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General Welding specification

 

1.0 Scope

This specification defines Buyer's minimum requirements for shop and field welding and heat treatment of equipment and fabricated production systems.

All works should conform to the requirements of this specification, other Buyer specifications referenced herein, and all other contract documents in conjunction with all applicable codes and standards, sound engineering principles and good fabrication and construction practices.

2.0 References

The following documents are considered part of this specification. Use the edition of each referenced document in effect on the date of the publication of this specification.

ASME Boiler and Pressure Vessel Code
ASME B31.3 Chemical Plant and Petroleum Refinery Piping
ASME B31.8 Gas Transmission and Distribution Piping Systems
AWS D1.1 Structural Welding Code
API Std. 1104 Welding of Pipeline and Related Facilities
ASME B16.5 Steel Pipe Flanges and Flanged Fittings
ASME B16.9 Factory-Made Wrought Steel Butt-Welding Fittings
MSS SP-75 Specification for High Test Wrought Butt Welding Fittings
MSS SP-44 Steel Pipeline Flanges

3.0 Welding and Welder Qualifications

Supplier should prepare, or have, a welding procedure specification (WPS) for each welding process proposed for the works.  Each procedure should conform to the following criteria:

  • Conform to Buyer's limitations for use.
  • Be identifiable by number and date.
  • Reference the applicable welding/fabrication code, and be documented in a manner that conforms to the presentation requirements of that code.
    • ASME B31.3 - Piping
    • ASME B31.8 – Piping
    • ASME Boiler and Pressure Vessel Code - Pressure Vessels
    • AWS 1 – Structural
  • Define the welding process.
  • Define all essential variables for the welding process, as being representative of the chemical and mechanical base material properties.
  • Define all physical and method limitations.

Each welding procedure specification (WPS) should be accompanied by a dated procedure qualification record (PQR).  Each PQR should be, or have been, signed as qualified by a welding laboratory experienced in shop and field welding or by a technician or welding engineer certified by the American Welding Society.  The registration of the signing certified welding inspector (CWI) or certified welding engineer (CWE) should be clearly stated.

Each WPS and PQR should be issued to Buyer for comment and approval at least two weeks prior to the scheduled start of any associated welding.  Any single welding procedure meant to cover the provisions of more than one code should be rejected.

Each welder and welding operator proposed for the work should be qualified to weld under one or more approved WPS.  The date of any existing qualification should conform to the time requirements as specified by the applicable code.  The qualification documents for each welder and welding operator, which state that individual's name and social security number, should be signed as certified and witnessed by a qualified individual.  These qualification documents should also be submitted to Buyer along with the WPS's and PQR's.  Supplier should be responsible for issuing the qualification documents of any new welder or welding operator to Buyer who is proposed to be assigned to the work during the course of fabrication.

All costs associated with the preparation of welding procedures, welding qualification reports, and welder or welding operator qualification documents (including testing) should be for Supplier's account.  Buyer reserves the right to reject the work of any welder or welding operator if that work is performed without approval of the specified documentation to cover such work.  All costs associated with the removal, rework, and/or replacement of rejected works should be for Supplier's account.

Records should be maintained of all welders who have been approved as qualified for the work.  This record should state each welder's name with confirmation of identity statement, last date of certification, WPS qualified under, and the qualified welding position limitations.

As stated, welders and welding operators should be qualified separately under each qualified welding procedure; e.g. a welder qualified for shielded metal arc welding for structural steel as conforming to the AWS D1.1 code is not qualified for welding that process on pressure piping.  He must also be qualified under a separate procedure conforming to ASME B31.3, ASME B31.8, and this specification.  Each welder should also be qualified for the welding positions anticipated as being required for the works.

The base metal for test specimens and its preparation for welding should conform to the referenced code and the limitations of the qualified welding procedure.  The length of the weld and the dimensions of the base metal(s) should be sufficient for each specimen as specified by the code and should be representative of the grades and sizes of welds required for the works.

Welding procedure specifications and procedure qualifications for welding structural steel shapes, plates, pipe, pipe supports and structural tubing should be in accordance with the "Structural Welding and Inspection" specification.

Welding procedure qualifications should include impact testing requirements for ferritic materials, as applicable to the weld metal and the heat affected zone.  Charpy impact tests should be performed as specified by the ASME Boiler and Pressure Vessel Code, as required.

Welding procedure qualification tests for submerged arc-welding with passes greater than 3/8 inch should include Charpy "V" notch impact tests at the lowest specified design metal temperature.  Impact values for the heat affected zone and weld metal should not be less than that for the base metal.

For submerged arc-welding, the brand name and the grade of flux should be considered as essential variables as well as changes in speed or heat input.  The welding procedure qualification report should state the manufacturer and trade names of the wire and flux used to qualify the welding procedure.

The welding procedure tests should normally demonstrate that all requirements are satisfactory for obtaining full penetration welds for the following types of joints:

  • Double-welded longitudinal and circumferential butt joints
  • Single-welded longitudinal and circumferential butt joints made without a backing ring

4.0 Welding Processes

The following welding processes and combinations thereof are preferred by the Buyer and will be accepted when properly qualified to the Specification.  These processes should be used exclusively in the fabrication of pressure vessels:

  • Shielded metal arc welding - (SMAW)
  • Submerged arc welding - (SAW)
  • Tungsten inert gas welding - (TIG)

The following welding processes may be accepted when properly qualified to the codes referenced in Section 2.0 and this specification at the discretion of the Buyer:

  • Gas metal arc welding - (GMAW); this process should be limited to the root pass
  • Flux cored arc welding - (FCAW)

Buyer reserves the right to place stringent restrictions on any intended use of a welding process utilizing short circuiting arc transfer.

5.0 General Welding

All piping welds made as a part of the work covered by these specifications should be stenciled with low stress concentration dies with a letter or symbol which should identify the welder.  These stenciled markings should be made prior to any type of testing.

All welding, welding inspection, and heat treatment should conform to the applicable portions of this specification and the codes referenced in Section 2.0.

Semi-automatic or fully automatic welds should be made with a multi-pass technique.

All filler materials, electrodes, and wire should be selected to achieve a quality equal to or superior to that demonstrated by the procedure qualification tests.  The physical properties of the weld metal should fulfill the minimum requirements for that of the base metal.  Exceptionally high-strength welds or excessively alloyed welds are not acceptable.

Backing rings should not be used unless specifically approved by Buyer.

All welding procedures should be identified by number and should be referenced on all fabrication drawings.

No welding should be done when weather conditions would impair the quality of the weld without shielding.  Wind shielding and other types of covering should be provided as required to conform with this requirement.

All edges and bevels prepared for welding should be protected from moisture, damage, and contamination and be welded out as soon as possible.

Welding equipment, both gas and arc, should be of a size and type suitable for the work and should be maintained in such condition as to ensure acceptable welds and continuity of operation.  Arc welding equipment should be operated within the amperage and voltage ranges given in the qualified welding procedure.  Gas welding equipment should be operated with the calibrations and tip sizes given in the qualified welding procedure.  Any equipment not meeting these requirements should not be used, should be repaired, or should be replaced as determined by Buyer.

Special care should be taken in the preparation and welding of stub-ins, weld-o-lets, reinforcing pads, and structural mitered joints.  All stub-ins should be properly fitted to ensure the production of sound welds.  Welds should merge smoothly with the surface of the pipe with no notches or undercutting.  Sharp corners on reinforcing pads should be removed.

The storage and handling of electrodes should conform to the provisions of sections 4.1.3 and 4.5 of the AWS D1.1 Welding Code.

Weld bevels should be suitable for the welding process used.  The contour should permit complete fusion throughout the joint.  Bevels should be in conformance with those used in the procedure qualification.

Weld bevels should be made by machining, grinding, or thermal cutting and the surfaces should be reasonably smooth and true.

Surfaces to be welded should be clean and free from paint, oil, dirt, scale, oxides, or other contaminants detrimental to welding.  Cleaning should be done in a manner not leading to contamination of the base metal.

Unless shown or specified otherwise, all joints should be welded to develop 100 percent joint efficiency and/or to fully develop the strengths of the members joined.

All welds connecting lugs, clips, brackets, and structural members should be sealed with weld all around the joint.  Any sides not accessible for back side seal welding should have a full penetration, melt through weld made from the opposite side.

Any prepared edge or bevel damaged should be either rejected or restored to minimum tolerances before welding.

Acceptable butt welded joint geometry for piping and tubular members with unequal wall thicknesses should be in accordance with the criteria given in API RP 14E, Appendix "B".

The root gap and offset of butted edges should be in strict accordance with the parameters given by ASME B16.5, ASME B16.9, MSS SP-75, MSS SP-44, ASME B31.3 and B31.8, and the ASME Boiler and Pressure Vessel Code, and as used in the procedure qualifications.  Root gaps and offsets not in conformance should be rejected.

Joint geometry in single-welded butt joints should be such that full penetrations can be attained.

Weld sizes and other instructions given on Buyer's drawings and/or on Supplier's approved drawings should be conformed to at all times.

Unless specified otherwise, the minimum weld size for structural integrity should be 3/16 inch as measured across the throat.

Weld beads should be contoured to permit complete fusion at the sides of the bevel and to minimize slag inclusions.  Flux and slag should be completely removed from weld beads and from the surface of completed welds and adjoining base material.  The flux removal should be done in a manner that will not contaminate or overheat the weld or adjoining base material.

Weld reinforcement and finish should be as required by the applicable code.  Undercutting of the base metal is not permitted.

Weld bevels and weld surfaces should be free of cracks, cold lap, excessive porosity, slag inclusions, and other defects indicative of poor workmanship.

For multi-pass welds, each pass should be completed and visually inspected prior to depositing the next pass.  Slag, scale, excessive thicknesses, improperly fused starts, and all cracks or faults should be removed as required and repaired prior to depositing the next pass.  Starts around a circumferential weld should be visually inspected and treated the same as the first pass.

6.0 Preheating and Post Weld Heat Treatment

Preheating and post weld heat treating should be performed as specified by the ASME B31.3 and B31.8 Codes, the ASME Boiler and Pressure Vessel Code, and Buyer's specifications.

When heat treating is performed, all traces of paint or other surface compounds should be removed.  Flange gasket faces, ring grooves, and threads should also be protected against possible damage.

The parameters for all post weld heat treatment should be defined in writing.  Such parameters should state the method of heating, of adequately measuring temperatures, critical temperatures, and the timed rate of heating and cool-down.

7.0 Repairs and Corrections

Any welded joint found to be defective or unsuitable should be repaired with a procedure conforming to Buyer specifications and the provisions of applicable codes listed in Section 2.0.

Heat treatment, welding, and any post weld heat treatment should be subject to the same original requirements.  Repaired components should be re-examined and/or tested by the original methods to determine freedom of defects.

All welds repaired on pressure containing piping, vessels, or other components should be radiographed or re-radiographed around the entire circumference.

No welds containing cracks, regardless of size, location, or service, should be acceptable.  Cracked welds should be removed in their entirety and repaired.

External undercut, contour, and arc burn defects should generally be repaired by grinding and cap welding the defective area to accommodate a suitable repair.  Peening to remove defects is prohibited.

No method of testing should relieve Supplier of the responsibility for any defects in materials and/or fabrication as specified by Supplier's warranty and guarantees.

All repair, re-testing, and/or replacement of any part of Supplier's works, performed by Supplier, at Buyer's direction and/or any certified code inspector's direction, should be for Supplier's account.  This should apply to all such work performed by Supplier prior to startup and should be at no cost to Buyer.

All repair, re-testing, and/or replacement of any part of Supplier's works, performed by Supplier after startup, should be as directed by Buyer in accordance with Supplier's warranty and guarantee, as stipulated in Supplier's proposal and as in accordance with Buyer's general procurement specification.

All assemblies and components found to have non-repairable defects, requiring excessive repairs, or found to be improperly fabricated in accordance with Buyer's specified requirements, should be subject to rejection and replacement even if the conditions are discovered during field testing and inspection prior to startup.  The resulting repairs, re-fabrication, or replacement should be for Supplier's account.

Welds shown by radiographic examination to have imperfections such as lack of fusion, incomplete penetration, slag inclusions, elongated defects, internal concavity, burn through, or porosity beyond the limits allowed by the applicable code should be removed and replaced as specified by the code and/or as directed by the code inspector and/or Buyer.

 

 

Tags: Welding