it is a pre welding procedure but often it turns out to be as important as final welding saving much time and material. Electro Slag Welding (ESW): Electro slag welding is a welding process of heavy plates in the vertical position, position, wherein fusion is produced by molten slag which melts the filler metal and the surfaces of the work to be welded. It’s an arc less process that utilizes resistance heating of the slag pool covering the molten steel as the weld’s heat source. Parts to be joined are positioned so that there is a gap between them and an electrode (weld wire)[sometimes two or more] in a guide tube is positioned between the parts. Copper cooling shoes are clamped to the sides of the joint and contain the molten slag and metal during the weld. These may be mechanized so that they move up the plate as the weld is completed. After the components components are are assembled assembled power power is applied and the wire is fed through the guide tube. When the wire reaches the start block there is momentary arcing which melts the granulated flux, forms the slag pool and extinguishes extinguishes the arc. The process is initiated by filling the joint with the flux and starting an an arc. The consumable consumable guide tube directs the electrode (welding wire) and conducts the welding current to the molten slag pool. The electrical resistance of the slag pool generates heat which melts the wire, the guide tube and the edges of the two components to be joined. The temperature obtained is approximately 1800 degree Celsius at the surface and 1930 degree Celsius inside under the surface. This much heat is sufficient to fuse the edges of the work pieces and the welding electrode. As the wire and guide tube are melted by the flux the liquid metal sinks through the slag to the metal pool below and solidifies. Since the slag i s less dense than liquid steel, it floats to the top and protects the metal from exposure to air. With continuing addition of weld wire the molten steel fills the gap, solidifies and fuses the two components. The electro-slag welding process is used for welding heavy casting structure components such as stern frames.

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Electro Gas Welding (EGW): Electro Gas Welding is an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool, employing vertical position welding , similar to ESW. Electro gas welding is very much similar to electro slag welding except that an inert gas, such as carbon dioxide, is used to shield the weld from oxidation and there is a continuous arc as in the case of submerged arc welding to provide the heat for heating the weld pool. Again the flux, instead of being supplied to the weld zone through a hopper, hopper, is i s incorporated in the electrode itself in the form of flux cored electrodes, or sometimes the process may be carried out without using the flux in which case there is no fl ux covering on the top of the molten metal pool.

Plasma Welding: This is very similar to TIG welding as the arc is formed between a pointed tungsten electrode and the plate. But, with the tungsten electrode positioned within the body of the torch, the plasma arc is separated from the shielding gas envelope (see Figure ). A plasma is a gas which is heated to an extremely high temperature and ionized so that it becomes electrically electrically conductive; conductive; the plasma arc welding process uses this plasma to transfer an electric arc to a work piece. By forcing the plasma gas and arc through a constricted orifice, the torch delivers a high concentration of heat to a small area. With high performance welding equipment, the plasma process produces exceptionally high quality welds. Plasma gases are normally argon. The torch also uses a secondary gas, argon, argon/hydrogen or helium which assists in shielding the molten weld puddle thus minimizing oxidation of the weld. The metal to be welded is melted by the intense heat of the arc and fuses together. Plasma is forced through a fine-bore copper nozzle that constricts the arc. By varying the bore diameter and plasma gas flow rate, three different operating modes can be achieved: 1. Microplasma—the arc is operated at very low welding currents (0.1–15 amps) and used for welding thin sheets (down to 0.1 mm thickness). 2. Medium current—the arc is operated at currents from 15 to 200 amps. Plasma welding is an alternative to conventional TIG welding, but with the advantage of achieving deeper penetration and having greater tolerance to surface contamination. Because of the bulkiness of the torch, it is more suited to mechanized welding than hand welding. 3. Keyhole plasma—the arc is operated at currents above 100 amps and by increasing the plasma flow a v ery powerful plasma plasma beam is created. This can penetrate thicknesses up to 10 mm, but when using a single-pass technique is normally limited to a thickness of 6 mm. This operating mode is normally used for welding sheet metal (over 3 mm) in the downhand position.

Typical welding faults Root faults: When laying the first bead along the root in a butt joint, penetration at the root

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may be irregular i rregular or insufficient. When current is excessive, penetration will be too high. Insufficient penetration penetration may be due to the current setting being too low, or the rate of travel too high. The electrode may also be too large for the groove to be welded. Fusion faults: If the current is too low or rate of travel too high, fusion f aults may result, i.e. insufficient melting and fusion between the filler and the base metal. Fusion faults may also occur if a small electrode is used on a large area of cold base material. A larger electrode diameter should be used, and the base material preheated. Bead edge defects: Bead edge irregularities irregulariti es can occur if current output is too high. Bead edge faults may also occur at correct current output if the arc is too long or if electrode movement is incorrect. When welding upwards on a vertical plane and using a weaving movement, the electrode should be momentarily held still at each side of the bead to obtain good penetration and avoid edge defects. Edge faults and undercut may act as fracture indicators in the welded connection. Pores: Pores in the weld weld may be due to moisture content in the electr electrode ode coating, especially when welding with basic electrodes. Pores in the weld may also arise if the base material to be welded is wet or damp. Other reasons can be because of too long an arc, allowing air into the weld zone. A porous weld will have reduced strength properties. Heat cracks: Heat cracks may appear during or just after the cooling off period. There are two main causes: Impurities in the base material which which have a tendency to segregate and may form a layer in the t he middle of the weld. This l ayer prevents prevents fusion of the crystals. Segregated substances are first and foremost carbon and sulphur. In cases where heat cracks are caused by these substances, switch to basic electrodes. If heat cracks appear when welding with basic electrodes, electrodes, the material is not weldable. weldable. Tension across Tension across the weld can cause heat cracks even if the base material does not segregate in the weld. At a narrow, critical temperature range, just after coagulation of the bead, there is very little deformation property in a weld, and if shrinking in the metal is greater than the stretch in the weld, a heat crack will result. This type of crack can be avoided by clamping work-pieces in special jigs which control shrinkage. A heat crack will occur in the middle of the bead and will appear as a straight crack on the surface. Shrinkage cracks: Shrinkage cracks occur when the deformation property (toughness) of the weld is less than the actual shrinkage movement. Shrinkage cracks will usually appear across the weld direction and be caused by considerable lengthwise shrinkage. Basic electrodes are the best safeguard against shrinkage cracks.

Hydrogen cracks (Cold cracks): Weld m etal cracks are caused by hydrogen and may occur in any type of steel which has been hardened or which may become hardened during the welding process. Steel with a high yield point will contain a certain amount of hardened structure, normally martensite. The higher the melting point, the higher is the risk of hydrogen cracks. The most common reason for hydrogen cracks is the use of moist or damp electrodes during welding. The water in the coating will change into hydrogen in the arc and end up as hydrogen porosity dissolved in the weld metal and the heat affected zone (HAZ) immediately adjacent to the molten zone. When combined with hard phases in the weld and sufficient stress it will form cracks. The cracks might occur long time after welding is completed and are therefore often referred to as cold cracks. Other hydrogen sources are rust, oil, paint or condensation along the welding groove. Preheating the groove to say 50 °C will help considerably in reducing the amount of hydrogen. Conclusion: Dry basic electrodes when there is risk of cold cracking.

Slag embedded in weld: Slag consists of non-metalli non-metallic c particles originating from the coating of the electrode. electrode. All slag must be properly removed after finishing each weld bead. Use a chipping hammer and wire brush for this purpose. Slag embedded in the weld will seriously affect the strength of the weld. Try to avoid burning cavities, as any slag deposited in such cavities will be difficult to remove. When preparing the welding groove, make sure there is sufficient gap to provide good fusion and easy slag removal. Clean off mill scale and rust from the surfaces to be welded and make sure you choose the correct electrode for the welding position to be used.

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Distortion: All fusion-welding fusion-welding methods methods produce produce the weld by moving a molten pool pool along the joint; when when the heated metal cools, the shrinkage introduces residual stresses and distortion in the welded structure. The stresses produce longitudinal and rotational distortion. Longitudinal distortion.(fig 1.12) "Shortens" the weld, but may in many cases not be a serious problem. An example of this type of distortion is a welded beam that can be bent if the weld is not located symmetrically (in the centre of gravity of the cross section). If more than one weld is used, they must be symmetrical. Rotational distortion. The rotational distortion (see Figure1.13) can be minimised by making the weld bead symmetrical about the neutral axis or by having a parallel-sided single pass weld, as with electron beam welding. A stiff section can also prevent this type of distortion from appearing.

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Minimisation of Distortion: Can be done in the following foll owing ways: REDUCING THE CAUSE – The main cause of distortion is t he weld itself; so f ollowing steps are useful:      

Reducing the number of joints. Improving Improvi ng joint design to reduce the amount of weld metal needed. Reducing the root gap and avoiding mis-match mis-matc h of joints. Reducing the number of runs. Using large diameter electrodes wherever possible. Using automatic automati c or semi-automatic welding.

MAKING USE OF FORCES CAUSING DISTORTION – An opposite opposite preset to compensate compensate for distortion; distortion; this can only only be achieved by experimentation experimentation and so so is good good for batch fabrication. It will v ary with plate thickness, plate width and welding process. BALANCING THE DISTORTION FORCES –   

The welds welds are arranged in a sequence to keep distortion distortio n to a minimum. The weld is broken up into short lengths of 15-200 mm each. Using special welding techniques such as ‘back-step’ ‘back-step ’ or ‘wandering’.

Residual Stress in welding: Residual stresses in welded joints primarily develop due to differential weld thermal cycle (heating, peak temperature and cooling at the any moment during welding) experienced by the weld metal and regions close to the

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fusion boundary i.e. heat affected zone (HAZ). The residual residual stresses in the weld joints develop mainly due to typical nature of welding process i.e. localized heating and cooling leading to differential volumetric expansion and contraction of metal around the weld zone. Volumetric changes occurring during welding contribute to major part of residual stress development and are caused by a) varying expansion and contraction and b) different cooling rate experienced by top and bottom surfaces of weld & HAZ. Type and magnitude of the residual stresses stresses vary v ary continuously during different stages of welding i.e. heating and cooling. During heating, primarily compressive residual stress is developed in the region of base metal, which is being heated for melting, due to thermal expansion and the same (thermal expansion) is restricted by the low temperature surrounding base metal. After attaining a peak value, compressive residual stress gradually decreases owing to softening of metal being heated. Compressive residual stress near the welded surfaces eventually reduces to zero as soon as melting starts and a reverse trend is observed during cooling stage of the welding. During cooling as metal starts to shrink, tensile residual stresses and their magnitude keeps on increasing until room temperature is attained. During welding, higher cooling rate is experienced by the top and bottom surfaces of weld joint than the core/middle portion of weld and HAZ . This causes differential expansion and contraction through the thickness (direction) of the plate being welded. Contraction of metal near the surface starts even when material in core portion is still hot. This leads to the development of compressive residual stresses at the surface and tensile residual stress in the core. In general, after the cooling down of the weld, residual TENSILE stress exists i n the weld metal and adjacent base metal while residual compressive stress exists in the areas farther away from the weld metal. Effects of Residual Stresses:    

Decrease in the fracture strength. Reduction Reductio n of buckling strength. Compressive Compressiv e residual stresses increase fatigue fati gue strength. In hostile hostil e environment, residual stress can cause cracking in a metal without without any applied load.

Reducing residual stresses:   

Selecting Selecti ng appropriate processes, procedures, welding sequence & fixtures. fixt ures. Selecting Selecti ng best methods for stress relieving reli eving and removing distortion. distortio n. Selecting Selecti ng design detail and materials materia ls to minimize minimi ze the effect of residual stresses.

Testing of Welds: Welds are tested by two main methods

 

Destructive Non-destructive

In destructive testing, a sample of the metal containing part of the weld is used which gets destructed during the process of testing. Tests under this are:      

Tensile test Bend test Hardness test Impact test Nick-break test Fillet test

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Tensile Test Test - A tensile test, also known as tension test,is performed on a specimen containing the weld in the centre of the specimen. By pulling on something, the values of ultimate tensile strength, yield strength, % elongation, fracture strain and Young's Modulus of the selected welded metals can be evaluated. In order to make comparisons between the results of tensile test pieces of different metals the test pieces must have the same proportions of sectional area and gauge length( i.e. a standard tensile test piece). Therefore, a standard gauge length equal to 5.65 times the square root of the cross-sectional area, which is equivalent to a gauge length of five tim es the diameter, is adopted by the major classification societies. The tensile testing is carried out by applying longitudinal or axial load, at a specific extension rate, to a standard tensile tensil e test piece, perpendicular to the load direction till f ailure. The applied tensile load and extension are recorded during the test for the calculation calcul ation of stress and strain. A standard test piece is prepared in a round section along the gauge length as shown beside:

A universal testing testing machine is commonly used,for used,for carrying out the tensile tests. These are driven by hydraulic hydraulic systems. The figure below shows a hydraulic testing t esting machine using the pressure of oil in a piston for load supply.

Components: Load frame - usually consisting of o f two strong supports for the machine. m achine. Load cell - A force transducer or other means of measuring the load is required. Cross head - A movable cross head (crosshead) is controlled to move up or down. Usually Usually this is at a constant speed: sometimes called a constant rate of extension (CRE) machine. Output device - A means of providing the test result is needed. Some older machines have dial or digital displays and chart recorders. Many newer machines have a computer interface for analysis and printing. The specimen is placed in the machine between the grips and an extensometer if required can automatically record the change in gauge length during the test. If an extensometer is not fitted, the machine itself can record the displacement between its cross heads on which the specimen is held. Once the machine is started it begins to apply an increasing load on specimen. Throughout the tests the control system and its associated software record the load and extension of the specimen. Experimental Procedure: Measure and record the specimen dimensions (diameter and gauge length), Fit the specimen on to the universal Testing Machine (UTM) and tighten the jaws at both end, to clamp tightly onto specimen; apply hydraulic hydraulic load(tensile) and carry on testing. Record load and extension for the construction of stress-strain stress-strain curve of each tested specimen. Bend Test: This is a test which i s carried out on plate materials and consists of bending a straight specimen of plate through 180 degrees around a former. For the test to be satisfactory, no cracks should occur at the outer surface of the plate (see Fig).

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Hardness Test - Hardness is the resistance of a material to indentation. This is the usual type of hardness test, in which a pointed or rounded indenter is pressed into a surface under a substantially static load. Brinell hardness is determined by forcing a hard steel or carbide sphere of a specified diameter under a specified load into the surface of a material and measuring the diameter of the indentation left after the test. The Brinell hardness test uses a desk top machine to press a 10mm diameter, hardened steel ball into the surface of the test specimen. The machine applies a load of 500 kilograms for soft metals such as copper, brass and thin stock. A 1500 kilogram load is used for aluminium castings, and a 3000 kilogram load is used for materials such as iron and steel. The load is usually applied for 10 to 15 seconds. After the impression is made, a measurement of the diameter of the resulting round impression is taken. The Brinell hardness number, or simply the Brinell number, is obtained by dividing the load used, in kilograms, by the actual surface area of the indentation, in square millimeters. The result is a pressure measurement, but the units are rarely stated. where BHN = the Brinell hardness number F = the imposed load in kg D = the diameter of the spherical indenter in mm Di = diameter of the resulting indenter impression in mm Impact Test ( Notch Notch Toughness Toughness Test ) - There are two main forms of impact test, the Izod and the Charpy test. Both involve striking a standard specimen with a controlled weight pendulum travelling at a set speed. The amount of energy absorbed in fracturing the test piece is measured and this gives an indication of the notch toughness of the test m aterial. aterial. The Charpy V-notch test or Charpy U-notch test is commonly specified. The object of the impact test is to determine the toughness of the material; that is, it s ability to withstand fracture under shock loading. In the figure, below the principle of the Charpy test machine is illustrated, along with the standard standard test specimen for a Charpy V-notch test.

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Nick Break test: test: In this test the weld is fractured along its length and examined for internal defects. A sample with a width of 1.5 times the throat thickness +12mm is used. The 12 mm is for a cut of 6 mm which is made at the centre on both sides of the weld. The specimen is fractured along the centreline of the weld by bending or with a blow from a chisel. The appearance appearance of the fractured surface and the type and location of any weld flaws are recorded.

The Fillet Test: It Test: It is i s similar in that the joint is fractured along the fillet weld and t he fractured surfaces examined examined for slag inclusions, gas entrapments, incomplete root fusion etc. The leg length, throat thickness and weld profile are also evaluated. A cut of 1.5 mm depth is made perpendicular to the weld surface and a force applied in the direction shown.

Non Destructive Tests:       

Visual examination Welding Gauges Dye Penetrant test Leak Test Magnetic Particle Inspection Radiographic Inspection Inspecti on Ultrasonic Inspection

Visual examination: Though being the simplest & cheapest form of examination, it is often ignored, though it can reveal more faults than many of the other methods of inspection. The only requirement is a trained & experienced eye and care during inspection. A visual examination is done before, during & after welding to reduce flaws & faults. Before welding the following checks are carried out: 





A study of the drawing, drawing, design specifications specifi cations and blueprint showing the welding welding symbols specifying specifyi ng the type and size of weld. The type and size of of base metals metal s to be welded welded and in relation to that, the type of electrode and other consumables that will be used, the welding process, the joint design, edge preparation etc. Alignment of the joint, fitup, fitu p, fixturing, fixturi ng, cleanliness, competence of the welder and safety procedures.

During welding a check must be maintained on the following:     

Rate of burning of the electrode and progress of the weld. Root penetration penetrati on and fusion. Flow of the weld weld metal which which will reveal reveal slag inclusion. Sound of the arc indicating indicati ng correctness of current and voltage volta ge and faults such as spatter. spatter . Welding sequence & distortion. distorti on.

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After welding, welding, faults such as: as:  

  

 

Incomplete fusion. Lack of penetration. Undercutting. Lack of reinforcement as indicated indicate d by a concave concav e surface. Pinholes or porosity. Spatter. Surface texture.

Welding Gauges: Welds Gauges: Welds are inspected for size and shape by welding gauges. Gauges can be of the fixed or adjustable type. The fixed type of gauges are shaped according to the size and type of weld. Numerals are marked on the gauge indicating reinforcement reinforcement for butt welds and leg length for fillet welds. The adjustable type of gauge consists of a mi crometer screw which moves between adjustable arms. It can be used to measure throat thickness, angle of edge preparation, depth of undercut, depth of pores etc.

Gas Cutting: Gas cutting is achieved by what is basically a chemical/thermal reaction occurring with iron and iron alloys only. Iron or its alloys may be heated to a temperature at which the iron will rapidly oxidize in an atmosphere of high purity oxygen. The principle of the process as applied to the cutting of steel plates and sections in shipbuilding is as follows. Over a small area the metal is preheated to a given temperature, and a confined stream of oxygen is then blown onto this area. The iron is then oxidized in a narrow band, and the molten oxide and metal m etal are removed by the kinetic energy of the oxygen stream. A narrow parallel sided gap is then left between the cut edges. Throughout the cutting operation the preheat flame is left on to heat the top of the cut since most of the heat produced by the reaction at the cutting front is not instantaneous, and tends to be liberated at the lower level of the cut only. Alloying elements in small amounts are dissolved in the slag and removed when cutting steel. However, if they are present present in large l arge quantities, quantities, alloying elements, especially chromium, will retard and even prevent cutting. The reason for this is that they either decrease the fluidity of the slag or produce a tenacious oxide film over the surface which prevents further oxidation of the iron. This may be overcome by introducing an iron rich powder into the cutting area, a process often referred to as ‘powder cutting’. When cutting stainless steels which have a high chromium content ‘powder cutting’ would be employed. Generally acetylene is used with oxygen to provide the preheat flame but other gases can be used: propane for example or hydrogen which is used for underwater work because because of its compressibility. Apart from the torch, the equipment is similar to that f or gas welding. The torch has valves for controlling the volume of acetylene and oxygen provided for the preheat flame, and it has a separate valve for controlling the oxygen jet. Laser Cutting Laser cutting is a precise method of cutting a design from a given material using a CAD file to guide it. Modern industrial cutting lasers are primarily carbon dioxide lasers where carbon dioxide gas is the stimulated medium. This is infra-red radiation, which cannot be seen with the naked eye but is a safety hazard to an unprotected eye. Lasers are adapted to cutting by the process of polarising and focusing a beam of high power laser light onto a work piece. This melts or burns the material along the cut line. To clear the cut and prevent rejoining, a cut assist gas aligned concentrically with the laser beam expels melted materials clean from the cut area. Cut assist gases in common use are oxygen, nitrogen and air. Oxygen is typically used for mild steel cutting. Nitrogen (an inert gas in this process) is used for stainless steel cutting, where it acts to shield the hot stainless steel from oxygen, much like argon is used in welding processes. Both air and nitrogen can be used for aluminium cutting. The laser beam is directed to the cutting

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head by specialised water cooled mirrors, where it is focused using a special lens made of zinc selenide. The beam diameter before the lens is about 25mm or 7 watts per square mm. This is reduced to 0.25 mm, or 71,000 watts per square mm, at the focal point where cutting occurs. One of the benefits of laser cutting technology is the cut product rarely needs any finishing work as this process ensures a high-quality high-quality surface finish. There are three main types of laser cutting. The CO2 laser is used to cut, bore, or engrave. Nd is used for boring when there are high-energy requirements but low repetition. Nd-YAG laser is used where high power is needed.

Aluminium Welding: Aluminium has high thermal thermal conductivity [3 to 5 times that of of steel] which means heat is easily conducted away from the welding area. It is essential that the heat source is powerful enough to rapidly reach aluminium's low melting point of 565 /650ºC. Welding hot and fast usually gives the best results. Heavy sections are best preheated to reduce the effect of rapid heat loss. Aluminum suffers a reduction in strength in the weld area [unlike steel]. When stressed, a welded aluminium structure will incur local deformation in the welded area first. Welding aluminium alloys demands very clean working practice as they are prone to contamination. [Tools such as brushes or mill wheels used on steel or other metals must not be used on it.] A variety of welding welding processes processes can be used used to join aluminium aluminium including the fusion methods methods GMAW GMAW (standard MIG) and GTAW (standard TIG) giving giving high quality, all-position welding, manual, mechanised or fully automatic. Also resistance, MMA(metal arc, stick) and advanced processes such as solid state and friction stir welding. Choice of process is based on technical and/or economic reasons. For most structural economical and quality welds, TIG and MIG are recommended for aluminium. TIG welding (sketch same as for steel welding ) is generally preferred for light gauge work up to 6 mm and for pipe work and intricate assemblies where excellent control over weld appearance and penetration is possible. TIG welding is widely used for welding aluminium and it produces welds of good appearance and quality. A constant current AC power source with a continuous high frequency is used with a water or air-cooled TIG torch and an externally supplied inert shielding gas. The AC process is used to provide a degree of cleaning of the aluminium surface during the electrode positive cycle though this is not a substitute for proper cleaning of the base material. The tungsten electrode diameter is usually about 2,4 mm and the method can be used with or without filler metal. The filler material is fed into the weld bead from outside. TIG welding gives the welder very good control, but welding speed is normally slower than for MIG and requires higher welder competence. The choice of torch cooling cooling depends upon welding parameters and duty cycle. They are usually water-cooled. Air-cooled torches can be used at up to about 100 amps. Zirconiated tungsten electrodes (which are preferred over the thoriated type), and of the correct diameter for the current, are used. The torch must be maintained at an angle of close to 90° to the workpiece surface and the filler material must enter the weld pool at an angle of typically 5°. As well as the workpiece being properly clean it is important that the filler rod is also clean. If the rod has been exposed to air for a long time it is advisable to clean it by pulling the rod through a 'Scotchbrite' type of abrasive pad or through stainless steel wool in order to remove the oxide layer. MIG welding (sketch same as for steel w elding ) is preferred for thicker sections [to over 75 mm] and where high productivity is needed for economic reasons. MIG welding can deposit up to about 4,5 kg per hour with weld travel speeds of 500 to 1000 mm per minute. MIG welding uses a standard DC constant voltage power source with a wire feed system and externally supplied inert shielding gas. Shielding gas for MIG welding aluminium is normally high purity argon or an argon helium mixture. The use of helium in the mixture increases the energy of the arc and is more suitable for welding thicker material. The welding current, arc length and electrode wire speed are controlled by the welding machine and, once adjusted for a welding procedure, do not require readjustment. The process is very adaptable to automatic welding. The feeding of aluminium wire is automatic off a spool. Aluminium in shipbuilding shipbuilding:: Pure aluminium has a low tensile strength and is of little use for structural purposes; therefore, the pure metal is alloyed with small percentages of other materials to give greater tensile strengths. There are three advantages that advantages that aluminium alloys have over mild steel in the construction of ships.

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





aluminium is lighter lighte r than mild steel (approximate weights being 2.723 tonnes/m3, mild steel 7.84 tonnes/m3), tonnes/m3) , and with an aluminium structure it has been suggested that up to 60% of the weight of a steel structure may be saved. high resistance to corrosion. Good corrosion properties can be utilized, utiliz ed, but correct and careful insulation from the adjoining steel structure are necessary - at present, aluminium alloys used in shipbuilding corrode 100 times slower than steel - during the first year of operation, steel corrodes at a speed of 120 mm/year, while aluminium – at a speed of 1 mm/year. nonmagnetic properties - The nonmagnetic properties can have advantages advantages in warships and locally local ly in the way of t he magnetic magnetic compass, but they are generally generally of little im portance in merchant merchant vessels.

Disadvantages of Disadvantages of the use of aluminium alloys: 





  

Higher initial and fabrication costs. In terms of Modulus Modulus of of Elasticity, which which is the measure of stiffness of a material, material, aluminium aluminium and steel measures at 69 GPa and 200 GPa respectively. Since aluminium’s stiffness is only a third of steel, it will likely be deformed three times more easily than steel if put under high strain.( Therefore the use of aluminium alloy is generally only limited to vessels of up to 130 meters in length - the longer the vessel the more stiffening is required) Coefficient Coeffi cient of thermal expansion expansion almost double that of steel ; may cause distortions distorti ons with temperature variations in service. Aluminium loses strength at elevated temperatures; detrimental to damage control. Difficult to join to steel structures structures - can lead to galvanic corrosion with steel. Potential Potenti al brittleness of high strength aluminium.

Aluminium-Steel joining Techniques: Nuts & Bolts: To prevent galvanic corrosion, the metals must be insulated from each other or protected by a good paint film. The higher in the galvanic series, steel, acts as cathode and aluminium as anode and corrodes. Steel (being higher in the galvanic series) must be used as f asteners asteners to join j oin the two metals.

The contact between the two metals is prevented by using neoprene washers and neoprene ferrule. Galvanised steel bolts are used and the nuts are fitted in the inside of the deck house and tack welded to boundary angles to allow the joint to be tightened tightened without without removal of the internal linings. linings. The top and bottom bottom of of the joints are specially specially welded with a compound known as “arambee” to form a watertight seal.

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Explosion Explosi on Bonding: Process uses an explosive detonation as the energy source source to produce a metallurgical metallurgic al bond bond between metal components. One of the metals is accelerated by explosive detonation detonati on at a very high rate over over a short distance resulting in a progressive progressive collision of the materials. The metals are f orced together under several several million psi pressure creating an electron-sharing electron-sharing bond that is typically stronger that the weaker of the parent metals.

Corrosion: Corrosion (commonly known as rust) is the oxidation of a metal due to an ELECTROCHEMICAL +

reaction. The oxidizing agent is most often O 2 (atmospheric corrosion) or H (chemical corrosion) or both.

Corrosion comes in many different forms and can be classified by the cause of the chemical deterioration of a metal. General Attack Corrosion: Corrosion : Also known as uniform attack corrosion, general attack corrosion is the most common type of corrosion and is caused by a chemical or electrochemical reaction that results in the deterioration of the entire exposed surface of a metal. Ultimately, the metal deteriorates to the point of failure. The electrochemical reactions occur at more or less the same rate over the entire surface. The loss of metal thickness is uniform over the entire surface. General attack corrosion accounts for the greatest amount of of metal destruction by corrosion, but is considered as a safe form of corrosion, due to the fact that it is predictable, manageable and often preventable. Localized Corrosion: Corrosion: Unlike general attack corrosion, localized corrosion specifically targets one area of the metal structure. Localized corrosion corrosion is classified as one of three types: Pitting : Pitting results when a small hole, or cavity, forms in the metal. This area becomes anodic, while part of the remaining metal becomes cathodic, producing a localized galvanic reaction. The deterioration of this small area penetrates penetrates the metal m etal and can lead to ffailure. ailure. This form of corrosion is often difficult to detect due to the fact that t hat it is usually relatively small and may be covered and hidden by corrosion produced compounds. Crevice corrosion: corrosion: Similar to pitting, crevice corrosion occurs at a specific location. This type of corrosion is often associated with a stagnant stagnant microen mic roenvironment, vironment, like those found f ound under gaskets and washers and clamps. Acidic conditions, or a depletion of oxygen in a crevice can l ead to crevice corrosion. Filiform corrosion: corrosion: Occurring under painted or plated surfaces when water breaches the coating, filiform corrosion begins at small defects in the coating and spreads to cause structural weakness.

Galvanic Corrosion : While corrosion of different metals can take many forms, the method of attack in aqueous solutions is always the same. Corrosion can only occur when three elements are present. Taken together, these elements form what we call the basic corrosion cell. The elements of the basic corrosion or galvanic cell are: 1) unprotected metals: anode & cathode. 3) electrolyte.

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4) the metallic path that connects the anode and the cathode. The anode is the component of the cell that corrodes and is the only part that corrodes. The cathode is the part of the cell that does not corrode. In fact, the corrosion process process of the anode protects it. The electrolyte is any liquid that conducts electricity and that is i n contact with the anode and cathode simultaneously. simultaneously. The metallic path is an electrical conductor that connects the anode and the cathode. This corrosion cell is really an electrical circuit with four components (anode, cathode, electrolyte, electrical connection between anode & cathode). If any one of the four components is isolated or removed, the reaction stops. Because of the energy potential differences between the anode and cathode, positively charged atoms of the metal leave the solid surface of the anode and enter the electrolyte as ions. At this point, metal is actually going into solution in the electrolyte. This produces the visible metal loss we characterize to be corrosion. The atoms leave their corresponding negative charges as electrons that are available to flow through the anode and metallic path to the cathode. The electrons travel through the metallic path to the cathode. There, corresponding reactions consume the electrons. In the illustration above, the anode and cathode are two different metals. More often times than not, the anode and cathodes are different areas on the same piece of metal. A metal surface will have thousands of areas that are cathodes and corresponding areas that are anodes. These areas can develop because of differences in the metal such as the t he inclusion of t races of other metals, stresses from metalworking, varying degrees degrees of protective coating effectiveness or differing environmental exposures. Galvanic corrosion is caused by the existence of a galvanic cell or a corrosion cell, essentially two metals submersed in an electrolyte that results in an attack on one metal(anode) at the expense the other(cathode). Metals and metal alloys all possess different electrode potentials a relative measure of a metal's tendency to become active in a given electrolyte. electrolyte. The more active, or l ess noble, a metal is t he more likely it will f orm an anode in an electrolytic environment. environment. While the m ore noble a metal is, the m ore likely it will form a cathode when in the same environment. The electrolyte acts as a conduit for ion migration, moving metal ions from the anode to the cathode. The anode metal, as a result, corrodes more quickly than it otherwise would, while the cathode metal corrodes more slowly and, in some cases, may not corrode at all.

The electrochemical series:

Aluminium – Zinc – Iron – Mild Steel – Stainless Steel – Lead – Copper – Silver – Gold – Platinum. Three conditions must exist for galvanic corrosion to occur: Electrochemically Electrochemically dissimilar metals must be present. present. The metals must be iin n electrical contact. The metals must be exposed to an electrolyte. The above conditions constitute a “Corrosion Triangle”

Environmental Cracking: Environmental cracking is a corrosion process that can result from a combination of environmental conditions affecting the metal. Chemical, temperature and stress related conditions can result in the following types of environmental corrosion:    

Stress Corrosion Cracking (SCC) Corrosion fatigue Hydrogen-induced cracking Liquid metal embrittlement

Flow Assisted Corrosion (FAC): (FAC ): Flow assisted corrosion, or flow accelerated corrosion, results when a protective layer of oxide on a metal surface is dissolved or removed by wind or water, exposing the underlying metal to further corrode and deteriorate. The corrosion is accelerated by impact of solid particles which may remove metal or they may remove just the protective oxide layer and allow the metal to corrode more quickly. Three types are:

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

 

Erosion assisted corrosion. Impingement. Cavitation.

Cavitation: Cavitation: A high velocity fluid / water flow leads to pressure falling below zero at points of highest flow. Vapour bubbles form in these regions as the liquid is ‘pulled apart’. When the pressure increases again, the collapse of the vapour bubbles creates an intense shockwave that removes metal or oxide from the surface. Intergranular corrosion: corrosion : Intergranular corrosion is a chemical or electrochemical attack on the grain boundaries of a metal. This often occurs due to impurities in the metal, which tend to be present in higher contents near grain boundaries. These boundaries can be more vulnerable to corrosion than the bulk of the metal. The most significant problem is weld decay of austenitic stainless steel whence the metal becomes susceptible to corrosion. The solutions to a weld decay:  



Use of low carbon grade stainless stainle ss steel. Use a stabili sed grade of steel which includes a strong carbide forming element (Nb or Ti) to lock up the carbon. For existing existin g components that have been sensitised, sensiti sed, heat treat to re-dissolve re-dissolv e the carbides.

Dealloying: Dealloying, or selective leaching, is the selective corrosion of a specific element in an alloy. The most Dealloying: common type of dealloying is dezincification of unstabilized brass. The result of corrosion in such cases is a deteriorated and porous copper. The prime cause of dealloying is galvanic effect and the problem can be reduced by addition of tin. Fretting corrosion: corrosion : Fretting corrosion occurs as a result of repeated wearing, weight and/or vibration on an uneven, rough surface. Corrosion, Corrosion, resulting in pits and grooves, grooves, occurs on t he surface. Fretting corrosion is often found in rotation and impact machinery, bolted assemblies and bearings, as well as to surfaces exposed to vibration during transportation. Stress corrosion: corrosion : It is the combined action of applied tensile stress and a corrosive environment which is caused by residual internal stresses in the metal. [ Cold forming, unequal cooling from high temperature, volume change, an externally applied stress, faulty design, vibrations, excessive flexing, thermal effect – expansion/contraction]. If an ordinary nail is dropped into a vessel of salt water, it will be attacked, and, after some time, rust will be observed discolouring the water. The initial points of attack will be, in almost every case, the point and the head; the two electrodes are of the same metal and the electrolyte is uniform. The difference lies in that one electrode is more mechanically stressed than the other. The area of high stress is always the anode of the cell, made that way by the extra energy supplied by the stress itself. Stress cell s can take on two basic forms. One, like the nail just described, has its anode established by residual internal stress or stress left because of something which has happened to the metal. In the case of the nail, the stress was caused by cold-forming of the head and point. If these stresses had been relieved by heating the nail at a moderate temperature and letting it cool slowly, the stresses will disappear and this type of stress cell will be eliminated. HighTemperature Corrosion: Corrosion : Fuels used in gas turbines, diesel engines and other machinery, which contain vanadium or sulfates can, during combustion, form compounds with a low melting point. These compounds are very corrosive towards metal alloys normally resistant to high temperatures and corrosion, including stainless steel. High temperature corrosion can also be caused by high temperature oxidization, sulfidation and carbonization.

Corrosion Prevention: Treatment of Steel in a shipyard: shipyard : Steel plates, supplied to the shipbuilders, have patches of a black oxide, known as mill scale adhering to the surface. This scale is insoluble and if maintained over the whole surface would reduce corrosion. It is, however, very brittle and does not expand either mechanically or thermally at the same rate as the steel plate. Unless this mill scale is removed before painting, the painted scale will drop off in service, leaving bare steel plate which will corrode rapidly. rapidly. Unfortunately mill scale is difficult t o remove completely. If the plate is left exposed to the atmosphere, rust will form behind the mill scale. On wire brushing, the majority of the scale will be removed. This is known as weathering. In modern times a good flow of material through the shipyard is essential and therefore the time allowed for weathering must must be severely limited. In addition, addition, it is found that in practice much of the mill scale is not removed by this process. process. The most common methods employed to treat steel surfaces(removal of mill scale) are: 

   

Blast cleaning Pickling Flame cleaning Preparation Preparatio n by hand High-pressure water blasting. blastin g.

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Blast cleaning is the most efficient method for preparing the surface and is in common use in all large shipyards. It , removes 95% to 100% of the mill scale and results in a slightly rough surface which allows adequate adhesion of the paint. Smaller shipyards, where the quantity of steel processed does not justify the capital investment in the preparation equipment, usually buy steel already prepared from a steel mill or stockist. Plates and sections are in almost all cases now shot-blasted to remove rust and mill scale. Shot-blasting plant in shipyards is generally of the impeller wheel type, where the abrasive is thrown at high velocity against the steel surface and may be re-circulated. The plant is installed so that the plate may pass through in the horizontal position, which allows the use of automated, roller conveyor systems. Following the blast cleaning it is desirable to brush the surface and apply a coat of priming paint as soon as possible, since the metal is liable to rust rapidly. Following the shot-blasting of plates and sections, the material passes immediately through an ai rless spray painting plant. In one pass the material is automatically sprayed with a priming paint of controlled coat thickness. A number of suitable priming paints are available. Following the priming paint stage a drying process may be provided. This is a tunnel with fans to create an airstream, in conjunction with the preheating, so that the plate that emerges is dry and ready for processing. The drying also reduces the potential for damage to the primer coating.

Pickling involves the immersion of the metal in an acid solution, usually hydrochloric or sulphuric acid, in order to remove the mill scale and rust from the surface. After immersion in these acids the metal will require a thorough hot water rinse, to remove all traces of the acid. It is then allowed to dry before further procedures. It is preferable that the treatment is followed by application of a priming coat. One disadvantage is that during the drying period a light coat of rust is formed on the plates and must be removed before painting. Pickling is no longer found in most of the ship construction industry. oxy-acetylene torch , having several several jets, the flame is used to brush the surface. It burns Flame Cleaning: Using an oxy-acetylene away any dirt and grease, loosens the surface rust and , due to the differential expansion between the steel plate and the mill scale, loosens the latter. The surface is immediately wire brushed and the primer coat applied while the plate is still warm. The process does not entirely remove the mill scale and rust, but it can be quite useful for cleaning plates under inclement weather conditions, the flame drying out the plate. Flame, or another heating process, is used as part of an automated preparation line in a shipyard, to preheat the steel, which assists the cleaning and drying of the primer paint coating. The process has lost favour in the last few years.

Hand cleaning by various forms of wire brush is often not very satisfactory, and would only be used where the millscale has been loosened by weathering, i.e. exposure to atmosphere over a long period. For ships in service hand cleaning may be used for very small corroded areas.

High-pressure High-pressure water blasting is superseding grit blasting for ship repair. It is capable of restoring a steel surface to SA 2.5, provided any corrosion has not been allowed to develop. Disposal of the waste material, in this case mainly water, is a main reason for the adoption of water blasting. Blast cleaning using shot or grit is preferred for best results and economy in shipbuilding, it is essential prior to application of high-performance paint systems used today. Pickling, which also gives good results, can be expensive and less applicable to production schemes; flame cleaning is much less effective; and hand cleaning gives the worst results. Water blasting is mainly a ship repair process. process.

Blast Cleaning Standards : Blast cleaning is done by sand blasting or shot blasting from special nozzles at a distance of 200 mm, as per following grades as per Swedish Standard SIS 055900: (i) Grade Sa 2: This involves light blast cleaning. Almost all mill scale, rust and foreign forei gn matter matt er shall be removed. Finally the surface is cleaned with a vacuum cleaner, clean dry compressed compressed air or clean brush. The surface shall lokk greyish in clolour and correspond in appearance to photographs designated as Sa-2. (ii) Grade Sa 2.5: This involves very thorough blast cleaning. Mill scale, rust and foreign matter shall be removed to the extent that only traces remain in the form of sli ght stains. Finally the surface is is cl eaned with a vacuum cleaner, cleaner, clean dry compressed air or clean brush. It shall then correspond in appearance to the photographs designated as Sa 2.5. (iii) Grade Sa 3: This involves blast cleaning to pure metal surface. Mill scale, rust and foreign matter shall be removed completely. Finally the surface is is cleaned with a vacuum cleaner, clean dry compressed air or clean brush. Then the surface shall have a uniform metallic colour and correspond in appearance to the photographs designated as Sa-3.

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Temporary paint protection during building : After the steel is blast blast cleaned it may may be several several months before before it is built into the ship ship and finally painted. painted. It is desirable desirable to protect the material against rusting in this period as the final paint will offer the best protection when applied over perfectly clean steel. The formulation of a prefabrication primer for immediate application after blasting must meet a number of requirements. It should dry rapidly to permit handling of the plates within a few minutes and working the plates within a day or so. It should be nontoxic, and it should not produce harmful porosity in welds nor give off obnoxious fumes during welding or cutting. For some high-speed welding processes it is necessary to remove the primer in way of the welds to avoid porosity. After cutting and welding, areas of damaged primer are usually strip coated by hand to cover the affected steel and retain the primer protection against corrosion. The primer must also be compatible with any subsequent subsequent paint finishes f inishes to be applied. Satisf actory formulations formulations are available, for example a primer consisting of zinc dust in an epoxy resin. Given the sophistication and cost of modern, long-life coatings, their application is critical to performance. It is common for shipyards to take complete units and blocks, once all the hot work is completed, completed, for final fi nal coating in a controlled environment. So-called ‘paint cells’ are temperature- and humidity-controlled buildings. The units are driven into the cells using self-elevating transporters. The units are then blasted, if no primer has been used or the primer is degraded and unsuitable for over-coating. Once cleaned, the coatings can be applied in near ideal conditions. Hull and internal coatings are applied. Where the units are to be joined in the building dock, unpainted areas are left. These are completed after the hull welding, using localized protection from unsuitable weather conditions.

Cathodic Protection: Protection : If three dissimilar metals are immersed in an electrolyte, the metal lowest on the electro chemical series becomes the anode, the remaining two being cathodes. Thus if copper and iron are immersed in sea water, they may be protected by a block of zinc, which is then known as the sacrificial anode, since it is allowed to corrode in preference to the copper and iron. Thus zinc or magnesium anodes may be used to protect the propeller and the stern frame assembly of a ship, and will at the same time, reduce corrosion of the hull, due to differences in the steel. Deep water ballast tanks may be protected by sacrificial anodes. It is first essential to remove any rust or scale from the surface and to form a film on the plates which prevents any further corrosion. Both these functions are performed by booster anodes, which have large surface area compared with their volume ( e.g. flat discs). These anodes allow swift movement of material to the cathode (the steel plates) thus forming the film. Unfortunately this film is easily removed in service and therefore main anodes are fitted, having large volume compared with surface area (e.g. hemispherical), which are designed to last about three years (time between dry docks). Protection is only afforded to the whole tank if the electrolyte is in contact with the whole tank. Thus it is necessary when carrying water ballast ballast to press the tanks up. electrically connecting connecting it to Impressed Current Cathodic Protection (ICCP): A metal also can be made cathodic by electrically another metallic component in the same electrolyte through a source of direct electric current. The current flow from this metallic component must be sufficient to overcome the natural corrosion current. Thus the current is directed to flow off the surface of the added metallic component (anode), into the electrolyte and onto the metal hull (cathode). All we need is to measure what what the natural corrosion corrosion current current is. So we we add one more electrode – reference cell cell – completely passive metal. The potential difference between the hull and reference cell will form the natural corrosion current. So another electrode – anode with a power source is introduced so that the current flow from this electrode is sufficient to overcome the natural corrosion current. Because an external current source is employed, this type of protection is termed 'IMPRESSED CURRENT CATHODIC PROTECTION'. A source of direct current is required , this i s generally obtained obtained from mains power units that contain a transformer and rectifier. The magnitude of this current may be automatically controlled in response to a continuous monitor of the cathode / electrolyte potential or may be m anually controlled after intermittent measurement. measurement. The impressed current anode material is ideally non-consumed by the passage of current from it into the electrolyte, in practice the materials used are a compromise between this ideal and the cost

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and physical properties of available materials. Impressed current anodes are made from graphite, silicon, iron, lead alloys some with platinum di-electrodes, platinised titanium or more exotic combinations such as platinum clad niobium. The selection of the correct anode material is critical in the f ormulation ormulation of an effective and economic economic cathodic protection scheme. Generally, for a given current demand, less impressed current anodes than sacrificial anodes are required for protection, as high anode currents are feasible. Non-consumable, relatively noble metals such as lead/silver are used for the anodes which are cast in fibre glass bodies. The bodies are bolted to flat bars which are welded to the shell plating , the cables from the anodes being led through the hull via special ducts which are built to stringent construction requirements. The anodes are insulated from the hull by shields which are fitted to prevent high density currents stripping the hull paints. For very large ships, such as VLCC / VLOC / Cape sizers, a second power unit is located forward and the anodes for that unit must be recessed to prevent them being damaged by the anchors. Impressed Impressed current systems of cathodic protection are more sophisticated in design than sacrificial systems. It can only give protection to the immersed immersed external hull. Painting: Painting: Paint is still the most important important protection system for ships. It consists of pigments in a l iquid which when spread out thinly allows the pigment to form an adherent film. It forms a barrier coating which prevents ingress of water and oxygen. To provide an effective protection the paint must be of adequate thickness so that it can provide an impervious layer above the prepared surface, free from flaws and firmly adherent throughout its life. It is an inhibitor carrier in which appropriate corrosion inhibitors such as zinc chromate are incorporated in the paint. It provides a degree of cathodic protection by incorporating a high concentration of metal powders, such as zinc, in the paint composition. This type of coating can be effective in the gaps or scratches in the paint film. Painting Schemes: Schemes: The paint system applied to any part of a ship will be dictated by the environment to which that part of the structure is exposed. Traditionally, the painting of the external ship structure was divided into three regions:   

Below the waterline, waterli ne, where the plates are continually immersed in sea water. The waterli waterline ne or boot topping region, where immersion immersio n is intermittent and a lot of abrasion occurs. The topsides and superstructure superstruct ure exposed to an atmosphere laden with salt spray, and subject to damage through cargo handling.

However, now that tougher paints are used for the ship’s bottom the distinction between regions need not be so well defined, one scheme covering the bottom and waterline regions. Internally, by far the greatest problem is the provision of coatings for various liquid cargo and salt water ballast tanks.

Below the waterline The ship’s bottom has priming coats of corrosion-inhibiting paint applied that are followed by an antifouling paint. Paints used for steels immersed in sea water are required to resist alkaline conditions. The reason for this is that an iron alloy immersed in a sodium chloride solution having the necessary supply of dissolved oxygen gives rise to corrosion cells with caustic soda produced at the cathodes. Further, the paint should have a good electrical resistance so that the flow of corrosion currents between the steel and sea water is limited. These requirements make the standard non-marine non-marine structural steel primer red l ead in linseed oil unsuitable unsuitable for ship use below the waterline. Suitable corrosion-inhibiting paints for ships’ bottoms are pitch or bitumen types, chlorinated rubber, coal tar/epoxy resin, or vinyl resin paints. The antifouling paints may be applied after the corrosion-inhibiting coatings and should not come into direct contact with the steel hull, since the toxic compounds present may cause corrosion. The painting is done in three l ayers – st 1 layer – primer 2 coats each of 50 microns. nd 2 layer – binder one coat of 50 microns rd st nd rd 3 layer – antifouling 1 coat 5 micron; 2 coat 30 micron; 3 coat 25 microns;

Waterline or boot topping region Generally, modern practice requires a complete paint system for the hull above the waterline. This may be based on vinyl and alkyd resins or on polyurethane resin paints. The layer should have good adhesion, maximum salt resistance, good abrasion resistance and good weather resistance.

Superstructures Red lead- or zinc chromate-based primers are commonly used. White finishing paints are then used extensively for superstructures. These are usually oleo-resinous or alkyd paints that may be based on ‘non-yellowing’ oils, linseed oilbased paints that yellow on exposure being avoided on modern ships. Where aluminium alloy superstructures are

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fitted, under no circumstance should lead-based paints be applied; zinc chromate paints are generally supplied for application to aluminium. aluminium.

Cargo and ballast tanks Severe corrosion may occur in a ship’s cargo tanks as the combined result of carrying liquid cargoes and sea water ballast, with warm or cold sea water cleaning between voyages. This is particularly true of oil tankers. Tankers carrying ‘white oil’ cargoes suffer more general corrosion than those carrying crude oils, which deposit a film on the tank surface, providing some protection against corrosion. The latter type may, however, experience severe local pitting corrosion due to the non-uniformity of the deposited film, and subsequent corrosion of any bare plate when sea water ballast is carried. Epoxy resin paints are used extensively within these tanks, and vinyl resins and zinc-rich coatings may also be used. Composition of Paints: Traditional paints have the following basic components:

 

 

Pigment. Binding agent or vehicle. vehicl e. Solvent. (A drying agent-sometimes). agent-sometim es).

PIGMENT : The pigment gives the paint its colour and covering capacity. capa city. In primer it should be the main contributor to the corrosion preventing properties and also enhance the adhesion of the top coats. Pigments are generally dry powders which are held in suspension in the paint and vary from natural minerals to man-made organic compounds. They can be broadly divided into: Colour pigments such as white(white lead, zinc oxide, titatnium dioxide), black(carbon). Primers such as red lead, zinc chromate, calcium plumbate, metals such as aluminium and zinc. BINDERS: The pigment is held in suspension in a solution of a binding medium. The binding medium is the most important component in paint and besides determining its consistency and application it also gives the paint its physical and chemical properties. The possible variation in binder properties is limitless and so only the two basic types will be considered: considered: The oleoresinuous oleoresinuous vehicle combines drying oils with natural and some synthetic resins. The alkyd vehicle combines drying oils with synthetic based alcohols and acids. Some of the basic ingredients found in binders are: Drying oils – linseed, tung, soya bean. Natural resins – copal, darmar, rosin. Synthetic resins – phenolic, vinyl, epoxy, polyurethane, silicone. SOLVENT : The solvent is the volatile component of paint and its function is to make the paint flow for ease of application. It is generally the action of the solvent evaporating that makes paint adhere to a surface. Modern Paint Types: Alkyd: The vehicle in this type of paint is based on alcohols and acids. It gives an improved drying time over vegetable oils and thus alkyds are mainly finishing paints suitable for surfaces exposed to the atmosphere. The performance is poor if the surface is immersed. Alkyd paints should only be used on superstructures and not underwater. Bitumen or pitch: The paint is made by dissolving bitumen or pitch in solvents such as naptha and white spirit and may be used as a superstructure paint but more commonly for internal surfaces exposed to a high degree of wetness such as fresh-water tanks. When pigmented with aluminium it is often used for plating which is constantly under water and for outer shell plating. Chlorinated rubber: This paint is used where good chemical and water resistant coatings are required. Normally it consists of pigments of plasticized chlorinated rubbers. The paint dries by the evaporation of the solvents and the temperature at the time of drying is not as critical as with some other paint types. It is often used when ships are being built in winter or in poor climatic conditions. It is designed for use in high-build systems i.e. intended for application with airless spray which gives very high film thickness(80 – 100 microns) and substantially reduces the number the number of coats required. This type of paint is particularly resistant to acids and alkalis and is often used to protect outer shell plating. Maintenance is assisted by its good adhesion to previous coats of the same material but it cannot be applied to conventional paint surfaces. This paint can also be used for superstructures but in some cases cracking has occurred after a few years. Coaltar Epoxy: A two-pack paint in which the components are pigments(bitumen or coaltar pitch blended with resin), epoxide resins and curing agents. The paint provides hard thick films in which the chemical resistant qualities of epoxy resin are combined with the water impermeability of coaltar. It is widely used in immersed conditions but it can be susceptible to atmospheric corrosion and is easily damaged.

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Epoxy: Epoxy resins are derived from chemicals which are extracted from petroleum and natural gases. The epoxy resin paints have extremely good chemical, water and abrasion resistant qualities but are very expensive. They are generally two-pack(two components) consisting of an epoxy base and a hardener or curing agent. Drying is caused by the chemical action of the polyamine or polyamide hardener with the epoxy resin base – the paint is of the reaction drying type. The paints are very hard when cured and give long term protection against corrosion. Their mechanical resistance properties are superior to chlorinated rubber and vinyl paints. Initial drying, which is by solvent evaporation takes place in between four and six hours, but this is followed by the chemical cure of the binder, the rate of which is dependent on the temperature. Drying and hardening will only occur satisfactorily in temperatures above 10 deg.C and in RH below 80%. Due to the expense involved and short pot life, only sufficient paint for a half day’s use should be mixed at any one time. The penetration quality is rather poor and first class surface preparation is essential to obtain a good performance from this paint; touching up is difficult and the previous coat must be roughened. Oleoresinuous: An improvement on oil based paints, the vehicle consists of drying oil and natural or synthetic resin, including phenolic resins, which are often synthesized from several different oils and resins. These paints have improved drying time and give a better performance than oil based paints but are not as sophisticated as the chemical resistant paints. Phenolic: Phenol is derived from coaltar and produces a water-resistant paint. Paints produced from 100% phenolic resins have excellent chemical resistance and a very hard finish. Although often used to coat tanks on chemical carriers, unmodified phenolic paints are sometimes used on weather deck plating and gives good corrosion resistance. Modified phenolic paints are often used in order to reduce costs. Polyurethane: Usually a two pack paint; an alkyd resin is mixed with an isocyanate hardener and the ensuing reaction produces polyurethane paint. These paints have many good qualities – abrasion resistance, hardness, a high gloss, chemical resistance and when well cured have very good water and weather resistance. Polyurethane paints are used for tanks’ coatings but white polyurethane is a good external superstructure paint as it remains bright for long periods and is not subject to rapid yellowing. This type of paint is approximately four times the cost of alkyd paints but the superior performance performance and reduced maintenance costs make it attractive. attractive. Unfortunately Unfortunately the paint is very sensitive sensitive to to moisture and high humidity during application and can be difficult use in the marine environment. The hardness does cause a tendency to chip or crack but the advantages of this paint vastly outweigh its disadvantages. Primers: Steel plates must be protected from corrosion while the ship is being built and prefabrication primers must:     

be rapid drying. have a non-toxic vapour. not affect weld quality or speed. be suitable for spray application. application. be a suitable first coat for the ship’s paint system.

The most successful anti-corrosive primers are those which are pigmented with iron oxide or zinc dust and which contain corrosion inhibitors such as zinc chromate or zinc phosphate. Zinc dust silicate paints are used both for prefabrication primers and as long term anti-corrosive paints for dry cargo holds, cargo tanks and ballast tanks. Such coatings resist high humidity & high temperatures, condensation and abrasion and are thus suitable for use in marine environment. The paints have exceptional durability and good protective properties and are frequently used in tanks which carry latex and alkalies. Zinc silicate paints can be over coated with finishing paints to give increased increased performance. The most effective primers which the mariner can use for routine maintenance are those which contain chemical corrosion inhibiting pigments. Calcium plumbate is a good alternative to red lead. When used with an alkyd base it is quick drying and has excellent adhesion. The major disadvantage is that it has toxic properties. One of the best primers available is zinc chromate chromate which is i s particularly suitable for use on zinc, galvanised galvanised steel, aluminium aluminium and other non-ferrous metals. metals. It is suitable for f or brush or spray application and i s non-toxic. Vinyl: The resins are produced by the polymerisation (combining of small molecules to form large molecules) of organic compounds in the vinyl group. The paints have a low solids content due to the relatively low solubility of the resins and this results in thin dry films. More coats are therefore required to build up an adequate paint thickness and this increases the application costs. Adhesion is poor if surface moisture is present therefore good weather is required during the application. Adhesion to bare steel is also poor and the paint must be applied over a pre-treatment primer, such as zinc chromate in a polyvinylbutyl resin which uses phosphoric acid as an etchant. Vinyls are usually pigmented with aluminium, zinc chromate or red lead and are generally not not suitable for brush application. The paints are one-pack and dry by loss of solvent. Despite the disadvantages, vinyls are excellent paints where resistance to abrasion, chemicals and water is required.

Anti-fouling Paints: Antifouling paints contain biocides that repel fouling organisms when released at a controlled rate into the water adjacent to t he hull. The rate of release of bi ocides is important; if it is too fast, the antifouling antifouling will fail prematurely, prematurely, especially after a period of intense activity, while if it i s too slow, the antifouling antifouling will be ineffective,

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particularly in areas with a high fouling challenge. It is at the settling stage of fouling organisms that the adhesion and growth must be prevented: once settled and firmly attached, growth is extremely rapid and the organisms are beyond the influence of antifouling paints, and can only be removed by scrubbing and scraping. Antifoulings look like paints, smell smell like paints and are applied applied like paints, but but in order to function they require require some water ingress in order to release the biocides, in a continuous and controlled manner throughout the lifetime of the composition. The antifouling film acts as a biocidal reservoir which gradually becomes depleted. All antifoulings will eventually fail when the concentration of biocide in the layer of water adjacent to the surface falls below the critical level necessary to control the larval fouling. The dissolution process which allows removal of biocide is called ‘leaching’ and the rate of removal the ‘leaching rate’. The effectiveness of the antifouling and its lifetime will depend on the types and level of biocide(s) it contains, along with the types of resin, natural or synthetic, used as binders. Anti corrosion Paints: Since paints paints are devised devised for protecting metal surfaces, surfaces, it is broadly believed believed that all all paints are anti-corrosion paints. But it is not a correct version. All oil-based paints, for example, are not anti-corrosion paints. They are merely decorative paints which protect the metal surface partially against the climatic corrosion but fail to stand against the drastic corrosion caused by various industrial chemicals & gases. It takes a strong bonding with the clean metal surface. The resultant coating is impermeable to air & gases. Corrosion resistant coatings protect metal components against degradation due to moisture, salt spray, oxidation or exposure to a variety of environmental or industrial chemicals. Anti-corrosion coating allows for added protection of metal surfaces and act as a barrier to inhibit the contact between chemical compounds or corrosive materials. It is often assumed that all paint coatings prevent attack on the metal covered simply by excluding the corrosive agency, whether air or water. This is often the main and sometimes only form of protection; however, there are many paints that afford protection even though they present a porous surface or contain various discontinuities. For example, certain pigments in paints confer protection on steel even where it is exposed at a discontinuity. If the reactions at the anode and cathode of the corrosion cell that form positive and negative ions respectively are inhibited, protection is afforded. Good examples of pigments of this type are red lead and zinc chromate, red lead being an anodic inhibitor and zinc chromate a cathodic inhibitor. A second mode of protection occurs at gaps where the paint is richly pigmented with a metal anodic to the basis metal. Zinc dust is a commercially available pigment that fulfills this requirement for coating steel in a salt water environment. The zinc dust is the sacrificial anode with respect to the steel. Safety Precautions: Precautions : Health hazards- Over exposure can lead to irritation of the eyes and respiratory system. Excessive exposure can result in headache, nausea, dizziness and drowsiness and in extreme cases even loss of consciousness. Splashes in the eye will cause discomfort and possible damage. Prolonged Prolonged contact with skin can l ead to skin irritation and in some cases dermatitis.

Precautions: Inhalation - While making the Primer/Compound application in non-ventilated or poorly ventilated conditions, arrange a powerful Exhaust Fan to evacuate the solvent vapours and protect the workmen from suffocation. Avoid flames and smoking to save from fire or explosion while working under under such closed - conditions. conditions. It is, however, advised to avoid the applications in closed conditions. First aid – remove the sufferer to fresh air, keep warm and give rest. Eye contact – avoid splashes in the eye by wearing suitable safety goggles or glasses. First aid – wash with plenty of clean, fresh water for at least ten minutes, holding the eyelids apart. Skin Contact – avoid skin contact by wearing suitable clothing and gloves. Barrier creams are not an acceptable alternative to the proper choice of glove. First aid – remove any contaminated clothing; wash the skin thoroughly with a proprietary skin cleanser. DO NOT USE A SOLVENT. Ingestion – whilst there is little hazard by this route during onboard maintenance painting, do not eat whilst handling paint. First aid – do not induce vomiting, seek medical advice. The primary source of health and safety information is the product Material Safety Data Sheet (MSDS). Surface Preparation for Maintenance Painting on board: The single most important function which can influence paint performance is the quality of the surface preparation. The importance of removing oil, grease, old coatings, rust and other surface contaminants cannot be over stressed. The following procedures are recommended: 

Freshwater wash- to remove all salt contamination. This is best achieved using something like a fan jet lance or a power washer if available.

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



Degrease – to remove all surface grease & oil. is usually done using rags or brushes soaked in solvent. If a painted surface is to be degreased without being damaged, a solvent must be chosen which will not dissolve the paint film. Steel preparation - hand and power tool cleaning is used for bare steel areas. The existing coating should be taken back to a sound edge and the edges should be “feathered” back using a combination of manual methods: Hard scraping or or slicing - this is carried out with various types of scraper. Scrapers are useful for o removing loose m aterial. aterial. Chipping hammers or hammers or chisels-chipping can be carried out using a wide variety of hammers or chisels, o best results are obtained if chipping is followed by secondary preparation such as wire brushing. Wire brushing can can remove loose contamination, but it is i neffective at removing scale scale and deep o seated corrosion. Power Tools - Power tools used for cleaning fall into two basic categories: o Rotary wire brushing using “braided” wire wheels - Radial brushes are used for preparing  awkward areas or welded seams. Cup brushes are often used for preparing large areas. Rotary discing cleaning cleaning of a surface is achieved by coated abrasive discs attached to angle  grinders or by using abrasive flap wheels attached to straight or in-line tools. Clean down – the prepared area should have all residual dust, paint flakes and debris removed by brushing or vacuuming. Paint application should begin as soon as possible after cleaning to prevent deterioration of the prepared surface. 

Stern and Bow doors: Roro vessels may be fitted with stern doors of the hingedown or hinge-up type, which if large are articulated. Bow doors are either of the vi sor type or of the side hinged type (‘barn door’ type). These are situated above the freeboard deck and where the bow doors lead to a complete or long forward enclosed superstructure, Lloyd’s require an inner door to be fitted that is part of the collision bulkhead. This would also be in keeping with the SOLAS requirements for passenger ships, where the collision bulkhead is to be extended weathertight to the deck next above the bulkhead deck, but need not be fitted directly above that bulkhead. A sloping weathertight vehicle ramp may be fitted in some ships to form the collision bulkhead above the freeboard deck and the inner door is omitted. This ramp may extend forward of the specified limit for the collision bulkhead above a height of more than 2.3 m above the bulkhead deck, i.e. above the height of a conventional tween deck space. Stern and bow door strengths are equivalent to the strength of the surrounding structure and where they give access to enclosed superstructures they are required to close weathertight. Stern doors and bow visors can be mechanically raised and lowered with wire rope and purchase arrangements, but in general they and the side-hinged bow doors are hydraulically opened and closed . These weathertight doors are casketed and cleated. Ramps Ro-ro ships fitted with ramps usually have a stern ramp, but some vessels fitted with bow doors may also have a bow ramp that doubles as the inner weathertight door and is lowered onto a linkspan when the bow visor or side-hinged doors have been opened. Ramps may also be fitted internally to give access from deck to deck. These can be hydraulically or mechanically tilted to serve more than one deck and can be fixed in the horizontal position to serve as decks themselves . In some ships they can even be raised into the hatch space and serve as weathertight covers.

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Hatch Covers – watertight integrity: Means of water-tight iintegrity: ntegrity: Gasket Type Sealing: Sealing:

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The cleats are used to restrict the movement of the hatch cover pontoon in a seaway. Double drainage, in both the side sealing and cross joints, is important to lead minor leakages away through the drain valves and is an essential component in the weathertight integrity system. In most systems the hatch cover weathertight seal is obtained when a compression bar seats into the rubber packings. The weight of some hatch covers is taken by the side-plate edges onto the coaming top. Heavier hatch covers led to landing pads being developed to take the weight. These also had the effect of improving weight transferral of any hatch top deck cargo into t he ship’s hull.

Labyrinth Type Sealing:

Rubber Skirt Type Sealing:

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Cleating Arrangements:

Maintenance for Hatch Covers: Hatch covers of cargo hold are generally made from light weight steel or high tensile steel. They are fitted over a steel bar of the hold with a rubber packing inserted in between them to avoid water ingress. A proper routine routine maintenance maintenance to be performed performed by qualified officer on ship ship which must include:include:   

     

Examination Examinati on of hatch cover, hatch beams for corrosion, cracks and material failure Keep Cleats, hauling wire, rollers, chains and wedges in operational condition conditio n at all time Keep clean hatch cover tops and all drainage drainage holes to be kept clear Look for any broken or missing gasket and replace it immediately. immediately . The length of renewed gasket must be minimum 1 m Before renewing rubber gasket, check and rectify steel to steel fault Gasket rubber to be of approved type by class Grease all the moving parts Check for any hydraulic hydraulic system system leakage leakage if cover cover is oil operated operated Oil test to be performed for hydraulic system Call surve surveyor yor after any major repair in the cover and its concerned parts

Testing of Hatch Covers:

After maintenance maintenance procedure procedure it is advised advised to test the water water tight integrity integrity of the hatch cover cover by different methods methods.. The three methods to check water tightness of hold covers are: 1 Hose water Test: In this test a water spray from a nozzle of 12mm diameter is sprayed over the joint of hold and cover from a distance of 1m to 1.5 m with a pressure of 0.5 m/ second water jet. The limitation or drawbacks of this test:   

 

it requires at least t wo persons. The leakage leakage if very minimal cannot be identified by naked eye. It should be noted that a lack of leakage leakage into the hold is not not in itself itself determinative determinative of a successful successful test. Checks Checks should also be made that leakage is not passing into the drain channels and being fed through the drain valves onto the deck. Cargo holds must be free of cargo(empty). The test is not viable in sub-zero temperatures. temperatur es.

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  

The test cannot pinpoint leakages accuracy. Water pressure pressure variance and and the distance distance of of the jet from the structure can affect affect results. results. Many port authorities do not allow allow it because excess water on deck can lead to pollution.

Hose tests are conducted in static conditions. conditions. When the ship i s at sea, the ship itself and its hatch and coaming structures are not completely rigid. They flex and “work” to cope with forces to which they are subjected by the ship’s motion and the forces of wind and waves. If cargo damage is to be avoided, the contact between the compression bars and the rubber packing has to be maintained during the periods when the covers and coamings are flexing. The extent to which that contact is maintained depends upon the degree of “compression” that is being achieved by the steel to rubber contact. The higher the degree of compression, the greater will be the watertight integrity in dynamic conditions. A hose test can only demonstrate “contact” not “compression”. It is this shortcoming that makes it a considerably less reliable indicator of overall watertightness than the ultrasonic test. 2. Ultrasonic Test: The Ultrasonic testing is a m ore accurate method of of testing water ti ghtness ghtness of hold and its cover. In this system an ultrasonic sound generator is kept inside a closed and intact cargo hold. A sensor of that unit is passed passed all over the compression compression joint joint and any low pressure area or point point detected by the instrument can be a leakage point. The test involves placing an electronic signal generator within the cargo hold(laden or not) and using the receiving sensor to first take a reading at the access or booby hatch with the main hatch cover closed. This provides the OHV (open hatch value). The sensor is then passed around the outside of all compression joints noting the reading on the receiving equipment. It is preferable to listen to the signal using headphones to determine the maximum reading at any single point. The readings obtained are then compared with the OHV. The closer they are to the OHV, the greater the degree of leakage. The comparison between actual readings and OHV indicates the degree of compression that exists within the seal, the greater the compression, the lower the reading as a percentage of the OHV. For the purpose of evaluation of results , the following guidelines are usually adopted: 

 

Readings of 50% of the OHV or more indicates significant signifi cant loss of compression and an immediate lack of watertight integrity. Readings of more than 10% indicate potential leakage. Readings of less than 10% indicate indica te watertightness watertig htness under normal conditions.

Drawbacks of this instrument is it is not normally kept onboard and qualified person is required to perform this test. 3. Chalk Test: This is the oldest or most traditional method for testing hold cover compression, but it cannot test the water tight integrity of the hold. A layer of chalk powder powder is applied all over over the steel back back of the hatch and then the hatch cover is closed and tightened to its normal values. The impression of chalk on the rubber packing is then studied to check lack of compression point shown by gap in the chalk m arks.

Purpose & work of Classification Societies: The purpose of a Classification Society: 



to provide provide classification classification and statutory services services and assistance assistance to the maritime maritime industry industry and regulato regulatory ry bodies as regards maritime safety and pollution prevention, based on the accumulation of maritime knowledge and technology. to verify the structural strength and integrity integrit y of essential parts of the ship’s hull and its appendages, and and the reliability and function of the propulsion and steering systems, power generation and those other features and auxiliary systems which have been built into the ship i n order to maintain essential services on board.

Classification Societies aim to achieve this objective through the development and application of their own Rules and by verifying compliance with international and/or national statutory regulations on behalf of flag Administrations.

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Condition of Class: ‘Recommendation’ and ‘Condition of Class’ are different terms used by IACS Societies for the same thing, i.e. requirements to the effect that specific measures, repairs, surveys etc. are to be carried out within a specific time limit i n order to retain class.   

 

Issued to a classed vessel. Issued by classification society surveyor. surveyor. Enables the vessel to proceed to voyage when when as per surveyor: survey or: The vessel is fit. o In efficient condition. o Certificates Certifi cates will embody surveyor’s recommendation recommendati on for continuance contin uance of class. Subjected Subject ed to the confirmation confirmatio n of the committee.

Issued in the Event of: 

 

Seaworthiness Seaworthiness of the vessel in question due to: Collision o Grounding o Any maritime maritime accident accident by which vessel sustained sustained damage damage to hull/ machinery. o Repair done as required. If surveyor thinks that the ship is only safe safe to proceed to next port for a cheaper or more thorough repair, an endorsement to be made on interim certificate as: “The vessel is safe for intended passage until the next port for further repair and examination.”

Work of Classification Societies: 











  

  

A technical review of the design plans and related documents for a new vessel to verify compliance with the applicable Rules; Attendance at the construction of the vessel in the shipyard shipyard by a Classification Classification Society Society surveyor(s) surveyor(s) to verify that the v essel is constructed in accordance with the approved approved design plans pl ans and classification Rules; Attendance by a Classification Classification Society surveyor(s) surveyor(s) at at the relevant relevant production production facilities that that provide provide key components such as the steel, engine, generators and castings to verify that the component conforms to the applicable Rule requirements; Attendance by a Classification Classification Society Society surveyor(s) surveyor(s) at the sea trials and other trials relating relating to the vessel and its equipment prior to delivery to verify conformance with the applicable Rule requirements; Upon satisfactory satisf actory completi completion on of the above, above, the builder’s/shipowner’s builder’s/shi powner’s request for the issuance of a class certificate will be considered considered by the relevant Classification Society and, if deemed deemed satisfactory, t he assignment of class may be approved and a certificate of classification issued; Once in servi service, ce, the owner owner must submit the vessel to a clearly specified programme of periodical class surveys, carried out onboard the vessel, to verify that the ship conti nues to meet the relevant Rule requirements for continuation of class. Develop technical standards (rules) for design and construction constructi on of ships. Approve designs against their standards. Acts as a Recognised Organisation carrying out statutory surveys & certification certifica tion as delegated by maritime administrations. Regulations Regulati ons for in-service in-servic e inspection inspecti on and periodic survey during operation. Research and development devel opment programmes. Support international internati onal organisations organisati ons – IMO, ISO, IACS.

Special Surveys: Special Surveys are to be carried out at 5 years intervals to renew the Classification Certificate. The first Special Survey is to be completed within 5 years from the date of the initial classification survey and thereafter 5 years from the credited date of the previous Special Survey. However, an extension of class of 3 months maximum beyond the 5th year can be granted in exceptional circumstances. In this case, the next period of class will start from the expiry date of the Special Survey before the extension was granted. For surveys completed within 3 months before the expiry date of the Special Survey, the next period of class will start from the expiry date of the Special Survey. For surveys completed more than 3 months before the expiry date of the Special Survey, the period of class will start from the survey completion date. date. 40


The Special Survey may be commenced at the 4th Annual Survey and be progressed with a view to completion by the 5th anniversary date. When the Special Survey is commenced prior to the 4th Annual Survey, t he entire survey is to be completed within 15 months if such work is to be credited to the Special Survey. Annual Surveys: Annual Surveys Surveys are to be held held within 3 months months before or after each anniversa anniversary ry date of the initial initial classification classification survey or the completion of the last Special Survey. The survey survey is i s to consist c onsist of an examination for the purpose of ensuring, as far as practicable, that the hull, hatch covers, hatch coamings, closing appliances, equipment and related piping are maintained in a satisfactory condition. condition. Intermediate Survey: The Intermediate Survey is to be carried out either at or between the second and third Annual Annual Survey. Those Those items which are additional to the requirements of the Annual Surveys may be surveyed either at or between the 2nd and 3rd Annual Survey. Harmonized System of Survey & Certification: Purpose: Surveys, made in accordance with the harmonised survey system for ships, are purported to harmonize intervals between surveys of all legitimate certificates issued to all m arine vessels. vessels. The harmonized system is presumed to facilitate all the troubles of periods between surveys so that any ship would not have to worry about going into the process of a survey schedule required by one convention right after having gone through the same thing concerned in connection with another instrument. All surveys are initiated initiated on the the same date so that all subsequen subsequentt surveys, eg annual annual , intermediate intermediate etc, all fall on on the same date for all t he certificates .1 A one-year standard interval between surveys, based on initial, annual, intermediate, intermediat e, periodical and renewal surveys, as appropriate, except for MARPOL Annex IV which is based on initial and renewal surveys; .2 A scheme providing providing the necessary flexibility flexibilit y to execute execute each survey, with provision for: 



completion completi on of the renewal surve survey y within within 3 months before the expiry expiry date of of the existing existi ng certificate certifi cate with with no loss of its period of validity; a "time window" window" of 6 months – from 3 months months before to 3 months months after the the anniversary anniversary date of of the certificate certificate for annual, intermediate and periodical surveys;

.3 a maximum period of validity validit y of five years for all cargo ship certificates; certifi cates; .4 a maximum period of validity validit y of 12 months for the Passenger Ship Safety Certificate; Certific ate; .5 a system for the extension of certificat certificates es limited to three months, enabling a ship to complete its voyage, or one month for ships engaged on short voyages; .6 when an extension exte nsion has been granted, the period of validity of the new certificate certifi cate starting from the expiry date of of the existing certificate before its extension; .7 a flexible system for inspection of of the outside of the ship's bottom on the following conditions: conditions: -

.1 a minimum of of two inspections inspecti ons during any five-year five-y ear period of of validity validit y of the Cargo Ship Safety Construction Certificate or the Cargo Ship Safety Certificate; and .2 the interval between any two such inspections inspect ions should not exceed 36 months;

.8 a Cargo Ship Safety Certificate Certific ate under SOLAS 74/88, as an alternative alternativ e to separate Cargo Ship Safety Construction, Constructio n, Cargo Ship Safety Equipment and Cargo Ship Safety Radio Certificates; .9 a flexible system concerning concerning the frequency and the period period of validity of certificates, subject to the minimum pattern of surveys being maintained. .

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TYPES OF SURVEY The types of survey used in the harmonized system are as follows: (I) 2.1 An initial survey is is a complete inspection inspection before a ship i s put into service service of all the items relating to a particular certificate, to ensure that the relevant requirements requirements are complied with and that these items are satisfactory for the service for which the ship i s intended. (P) 2.2 A periodi A periodical cal survey is is an inspection of the items relating to the particular certificate certificate to t o ensure that they are in a satisfactory condition and fit for the service for which the ship is intended - should be held within three months before or after the second anniversary date or within three months before or after the third anniversary date in the case of the cargo ship safety equipment certificate and should take the place of one of the annual surveys and within three months before or after each anniversary date in the case of the cargo ship safety radio certificate. With respect to safety radio surveys the HSSC uses the term ‘periodical’ instead of ‘annual’ and w and with ith respect t o safety equipment surveys, HSSC uses the term ‘periodical’ instead of ‘intermediate’. (R) 2.3 A renewal survey is is the same as a periodical survey but also leads to the issue of a new certificate completion of the renewal survey within 3 months before the expiry date of the existing certificate with no loss of its period of validity; v alidity; (In) 2.4 An 2.4 An intermediate intermediate survey is is an inspection of specified items relevant to the particular certificate to ensure that they are in a satisfactory condition and fit for the service for which the ship is intended - should be held within three months before or after the second anniversary date or within three months before or after the third anniversary date of the appropriate certificate and should take the place of one of the annual surveys. (A) 2.5 An annual survey is is a general inspection of the items relating to the particular certificate to ensure that they have been maintained and remain satisfactory for the service for which the ship is intended - should be held within three months before or after each anniversary date of the certificate. (B) 2.6 An inspection of the outside of the ship's bottom is bottom is an inspection of the underwater part of the ship and related items to ensure that they are in a satisfactory condition and fit f or the service for which the ship i s intended - There should be a minimum of two inspections of the outside of the ship's bottom during any five year period (Ad) 2.7 An additional survey is is an inspection, either general or partial according to the circumstances, to be made after a repair resulting from investigations or whenever any important repairs or renewals are made. List of Surveys under HSSC: 1. Cargo Ship Safety Equipment Equipment Certificate; 2. Cargo Ship Safety Construction Constructio n Certificate; Certifi cate; 3. Cargo Ship Safety Radio Certificate; Certifi cate; 4. International International Load Line Certificate; 5. International International Oil Pollution Prevention Certificate; 6. International Internati onal Pollution Prevention Certificate Certifi cate for Carriage of of Noxious Liquid Substances in Bulk; Bulk; 7. International Internati onal Sewage Pollution Prevention Certificate; Certific ate; 8. International International Air Pollution Prevention Certificate; 9. International Internati onal Certificate Certific ate of Fitness for the Carriage of Dangerous Chemicals Chemi cals in Bulk 10. Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk; 11. International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk; 12. Passenger Passenger Ship Safety Certificate; (i) The Passenger Certificate (PC) requires a Renewal survey each year. (ii) The Cargo Ship Safety Radio Certificate (RADIO) requires a Periodical survey each year. (iii) The International Load Line Certificate (LOADLINE) requires an Annual survey each year. (iv) The Cargo Ship Safety Equipment Certificate (SEC) requires an Annual survey every year. On either the second or third year this is replaced with a Periodical survey. (v) The Cargo Ship Safety Construction Certificate (SAFCON), the International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk (IGC/GC), the International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk (IBC/BCH), the International Oil Pollution Prevention Certificate (IOPPC) and the International International Pollution Prevention Certificate for the Carriage of Noxious Liquid Substances in Bulk all require Annual surveys each year. On either the second or third year this is replaced with an Intermediate survey.

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Tanks intended to hold liquids and which form part of the subdivision of the t he ship shall be tested by flooding with water to a head corresponding to the deepest subdivision load line or to two thirds of the depth from the top of the keel to the freeboard deck whichever is the greater. In no case shall the test head be less than 0.9 metres above the top of the tank. In every ship each transverse and longitudinal watertight subdivision bulkhead shall bulkhead shall be constructed in such a manner that it shall be capable of supporting the pressure due to the maximum head of water which it might have to sustain in the event of damage to the ship. The head of water shall be at least up to the freeboard deck.

Matrix for the HSSC of the different certificates

Load Line Survey: A ship will be subject subject to the following following surveys: surveys: * Initial survey before the ship is put into service; * Renewal survey at intervals not exceeding five years; Annual survey survey within 3 months either either way of the annivers anniversary ary date of the load load line certificate. certificate. The surveyor surveyor will endorse endorse the load line certificate on satisfactory completion of the annual survey. The period of validity of the load line certificate

43


may be extended for a period not exceeding 3 months or the purpose of allowing the ship to complete its voyage to the port in which it is to be surveyed.

PREPARATION FOR A LOAD LINE SURVEY: 1. Check that all access openings at ends of enclosed structures structur es are in good conditions. conditio ns. All dogs, clamps and hinges to be free and well greased. All gaskets and water-tight seals should be crack free. Ensure that the doors open from both sides 2. Check all cargo hatches and access to holds for weather tightness tightn ess 3. Check the efficiency efficie ncy and securing of portable beams 4. If portable wooden hatch covers are used check that they are in good condition 5. If tarpaulins are used at least two should be provided for each hatch and in good condition conditi on 6. Inspect all machinery space opening on exposed deck 7. Check that any manholes and flush scuttles are capable of being made watertight 8. Check that all ventilator ventilato r openings are provided with efficient efficie nt weathertight closing appliance 9. All airpipe should be provided with satisfactory satisfact ory means for closing and opening 10. Inspect any cargo ports below the freeboard deck and ensure that all of them are watertight 11. Ensure that non return valves on overboard valves valv es are operating in a satisfactory satisfa ctory manner 12. Side scuttles scuttle s and openings below the freeboard deck must have efficient effici ent internal watertight deadlights 13. Check that all freeing ports are in satisfactory conditions 14. All guard-rails and bulwarks should be satisfactory satisf actory condition 15. Derust and paint the deck line, loadline marks, load line and the draught marks Cargo Ship Safety Equipment Survey: An initial survey survey of cargo ship safety safety equipment equipment shall include include an inspection inspection of the fire safety safety systems and appliances appliances,, lifesaving appliances and arrangements except radio installations, the shipborne navigational equipment, means of embarkation for pilots and other equipment to which Chapters II1, II2, III and V of the 1974 SOLAS Convention apply, to ensure that they comply with the requirements of the relevant regulations, and they are in satisfactory condition and are fit f or the service for which the ship i s intended. In addition the fire control plans, nautical publications, lights, lights, shapes, means of making sound signals and distress signals shall also be subject to this survey. An annual survey survey shall include include a general general inspection inspection of the equipment equipment referred to above to ensure ensure that it has been been maintained to conform with the provisions of the relevant regulations to ensure that the ship in all respects will remain fit to proceed to sea without danger to the ship or persons on board and that it remains satisfactory for the service for which the ship is intended. A renewal renewal survey and a periodical periodical survey survey shall include an inspection of of the equipment equipment referred to in the initial survey survey to ensure that it complies with the relevant requirements of the relevant regulations, is in satisfactory condition and is fit for f or the service for which the ship i s intended. PREPARATIONS: 1.Inspect all the lifeboat stores and equipment. Overhaul and renew as necessary 2. Inspect the lifeboats pay particular attention to buoyancy material and check that the bottom boards and thwarts are not cracked. Repaint the ship’s name and port of registry 3. Thoroughly over haul davits, winches and blocks and grease all moving parts. Renew or ‘end for end’ the falls 4. When the boats are in water run any lifeboat engines both ahead and astern. 5. Check that t hat the inflatable liferafts have been serviced within the last 12 months. 6. Inspect the survival craft portable radio equipment. 7. Over haul the lifebuoys especially the self ignighting lights and check that they are correctly located. 8. Examine the life jackets and check they are correctly distributed. 9. Check expiry dates of pyrotechnics. 10. Test the emergency lighting system. 11. Check fire control plans are posted and still legible. 12. Test the fire/smoke detection system. 13. Test and try out the fire pump including the emergency fire pump. 14. Check fire hoses, nozzles and applicators are in good conditions.

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15. Test and overhaul the fixed firefighting system. 16. Overhaul portable and non portable fire extinguishers. 17. Confirm that all remote controls are operable. 18. Overhaul any applicable closing arrangement for ventilators, skylights, doors, funnel spaces and tunnels. 19. Overhaul the fireman’s outfit and recharge the compressed air B.A. 20. Inspect the pilot ladders, pilot hoists if carried. 21. Navigational equipment is also surveyed. 22. FORM E (RECORD OF EQUIPMENT TOGETHER WITH SEC)

Condition Assessment Scheme (CAS): CAS is a mandatory statutory survey scheme that Category 2 and Category 3 (non-doubl e hull) oil tankers must satisfactorily complete (with no outstanding recommendations) by 15 years of age or by the first intermediate or renewal survey due after 5 April 2005, whichever occurs later, in order to trade to their respective phase out date as per MARPOL 13G, which was accelerated by resolution MEPC.111(50) which entered into force on 5 April 2005. CAS is required to be conducted in conjunction with, the mandatory Enhanced Survey Program (ESP) and builds upon ESP by requiring additional thickness measurements and close-up surveys. Relative to ESP, CAS is unique in two respects: • CAS contains very specific responsibilities and deadlines for planning the survey, which must begin 8 months in advance of the survey’s commencement; and • The flag Administration must review/monitor the survey and reporting process and issue the five-year full term CAS Statement of Compliance. The requirements of the CAS apply to: Oil tankers of 5,000 tons deadweight and above, 15 years or over after the date of delivery of the ship. The Scheme requires that compliance with the CAS is assessed during the Enhanced Survey Program of Inspections concurrent with intermediate or renewal surveys currently required by resolution A.744(18), as amended. [Category 1 oil tanker means an oil tanker of 20,000 tons deadweight and above carrying crude oil, fuel oil, heavy diesel oil or lubricating oil as cargo, and of 30,000 tons deadweight and above carrying oil other than the above, which does not comply with the requirements for new oil tankers as defined in regulation 1(26) of Annex I of MARPOL 73/78. Category 2 oil tanker means an oil tanker of 20,000 tons deadweight and above carrying crude oil, fuel oil, heavy diesel oil or lubricating oil as cargo, and of 30,000 tons deadweight and above carrying oil other than the above, which complies with the requirements for new oil tankers as defined in regulation 1(26) of Annex I of MARPOL 73/78. Category 3 oil tanker means an oil tanker of greater than 5000 tons deadweight and less than 20,000 tons deadweight carrying crude oil, fuel oil, heavy diesel oil or lubricating oil as cargo or an oil tanker less than 30,000 tons .] deadweight carrying other types of oil .] Timing: 2.1 Initial survey: For Category 2 and 3 tankers, the first CAS survey in accordance with regulation 20.6 shall be carried out concurrent with the first scheduled intermediate or renewal survey after 5 April 2005, or the first scheduled intermediate or renewal survey after the date when the ship reaches the 15 years of age, whichever occurs later. 2.2 Subsequent surveys: Any subsequent CAS surveys, required for the renewal of the Statement of Compliance shall be carried out concurrently with the intermediate or renewal survey which has to be completed by the date of expiry of the Statement of Compliance. 2.3 Early Implementation: Notwithstanding the above, the Company may, with the agreement of the Administration, opt to carry out the CAS survey at a time earlier than the survey due date referred to above, provided that the vessel survey complies with all the requirements of the CAS. Upon satisfactory completion of the survey, shall issue an Interim Statement of Compliance, for a period not exceeding 5 months. It shall remain valid until its expiry date or the date of issue of a Statement of Compliance, whichever is the earlier date. When the results of the CAS Final Report are deemed acceptable to the Administration, it shall issue the requisite with an expiry date of not more than five (5) years and six (6) months from the date of Statement of Compliance Compliance with completion of the CAS survey.

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Condition Assessment Programme(CAP): It is a consultancy / rating service service by classification societies such as ABS, NKK, BV, LRS etc. The purpose of CAP is:  To have the vessel judged based on the actual condition on board rather than age  To contribute to protecting life, property and the environment and to ensure safest possible transportation of the cargo  To establish a sound basis for decisions on repair or investments in order to extend the lifetime of the vessel.  To document a vessel's technical condition towards/in connection with: - Charterers - Cargo owners and/ or authorities in connection with entry into new charters or extension of existing charters - Refinancing of the vessel - Sale or termination of management agreements etc. - Ports and terminals - Flag states Achieving a good CAP rating rating from a reputable classification classification society has become de facto facto requirement or f trading old vessels in the market.

Difference Between CAS and CAP:    

CAP is a consultancy consultancy service service and is independent independent from from CAS, which is a regulatory regulatory survey survey on behalf behalf of the flag state. The CAP-service is rendered according to a contract with the client and rendered to ships. CAP is a voluntary service. CAS is aimed at ensuring a minimum minim um standard for the vessel whereas whereas the main purpose of CAP is to evaluate evaluate and report the vessel’s condition above minimum class standard.

Market Requirement of CAP: CAP is required for oil, chemical and LPG vessels above 20,000 dwt and older than 15 years or LNG vessels older than 20 years. CAP for the f ormer set of vessels should also include a simplified fatigue analysis. The acceptable overall overall CAP rating for the vessel is 2 or better. Enhanced Survey Programme: (In accordance with the regulation 13G, crude oil tankers of 20,000 tons deadweight and above and product carriers of 30,000 tons deadweight and above AND bulk carriers shall be subject to the enhanced programme of inspections.) The ESP is carried out in conjunction with annual, intermediate, periodic and SS with additional inspection/testing requirements. Terms related to ESP: 1. Substantial corrosion is an extent extent of corrosion such that assessment of corrosion pattern indicates a wastage in excess of 75% of allowable margins, margins, but within acceptable acceptable limits. [In general, allowable diminution of plate thickness up to 20% and for profiles up to 25% on original values will be accepted. However, the thickness of plating is not to be less than:

For deck tmin > 0.9 (5.5 + 0.02 · L) and side/bottom t min > 0.9 (5.0 + 0.04 · L) ] 2. Overall survey is a survey intended to report on the overall condition of the hull structure and determine the extent of additional close-up surveys. 3. Close-up survey is a survey survey where the details of structural components are within the close visual inspection i nspection range of the surveyor, i.e. preferably within reach of hand. 4. Representative Representativ e spaces are those which are expected to reflect the condition of other spaces of similar type and service and with similar corrosion prevention systems. When selecting representative spaces account should be taken of the service and repair history on board and identifiable critical and/or suspect areas. 5. Suspect areas are locations showing substantial corrosion and/or are considered by the survey surveyor or to be prone to rapid wastage. 6. Corrosion prevention system is normally considered either: .1 a full hard coating supplemented by anodes; .2 a full hard coating. 46


Other coating systems (e.g. soft coating) may be considered acceptable as alternatives provided that they are applied and maintained in compliance with the manufacturers specification. 7. Coating condition is defined defined as follows: foll ows: GOOD condition with only minor mi nor spot rusting; FAIR condition with local breakdown of coating at edges of stiffeners and weld connections and/or light rusting over 20% or more of areas under consideration, but less than as defined for POOR condition; POOR condition with general breakdown of coating over 20% or more of areas or hard scale at 10% or more of areas under consideration. 8. Critical structural structu ral areas are locations which have been identified from calculations to require monitoring or from the service history of the subject ship or from similar or sister ships to be sensitive to cracking, buckling or corrosion which would impair the structural integrity of the ship. 9. Cargo length area is that part of the ship which includes all cargo holds and adjacent areas including i ncluding fuel tanks, cofferdams, ballast tanks and void spaces.

ITEMS TO BE INSPECTED UNDER ESP: A. Annual Survey: Dry bulk cargo ships subject ships subject to Enhanced Survey Programme (class notation ESP) – additional requirements 301. For hatch covers and coamings the survey shall include: — close-up examination of hatch coaming plating with panel stiffeners and brackets — close-up examination of hatch cover plating and stiffener attachments that may be accessible in the open position where mechanically operated steel hatch covers are fitted — close-up examination of removable hatch cover steel pontoon plating. 302. For mechanically operated hatch covers, hatch cover sets which are wholly wholly or partly within the forward 25% of the ship's length and at least one additional set shall be surveyed open, closed and in operation to the full extent on each direction, such that all sets on the ship are surveyed at least once in every 5-year period including: — stowage and securing in open condition — proper fit and efficiency of sealing in closed condition — operational testing of hydraulic and power components, wires, chains and link drives — examination of the fastening of all peripheral and cross joint cleats or other securing devices in closed condition. If there are indications of difficulty in operating and securing hatch covers, additional sets shall be tested in operation as deemed necessary by the surveyor. 303. For single skin bulk carriers over over 10 years of age the survey shall include: — overall examination of all cargo holds — close-up examination in the forward cargo hold, of approximately lower 1/3 length of the side frames, including the frame end attachment and the adjacent shell plating to a sufficient extent, minimum 25% of frames — examination of all piping and penetrations in cargo holds, including overboard piping. 304. For single skin bulk carriers over over 15 years of age, in addition to the requirements in 303, the survey shall include: — close-up examination of one other selected cargo hold to the same extent as required for the forward cargo hold 305. Where the close-up examination required in 303 and 304 reveals need for remedial measures, the survey shall be extended to include close-up examination of all side frames and adjacent shell plating of the relevant cargo hold, as well as close-up examination of sufficient extent of all remaining cargo holds. 306. For double skin bulk carriers 10 to 15 years of age the survey survey shall include: — overall examination of two selected cargo holds — examination of all piping and penetrations in selected cargo holds, including overboard piping. 307. For double skin bulk carriers over 15 years of age age the survey shall include: — overall examination of all cargo holds — examination of all piping and penetrations in cargo holds, including overboard piping.

Oil and chemical tankers subject tankers subject to Enhanced Survey Programme (class notation ESP) – additional requirements 401. Wheelhouse doors and windows, side scuttle scuttles s and windows in superstructure and deckhouse bulkheads facing the cargo area and possible bow or stern loading and unloading arrangements shall be examined for gas and vapour tightness. 402. Segregation between cargo and segregated ballast system system shall be confirmed. For chemical tankers, removable pipe lengths or other approved equipment necessary for cargo segregation shall be overall examined. 403. Pump rooms shall shall be examined examined with special attention to: — piping with pumps — bulkheads for signs of oil leakage or fractures and, in particular, the sealing arrangements of all penetrations of cargo pump room bulkheads

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— access ladders. 404. For combination ships with protected slop slop tanks, (including ships with class notation PST), the following foll owing shall be examined: — closing arrangement for hatches and other slop tank openings — blanking arrangement for slop tank pipes. B.Intermediate Survey: Dry bulk cargo ships subject ships subject to Enhanced Survey Programme (class notation ESP) – additional requirements 301. For bulk carriers with hybrid cargo hold arrangements, the following foll owing shall be applied: — full breadth cargo holds and associated topside tanks and hopper side tanks are subject to the single skin bulk carrier requirements — cargo holds of double skin and associated side tanks are subject to the double skin bulk carrier requirements. 302. For ships 5 to 10 years of of age the survey survey shall include: a) overall examination of representative ballast tanks selected by the surveyor. The selection shall include fore and aft peak tanks and a number of other tanks, taking into account the total number and type of ballast tanks b) overall examination of all cargo holds c) close-up examination as f ollows: ollows: — for single skin bulk carriers: in the forward cargo hold and one other selected cargo hold, of the transverse bulkheads at the shell plating and side frames, including their upper and lower end attachments and adjacent shell plating to a sufficient extent, minimum 25% of frames. Where considered necessary by the surveyor as a result of the overall and close-up examination, the survey shall be extended to include close-up examination of all side frames and adjacent shell plating of the relevant cargo hold, as well as close-up examination of sufficient extent of all remaining cargo holds. — for double skin bulk carriers: of those areas of structure considered necessary by the surveyor as a result of the overall examination. — thickness measurements shall be carried out to an extent sufficient to determine both general and local corrosion levels at areas subject to close-up examination. The extent of thickness measurement may be specially considered provided the surveyor is satisfied by the close-up examination that there is no structural diminution and the hard protective coatings are found to be in a GOOD condition. 303. For ships over over 10 years of age the survey shall include: a) a thorough examination of hatch covers and coamings with closing, sealing and securing devices. b) testing for satisfactory operation of all mechanically operated hatch covers, including: — stowage and securing in open condition — proper fit and efficiency of sealing in closed condition — operational testing of hydraulic and power components, wires, chains and link drives. c) testing for effectiveness of sealing arrangement of all hatch covers by hose testing or equivalent. d) overall examination of all cargo holds and ballast tanks and in way of all cofferdams, pipe tunnels and void spaces within the cargo area e) examination and performance testing of all piping systems within all cargo holds and ballast tanks as well as cofferdams, pipe tunnels and void spaces within the cargo area. f) close-up examination of stipulated parts: for single hull bulk carriers – cargo hold hatch covers and coamings plating & stiffeners; deck plating & underdeck structures inside line of hatch openings between cargo hold hatches; cargo hold transverse shell frames; cargo hold transverse bulkheads plating, stiffeners & girders, including internal structures of upper and lower stools; ballast tanks transverse bulkheads including stiffening system; ballast tanks transverse web frames with associated plating & longitudinals. for double skin bulk carriers – cargo hold hatch covers and coamings plating & stiffeners; deck plating & underdeck structures inside line of hatch openings between cargo hold hatches; ordinary transverse frames in double side tanks; cargo hold transverse bulkheads plating, stiffeners & girders, including internal structures of upper and lower stools; ballast tanks transverse bulkheads including stiffening system; double bottom structure. For ore carriers – deck transverse including adjacent deck structural members; cargo hold hatch covers plating & stiffeners; deck plating & underdeck structures inside line of hatch openings between cargo hold hatches; transverse web frame rings including adjacent structural members; transverse bulkheads including girder system and adjacent structural members; cargo hold transverse bulkheads plating, stiffeners and girders, including structures of upper & lower stools. g) thickness measurement of stipulated parts. h) a bottom survey. Oil and chemical tankers subject tankers subject to Enhanced Survey Programme (class notation ESP) – additional requirements

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401. For single hull oil tankers from 5 to 10 years of age over overall all examination of all ballast ballast tanks shall be carried out. 402 For ships over 10 years of age the survey shall include: — overall examination of all cargo tanks and ballast tanks and all pump rooms, cofferdams, pipe tunnels and void spaces within the cargo area — examination and performance testing of all cargo piping on deck, including crude oil washing (COW) piping, cargo and ballast piping within all cargo tanks and ballast tanks as well as cofferdams, pipe tunnels and void spaces within the cargo area. Special attention shall be given to any ballast piping in cargo tanks and cargo piping in ballast tanks and void spaces. Thickness measurement shall be taken if deemed necessary by the surveyor. — close-up examination of stipulated parts — thickness measurement of stipulated parts. — a bottom survey. 403. A ballast tank shall be recorded for examination at subsequent annual surveys where, i n addition to the conditions given in 101[ For ships 5 to 10 years of age, an overall examination of representative ballast tanks selected by the surveyor shall be carried out. If there is no protective coating, soft or semi-hard coating, or POOR coating condition, the examination shall be extended to other ballast tanks of the same type . For ships over 10 years of age, an overall examination of all ballast tanks and tanks used as bilge water holding tanks shall be carried out.] and 106 [ the survey shall include examination of the condition of corrosion prevention system, where provided. A ballast tank, except except bilge water water holding tanks, shall be recorded recorded for examination examination at at subsequent annual annual surveys surveys where: — a hard protective coating was not applied from the time of construction, or — a soft or semi-hard coating has been applied, or — the hard protective coating is found in POOR condition and it is not renewed. — the hard protective coating is found to be less than GOOD condition and is not repaired to the satisfaction of the surveyor. ]

— the hard protective coating is found to be less than GOOD condition and is not repaired to the satisfaction of the t he surveyor. C. Renewal Survey: Dry bulk cargo ships subject ships subject to Enhanced Survey Programme (class notation ESP) – additional requirements 301. For bulk carriers with hybrid cargo hold arrangements, the following shall be applied: — full breadth cargo holds and associated topside tanks and hopper side tanks are subject to the single skin bulk carrier requirements. — cargo holds of double skin and associated side tanks are subject to the double skin bulk carrier requirements. 302. Close-up examination of stipulated parts. 303. Thickness measurements shall be carried out of stipulated parts. 304. A bottom survey in dry dock shall be carried out as part of the renewal survey. 305. For single skin bulk carriers subject, additional thickness measurements shall be carried out of the vertically verticall y corrugated transverse watertight bulkhead between cargo holds Nos. 1 and 2. For ships built 1996-1998 the thickness measurements at the 2nd renewal survey may be required as part of the initial evaluation for compliance in order to determine the general condition of the structure and to establish the extent of possible steel renewal and or reinforcements of the bulkhead. Oil and chemical tankers subject tankers subject to Enhanced Survey Programme (class notation ESP) – additional requirements 401. For single hull oil tankers with double bottom or double side spaces (for water ballast, or void spaces), the survey requirements requirements for double hull oil tankers shall be applied in way of the double bottom or the double sides. 402. Close-up examination shall be carried out of stipulated parts. The survey of stainless steel tanks may be carried out as an overall examination supplemented by close-up examination as deemed necessary by the surveyor. 403. Thickness measurements shall be carried out. 404. A bottom survey in dry dock shall be carried out. 405. Cargo tank boundaries facing ballast tanks, void spaces, pipe tunnels, pump rooms or cofferdams shall be pressure tested. All cargo tank bulkheads bulkheads shall be pressure pressure tested at the the 2nd and and subsequent subsequent renewal renewal surveys. The pressure shall, in general, correspond to a head of liquid to the highest point that liquid will rise under service conditions. Pressure testing of cargo tanks may be accepted based on confirmation from the Master, stating that the pressure testing has been carried out according to the requirements, with a satisfactory result. The testing of boundaries facing double bottom tanks and other spaces not designed for the carriage of liquid may be omitted, provided a satisfactory internal examination together with an examination of the tanktop is carried out. The surveyor may extend the tank testing as deemed necessary. 406. A ballast tank shall be recorded for examination at subsequent annual surveys where, in addition to the conditions given in 104 [ Suspect areas identified shall be recorded for examination at subsequent annual surveys.

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Areas found with substantial substantial corrosion, corrosion, which which are not upgraded, upgraded, shall also also be recorded recorded for thickness measurements measurements at subsequent subsequent annual surveys. Note: Annual surveys of suspect areas and areas found with substantial corrosion are not applicable to cargo tanks of oil and .] : chemical tankers .]

— the hard protective coating is found to be less than GOOD condition and is not repaired to the satisfaction of the t he surveyor. 407. For independent cargo tanks in chemical tankers the survey shall include: — thickness measurement as found necessary by the surveyor — hydraulically pressure testing of all tanks to their MARVS (Maximum Allowable Relief Valve Setting). The testing of cargo tanks type a3 may be omitted if the tanks are found without corrosion and other damage and otherwise found acceptable by the surveyor. Preparing for an Enhanced Survey: A. Planning – the the Survey Planning Planning Document. Document. 1. A specific survey programme should be worked out in advance of the periodical survey by the owner in cooperation with the Administration. 2. The survey programme should include conditions for survey, access to structures and equipment for surveys, taking into account the requirements for close-up survey and thickness measurements and tank pressure testing. 3. Alternatively the close-up survey in this survey programme may be based on a planning document, approved by the Administration. The planning planning document document [Survey Planning Planning Document] Document] should comply comply with a procedure procedure for the application of risk assessment developed by the Organization. 4. The survey programme should take into account the information included in the documentation on board. B. Conditions for survey 1. The owner should provide the necessary facilities for a safe execution of the survey. 2. Tanks and spaces should be safe f or access, i.e. gas freed, v entilated, entilated, etc. 3. Tanks and spaces should be sufficiently clean and free from water, scale, dirt, oil residues, etc., to reveal significant corrosion, deformation, fractures, damages or other structural deterioration. In particular this applies to areas which are subject to thickness measurement. 4. Sufficient illuminati on should should be provided to reveal significant corrosion, deformation, fractures, damages or other structural deterioration. C. Access to structures 1. For overall survey, means should be provided to enable the survey surveyor or to examine the structure in a safe and practical way. 2. For close-up survey, one or more of the following means for access, acceptable to the surveyor, should be provided: - permanent staging and passages through structures - temporary staging and passages through structures - lifts and moveable platforms - other equivalent means. D. Equipment for survey 1. Thickness measurements should normally be carried out by means of ultrasonic test equipment. The accuracy of the equipment should be proven to the surveyor as required. 2. One or more of the following followin g fracture detection procedures may be required if deemed necessary by the survey surveyor: or: - radiographic equipment - ultrasonic equipment - magnetic particle equipment - dye penetrant - other equivalent means 3. A communication system should be arranged between the survey party in the spaces and the responsible officer offi cer on deck. 4. Explosimeter, Explosimet er, oxygen-meter, breathing apparatus, lifeline and whistles should be at hand during the survey. A safety checklist should be provided. E. Documentation on board General 6.1.1 The owner should supply and maintain on-board documentation as specified in 6.2 and 6.3, which should be readily available for the surveyor. The condition evaluation report referred to in 6.2 should include a translation into English. English. 6.1.2 The documentation should be kept on board for the lifetime of the ship.

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6.2 Survey report file 6.2.1 A survey report file should be a part of the documentation on board consisting of: .1 reports of structural surveys (annex 6); .2 condition evaluation report (annex 7); .3 thickness measurement reports (annex 8); and .4 survey planning document according to principles in annex 4, where provided. 6.2.2 The survey report file should be available also in the owner's and the Administration offices. 6.3 Supporting documents 6.3.1 The following additional documentation should be available on board: .1 main structural plans of holds and ballast tanks .2 previous repair history .3 cargo and ballast history .4 inspections by ship's personnel with reference to: - structural deterioration in general; - leakages in bulkheads and piping; - condition of coating or corrosion prevention system, if any, and any other information that would help to identify critical structural areas and/or suspect areas requiring inspection.

Pounding stresses exist stresses exist when a ship is pitching. Ship’s bow lifts clear of the water and comes down heavily. It causes damage to the bottom end girder at the bow. The structure is strengthened to resist the effects of pounding/slamming from the collision bulkhead to 25% of the ship’s length from the f orward. orward. The flat bottom shell plating , adjacent to the keel on either side of the ship is increased in thickness from between 15% to 30% depending on the length of the ship; larger ships having smaller increases. In addition to increasing the plating thickness, the unsupported panels of platings are reduced in size. In transversely framed ships the frame spacing in this region is 700 mm compared to 750 to 900 mm amidships. Longitudinal girders are fitted 2.2 m apart apart extending extending vertically from shell shell plate to the the tank top, while intermediate half-height half-height girders are fitted to the shell to reduce the unsupported width to 1.1 m. Solid floors are fitted at every frame space and are attached to the shell by continuous welding. collision

Panting Stresses: As Stresses: As the waves pass along the ship they cause bulkhead fluctuations in water pressure which tend to create an in-out movement of the shell plating. The effect of this is found to be greatest at the ends of the ship, particularly at the fore end, where the shell plating is relatively fl at than at the after end. Such movements are termed PANTING and if not resisted, could lead to fatigue f atigue loading of the material. The structure of the ship i s strengthened strengthened to resist the effects of panting from 15% of the ship’s length from forward to the stem and aft of the after peak bulkhead. In the fore-peak:  Tiers of panting beams are fitted forward of the collision bulkhead below the lowest deck. These are similar to deck beam and are connected to frames by beam knees, but are only fitted at alternative frames.  The intermediate frames are bracketed to the stringers. bulkhead stringer may be stiffened  The free edge of the bulkhead by one of the beams. stringers are fitted in the panting panting area in line with those those in the forepeak. forepeak. These stringers stringers are of  Light side stringers intercostals plates connected to the shell and to a continuous face angle running along the toes of the frames.  Tiers of beams are spaced 2 meters apart vertically and supported by wash plates or pillars.  Panting stringers, similar to deck stringers, are laid on each tier of beams.  To stiffen the joint between each beam and the inner edge of the stringer, the plate edge may be shaped or gussets fitted.

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

At intermediate frame without beams, the stringer is support by a beam knee of half its depth.  At fore ends, the stringers are joined by flat plate called “Breasthooks”.

Fore Peak structure to resist Panting:

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ShipCo Notes - Phase 1 MMD

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