ABOUT PIPING
WHAT IS PIPING ABOUT? We can say PIPING is about designing, fabricating and constructing lines conveying FLUIDS.
What is a FLUID? It can be any of the following •
a GAS
•
a LIQUID
•
a mixture of GAS and LIQUID
•
a SUSPENSION of small SOLID PARTICLES inside a LIQUID.
Basic properties of conveyed FLUIDS •
FLUID TYPE with particular attention to ü the CORROSION characteristics ü the DANGER for HEALTH and the ENVIRONMENT
•
FLOW RATE
•
PRESSURE
•
TEMPERATURE
What is a PIPELINE? A PIPELINE conveys a fluid from one given point of the plant usually called INLET point of the line, to another part of the plant usually called OUTLET point of the line. A PIPELINE can also connect one PIPELINE to another PIPELINE. PIPELINES can also discharge the conveyed fluid into the environment (VENTS and DRAIN)
Basic characteristics of a PIPELINE •
SIZE (or DIAMETER)
•
WALL THICKNESS
•
TYPE OF JOINTS BETWEEN PIECES
•
EXTERNAL FINISHING
•
QUALITY CHECKS
ü welded joints (butt welding / socket welding) ü threaded joints ü flanged joints
ü Painting ü Insulation
ü Hydraulic Testing ü Non Destructive Examination of Joints
Other characteristics of a PIPELINE •
ROUTING ü ü
The routing is how the Pipeline is developed into the space.
ü
Cold Pipelines connecting static objects (something that does not move like Tanks, Vessels, other Pipelines, Headers) can be straightly routed between the inlet and the outlet point.
ü
Cold Pipelines connecting MACHINES that vibrate or rotate may need a flexible part between the inlet and the outlet point.
ü
Hot Pipelines must be flexible enough to adsorb the thermal expansion of the Pipeline from cold to hot condition
There are rules and regulations to route a Pipeline according the “Good Engineering Practice”
•
SUPPORTING SYSTEM ü
Every Pipeline must be supported. Not all Pipelines are supported in the same way
ü
Cold Pipelines can be supported everywhere with FIXED POINTS
ü
Hot Pipelines cannot be supported only with fixed points, but certain points must be only GUIDED, meaning that in those points the Pipeline retains a certain numbers of degree of freedom in certain directions, while are constrained in certain other directions
PIPING DESIGN •
Specification of Lines It is a document that summarizes all the characteristics of a PIPELINE. Starting from the PROPERTIES of the CONVEYED FLUID, the document specifies all the CHARACTERISTICS of the PIPELINE
FLUID TYPE ü Choice of material Non corrosive fluids Services where impurities are accepted industrial water lines (cooling water) steam lube oil return / before filter lines air lines vents and drains Corrosive fluids Services where impurities are not accepted demineralized water lube oil after filters fuel gas / oil sea water (water containing Chlorine) Agressive Chemicals Strong Acids / Bases
Carbon Steel Low Alloy Steel (High T)
Stainless Steel
No Iron (Fe) Copper/Nikel Alloys (Cu-Ni) Plastic: PVC – TEFLON – PE Rubber: NBR, Viton Composites: RESIN GLASS
FLUID TYPE ü Choice of CORROSION ALLOWANCE Thickness increasing taking into account CORROSION Typical corrosion allowance for water is 3 mm that affects THICKNESS
ü Choice of joints. DANGEROUS fluids are conveyed in fully welded pipes, were leaks cannot occur.
ü Choice of NDE For Dangerous Fluids 100% of joints are likely to be X-Ray examined
FLOW RATE ü Choice of Diameter For a given flowrate - SMALL DIAMETER means HIGHER VELOCITY of the conveyed fluid - BIG DIAMETER means SLOWER VELOCITY of the conveyed fluid Velocity of fluids in Pipelines affects - Pressure Losses along the Pipeline Pressure Losses are PROPORTIONAL to the square velocity (v2) - Vibration of the Pipeline Usual Velocity of Fluids inside pipelines are: Gas: 20 m/s - max. 40 / 50 m/sec Liquid: 2 to 4 m/s - max. 10 m/sec
TEMPERATURE ü Choice of MATERIAL - Steel for High Temperature (Low Alloy Steel Creep Resistant) ü Calculation of wall THICKNESS ü Routing Design and calculation of SUPPORTS (STRESS ANALYSIS) - Hot Lines must be routed properly. Provisions shall be taken so that when temperature rises from ambient to Operating Temperature the thermal expansion of Pipelines does not generate stresses too high for the pipes to withstand.
ü Application of Thermal Insulation - T>60°C Insulation for Personnel Protection is mandatory for all pipeline parts that can be reached by hands.
PRESSURE ü Calculation of Wall Thickness ü Choice of the Joint - Low pressure pipelines can be threaded or socket welded - High Pressure pipelines are Butt Welded ü Extension of NDE of the joints -
Non process Pipelines (For Example Vents and drain lines) may even have no tests at all Low Pressure Pipelines can undergo only the Hydraulic Test
-
For intermediate pressures a 10% to 50% of joints must be examined with X-rays
-
High Pressure Pipelines are usually 100% X-ray examined.
AMERICAN STANDARDS FOR PIPING DESIGN ANSI =
AMERICAN NATIONAL STANDARDIZATION INSTITUTE
ASME =
AMERICAN SOCIETY of MECHANICAL ENGINEERS
ANSI/ASME B31.1: POWER PIPING ANSI/ASME B31.3: PROCESS PIPING THESE STANDARDS GIVE TECHNICAL RECOMMENDATIONS FOR DESIGNING PIPING SYSTEM FOR POWER PLANTS AND CHEMICAL PLANTS ü THEY CONTAINS FORMULAS TO CALCULATE THE MINIMUM THICKNESS OF PIPELINES ü THEY CONTAINS FORMULAS TO CALCULATE THE EXTRA THICKNESS THAT A PIPE MUST HAVE WHEN A BRANCH IS CUT INTO IT. ü THEY CONTAINS REGULATIONS FOR STRESS ANALYSIS ü THEY CONTAINS TABLES THAT GIVE MAXIMUM ALLOWABLE STRESS FOR METALLIC MATERIALS ACCEPTED BY ANSI FOR PIPELINE CONSTRUCTION DEPENDING ON TEMPERATURES.
STANDARD MATERIALS FOR PIPING ASTM =
AMERICAN SOCIETY for TESTING MATERIALS
ü
ASTM developed a collection of documents called MATERIAL SPECIFICATIONS for standardising materials of large use in the INDUSTRY. Specifications starting with “A” are for STEEL. Specifications starting with “B” are for non-ferrous alloys (Bronze, Brass, Copper Nickel alloys, Aluminium alloys and so on). Specifications starting with “D” are for plastic material, as PVC.
ü
An ASTM Specification does not only specify the basic CHEMICAL COMPOSITION of material, but also the PROCESS through which the material is shaped into the final product.
ü
This is why for a given base material SEAMLESS PIPE have a specification, WELDED PIPE have another specification WROUGHT FITTINGS have another specification, FORGED FITTINGS have another specification, large VALVE bodies (normally CAST) have another specification
CARBON STEEL Steel is basically a solution of carbon (C) into iron (Fe). The presences of carbon into the crystal structure of the iron improve very much the mechanical caracteristics of the iron alone. Carbon steel is a conventional denomination for steel that has almost no other metallic elements added into it. ASTM most employed carbon steel for pipes are ASTM A53 Grade A and B and ASTM A106 Grade A and B. A53 used to be cheaper than A106 and Grade A cheaper than Grade B. Today the difference is not so big, so that for small quantities ASTM A106 Gr. B is usually choosen. ASTM Specifications belonging to same family of Carbon Steel SEAMLESS PIPES ASTM A53 (Gr. A / B) or A106 (Gr. A / B) WELDED PIPES ASTM A134 / A135 / A139 WROUGHT FITTINGS ASTM A234 (WPA / WPB) FORGED FITTINGS A105 CAST PARTS A216 (WCB)
API Standards For Oil and Gas Industry, another American Standardization Institute is common and important. This Institute is
API =
AMERICAN PETROLEUM INSTITUTE
Rules, Practices and Standards for Oil and Gas Industry are issued by this Institute and followed by almost all Oil and Gas Companies in the world. Among the many Standards issued by the Institute there is also a Standard for design of Pipelines: API STANDARD 5L Within this Standard Materials for Oil and Gas transportation pipelines are specified, with denomination API 5L This is a family of Carbon Steels almost equivalent to ASTM A53 / A106.
LOW ALLOY STEEL The introduction of other elements into steel can change very much its mechanical characteristics. ü
Steel is subject to a process called “creep” at high temperatures (T > 540 °C) Creep is a reduction of strength over time due to high temperature. It means that if today the steel can withstand a certain pressure, after a long time at high temperature same steel can withstand much lower pressures, since its resistance is decreasing with time due to the high temperature.
ü
Steel becomes also particurarly fragile if submitted to sudden impacts at low temperatures (< - 20 °C).
The introduction of small percentages of chromium (Cr), nichel (Ni), magnesium (Mg), manganese (Mn), molybdenum (Mo), proves to improve the strength of the steel and its resistance to corrosion also at high temperatures (>500 °C) or at low temperaturea (< -20 °C).
Low Alloy Steel is a conventional denomination for steels where there are small percentages of elements, usually metallic, other than carbon only. Alloy steels are usually identified with denominations that recall composition. As for example following high temperature resistant steels: Denomination
Alloy percentage
Grade
5Cr-½Mo 1¼Cr-½Mo-Si 1Cr-½Mo 2¼Cr-1Mo
(5% Cr – 0.5% Mo ) (1.25%Cr – 0.5% Mo – Si) (1% Cr – 0.5 Mo) (2.25 Cr – 1% Mo)
P5 P11 P12 P22
Grade for Castings C5 (WC5) (WC5) WC9
ASTM Specifications belonging to same families of Low Alloy Steels SEAMLESS PIPE A335 (P5 – P11 – P12 – P22) WELDED PIPE ASTM A358 WROUGHT FITTINGS ASTM A234 (WP5 – WP11 – WP12 – WP22) FORGED FITTINGS A182 (F5 – F11 – F12 – F 22) CAST PARTS A217 (C5 – WC5 – WC9)
STAINLESS STEEL One of most important problems with carbon and low alloy steels, is that the iron exposed to air and water combines with oxygene (O2) and generates rust (di-iron tri-oxyde Fe2O3) that peels out from the surface. High percentages of chromium (Cr) and nichel (Ni) added into the steel stop this problem. Stainless Steel is conventional generic denomination for steels with high percentages of chromium (minimum 16%) and nichel (minimum 8 %). Traditional denomination for stainless steel was given first from AISI (American Institute for Steel and Iron) and is still in the tradition and retained in the Grade of ASTM Specifications. But as usual for alloy steels, a more precise denomination can refer to composition.
AISI
Denomination
304 / 304L 316 / 316L 321
18Cr-8Ni 16Cr-12Ni-2Mo 18Cr-10Ni-Ti
Alloy Percentage
Grade for Castings (18%Cr – 8%Ni) CF3 / CF8 (16%Cr – 12%Ni – 2%Mo) CF3M / CF8M (18%Cr – 10%Ni – Ti) Not Available
The “L” suffix stands for “Low Carbon”. In fact the presence of high percentages of Cr and Ni improves the resistance of steel against rust, but at one cost: stainless steel is very difficult to weld. Welding of stainless steel can be improved by reducing the content of carbon in it. ASTM Specifications belonging to same family of Stainless Steel SEAMLESS PIPE A312 TP304 – 304L - 316 - 316L - 321 WELDED PIPE ASTM A249 TP304 - 304L - 316 - 316L - 321 WROUGHT FITTINGS ASTM A403 WP304 - 304L - 316 - 316L - 321 FORGED FITTINGS A182 F304 – 304L - 316 - 316L - 321 CAST PARTS A351 (CF3 – CF3M / CF8 – CF8M)
How Pipeline CHARACTERISTICS are defined by the Standards.
SIZE NOMINAL PIPE SIZE : NPS It is a conventional size expressed solely in INCHES, related to the cross section diameter of the pipeline. For smaller sizes the NPS is not usually exactly equal to any real diameter, but bigger. This comes from the fact that for uniformity, pipelines must have same Outside Diameter, and change Inside Diameter with different thickness. But in fluid transportation the internal diameter is more significant, so if the Outside Diameter is bigger of the NPS, taking away the thickness, the NPS gives more an idea of the internal diameter.
NOMINAL DIAMETER : DN Same as NPS, but in mm. It is the usual denomination of Size in Europe where S.I. is adopted. All external diameters pipes according EUROPEAN Standards (DIN - Germany, UNI - Italy, AFNOR – France) are exactly equal of the equivalent NPS Sizes according AMERICAN and BRITISH Standars (BS) EXCEPT 5” (DN125)
WALL THICKNESS (1) 1. For PIPES and WROUGHT BW FITTINGS, wall thickness is given in INCHES or mm. Some series of thicknesses are standardized. There are two series of systems of standardized thicknesses.
Schedule
Weight Series
Carbon Steel ANSI B16.10
5, 10, 20, 30, 40, 60, 80, 100, 120, 160.
Stainless Steel ANSI B16.19
5S, 10S, 20S, 30S, 40S, 60S, 80S.
Std
Standard
XS
Extra Strong
XXS
Extra Extra Strong
It happens that for a given diameter the thickess of one Schedule is equal to the thickness of one Weight Series. For example for small diameters, Sch. 40 is equal to Std Weight. THIS IS NOT A RULE, and this idea is one of the most common mistakes in piping design.
WALL THICKNESS (2) 2. For FLANGES, VALVES and FORGED FITTINGS, a different system of indicating the wall thickness is used. This is called PRESSURE RATING. It is a NUMBER expressed in POUNDS per SQUARE INCH (PSI symbol #) that refers to the maximum internal pressure acceptable for normal operation inside that part. 125#
150#
Cast Iron
900#
300#
400#
600#
Flanges & Valves
(Not in NP Standards)
Fl. & Valves Forged Small
1500#
3000#
6000#
2500#
Flanges & Valves
800# Valves (≤ ≤ 2”)
9000#
Forged Fittings
This conventional number is not exactly the actual maximum pressure acceptable inside the part. The maximum pressure allowed for a given rating is tabulated in the ANSI standards and depends on ü Temperature ü ASTM Material
TYPE OF JOINTS BETWEEN PIECES (1) 1. BUTT-WELDING ENDS The end is machined to allow head to head full penetrating welding
TYPE OF JOINTS BETWEEN PIECES (2) 2. SOCKET WELDING ENDS A socket is provided where pipe can be inserted
TYPE OF JOINTS BETWEEN PIECES (3) 3. THREADED ENDS Parts to be connected are threaded. For services where leaks are strongly undesired, a light weld is carried out at the surface, this is called “Seal Weld”.
“Seal” weld
STANDARDIZED PIPING OBJECTS PIPES
FITTINGS FLANGES
VALVES
GASKETS BOLTS AND NUTS
PIPES: ANSI B36.10 CS / B36.19 SS Seamless Electric Resistance Welded No material is added during welding process
Electric Fusion Welded Material (Filler Metal) is added during the process of welding
HOW TO IDENTIFY A PIPE SIZE
NPS 12”
(DIAMETER)
(DN 300)
WALL THICKNESS
Sch. 40
MATERIAL
ASTM A106 Gr. B
BW FITTINGS : ANSI B16.9 Bends 30° - 45 ° - 60° - 90° Long Radius R=1.5 D Short Radius R=D
Tees Straight Full Tees Reducing Tees
Reducers Concentric Reducers Eccentric Reducers
Caps
HOW TO IDENTIFY A BW FITTING 1. Straight Fittings TYPE BEND 90° LR SIZE
NPS 12”
(DIAMETER)
(DN 300)
WALL THICKNESS
Std
MATERIAL
ASTM A234 WPB
2. Reducing Fittings TYPE
REDUCING TEE
SIZE
NPS 12”x8”
(DIAMETER)
(DN 300x200)
WALL THICKNESS
Sch. 30x20
MATERIAL
ASTM A234 WPB
FORGED FITTINGS ANSI B16.11
HOW TO IDENTIFY A FORGED FITTING TYPE
ELBOW 90°
SIZE
NPS 1”
(DIAMETER)
(DN 25)
WALL THICKNESS
Rating 3000#
JOINT
NPT
MATERIAL
ASTM A105
PIPE NIPPLES They are standardized short pieces of pipe usually 50 mm or 100 mm long normally used between two close fittings. They can come in straight size or in reducing size and can have one end machined in a different way than the other. Such a variety of combinations is summarized using abbreviations B = Bevelled L = Large E = End P = Plain S = Small T = Threaded
Pipe nipples can be used to change among joint types. For example a PExBE Pipe Nipple changes a Socket Welding Line into a Buttwelding Line Beveled End
Plain End
BW SW
FLANGES ANSI B16.5 1. Pipe Connection Welding Neck Slip On Lap Joint Socket Welding Threaded 2. Mating Flat Face Raised Face Ring Joint
WELDING NECK Used for all sizes, they allow full penetration weld between pipe and flange. For this reason they are used for severe applications where failure of welda cannot be accepted. This does not come free of cost, since the shape of the flange obliges to start from a heavy forging and waste a lot of material from machining. SLIP ON Used for all sizes, they are very much economical because they are flat and can be obtained from sheets or plates with minimum waste of material from machining. But they do not allow full penetration weld, so that they are use for low ratings (usually 150# only) and unsevere applications
THREADED Can be used for all sized, but are preferably used for small sizes (< or equal to 2”). Cheap manufacturing, cheap installation (no weld is required) but limited to threadel lines, that means unsevere applications where leaks are not a major issue LAP JOINT A Stub End is welded on the pipe after the flange insertion of it. This solution is used for Stainless Steel lines at low pressure, since the heavy flange does not come in contact with the conveyed fluid and can be provided in much cheaper Carbon Steel material. Moreover no weld is required, also a good thing for Stainless Steel lines.
SOCKET WELDING Used for small sizes (< or equal to 2”) for unsevere services on Socket Welding lines.
Flat Face Gasket:
Full Face Flat It covers the entire surface of the flange
Raised Face Gasket: Flat It covers the raised surface of the flange
Spiral Wound Also known as Spirometallic, or Spirotallic, its a wounded spiral of Stainless Steel and Graphite to withstand high temperatures or severely aggressive fluids
Ring Joint Gasket:
Metallic Ring It is normally made up of Steel. It deforms inside the ring joint grooves assuring sealing at very high pressures.
Surface Finishing of Flanges To improve the sealing effect of plane gaskets, the surface of a flange can be machined. A set of circular scares is machined in the surface. When the gasket is tightenly squeezed between the flanges, it penetrates into the scares improving sealing.
HOW TO IDENTIFY A FLANGE JOINT TYPE
SLIP ON
SIZE
NPS 6”
(DIAMETER)
(DN 150)
WALL THICKNESS
Rating 300#
MATING - FINISH
RF – R9
MATERIAL
ASTM A105
VALVES: CAST STEEL Globe
Gate
Check
VALVES: FORGED STEEL Globe
Gate
Check
Ball
Butterfly
ACTUATION OF VALVES To open and close a valve, you can use Hands Electric Power Compressed Air High Pressure Oil
in which case you need a valve provided with Handwheel Electric Actuator Pneumatic Actuator Hydraulic Actuator
and the valve is called Manual Electric Pneumatic Hydraulic
CONTROL VALVES These valves are used to CONTROL one or more of the PROPERTIES of the conveyed fluid in order to mantain the VALUES of the controlled property within a specific range. The internal parts of these valves are specially designed tu suit the particular control task and are non subject to particular Standards. Anyway, the majority of Control Valve Manufacturers try to respect at least the end to end dimensions given in ANSIB16.25. Also connections follows the recognized international standards.
SAFETY AND RELIEF VALVES These valves are installed on pipelines where pressure can exceed by accident the DESIGN PRESSURE of the pipeline. These valves are designed to open and discharge the conveyed fluid when the pressure in the pipeline becomes greater than a specified value called SET. RELIEF
The valve opens when the pressure goes over the SET, but close again when the pressure returns under the SET
SAFETY
The valve opens when the pressure goes over the SET, but never closes again. Personnel intervention is required on the pipeline to check the event and the condition of the area, before re-arming the valve and starting operation again
TUBING A TUBE is a circular section of given DIAMETER and THICKNESS. It is normally specified giving the Ouside Diameter (OD) and the thickness. But it can also be specified giving the Inside Diameter (ID) and the thickness. The given numbers correspond exactly to the geometrical dimension they refer. So A 2” OD TUBE has exactly a 2” Outside Diameters.
Dimensionally, there are two big families of tubing 1. FRACTIONAL TUBES The INCH is the unit of measure, and since tubes for piping purpose (REMEMBER: CONVEYING FLUIDS!) are small, usually less than 1”, FRACTIONS of inch are used, hence the name FRACTIONAL 2. METRIC TUBES
As per SI requirements, mm is the unit of measure. Again the value in mm is the actual ouside diameter of the tube, so that a DN15 pipe has a rather different OD then a 15 mm tube.
TUBES in PIPING DESIGN. Tubes are not usually used in PIPING DESIGN except for some very particular services. In typical Oil and Gas Machinery installations, like Nuovo Pignone’s, TUBES are basically used for: 1. Parts of HP Hydraulic Lines 2. Instrument connecting Lines 3. Pneumatic Lines
These Lines are small size (usually less than 1”). COMPRESSION FITTINGS Tubing is usually BENT. A large variety of fittings are available for 1. detachment of BRANCHES (Tees) 2. Passing through steel walls (Bulk Unions) 3. Unite tube to tube (tubing is not welded)
4. Connecting Tubing to PIPES (Connectors) 5. Connecting Tubes to Flexible Hoses Connection of TUBING with the fitting is achieved through a particular locking system where a RING (“FERRULE”) is forced to COMPRESS the Tube walls for sealing and joining.
These fittings are not STANDARDIZED, but are branding based and patented. Most popular manufacturers of compression fittings are PARKER SWAGELOCK GARILOCK
