Piping Shop Fabrication Specification

This content provides you with a example piping shop fabrication specification that is used and applied in the industrial plant construction projects. 

piping fabrication specification


1.1. SCOPE

1.1.1. This specification covers the minimum requirement of preparation of detail shop drawings and the fabrication, inspection and testing of shop fabricated piping required for the industrial plants. All work shall be done in accordance with applicable standards as listed herein unless otherwise stated. Sound engineering practices shall be followed in the absence of specified standards or specifications subject to Owner prior approval. All required equipment, devices, tools, materials and labors for any construction work, test and inspection shall be provided by Construction Contractor.

1.1.2. Jacketed piping, tubing systems, orifice runs; lined or coated metals and fabrication by methods other than threading, welding and flanging are not within the scope of this specification.

1.1.3. Fabrication of piping subject to the requirements of the ASME Boiler and pressure vessel code, Section I  power boilers is not covered in this specification.

1.1.4. SI unit shall be applied except nominal size of pipe and nozzle shall be in inches and flange rating shall be in pounds. “BEDD” shall also be considered.

1.2. CODES AND STANDARDS - Piping Shop Fabrication Specification

Process Piping ASME B31.3

Unified Inch Screw Threads ASME B1.1

Pipe Threads, General Purpose (Inch) ASME B1.20.1

Pipe Flanges and Flanged Fittings NPS 1/2”Through NPS 24” ASME B16.5

Factory-Made Wrought Steel Butt welding Fittings ASME B16.9

Forged Steel Fittings, Socket Welding and Treaded ASME B16.11

Butt Welding Ends ASME B16.25

Square and Hex Nuts (Inch Series) ASME B18.2.2

Welded and Seamless Wrought Steel Pipe ASME B36.10

Stainless Steel Pipe ASME B36.19

Wrought Stainless Steel Butt Welding Fittings MSS-SP-43

For other applicable standards refer to piping material specification.


The following related engineering and construction specifications are applied as supplement of this specification.

A. Piping Material 

B. Piping Fabrication and Erection 

C. Construction Work for Piping 

D. Pressure Test of Piping System 

E. Cleaning of Pipe Lines                                      

F. Welding Procedure for Piping 

G. Welder Qualification Test 

H. Inspection & Test of Piping Construction 

I. Piping hanging & support 

J. Marking and Color Coding 

2. RESPONSIBILITIES - Piping Shop Fabrication Specification

2.1. Fabrication Shop Engineering shall be responsible for Quality control (Welding & Inspection), Inventory control (Piping & Instrument Bulk Material), Schedule of Production and Quality Assurance plan on behalf of the Fabricator.

2.2. Fabrication Shop Superintendent shall be responsible for All manufacturing activities on behalf of the Fabricator.

3. DRAWINGS (SHOP SPOOL DRAWINGS) - Piping Shop Fabrication Specification

3.1. The shop fabricator (Fabrication Shop Engineering) shall prepare the necessary detail shop spool drawings for fabrication from piping drawings onsite under Shop Engineer’s direction. Shop spool drawings must show the detail field welds, spool number, materials, dimensions, fabrication details and the applicable code and procedures.

Shop spool drawings must identify all equipment, lines or spools connecting to that spool. The arrangement or isometric drawing must be shown as a reference.

3.2. All piping drawings is dimensioned and shown in normal assembly and operating position. When specifically required, thermal expansion requirements and cold springing will be shown on drawings.  Cold Spring (CS) and Pre Spring (PS) are indicated on the spools with the amount added or deducted.  This amount is added or deducted from the dimension and the pipe shall be fabricated to the dimension.

3.3. Pipe detail pieces shall be fabricated in accordance with the piece marks shown on the drawings, unless otherwise required for handling and/or shipping.  Changes from the piece mark arrangement shown  on  the drawings shall require approval of Consultant.

3.4. Preparation of isometric drawings by the shop fabricator is not required.

3.5. Piping drawings show the limits of field run piping and the locations of any field welds required between spool pieces.  The shop fabricator is not to supply or fabricate that portion of the field runs.

3.6. Spool piece numbers will consist of the isometric line number followed by suffix letters A,B,C, etc.

3.7. Except for ring joint flanges, dimensions are to the centerline of pipe and the contact face of flanges.  

This includes the contact face of male and female tongue and groove flanges. 

Ring joint flanges are dimensioned to the centerline of pipe and to the extreme face of flange and not to the contact surface of the groove.

3.8. The Shop Fabricator (Fabrication Shop Engineering) shall verify all spool drawings and list of materials for accuracy and compliance with the project specifications.

1) Quantity of materials correct for the spool

2) Description of materials correct per project specification

3) Pipe cut lengths

4) All weld numbered for identification on the shop spool drawings and its’ document concerned

4. EXTENT OF SHOP FABRICATION - Piping Shop Fabrication Specification

4.1. SIZE

Two inches nominal bore and larger is shop fabricated, except for straight runs which are field run. Piping less than two inch nominal bore is field run in principle.


Shop fabricated spools are to include appropriate fittings or stubs for field fabricated branch connections. Branches larger than 1 ½” are to extend to the first flange or field weld point as indicated on the shop spool drawings or as required for reasonable piece size.

Where reinforcement pads are required at branch connections which are to be field welded they must be fabricated by the shop Fabricator and tack welded to the "stub in" spool for shipment. A vent/tale hole is to be drilled in each reinforcement pad or reinforcement pad section.

4.3. ATTACHMENTS - Piping Shop Fabrication Specification

Attachments, such as supports, braces, lugs and T bars are to be field installed. Where pipe fabrications require pre or post weld heat treatment than such attachments shall be on pads or stubs to which the Erector can weld; pads or stubs shall be installed by the fabricator and receive the appropriate heat treatment.

4.4. DUMMY LEGS - Piping Shop Fabrication Specification

Dummy legs are to be installed in the shop.


Field runs are designated on piping drawings by the Fabricator.  Usually the piping on the pipe racks, pipe sleepers & etc. shall be installed in Field directly.

5. MATERIALS - Piping Shop Fabrication Specification

5.1. All material shall be as described in the piping material specification. The piping drawing and Line Designation Table will identify the particular classification which is applicable.

5.2. A complete Material Purchase Description Listing should be requested from and furnished by Consultant.  This listing is complete description of the items and will supplement the abbreviated description in the Piping Material Specification.

5.3. All materials shall be new and Color coded according to Marking of piping material before issuing materials.

5.4. Elbows shall be long radius (centerline radius = 1.5 times nominal diameter).

6. FABRICATION - Piping Shop Fabrication Specification

6.1. CODES

Fabrication shall be in accordance with an American National Standard, Chemical Plant and Petroleum Refinery Piping, ASME B31.3.

Any exceptions will be noted on the Piping Drawings of Piping Material Specifications.

For other requirements refer to para. 4 &  para. 3.9

6.2. WELDING - Piping Shop Fabrication Specification

6.2.1. Welding procedures and Welders/Welding operators shall be qualified in accordance with Welding Procedure for Piping  and Welder Qualification Test.

6.2.2. The design of weld joint, welding bevel and reinforcement, shall be in accordance with ASME B31.3.

6.2.3. Prior to welding, the welding groove and adjacent base metal shall be cleaned inside and outside of all scale, rust, oxides, paints, oils, or other materials that may affect the welding.

6.2.4. The ends of piping components to be joined by welding shall be aligned as accurately as practicable within the tolerances of diameter, wall thickness, etc. Where the misalignment exceeds 1.6 mm, the ID of the pipe extending internally shall be trimmed with the angle of the bevel not to exceed 30 degree.  

However, this trimming shall not result in a piping component wall thickness less than the design thickness plus corrosion allowance.

6.2.5. Alignment shall be preserved during welding by tack welds, spaced as required, but with at least one tack weld in each quadrant.

Tack welds shall be of the same quality and material as the complete weld and shall be thoroughly fused with the weld beads.  Otherwise they shall be removed during the welding operation.

6.2.6. The use of backing rings or strips is not permitted in the welding of girth or longitudinal joints.

6.2.7. The acceptance criteria for all welding imperfection i.e., incomplete penetration, lack of fusion internal porosity, inclusion, undercut, roughness, concavity, reinforcement, protrusion & etc. shall be in accordance with table K341.3.2 of ASME B31.3 (Latest Edition).

6.2.8. On large diameter lines, where practicable, weld metal shall be deposited from both sides (double welded).

6.2.9. Prior to depositing each weld layer, the previous weld shall be thoroughly cleaned to remove all oxide, scale, slag, flux, or defects. Grinding or chipping may be required to correct the defects.  Peening shall not be used to close cavities in the weld metal.

6.2.10. Longitudinal seams shall be located to clear openings and attachments where practicable, and shall be staggered a minimum of 5t or 50 mm whichever is less in adjoining courses. Where necessary to add outside structural attachment to pipe across longitudinal seam weld, omit attachment weld where crossing seam weld and notch out attachment.

6.2.11. The fabricator shall bevel, or otherwise prepare joint ends that are to be field welded.

6.2.12. Alloy welding electrodes (filler metal) shall be of the same approximate analysis as piping material being welded.


6.3.1. The type of branch connection shall be as specified in the particular piping class of the Piping Material Specifications.

6.3.2. Nozzle joints may be either "set in" or "set on" type and shall be prepared to provide full penetration welds or a quality equal to the girth welds in the same piping system. 

For severe cyclic conditions and reciprocating compressors nozzle joints shall be set in type per paragraph 306. 5.2 of ASME B31.3.

6.3.3. The fabricator shall check all welded nozzles in accordance with ASME B31.3 and provide reinforcement where necessary.

6.4. REINFORCING PADS - Piping Shop Fabrication Specification

Reinforcing pads shall not be installed except when specified on spool drawings.  Pad material shall be the same as the pipe material unless otherwise approved by Consultant. Drawings will specify size and pad thickness. It is preferable to have pad shapes similar, but pad size may be altered, provided equivalent that the cross sectional area is maintained and code requirements are met.  Each pad or each piece, if the pad is made from more than one piece, shall have a 3-5 mm vent hole provided (at the side and not at the crotch) in the pad.  In fitting pads to curvature of pipe there shall no where be a gap greater than 3.0 mm.  Pad thickness shown on spool drawings are nominal. Mill tolerances are allowed per code.

6.5. MITER ELBOWS - Piping Shop Fabrication Specification

Miter elbows are to be used only when permitted by the piping specifications and shall be according to para.306.3 in ASME B31.3 in principle.

6.6. BENDING - Piping Shop Fabrication Specification

6.6.1. Only seamless pipe shall be used for bends.

6.6.2. The radius of bends shall be as specified on piping drawings.

6.6.3. Hot bend is not permitted.

6.6.4. Cold bends shall be limited to NPS1 and smaller for C.S & low alloy steel and NPS ¾ and smaller for stainless steel.

6.6.5. The fabricator may substitute the next heavier weight of pipe, if necessary, to produce satisfactory bends.

6.6.6. Bends shall be substantially free of buckles, with no buckle being deeper than 1% of pipe outside diameter.

6.6.7. The difference between the maximum and minimum outside diameters at any cross section along the axis of pipe bend shall not exceed 8% and 3% of the normal outside diameter for internal and external pressure, respectively.

6.6.8. When bends are trimmed close to the tangent point for field welding, the open ends shall be carefully squared up and prepared for welding.

6.7. THREADING - Piping Shop Fabrication Specification

Threads shall conform in quality and workmanship to the American National Standard for Pipe Threads, ASME B1.20.1   latest issue. Threading shall be done after bending or heat treatment if possible. Threads shall be clean and full cut, concentric with outside of pipe and protected against damage by any subsequent fabricating operations. Threads cut before bending or heat treatment shall be protected with Hi Temp Silicone Paint.

All threaded connections must be gauge checked or chased after welding or heat treating. Openings for thermo wells and other inserts are to be drilled through the connections and be free from obstruction.

6.8. DIMENSIONAL TOLERANCES OF COMPLETED DETAILS - Piping Shop Fabrication Specification

These tolerances apply to inline items and connections for other lines. These tolerances can be exceeded on items such as vents, drains, dummy supports, temperature and pressure connections, where the deviation will not affect another spool.

Below mentioned tolerances are not cumulative.

6.8.1. Straight length or offset bends with raised face or lap joint flanges.

Face to face of flanges or laps. ± 3.2 mm

6.8.2. Straight lengths or offset bends with RTJ or tongue and groove flanges.

Face to face of flanges ± 2.4 mm

6.8.3. Straight length or offset bends with beveled ends

End to end ± 4.8 mm

6.8.4. Flanged branches with raised face or lap joint flanges

Center of header to face of flange or lap ± 3.2 mm

Maximum lateral offset ± 1.6 mm

6.8.5. Flanged branches with RTJ or tongue and groove flanges

Center of header to face of flange ± 2.4 mm

Maximum lateral offset ± 1.6 mm

6.8.6. Beveled end branches

Center of header to end of bevel ± 3.2 mm

Maximum lateral offset ±  1.6 mm

6.8.7. U bends and offsets

Center to center ± 3.2 mm

6.8.8. In fitting reinforcing pads to the curvature of the pipe the maximum allowable gap shall be less than 3.2 mm.

6.8.9. Flange faces must be square with the pipe. The tolerance measured across the outside diameter of the gasket surface with a level and thickness gage shall be within the following:

Up to 4" ±  0.8 mm

6" to 8" ±  1.6 mm

10" ±  2.4 mm

12" and up ±  3.2 mm

6.8.10. Flange bolt holes shall be oriented as follows, unless otherwise indicated on spool drawings:

A. Flange face vertical   bolt holes to straddle against vertical centerlines.

B. Flange face horizontal   bolt holes to straddle against north south centerlines.

CAUTION :   The fabricator shall insure that this information is transferred to the shop drawings.

6.8.11. Orifice flanges shall be installed with the taps in the exact orientation shown on the spool drawings.  The sections of pipe to which the orifice flanges are attached may be standard mill  run  pipe, but shall be choice selected pieces and shall be round, smooth and free from blisters and scale. The interior of the pipe, at welds, shall be ground smooth in the shop. Field welds will be kept at a maximum distance back from the face of the orifice flange to the first weld.  Orifice flanges are to be drilled and tapped for jackscrews, where no other provision has been made for spreading flanges.

6.8.12. Slip on flanges, when specified in piping material specification shall be welded inside and outside. There shall be a distance from the face of the flange to the pipe end equal to the pipe wall thickness plus. 

If slip-on flanges are single welded, the weld shall be at the hub.

(See Fig.  328.5.2B (1) of ASME B31.3)

6.9. LICENSOR REQUIREMENT FOR CATALYST SERVICE - Piping Shop Fabrication Specification

Licensor requirement for catalyst service (BCDX class) shall be considered as attachment #2.

7. TESTING - Piping Shop Fabrication Specification

7.1. A general hydrostatic test of individual shop fabricated spool is not required except when specified by Owner.

7.2. In special cases when a test in the shop is necessary, the requirements will be stated on the piping drawings.

7.3. The test pressures and holding time shall be as specified on the Line Designation Table, and may be referred to Inspection & Test of piping construction and/or Pressure test of piping system.

7.4. All defective welds shall be chipped or ground out and re-welded for the satisfaction of the requirements.

7.5. Field tests of completed piping systems will be made.  The cost of repairing leaky shop welds will be back charged to the fabricator.

7.6. Any appreciable amount of re-welding after checking and/or testing will require detail to be rechecked for fabrication dimensional tolerance.

7.7. Materials which required post weld heat treatment shall be given a Brinell hardness test after PWHT and the Hardness must be below the maximum specified for the material in table 331.1.1 of ASME B31.3. and in accordance with para.331.1.7 of ASME B31.3.


8.1. EXAMINATION - Piping Shop Fabrication Specification

8.1.1. The fabricator shall examine all welds per Inspection & Test of piping construction which shows the type and extent of the required examination for the different piping systems.

8.1.2. R1 The Consultant and/or Owner’s Inspector may specify further examination in any category where he feels it is necessary.

8.1.3. The intent of these examinations is to provide the examiner and the Inspector with reasonable assurance that the requirements of ASME B31.3 and the engineering design have been met.

8.1.4. Where examination reveals a failure to meet design or code requirements the Construction Contractor must make such repairs as are necessary to meet the design or code requirements. 

If cracks are detected, the complete weld must be removed, re prepared and re welded.

8.1.5. All costs incurred in repairing defective or rejected work and all consequential heat treatment and additional examination costs are to be borne by the Construction Contractor.

8.2. INSPECTION AND RECORDS - Piping Shop Fabrication Specification

8.2.1. Inspection as defined by ASME B31.3 will be performed by Consultant or a Consultant authorized inspector. Such authorized inspector may reject any material, procedure or work which, in his opinion alone, fails to meet the requirements of applicable codes, specifications, procedures, drawings, purchase orders or contract.

8.2.2. Where inspection reveals a failure to meet design or code requirements the Fabricator must make such repairs as are necessary to meet the design or code requirements.

8.2.3. All costs incurred in repairing defective or rejected work and all consequential heat treatment and additional examination costs are to be borne by the Fabricator.

8.2.4. The following records, fully identified with the specific material or part of the piping represented, must be available for reference or examination by the authorized inspector. On job completion, they must be collated, indexed and bound, and forwarded to Consultant.

A. Certificates attesting that all the quality control requirements of the applicable code and of the engineering design have been met.

B. Pyrometer charts and records of heat treatment.

C. Radiographic films.

D. Results of magnetic particle and fluid penetrant examinations.

E Charts or other records of hydrostatic, pneumatic and Brinell hardness tests.

F. Results of any other supplemental types of examination, test or analysis specified.

G. Welding procedure qualifications and their qualification test results.

H. Welders/Welding Operators qualification test results.

I. Others. (i.e., Inspection Reports, MTC (material test certificate) and etc.)

8.3. CLEANING - Piping Shop Fabrication Specification

For general requirement refer to.

9. PAINTING - Piping Shop Fabrication Specification

Shop painting of pipe spools, if required, is the subject of a painting specification.

10. PREPARATION FOR TRANSPORTATION - Piping Shop Fabrication Specification

Shop fabricated pipe is sectionalized to fit into a box 12.0m x 3.0m x 3.0m in accordance with Attachment 1; Shipping length.  

When heat treated pipe of this size cannot be contained within the furnace, the fabricator shall inform Consultant of the maximum size.


10.1.1. Before pipe spools are transported from the fabricating shop, the following preparation and protection shall be carried out:

Flanged Ends:

Coat flange faces with a grease type rust preventive, and cover faces with plywood, hardboard, steel or equivalent covers securely wired or bolted to the flange proper on at least four bolt holes.  All ferrous flange facings shall be coated with anti rust material.

Beveled and Plain Ends:

Provide heavy gauge plastic cover completely sealing the opening and protecting the pipe ends (or Consultant approved alternate).

Threaded Ends:

Provide plastic or metal plugs for female threads, and plastic caps for male threads.

Machined Surfaces:

Coat with a grease type rust preventive and provide securely fastened wooden or metal covers.

Socket Weld Ends:

Provide a plastic plug.

Note: Ring type joint flanges shall have groove packed with grease prior to attaching flange protective covers.

10.1.2. The inside of each fabricated pipe spools shall be thoroughly cleaned of all welding spatter or icicles, sand, scale, or other foreign debris.

10.1.3. Small pieces shall be boxed or wired together to avoid loss in transit.

10.1.4. Loading and handling shall be done with reasonable care and details braced where required to prevent damage during transit.

10.1.5. Piece Marking shall be considered for each spools.

10.1.6. Spools are to be identified by their line number and spool suffix, which shall be painted or stenciled as characters at least 50 mm high. The size of character shall be suitable with size of the pipes. Painted numbers shall be located, and repeated as necessary, in such a manner that any spool may be easily identified without turning or lifting it.

10.1.7. Stamping of piece mark numbers on carbon steel pipe with steel die low stress stamps is permitted if done lightly and carefully, so as to minimize notch effect and so that the marking will not cause cracks or reduce the wall thickness below the minimum allowed. Stamping of alloy pipe and stainless steel is not permitted without Consultant's approval. Waterproof paint or paint protected with a clear waterproof varnish shall be used on alloy pipe and stainless steel.

10.1.8. The welders identification symbol shall be marked adjacent to each weld.  Metal stamping of carbon steel pipe per para. 10.6.2 is permissible.  On alloy pipe the marking shall be as per para. 10.6.2.

10.1.9. Heat numbers shall be transferred onto spools and onto spool drawings.  

Weld identification symbols to be added to spool drawing. 

10.1.10. The paint for marking shall be non-zinc type to prevent zinc contamination.

11. TRANSPORTATION - Piping Shop Fabrication Specification

11.1. All transportation of fabricated pipe spools shall include with the packing list a complete listing of the spools being shipped.

11.2. Fabricated pipe spools shall bead-equally blocked, strapped or otherwise held in position during shipment and shall be further separated by dunnage as may be necessary to prevent damage.

12. QUALITY ASSURANCE PLAN FOR SPOOL FABRICATION - Piping Shop Fabrication Specification

12.1. The fabricator shall prepare the quality assurance plan for spool fabrication in accordance with the project specification and the code concerned.

The plan shall be discussed and agreed by Consultant and/or Owner before application.

12.2. The Quality Assurance Plan shall include followings and How to control it.

12.2.1. Pre-Fabrication Stage

1) Receipt of Materials

2) Identification and Color coding

3) Store of Materials

4) Qualification of Welding Procedure

5) Welder and/or Welding operator Qualification

6) NDT procedure and Qualification

7) Surface cleaning Application of primer

12.2.2. Fabrication Stage

1) Checking Materials as per Piping class and Material Identification

2) Cutting and Edge preparation

3) Fit-up and Dimensional Checking

4) Preheat and Inter-pass Temperature

5) Verification of Welding filler material

6) Reinforcement

7) Non-Destructive Examination procedure

8) Visual and Dimension Measurements

9) Heat Treating

10) Repair procedure for Defective joints

11) Painting and Identification

12) Code Stamping (where required)

12.2.3. Inspection and Test Plan

1) The Fabricator’s Q.C. Engineer shall prepare the Inspection & Test Plan to assure that all activities for spool fabrication are satisfactorily performed in accordance with the Project specification and the contract. ITP shall be submitted to Owner for approval.

2)  The minimum requirement for each activities shall be verified with Inspection and/or Test results and confirmation made by Owner.

3)  All activities for Inspection & Test shall be witnessed by the Fabricator’s Q.C. engineer, and Consultant and/or Owner’s representative shall witness the Inspections that have stipulated as “Hold Points” in accordance with the Project specification and mutual agreement among the Fabricator, Consultant and Owner.

4) No work can proceed beyond the operation stipulated as “Hold Point” until Consultant and/or Owner has witnessed the “Hold Point” operation and has indicated his approval by initialing and dating on the Inspection report prepared by the Fabricator.

12.3. DOCUMENTATION AND MATERIAL TRACE ABILITY - Piping Shop Fabrication Specification

12.3.1. All activities for quality assurance shall be performed and controlled as verified by documentation.

12.3.2. All piping materials used for spool fabrication shall be identified and documented as traceable.

12.3.3. The heat no. and Material Test Certificate (MTC) of all piping bulk material supplied by manufacturer shall be recorded and filed for the material trace ability.

12.3.4. The application of the Fabricator’s in-house Q.A. procedure and formats may be allowed to assure the quality control, The procedure and formats, however, shall be agreed by Consultant before application.

13. INFORMATION SOURCES - Piping Shop Fabrication Specification

The following documents will be issued to the Fabricator:

13.1. Piping Material Specification showing the pipe, valve, flange, fitting, branch connection, and other specific materials requirements for piping services.

The specification includes the individual piping material classifications. 

Branch reinforcements to be in accordance with unless otherwise specified on isometric drawings.

13.2. Piping drawings that may be orthographic arrangements and/or line isometrics.

These drawings show routing, controlling dimensions, component parts, attachments, piping classifications and identification number for each line.

13.3. Isometric Listing - Piping Shop Fabrication Specification

13.4. Line Designation tables showing line design pressures and temperatures.

13.5. Supplementary tables of wall thickness showing wall thickness and branch reinforcement requirements where piping specifications indicate that individual calculations are required.

13.6. Standard and other drawings and specifications stating typical and specific requirements relating to pipe spool fabrication.

13.7. Material listing for all pipes, fittings and flanges required for fabricating spools.

13.8. Project calendar showing the relationship between project week numbers and actual dates.

Piping Shop Fabrication Specification - Attachment 1:


shop piping fabrication

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