Piping-Construction EPT 09-T-04 August 1998
Scope This Engineering Practice Tutorial (EPT) supplements the requirements for fabrication, assembly and erection, inspection, testing and cleaning of piping contained in MP 16-P-40 by providing tutorial information for these topics. topi cs. It covers all piping for onshore and offshore production and processing facilities.
Version 0
EPT 09-T-04
Piping -Construction
August 1998
Table of Contents 1.
2.
Refer Ref erenc ences es.................................................................................................................................. .................................................................................................................................. 4 1.1.
MEPS –Mobil –Mo bil Enginee Eng ineerin ring g Practic Pra ctices es....... .............. .............. .............. ........... ........... .............. .............. .............. ........... ............ ............ ....4 4
1.2.
AP I–American –Americ an Petroleu Petr oleum m Institute Inst itute ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........ ..4 4
1.3.
ASME–Amer ASME –American ican Society of Mechanical Mechani cal Engineers Engine ers ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ....... ....... ...... ...... ......4 ...4
1.4.
ASTM ASTM –American Society for Testing and Materials ...... ......... ...... ...... ...... ...... ...... ...... ...... ...... ....... ....... ...... ...... ......4 ...4
1.5.
PFI PF I–Pipe –Pi pe Fabrication Fabri cation Institute Instit ute ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... .......... ....5 5
Additio Addi tional nal Referenc Refer ences es...... ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ........ ..5 5 2.1.
MEPS –Mobil –Mo bil Enginee Eng ineerin ring g Practic Pra ctices es....... .............. .............. .............. ........... ........... .............. .............. .............. ........... ............ ............ ....5 5
3.
Defini Def initio tions ns .................................................................................................................................. 5
4.
Fabric Fab ricati ation on.................................................................................................................................. .................................................................................................................................. 8
5.
4.1.
Weldin Wel ding g Proced Pro cedure ures s ........... ................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........ ...8 8
4.2.
Joint Joi nt Prepar Pre parati ation on and Alignm Ali gnment ent ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............. .......... ...9 9
4.3.
Welding Weld ing Recommen Reco mmendati dations ons ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ..........11 ....11
4.4. 4.4 .
Preh Pr ehea eatt ...........................................................................................................................1 2
4.5.
Postwel Pos tweld d Heat Hea t Treatm Tre atment ent ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........... .........13 ....13
4.6.
Bendin Ben ding g of Pipe Pip e ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........1 ...14 4
4.7.
Shop and Field Fie ld Fabric Fab ricated ated Piping Pip ing ............ ................. ........... ............ ............ ............ ............ ............ ............ ............ ........... ........... ........1 ..16 6
Assemb Ass embly ly and Erecti Ere ction on..... .......... .......... .......... .......... .......... ............... ............... .......... .......... .......... ............... ............... .......... .......... .......... .......... ...............1 ..........17 7 5.1.
Field Fie ld Welding .......... ............... .......... .......... .......... ............... ............... .......... .......... .......... ............... ............... .......... .......... .......... ................ ................. ............17 ......17
5.2.
Misalign Misa lignment ment Correcti Corr ections ons ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........... .........18 ....18
5.3.
Flanged Flange d Joints ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ............ ............ ..........18 ....18
5.4.
Threaded Thre aded Joints Join ts ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... .......1 ..19 9
5.5.
Valve Valv e Install Ins tallatio ation n ............ .................. ............ ............ ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ........... .......... .......1 ..19 9
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6.
Examina Exa minatio tion n and Inspec Ins pectio tion n ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............20 ......20
7.
Pres Pr essu sure re Test Te stin ing.....................................................................................................................2 g.....................................................................................................................2 0
8.
9.
7.1.
Hydro Hyd rosta static tic Test Tes t ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... .......2 ..21 1
7.2.
Pneumati Pneu matic c Leak Lea k Test....... Tes t............. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .........22 ...22
7.3.
Initia Ini tiall Serv Ser vice Leak Lea k Test........ Tes t.............. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ..........23 ....23
7.4.
Alterna Alte rnative tive Leak Test....... Tes t............. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .........23 ...23
Pipe Cleaning...........................................................................................................................24 8.1.
Water Flushing Flushin g ............ .................. ............ ............ ............ ............ ............ ........... ........... ............ ............ ............ ............ ............ ............ ............ ........... .........24 ....24
8.2.
High Pressu Pre ssure re Jet Flushin Flus hing g .......... ............... .......... .......... .......... ............... ............... .......... .......... .......... ................ ................. ............ ............25 ......25
8.3.
Pneumatic Pneu matic (Air) (Air ) Flushing Flus hing ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........... ........... ...........25 .....25
8.4.
Steam Flushing Flush ing ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........2 ...26 6
8.5.
Slug Flow Flushing Flushi ng ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ .......2 .26 6
8.6.
Chemical Cleaning ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........2 ..26 6
8.7. 8.7 .
Han Ha nd Cleani Cle aning ng ...............................................................................................................2 7
Fabrication, Erection, Inspection Inspection and Testing of Nonmetallic Piping .... ...... .... .... .... .... .... .... .... ...27 .27
10. 10. Pre-Sta Pre- Startu rtup p Review Rev iew ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ..........27 ....27 10.1. 10. 1. Piping Pip ing Checkl Che cklist ist...... ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... .......... ........2 ...28 8 11. 11. Post Pos t Completi Compl etion on Technic Tec hnical al Audit Audi t ............ .................. ............ ........... ........... ............ ............ ............ ............ ............ ............ ........... ........... ..........29 ....29 11.1. 11. 1. Techni Tec hnical cal Audit Checkl Che cklist ist ............ .................. ............ ............ ............ ............ ............ ............ ............ ............ ............ ........... ........... ........... .........29 ....29
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References The following publications form a part of this Tutorial. Unless otherwise specified herein, use the latest edition.
1.1.
MEPS–Mobil Engineering Practices
MP 16-P-01
Piping-General Design
MP 16-P-40
Piping-Fabrication, Erection, Inspection, & Testing
1.2.
API–American Petroleum Institute
API SPEC 5L
1.3.
Specification for Line Pipe Forty-First Edition
ASME–American Society of Mechanical Engineers
ASME B16.5
Pipe Flanges and Flanged Fittings NPS 1/2 Through NPS 24
ASME B16.20
Metallic Gaskets for Pipe Flanges - Ring-Joint, Spiral-Wound, and Jacketed Errata - 1994
ASME B16.25
Buttwelding Ends
ASME B31.1
Power Piping
ASME B31.3
Process Piping
ASME SEC IX
BPVC SECTION IX Qualification Standard for Welding and Brazing Procedures, Welders, Brazers, and Welding and Brazing Operators Addenda - 1995; Addenda - 1996; Interfiled (Boiler and Pressure Vessel Codes)
1.4.
ASTM–American Society for Testing and Materials
ASTM A106
Standard Specification for Seamless Carbon Steel Pipe for HighTemperature Service
ASTM A587
Standard Specification for Electric -Resistance-Welded Low-Carbon Steel Pipe for the Chemical Industry
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1.5.
2.
Piping -Construction
August 1998
PFI–Pipe Fabrication Institute
PFI ES-3
Fabricating Tolerances R(1994)
PFI ES-24
Pipe Bending Methods, Tolerances, Process and Material Requirements R(1995)
Additional References The following documents are not specifically referenced herein but are included as additional sources of information on piping.
2.1.
3.
MEPS–Mobil Engineering Practices
MP 16-P-30A
Piping - Materials and Service Classifications (M&R)
MP 16-P-31A
Piping-Classifications-(E&P, On/Offshore)
MP 57-P-02
Pressure Containing Equipment - Welding & Inspection
Definitions Annealing
Heating to and holding at a suitable temperature and then cooling at a suitable rate for such purposes as: reducing hardness, improving machinability, facilitating cold working, producing a desired microstructure or obtaining desired mechanical, physical or other properties.
Arc cutting
A group of cutting processes wherein the severing or removing of metals is effected by melting with the heat of an arc between an electrode and the base metal.
Arc welding
A group of welding processes which produces coalescence of metals by heating them with an arc or arcs, with or without the application of pressure and with or without the use of filler metal.
Assembly
The joining together of two or more piping components by bolt ing, welding, bonding, screwing, brazing, soldering, cementing or use of packing devices as specified by the engineering design.
Automatic
Welding with equipment which performs the welding operation without
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welding
adjustment of the controls by an operator. The equipment may or may not perform the loading and unloading of the work.
Backing ring
Material in the form of a ring used to support molten weld metal.
Base metal
The material to be brazed, soldered, welded or otherwise fused.
Branch connection fitting
An integrally reinforced fitting welded to a run pipe and connected to a branch pipe by a buttwelding, socket welding, threaded or flanged joint; includes a branch outlet fitting conforming to MSS SP-97.
Brazing
A metal joining process wherein coalescence is produced by use of a nonferrous filler metal having a melting point above 427 °C (800°F), but lower than that of the base metals being joined. The filler metal is distributed in the joint by capillary attraction.
Butt joint
A joint between two members aligned approximately in the same plane.
Category D Fluid Service
A fluid service in which all of the following apply: 1. The fluid handled is nonflammable, nontoxic and not damaging to human tissues. 2. The design pressure does not exceed 1035 kPa (150 psi). 3. The design temperature is from -29°C (-20°F) through 186 °C (366°F).
Construction (Erection)
The complete installation of a piping system in the locations and on the supports designated by the engineering design including any field assembly, fabrication, examination, inspection and testing of the system.
Consumable insert
Preplaced filler metal that is completely fused into the root of the joint and becomes part of the weld.
Fabrication
The preparation of piping for assembly, including cutting, threading, grooving, forming, bending and joining of components into subassemblies. Fabrication may be performed in the shop or in the field.
Face of weld
The exposed surface of a weld on the side from which the welding is done.
Filler material
The material to be added in making metallic or nonmetallic joints.
Fillet weld
A weld of approximately triangular cross section joining two surfaces approximately at right angles to each other in a lap joint, tee joint or corner joint.
Full fillet weld
A fillet weld whose size is equal to the thickness of the thinner member joined.
Fusion
The melting together of filler material and base material, or of base material only, which results in coalescence.
Gas metal-arc welding (GMAW)
An arc-welding process which produces coalescence of metals by heating them with an arc between a continuous filler metal (consumable) electrode and the work. Shielding is obtained entirely from an externally supplied gas or gas mixture. Some variations of this process are called MIG or CO2 welding.
Gas tungstenarc welding (GTAW)
An arc-welding process which produces coalescence of metals by heating them with an arc between a single tungsten (non-consumable) electrode and the work. Shielding is obtained from a gas or gas mixture. Pressure may or
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may not be used and filler metal may or may not be used. (This process is sometimes called TIG welding.) Groove weld
A weld made in the groove between two members to be joined.
Heat affected zone
That portion of the base material which has not been melted, but whose mechanical properties or microstructure have been altered by the heat of welding, brazing, soldering, forming or cutting.
Inspector (owner's Inspector)
The person who has the overall responsibility to verify that all required examinations and testing have been completed and who shall inspect the piping to the extent necessary to be satisfied that it conforms to all applicable examination requirements of the B31.3 code and of the engineering design. See Chapter VI in ASME B31.3 for additional information regarding the owner's Inspector.
Manual Welding A welding operation performed and controlled completely by hand. May
A term which indicates that a provision is neither required nor prohibited.
Mechanical joint
A joint for the purpose of mechanical strength or leak resistance, or both, in which the mechanical strength is developed by threaded, grooved, rolled, flared or flanged pipe ends; or by bolts, pins, toggles or rings; and the leak resistance is developed by threads and compounds, gaskets, rolled ends, caulking or machined and mated surfaces.
Normalizing
A process in which a ferrous metal is heated to a suitable temperature above the transformation range and is subsequently cooled in still air at room temperature.
NPS
Nominal Pipe Size (followed, when appropriate, by the specific size designation number without an inch symbol).
Piping
Assemblies of piping components used to convey, distribute, mix, separate, discharge, meter, control or snub fluid flows. Pip ing also includes pipesupporting elements, but not support structures.
Piping components
Mechanical elements suitable for joining or assembly into pressure-tight fluid-containing piping systems. Components include pipe, tubing, fittings, flanges, gaskets, bolting, valves and devices such as expansion joints, flexible joints, pressure hoses, traps, strainers, in- line portions of instruments and separators.
Piping System
Interconnected piping subject to the same set or sets of design conditions.
Postweld heat treatment (PWHT)
Uniform heating of a structure or portion thereof to a sufficient temperature to relieve the major portion of the residual stresses, followed by uniform cooling slowly enough to minimize development of new residual stresses.
Preheating
The application of heat to the base material immediately before or during a forming, welding or cutting process.
Radiography (100 percent)
Radiographic examination of the complete circumference of all the butt and miter welds in a designated lot of piping. Applies only to butt and miter welds unless otherwise specified in the engineering design.
Radiography (Random)
Radiographic examination of the complete circumference of a specified percentage of the welds in a designated lot of piping. Applies only to butt and
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miter welds unless otherwise specified in the engineering design.
4.
Radiography (Spot)
It is making a single exposure radiograph at a point within a specified extent of welding. The required coverage is generally specified in the applicable ASME code.
Root opening
The separation between the members to be joined, at the root of the joint.
Seal weld
A weld intended primarily to provide joint tightness against leakage in metallic piping.
Shall
A term which indicates that a provision is required.
Shielded metalarc welding (SMAW)
An arc welding process which produces coalescence of metals by heating them with an arc between a covered metal electrode and the work. Shielding is obtained from decomposition of the electrode covering. Pressure is not used and filer metal is obtained from the electrode.
Structural attachments
Structural attachments include elements which are welded, bolted or clamped to the pipe, such as clips, lugs, rings, clamps, clevises, straps and skirts.
Submerged arc we lding (SAW)
An arc welding process which produces coalescence of metals by heating them with an arc or arcs between a bare metal electrode or electrodes and the work. The arc is shielded by a blanket of granular, fusible material on the work. Pressure is not used and filler metal is obtained from the electrode and sometimes from a supplemental source (welding rod, flux, metal granules).
Tack weld
A weld made to hold parts of a weldment in proper alignment until the final welds are made.
Tempering
Reheating a hardened metal to a temperature below the transformation range to improve toughness.
Transformation range
A temperature range in which a phase change is initiated and completed.
Undercut
A groove melted into the base material adjacent to the toe or root of a weld and left unfilled by weld metal.
Weld reinforcement
Weld material in excess of the specified weld size.
Fabrication 4.1.
Welding Procedures •
Welds shall be made by the shielded metal arc (SMAW), gas tungsten arc (GTAW), gas metal arc (GMAW) and submerged arc (SAW) welding process. All other welding processes, including the flux cored arc welding process (FCAW), require Mobil approval.
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Welding procedures for all piping materials to be welded on a project shall be submitted to Mobil for approval prior to the start of welding. These welding procedures shall include the following: welding procedure specifications (WPS), procedure qualification test records (PQR), ranges of variables qualified, a weld map or description identifying which welding procedure will be used, and the method(s) and extent of inspection.
•
A WPS is a brief two or three page description of instructions listing all the parameters to be used in making a weld in accordance with the piping code. The information contained in each WPS shall include the information contained on Form QW-482 in the ASME SEC IX.
•
The ASME B31.3 code states that each employer is responsible for qualifying any welding procedure (WPS) used by his personnel. Within the guidelines listed in Paragraph 328.2.2 of ASME B31.3, welding procedures qualified by others may be used.
•
All WPS's shall be validated by performing welding procedure qualification tests. The test involves welding a test pipe or plate in accordance with the WPS, and performing a series of tests to determine the acceptability of the weld. The test data results are recorded on a Procedure Qualification Record (PQR) form. The information contained in each PQR shall include the information contained on Form QW-483 in the ASME SEC IX.
•
All welders and welding operators shall be qualified in accordance with the ASME SEC IX. Welder performance qualification (WPQ) tests shall be completed prior to start of fabrication. The information contained in each WPQ shall include the information contained on Form QW-484 in the ASME SEC IX.
•
4.2.
August 1998
A WPQ made for another employer may be accepted, if approved by Mobil's Inspector. Prior to acceptance, the Inspector shall obtain a copy from the previous employer of the performance qualification test record, showing the name of the employer, name of welder or welding operator, procedure identification, date of successful qualification and the date that the individual last used the procedure on pressure piping. At Mobil's option, witnessing of a welder's performance qualification welding and testing may be required.
•
Qualification of welders and welding operators solely by means of radiography of a weld sample is not recommended.
•
All welding procedures shall be identified by a unique number.
•
Each qualified welder and we lding operator shall be assigned an identification symbol.
Joint Preparation and Alignment 4.2.1.
Cleaning All surfaces to be welded shall be clean and free from paint, oil, dirt, scale, oxides and other contaminants detrimental to welding. Cleaning shall be
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performed in a manner that will not lead to additional contamination of the weld or adjoining base metal.
4.2.2.
Bevels Weld edge preparations (bevels) shall be suitable for the welding process to be used. For pressure-containing welds, the contour shall permit complete fusion throughout the joint. Bevels shall conform substantially to those used in the WPS. All weld bevels and weld surfaces shall be free from cracks, porosity, slag inclusions and other defects indicative of poor manufacture. Any beveled edge of pipe that has been damaged shall be repaired before welding. Any joint of pipe containing laminations or split ends shall be removed and discarded, and no portion of the joint shall be used. Weld bevels shall be made by machining, grinding or thermal cutting, and the surfaces shall be reasonably smooth and true. Materials that require preheat for welding shall be preheated in the same manner for thermal cutting and gouging.
4.2.3.
Root Gap and Land The root gap and land shall be the same as those used in the WPS. Singlewelded joints shall be such that full penetration is obtained. A root gap of 1 1 3.2 mm ± 1.6 mm ( /8 in ± /16 in) is generally used for butt weld joints, 3 including branch joints. For a pipe wall thickness less than 4.8 mm ( /16 in), 1 1 the root gap shall be 1.6 mm ( /16 in) with a tolerance of + 1.6 mm ( /16 in) and minus zero.
4.2.4.
Stainless Steel Brushes and Tools Only stainless steel brushes and tools shall be used on stainless steel and nickel-alloyed materials.
4.2.5.
Grinding Disks Grinding disks containing sulfur (iron sulfide) shall not be used on 5–9 percent nickel steels, stainless and alloy steel or nonferrous materials.
4.2.6.
Socket Welds Pipe for socket welding shall be square cut. Socket-welded joints shall have 1 a gap after welding of approximately 1.6 mm ( /16 in) between the socket and the end of the pipe to be welded.
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August 1998
Branch Connections Branch connections which abut the outside surface of the run pipe (set-on type) shall be contoured for groove welds with a root gap that meets the WPS requirements. Welds without a root gap do not meet ASME B31.3 requirements. Branch connections that are inserted through a run opening (set-in type) shall be inserted at least as far as the inside surface of the run pipe at all points. The opening in the run pipe shall be contoured for a groove weld with a root gap that meets the WPS requirements. Set-in types of branch connections are not recommended, because the excess branch pipe projecting into the run pipe creates unnecessary turbulence in the flow stream, which may result in erosion and extra pressure drop. Also, good fit-up (root gap, etc) of set-in types of connections is difficult. Branch reinforcement pads or saddles shall be formed and contoured to provide a good fit to both main and branch pipe. Branch connection joints shall be prepared to permit full-penetration welds of a quality equal to the circumferential welds in the same piping system.
4.2.8.
Root Openings The root opening of all pipe joints shall be within the tolerance limits in the WPS.
4.2.9.
Consumable Insert Rings Consumable insert rings are not permitted, nor are permanently installed backing rings and strips to be used.
4.3.
Welding Recommendations 4.3.1.
Tack and Seal Welds Tack welds and seal welds shall be performed by qualified welders or welding operators. Tack welds to be incorporated into the main welds shall have the ends ground and feathered. Tack welds that have cracked shall be removed.
4.3.2.
Weld Contours A good weld contour is very important, especially on welds for branch connections. The weld metal shall merge smoothly into the component surfaces. Undercutting, lack of fusion and sharp transitions increase the potential for cracking, and also cause higher stress intensification factors (SIF) at branch connections.
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4.3.3.
August 1998
Weld Beads Weld beads shall be contoured to permit complete fusion at the sides of the bevel and to minimize slag inclusions. Flux and slag shall be removed completely from weld beads and from the surface of completed welds and adjoining base material.
4.3.4.
Weld Reinforcement Weld reinforcement (maximum height) and finish shall comply with Table 341.3.2 in ASME B31.3. No lack of fusion, undercut or incomplete root penetration shall be permitted.
4.3.5.
Peening Peening is prohibited on the root pass and final pass of a weld.
4.3.6.
Welding Groove All arc strikes, starts and stops shall be confined to the welding groove. Accidental arc strikes outside the welding groove shall be dressed and examined by magnetic particle or dye penetrant. Any defects shall be repaired.
4.3.7.
Weld Layering Welded joints shall be made by completing each layer before succeeding layers are deposited. Block welding is not allowed.
4.3.8.
Capping Capping of horizontal welds shall be done by multiple passes. "Lace" caps are unacceptable.
4.3.9.
Marking Welds Each pressure-containing weld shall be ma rked with the identification symbol of the welder or welding operator. In lieu of marking the weld, appropriate records shall be kept so that each welder's work can be identified.
4.4.
Preheat •
Preheating is used to minimize the detrimental effects of high temperature and severe thermal gradients inherent in welding. When preheating is required or recommended, it applies to all types of welding, including tack welds, repair welds and seal welds of threaded joints.
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•
Requirements and recommendations for preheating are listed in Table 330.1.1 of ASME B31.3. If the ambient temperature is below 0°C (32°F), the recommendations in the table become ASME B31.3 requirements. For Mobil projects, the recommendations shall be considered as requirements, regardless of ambient temperature.
•
Preheat temperature shall be checked by use of temperature indicating crayons, thermocouple pyrometers or other suitable means to ensure that the temperature specified in the WPS is obtained prior to and maintained during welding. Preheat shall be uniform and involve the entire weld preparation area. The preheat zone shall extend at least 25 mm (1 in) beyond each edge of the weld.
•
Carbon steel shall be preheated to 10 °C (50°F), minimum, unless low-hydrogen electrodes are used.
•
The main purposes of preheat are: −
To avoid the cold cracking in the heat affected zones of hardenable steels
−
To increase the toughness of the weld joint and improve resistance to impact loading and low temperatures
−
To alleviate the effects of hydrogen that enters the weld metal and heat affected zone (HAZ)
−
To reduce residual stresses
−
To minimize shrinkage and distortion
Postweld Heat Treatment •
Postweld heat treatment (PWHT) is used to avert or relieve the detrimental effects of high temperature and severe thermal gradients inherent in welding, and to relieve residual stresses created by bending or forming.
•
ASME B31.3 requirements for PWHT are listed in Table 331.1.1. In general, carbon steel piping does not require PWHT except for pipe wall thickness greater tha n 19 mm (3 /4 in), and for certain fluid services specified in MP 16-P-40.
4.5.1.
Thickness The governing thickness for PWHT shall be that of the thicker component measured at the joint, except for branch connections and fillet welds, heat treatment is not required until the thickness through the weld in any plane is more than twice the minimum material thickness requiring treatment.
4.5.2.
Holding Time Holding time at PWHT temperatures shall be one hour per 25 mm (1 in) of thickness, with a one-hour minimum. For chromium-molybdenum steels
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(1/2 –9 percent chromium) and 12 percent chromium stainless steels, the minimum holding time shall be two hours.
4.5.3.
Cooling Heat-treated welds/components shall be cooled in the furnace or under suitable insulation to assure slow cooling rates. The maximum cooling rate above 315°C (600°F) shall be 222°C (400°F) per hour. If a weld is allowed to cool prior to heat treatment, the rate of cooling shall be controlled or other means shall be used to prevent detrimental effects in the piping.
4.5.4.
Instrumentation Instrumentation used to verify the PWHT temperatures shall have been calibrated within 60 days of the performance of the heat treatment.
4.5.5.
Thermocouples If PWHT is performed in a furnace, the temperature shall be measured by a minimum of two resistance-welded thermocouples attached to the piping being heat treated. Neither temperature shall be outside the specified PWHT range. If local PWHT is performed, each weld shall be equipped with one thermocouple (attached by welding) for every 600 mm (24 in) length of weld seam being heat treated. Temperature, heating rate and cooling rate shall be measured and recorded by using an automatic recorder.
4.5.6.
Heat Treatment Use of exothermic heat treatment kits is not recommended.
4.5.7.
Hardness The maximum Brinell hardness of welds (weld deposits and heat-affected zones) in all steels after heat treatment shall be 225 HB (238 HV10). If welds are furnace heat treated, a minimum of 10 percent shall be tested to verify that the hardness criterion has been met. If local heat treatment has been applied, each weld shall be tested.
4.6.
Bending of Pipe •
Mobil approval of written bending and forming procedures, including any required preheat and postweld heat treatment, is required. The written procedures shall specify the following elements: materials, size range, wall thickness range, equipment and operating conditions, operator training, test and examination methods and test
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acceptance criteria. Evidence of ASME B31.3 code compliance shall also be provided to Mobil. •
Pipe to be bent shall be protected from the contamination of harmful materials such as the low melting temperature alloys of copper, brass and lead. Bending equipment shall be thoroughly cleaned prior to bending, particularly prior to bending stainless steel.
•
All bends shall be free of cracks and substantially free from buckling. The minimum wall thickness after bending shall not be less than that required by the design. This shall be verified by calculating the minimum wall requirements, including corrosion allowance, for each line class where bends are used.
•
All pipe bends shall comply with PFI ES-24, as well as Mobil's requirements listed in MP 16-P-40. End preparation for all bending spools shall be bevel end, as per ASME B16.25, Fig. 2(a) 0r Fig. 3(a).
4.6.1.
Cold Bending •
4.6.2.
ASME B31.3 requires that cold bending of ferritic materials be done at a temperature below the transformation range. For carbon steel, Mobil's recommendation is that cold bends not be heated above 650 °C (1200°F) prior to the start of bending, and the bends themselves shall be made below 650°C (1200°F). For information on the transformation range of various piping materials, refer to Table 129.3.2 in ASME B31.1.
•
Cold bends in carbon steel pipe shall be limited to ASTM A106 Gr. B material with a minimum bend radius of 3-D (three times pipe diameter), 1 unless approved otherwise by Mobil. NPS 1 /2 and smaller Schedule 40S austenitic stainless steel pipe may be bent cold to a bend radius not 1 smaller than 1 /2 pipe diameters. With Mobil approval, ASTM A587 may be also be used for bends with a minimum radius of 11 /2 pipe diameters.
•
Cold bends shall be stress relieved when required by ASME B31.3 (see Paragraph 332.4.2).
•
Inspection and acceptance criteria for cold bends shall be the same as listed for induction bends below.
Induction Bending •
Induction bending is a specialized form of hot bending that bends the pipe at a temperature above the transformation range of the material. It is sometimes referred to as "High Frequency Induction Bending". For making induction bends, special automated/computerized machines "push" the pipe through the machine, while medium/high frequency inductive power heats the pipe over a narrow area. The moving 3 circumferential heated band, approximately 19 mm to 25 mm ( /4 –1 in) in width, is produced by utilizing the steady forward travel of the pipe through fixed 360 degree induction coils fitted with a water quench curtain. Bending temperature is generally about 880°C (1800°F).
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Induction bending equipment may be used for bending carbon steel and 1 stainless steel pipe to a bend radius as small as 1 /2 D (pipe diameter). With Mobil approval, it may also be used for bends made with internally clad pipe. On large international projects, bending machines have been shipped to the job site.
•
Bend properties that must be within acceptable limits include wall thickness (thinning), hardness (Brinell), ovality (flattening) and toughness (impact properties). −
4.6.3.
Pipe used for bends shall be on the plus side of the nominal wall thickness prior to bending, or excessive thinning will generally occur. Thinning will be a greater problem for bends with a small bend radius. For this reason, some projects have limited bend diameter to 2D bends, to minimize thinning problems. Thickness measurements shall be taken on the bend outside diameter, and the minimum thickness shall not be less than the thickness required for design conditions.
−
If the hardness of the bend exceeds 225 Brinell, then heat treatment shall be carried out. Pipe used for bending shall have a carbon content on the low side of that required in the material specification. Pipe with a high carbon content will result in high bend hardness.
−
The maximum flattening ratio (out-of-roundness, or ovality) shall be 8 percent, as required by ASME B31.3. For lines that require pigging, a smaller flattening ratio may be required. Bend diameter and feed rate of the induction bending machine influence the flattening ratio.
−
The toughness of the pipe bend in a function of the initial pipe material properties, and the bending temperature. Impacts shall be taken on test bends to determine that the production bends will have acceptable impact qualities.
Hot Bending •
•
4.7.
August 1998
ASME B31.3 requires that hot bending of ferritic materials be done at a temperature above the transformation range. For information on the transformation range of various piping materials, refer to Table 129.3.2 in ASME B31.1. Hot bending (by placing the pipe in a furnace for heating and then bending while hot) has become less common since the purchase of induction bending equipment by many fabrication shops. Hot bending shall be tested.
Shop and Field Fabricated Piping •
Linear and angular tolerances for prefabricated piping details shall be in accordance with PFI ES-3.
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5.
August 1998
Short pipe runs shall be one continuous piece of pipe. Splices shall not be permitted between fittings that are 3 m (10 ft) or less apart.
•
Connections for high point vents and low point drains shall be installed in the fabrication shop. Valving shall be installed after erection of the piping, unless it is determined that shop-installed valves can be adequately protected from damage during shipment.
•
Branch reinforcing pads shall be tested in the shop. However, hydrotest of individual shop spools is generally not required, since a "system" test on the assembled piping is required by ASME B31.3.
•
Piping subassemblies may be tested either separately or as assembled piping. Skid assemblies shall be hydrotested in accordance with ASME B31.3 by the skid fabricator prior to shipment.
•
All piping shall be fabricated and inspected in accordance with the requirements of MP 16-P-40.
Assembly and Erection 5.1.
Field Welding 5.1.1.
Protection •
No welding shall be done if there is impingement on the weld area of rain, snow, sleet or excessive wind, or if the weld area is frosted or wet. For these conditions, adequate protection shall be provided for the parts to be welded and for the welder, so as to ensure the weld quality is acceptable.
•
Piping spools shall not be stored directly on the ground. Additionally, stainless steel piping spools, as well as stainless steel piping components, shall be protected from a salty environment.
•
Segregated workshop areas shall be provided for carbon steel, low temperature carbon steel, stainless steel and non-ferrous piping fabrication. Tools such as grinders, wire brushes, files, etc., shall be uniquely color coded for ferritic and austenitic materials and shall not be interchanged.
•
Austenitic stainless steel shall be protected from zinc contamination during all phases of construction, such as storage, fabrication and installation.
•
Pipe ends, including beveled ends, shall not be left unprotected when shift ends. If time does not permit completion of pipe spool installation, the protective covers shall be restored until work is once again resume. © Mobil Oil,1998
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5.1.2.
5.2.
5.3.
August 1998
Other Requirements •
Cold pulling during welding alignment shall not be allowed.
•
All piping shall be installed square and plumb, except where a slope is required for drainage.
•
A sufficient number of field welds shall be provided, so flanged joints can be assembled in accordance with the requirements listed in ASME B31.3, Paragraph 335.1
Misalignment Corrections •
Local heating to overcome misalignment of PWHT lines and piping connected to rotating equipment shall not be permitted. Local heating to overcome misalignment of other piping shall not be done without Mobil approval.
•
Piping that has been heated to correct minor misalignments shall be allowed to cool to ambient temperature before bolt up.
•
After heating to correct misalignment, hardness shall not exceed 200 HB for wet H 2 S (sour/NACE) and other services such as HF Acid and amine.
•
Cold spring shall not be allowed, especially for lines connected to rotating equipment and air coolers.
Flanged Joints •
Three distinct elements of a flanged joint must act together if a leak-free joint is to be obtained. These are the flanges, the gasket and the bolting. If just one of these elements is not adequate for the service conditions, then the joint is likely to leak.
•
Before assembly, flanges shall be clean and free from any foreign material (e.g. rust, dirt or other contamination). The joints shall be brought up flush and square without forcing so that the entire mating surfaces bear uniformly on the gasket and the n mated-up with uniform bolt tension. Note: MP 16-P -40, Appendix A, contains a flange bolt-up procedure.
•
The maximum permissible imperfections in the flange facing finish for raised face flanges shall be in accordance with Table 3 in ASME B16.5.
•
All equipment, valves and pipe spools shall have flanges covered until ready to connect the mating piping.
•
When the mating flanges are in alignment, the following tolerances shall be maintained: −
Bolting shall move freely through accompanying bolt holes at right angles to the flange faces.
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There shall be a clear gap between the two flange faces before gasket installation. There shall be sufficient flexibility to install and replace gaskets.
−
Before bolting up, flange faces shall be aligned to the design plane within 1 mm in 200 mm (1 /16 in/ft) measure across any diameter; flange bolt holes shall be 1 aligned within 3 mm ( /8 in) maximum offset.
•
In general, flange connections to equipment shall be the last connection made on completion of a line or interconnecting system of lines.
•
Flanges connecting to mechanical equipment that are sensitive to pipe strain shall be fitted-up in close parallel and lateral alignment prior to tightening the bolting. This shall include equipment such as pumps, compressors, turbines and air coolers.
•
Spiral wound gaskets shall not be coated with a lubricant or parting compound prior to assembly. RTJ gaskets shall be lightly coated with an anti-friction lubricant prior to fitting between the flange grooves.
•
5.4.
August 1998
No more than one gasket shall be used between contact faces in assembling a flanged joint.
•
Stud bolts shall be used on all flanged joints. Except for coated bolting, no bolting shall be installed without being properly lubricated (see MP 16-P-40).
•
Generally, manual wrenches may be used for tightening flanged joints with a bolt diameter of 25 mm (1 in) or less. Hydraulic torque wrenches (or hydraulic tensioning 1 equipment) shall be used for all bolts diameters 28 mm (1 /8 in) and larger.
Threaded Joints Where threaded joints are intended to be seal welded, thread sealing compound shall not be used. If threaded joints have been made-up with a lubricant, and it is decided to seal weld the joints, all lubricant shall be removed from exposed threads.
5.5.
Valve Installation It is important, before making a valve installation, to determine that the valve is in satisfactory condition. The following points are helpful in avoiding subsequent valve problems: •
Leave end covers on valve ends until ready for installation.
•
Check valve tag and/or identification plates against specifications, etc., to make certain the proper valve is being installed.
•
Note any special instructions or warnings attached to or accompanying the valve, and take appropriate action.
•
Check valves for any marking indicating flow direction or preferred pressure end. If markings are observed, appropriate care shall be exercised to install the valve in proper orientation.
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•
6.
August 1998
Inspect valve interior to the extent practical through the end ports. Make sure it is reasonably clean, free of foreign matter and harmful corrosion. Remove any special packing materials, such as blocks used to prevent disc movement during shipping and storage. Immediately prior to valve installation, check the piping to which the valve is to be fastened for cleanliness and freedom from foreign materials.
Examination and Inspection The ASME B31.3 code distinguishes between examination and inspection as follows: •
Examination applies to quality control functions performed by the manufacturer (for components only), fabricator or erector. Reference in the code to an examiner is to a person who performs quality control examinations. Examples of examination are visual examination, radiography, ultrasonic examination, liquid penetrant examination, etc.
•
Inspection refers to functions performed for Mobil by Mobil's Inspector or the Inspector's delegates. When the ASME B31.3 code refers to "Inspector," it is capitalized and means the owner's Inspector. The code requires that the owner's (Mobil's) Inspector shall not be an employee of the piping manufacturer, fabricator or erector unless the owner (Mobil) is also the manufacturer, fabricator or erector.
All new piping systems shall be examined, inspected and tested in accordance with MP 16-P- 40.
7.
Pressure Testing •
Prior to initial operation, and after completion of the applicable examinations, the ASME B31.3 code requires that each piping system be tested to ensure tightness. The test shall be a hydrostatic leak test, except with Mobil's approval, either a pneumatic test, an initial service leak test or alternative leak test may be performed (see comments below concerning each test).
•
Prior to any pressure test, a "Test Pack" for each pressure test system shall be prepared and approved by Mobil. Each Test Pack shall be individually numbered for identification and shall contain the following information: −
P&ID marked to show extent of system to be tested.
−
Line List for system to be tested, with piping line number(s), test type and test pressure highlighted.
−
Test Data Sheet for recording the test system number, date and time of the pressure test, identification number and calibration date of test equipment used, test medium, test pressure, test duration, ambient temperature at start and end of test and the test results. The Test Data Sheet shall also include a checklist to confirm all blinds, valves, instrumentation, etc. were properly installed and/or removed, both prior to and upon completion of the test. © Mobil Oil,1998
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•
A list shall be prepared for sensitive equipment that shall be removed, blocked off or isolated during testing, such as relief valves, inline instruments, turbines, pumps, compressors and vessels. Critical valves, such as ESD, control and soft-seated ball valves shall be removed where lines have not been flushed. Instruments shall normally be excluded from the system test, but process leads shall be included in the test, up to the first block valve. This list shall be a part of the test procedure.
•
Piping joints and welds shall not be insulated or physically covered until satisfactory completion of testing, except painting of full penetration buttwelds is permitted.
•
All piping shall be adequately supported before the pressure test. Spring supports shall not have shipping blocks removed until after completion of pressure test.
•
Piping containing check valves shall have the source of test pressure on the upstream side. If this is not possible, the check valve disc shall be removed, or the valve shall be removed and replaced with dummy spools.
7.1.
Hydrostatic Test •
For hydrostatic testing, the test fluid shall in general be fresh water, except that other suitable liquids may be used if: −
The piping or inline equipment would be adversely affected by water. An example would be lube or seal oil systems, which are generally tested with the service fluid or nitrogen.
−
Category D piping systems which may be tested with the service fluid. Examples would be potable water, cooling water, etc.
•
The test pressure shall be maintained for a sufficient length of time to permit visual examination to be made of all surfaces, welds and connections, but a test duration of at least 30 minutes is recommended. For Class 600 and higher piping systems, a test duration of one hour is recommended. The piping system shall not show any sign of leakage or deformation.
•
All valves included in the system test shall be examined for signs of external leakage. The most common leakage problem is either through-wall leakage in the casting, or leakage at the valve/bonnet joint.
•
Socket-welded joints, threaded joints and seal-welded threaded joints shall be examined thoroughly for leaks. These types of joints shall not be painted prior to testing.
•
Following the completion of a successful hydrotest, the piping system shall be depressurized by opening the valve at the test pump. After depressurization, all vents and low point drain valves shall be opened and the system shall be thoroughly drained if the test medium was water. If the piping system is required to be completely dry, blowing with dry air to remove any trapped water is recommended.
•
If vessels and towers have been included in the hydrotest, ensure that adequate vents are open and the equipment is drained slowly, to avoid pulling a vacuum on the equipment and causing damage.
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7.2.
August 1998
Vent holes in reinforcing pads shall be sealed upon completion of the pressure test.
Pneumatic Leak Test If a hydrostatic leak test is not practical or not permitted, a pneumatic test may be substituted with Mobil's approval. Guidelines and recommendations for conducting a pneumatic test a re listed below.
7.2.1.
Fluid Test fluid is generally dry air. Nitrogen may also be used, subject to provision of suitable safety procedures.
7.2.2.
Precautions The code cautions about the hazard of energy stored in compressed gas. However, for Class 300 and lower systems, the chances of a catastrophic failure are near zero if the following precautions are taken: •
Pipe used for lines to be pneumatic tested shall be seamless, or welded pipe in which the full length of the longitudinal seam has been examined by RT or UT in accordance with API SPEC 5L (or equivalent test standard).
•
Each length of welded pipe shall have been hydrotested by the manufacturer at a test pressure at least as high as required by API SPEC 5L.
•
For carbon steel pipe, the minimum design temperature shall be equal or lower than temperature for Curve B in Figure 323.2.2 in ASME B31.3. The ambient temperature at the time of test shall be a minimum of 10°C (15°F) above Curve B for the applicable wall thickness.
•
All flanges shall have the full number of bolts installed and tightened, including bolting at locations where line blinds are installed.
•
A pressure relief valve shall be installed in accordance with Paragraph 345.5 in ASME B31.3.
•
For lines NPS 24 and smaller, the pneumatic test procedure shall be in accordance with Paragraph 345.5.5 of ASME B31.3.
•
For lines NPS 26 and larger, the pneumatic test procedure shall be as outlined below.
•
In addition to the recommendations listed above, NPS 26 and larger lines that will be pneumatically tested shall be pressurized as follows: −
Gradually increase the pressure until a gage pressure of 170 kPa (25 psi) or one-half of the test pressure is obtained (use the lower of these two pressures).
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7.2.3.
7.4.
−
Hold pressure for a minimum of 10 minutes, then visually check all joints with a soapy water solution (or a similar bubble test solution, such as Snoop).
−
Increase pressure to 50 percent of test pressure, and hold for a minimum of 10 minutes before checking all joints again with a bubble test solution.
−
Increase pressure to 100 percent of test pressure, and hold for a minimum of 10 minutes.
−
Decrease pressure to design pressure and visually check all joints with a bubble test solution.
Procedures Following Test •
7.3.
August 1998
Following a pneumatic test, the pressure shall be bled off in a controlled manner, taking full account of hazards, including noise, to personnel.
Initial Service Leak Test •
An initial service leak test may be used for piping systems with fluids that meet the requirements for Category D fluids (see definition in Section 3 of this Tutorial).
•
For an initial service leak test, the test fluid is the fluid that will be in the piping system. Examples are air, water, nitrogen and low pressure steam lines that meet the requirements for Category D fluids.
•
The initial service leak test procedure shall be as follows: Gradually pressurize the piping system with the process fluid, in steps of 25 percent, 50 percent, 75 percent and 100 percent of the operating pressure, until the operating pressure is reached. The pressure shall be held at each intermediate step until the piping strains have equalized. Additionally, if the fluid is a gas/vapor, all joints shall be examined for leaks at each intermediate step.
Alternative Leak Test •
An alternative leak test, as described in ASME B31.3, Paragraph 345.9 shall only be used when approved by Mobil, and the requirements in Paragraph 345.1(c) of ASME B31.3 are met.
•
With Mobil approval, NPS 36 and large diameter flare lines may be tested using the alternative leak test, even if only one of the requirements in Paragraph 345.1(c) of ASME B31.3 is met. However, the flare line shall meet the design requirements listed in Section 5.7 of MP 16-P-01.
•
The alternative leak test consist of three distinct parts as follows: −
All circumferential, longitudinal and spiral groove welds that have not been subjected to a hydrostatic or pneumatic leak test shall be 100 percent
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radiographed. All other welds, including structural attachment welds, shall be examined by PT or RT. NOTE: All welded pipe shall be purchased to a specification that requires 100 percent RT, so that field RTs of longitudinal joints will not be required.
8.
−
A flexibility analysis of the piping system shall be made. NOTE: The flexibility analysis may be either manual or computer analysis in accordance with Table 1 in MP 16-P-01.
−
The piping system shall be given a sensitive leak test (this consists of examining all joints for leaks with a soapy solution, or a bubble test solution such as Snoop). The test pressure shall be at least 105 kPa (15 psi) or 25 percent of the design pressure (use the smaller of these pressures).
Pipe Cleaning Prior to commissioning a new piping system, it shall be cleaned to remove dirt, rust, scale, welding rods, rags and other construction debris. Cleaning shall normally be carried out after pressure testing, unless otherwise specified. Water, air and steam are the usual choices available for flushing, and combinations of these fluids may be used depending upon the line size and degree of cleanliness required. Process hydrocarbon systems are usually flushed with water, unless it is not available in sufficient quantities or at high enough pressure. Certain systems, such as centrifugal/positive displacement compressors and lube/seal oil systems, require special cleaning procedures in order to achieve a high level of cleanliness. The cleaning contractor is responsible for developing detailed procedures, including safety considerations.
8.1.
Water Flushing •
Piping components, inline instruments and other equipment that would be sensitive to damage during water flushing shall be removed, blocked off or isolated. Control valves and orifice plates shall be removed, or shall not be installed until completion of cleaning. Additionally critical resilient seated ball valves, such as ESD valves, shall be removed prior to the water flushing. All other ball valves shall be fully open during the flushing operation.
•
Water flushing is generally safer than that of air or steam blowing where flying debris and jet thrust can pose hazards. Additionally, water is a natural solvent and will dissolve some dirt that air blowing alone may not remove. The availability of water for flushing is also an important consideration in determining the need for water flushing.
•
The water used for flushing shall be clean and have a chloride content of less than 50 ppm if used for flushing austenitic stainless piping. The use of treated water
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(demineralized) is generally only necessary if the piping has been chemically cleaned. The use of treated cooling tower water shall be avoided if during the flushing operation cooling water is dumped into the sewer and thereby contaminating the sewer with untreated chemicals, such as chromates.
8.2.
8.3.
•
The higher the velocity of the flushing medium, the more effective a line will be cleaned. Therefore, if the supply of water is limited for larger pipe sizes, slug flow flushing with a mixture of water and air will achieve higher velocities. Piping may also be flushed using high-pressure jet flushing equipment, such as rotating hose or rotating nozzle.
•
Flush downward or horizontally and out at low points, which often will be temporary openings made by removing valves, or disconnecting flanges/fittings. Normal low point drains shall only be used if they are approximately full line size. Small drain valves shall be checked to make sure no debris is lodged in them.
•
There must be no restriction at the outlet of the section being flushed. If it is necessary to throttle the flow rate of the flushing medium, this shall be done at the supply end.
•
Water Velocity shall be at least 5 m/sec (16 ft/sec).
High Pressure Jet Flushing •
This method of internal pipe cleaning requires special cleaning equipment and special training for the equipment operators. Generally, a company that specializes in equipment/pipe cleaning performs high pressure jet flushing.
•
This method requires a high-pressure water pump with a discharge pressure of 69,000 kPa (10,000 psi) or higher. High-pressure nozzles "pull" the connected hose through the inside diameter of the pipe, and then is pulled back under pressure to drag the loosened debris out of the pipe.
•
High pressure jet flushing can be used to clean large lines, with much less water than is required for water flushing.
Pneumatic (Air) Flushing •
Air blowing can be used to remove debris and loose scale from air lines and other piping systems where water flushing or high-pressure jet flushing is not feasible. It shall also be used upon completion of water or jet flushing to remove trapped water and moisture so additional corrosion is minimized.
•
Air used for blowing shall be clean and oil free. Generally, an air supply pressure of 690-860 kPa (100-125 psi) is adequate for most air blowing operations. The air velocity shall be approximately 35 m/sec (115 ft/sec).
•
Prior to air blowing, all control valves, flow orifices, transmitters and other instruments and equipment that may be damaged by air blowing shall be removed or
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isolated. All manual valves within the designated flow path shall be fully opened to prevent damage and to reduce the pressure drop.
8.4.
8.5.
8.6.
•
Air blowing shall be accomplished by blowing main headers, then sub-headers and finally individual laterals.
•
The duration of all blows shall be kept relatively short, as air blowing tends to be most effective when utilizing the surge type of blowing method. The air blows shall be repeated until blowing effluent appears clear and free of all dirt and debris. Inspection screens/cloths shall be used to verify acceptable cleanliness.
•
High velocity air released from temporary piping is hazardous (flying debris) and creates excessive noise. Also the piping must be secured to ensure that the jet thrust which is created during blowing does not pose a hazard to personnel or equipment.
Steam Flushing •
Steam lines are typically blown with the steam they will carry in service. When flushing with steam, the line shall be heated slowly and checked for proper support and clearance as it expands. Mufflers and silencers are usually required to reduce noise at the outlets.
•
Steam traps shall either be bypassed or removed until flushing is completed. When steam traps are placed back in service, check to see that the operation of each one is satisfactory.
Slug Flow Flushing •
Slug flow flushing is a two-phase method of removing debris without the need for excessive quantities of water, steam or air. Turbulence in the piping is maximized by the interaction of water and gas slugs, thus providing an effective flush.
•
The advantages of slug flow flushing are that much less water is required, and the sizes of pumps, hoses and piping to supply water, air or steam are reduced. The disadvantage of slug flow flushing is the potential for pipe damage due to excessive vibration and impact pressures on elbows from the water slugs.
•
Experience indicates that if superficial water velocities are held in the range of 0.8–2.0 ft/sec, and gas velocities are within the range of 10– 20 ft/sec with the gas volume at about 90 percent of the mixture, adequate flushing is obtained without excessive impact pressures.
Chemical Cleaning •
Refer to MP 16-P-40 for chemical cleaning information.
•
Consider impact pressures.
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8.7.
Piping -Construction
Hand Cleaning •
9.
August 1998
Internal hand cleaning of large lines (with wire brushes, etc.) may be substituted for other methods of cleaning provided the cleaning contractor can demonstrate that the lines will be adequately cleaned.
Fabrication, Erection, Inspection and Testing of Nonmetallic Piping •
Metallic valves in nonmetallic piping systems shall be independently supported and shall not be supported by supports under the nonmetallic pipe near the valves.
•
All bonding procedure specifications (BPS) and bonders or bonding operators shall be qualified in accordance with ASME B31.3, Chapter VII.
10. Pre-Startup Review Although a pre-startup review shall cover a review of all systems, including training, operating procedures, safety, etc., only piping systems are addressed in this MEP. During the final stages of construction, it is necessary that a number of pre-commissioning piping activities be performed before a unit is ready for start-up. This includes inspecting, testing, cleaning, purging/draining and preparing piping systems for initial operation. A successful start-up depends, to a large extent, on the thoroughness with which pre-commissioning procedures are carried out. •
Final issues of the Piping and Instrument Drawings (P&ID's) shall be used to mark off each line, instrument, etc. as the commissioning activity is completed. A "punch" list shall be prepared which includes all deficiencies and omissions identified.
•
Required items such as valves, bleeders, vents, drains and blinds shall be confirmed. Orientation of check valves, globe valves and control valves shall be checked for proper flow direction (during flushing of the piping system, check valve internals may have been removed or the check valve may have been reversed so line could be flushed). Verify that vent and drain plugs used for hydrostatic pressure testing are in-place and seal-welded if required. Verify that low point drains are provided where needed. All line blinds shall be located and their normal operating position (blanked or open) verified.
•
All piping shall be checked to make sure it is properly supported, that shipping "stops" have been removed from spring supports and that required anchors and guides are in their required locations. Verify that small bore piping (NPS 2 and smaller) has been adequately supported.
•
Orifice plate sizes, locations and correct orientation shall be verified. Make sure start-up strainers are installed at pumps, compressors, etc.
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EPT 09-T-04
10.1.
Piping -Construction
August 1998
Piping Checklist
Pre-Startup Piping Checklist
Yes
No
N/A
Has the latest edition of the P&ID drawings been used to verify that all piping components been installed (i.e. pressure, temperature, flow elements/indicators, control valves, relief valves, pipe sizes, materials of construction, etc.)? Have lines requiring insulation been insulated properly (correct thickness/covering/insulation material)? Have all "directional" valves been verified for the correct flow direction (check valves, control valves, etc)? Have all valves with a "preferred pressure end" been installed correctly (such as Orbit valves)? Do valves have correct packing? Have valves and/or gear operators been lubricated? Do relief vents have drain holes? Are flare lines, relief lines and vent lines free of liquid traps or low points? Have all block valves at relief valves been locked open? If relief valve has a bypass line, in valve closed? Do pressure relief valves have correct settings? Tagged correctly? Do flanges and valves have proper metallurgy? Correct pressure rating for system pressure? Have valve stems been protected from paint over-spray? If not, stems need to be cleaned so packing is not damaged. Is packing gland tight? Is there adequate packing to permit additional tightening of the gland? Check flange/valve bolting for proper size, length and metallurgy. Have correct gaskets been used (spiral wound gaskets shall have color coding on outer edge of centering ring per ASME B16.20)? Have hydrostatic and/or pneumatic tests been conducted in accordance with code requirements? Have all piping systems been cleaned and/or flushed in accordance with project specifications? Have all construction blinds been removed? Were new gaskets used at blinding locations after removal of blinds? (RTJ metal gaskets may be inspected and reused; sheet and spiral wound gasket shall not be reused.) Are Figure 8 type blinds turned correctly? Are all open-ended valves, such as vents and drains, plugged or blinded?
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EPT 09-T-04
Piping -Construction
Pre-Startup Piping Checklist
August 1998
Yes
No
N/A
Is metallurgy of plugs and/or blinds correct? Have all startup screens, strainers and/or filters been installed? Have piping systems been dried and purged if required (of oxygen, etc.)? Have all pipe supports been installed? Do supports need shims? If shims have been installed, are they welded or bolting to supports? Are lines NPS 2 and smaller properly supported? Have shipping stops been removed from spring supports? Are loads on spring supports about mid-range of the load scale?
11. Post Completion Technical Audit A post completion technical audit shall be conducted within the first year of startup of a new processing unit/facility. Piping systems will generally give warnings or "tell-tale" signs that something is wrong, before they fail. An inspection of the piping systems, while the piping is in operation may detect problems before they become major problems. A post audit shall include discussions with operations personnel to determine if they have noticed any piping systems with problems.
11.1.
Technical Audit Checklist
Post Completion Piping Checklist
Yes
No
N/A
Do any lines have excessive vibration? Have lines "lifted off" of any support points? Any lines with excessive sag? Are shims missing and/or needed? Any visible damage to pipe anchor points, guides, u-bolts, support beams, etc.? Has any rotating equipment experienced excessive seal/bearing problems that might be contributed to high piping loads on equipment? Are any lines "pushing" into adjacent lines on supports? If so, is insulation damaged? Are adjustable type supports, especially at rotating equipment, adjusted so the piping is supported by the supports and not the equipment? Is the load indicator on spring supports near the top or bottom of the load scale? Any visible damage to spring supports?
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