Welding Technical Specification | Welding Requirements | Qualification | Materials
6.1 General Welding Requirements
6.1.1 Nomenclature Used in Welding Sections
FCAW Flux Cored Welding
GMAW Gas Metal Arc Welding (MIG) GTAW Gas Tungsten Arc Welding (TIG)
SMAW Shielded Metal Arc Welding (Coated Electrode/Stick)
6.1.2 At least one pass per 3 mm (1/8 in) of wall thickness shall be made. Downhill welding using SMAW (stick) process is prohibited. Slag shall be removed before depositing succeeding layers. The finished weld shall be uniform with the toe or edge of the weld merging smoothly into the base metal. Butt welds shall have a slight, gradual reinforcement built up from toe or edge toward the center of the weld. Fillet welds may be slightly concave on the finished surface. No undercutting or overlapping is permitted.
6.1.3 If cracks or blow holes occur on the surface of any welding bead, they shall be chipped or ground out to remove the defect, and then wire brushed to present a surface from which complete fusion may be obtained with the next successive welding bead. Peening to cover defects shall not be allowed.
6.1.4 Welding by creating a heat pattern at a circumferential joint can “draw in” the weld and the base metal in the heat-affected zone, thereby creating a “belling in” and giving a reduction in the area of the pipe or tube. This belling or distortion is undesirable and is subject to the following limitations:
6.1.4.1 The belling or distortion tolerance may not exceed 1% of the actual outside diameter (OD) or 1.5 mm (1/16 in); whichever is larger. This belling or distortion can be measured by comparing the actual OD at the belled or distorted area.
6.1.5 Welds of orifice flanges shall be made without the use of backing rings. The upstream and downstream welds shall be ground internally so that the inside diameter (ID) at the weld is within 1% of the published ID for the schedule of pipe specified. Any purchased meter runs require installation in the process pipe at the upstream and downstream ends without the use of backing rings. Backing rings shall be used for aluminum welds and removed after welding unless there is sufficient access to complete a double-sided weld. In either case, the inside of the pipe shall be ground as described above.
6.1.6 All slip-on flanges shall be welded internally and externally.
6.1.7 When backing rings are permitted and they have not been supplied by Company, they shall be cut by the fabricator from piping material provided as contingency material by Company. The backing ring composition shall match the P number or the pipe base metal composition.
6.2 Qualifications Required for Welding Procedures and Welders
6.2.1 All pipe welding, including attachment welds to piping, shall be performed according to qualified procedures developed by the fabricator and by welders qualified to the procedures in accordance with ASME BPVC Section IX and as modified by ASME B31.3, paragraph 328.2. Each weld shall be completed by a single welder unless agreed otherwise with the Company representative.
6.2.2 Welding procedures for stainless steel as listed in ASME B31.3, Appendix A, shall be qualified to the minimum material temperature listed therein (that is, ASTM A 312, TP304 and 304L; ASTM A 403, WP304 and 304L) and shall have weld procedures qualified to 320°F (160oC).
6.2.3 Impact testing for weld procedure qualifications shall be according to ASME B31.3. For stainless steel in cryogenic service, the weld metal shall be Charpy impact tested with a minimum of 0.53 mm (0.021 in) lateral expansion for each specimen, with three specimens required per procedure qualification.
6.2.4 Fourteen calendar days before commencement of welding, the fabricator shall deliver to Company Engineering Services, Engineering Data Group, prepared in accordance with the purchase order, the applicable codes and the VDR Set, two copies of all welding procedure specifications (WPS) plus two copies of the weld procedure qualifications record (PQR) relating to the specifications. No welding shall be performed until Company has approved, in writing, the welding procedure specifications.
6.2.5 Each welder shall be qualified according to the approved WPSs, and the welder qualification (WPQ) record shall be maintained on file at the fabricator’s job site office. Welder qualifications shall be valid and within the time limits specified in the applicable code.
6.2.6 All the cost of qualifications shall be borne by the fabricator, including the provision of all necessary materials and consumables. If there are any specialty pipe materials required that cannot be procured in time to support the erection schedule, the fabricator shall notify Company at the time of his tender so that Company can procure this material for the development of PQR to support the overall fabrication schedule.
6.2.7 Indexed copies of all PQRs, WPQs, and WPSs shall be placed in the “Quality Assurance and Inspection Book.”
6.3 Filler Material
6.3.1 See Appendix C or Appendix D (for aluminum filler material).
6.4 Weld-joint Preparation
Note: See Appendix D for aluminum welding requirements.
6.4.1 The fabricator shall prepare all welding joints according to the specified code and the approved WPS.
6.4.2 Stainless steel pipe shall only be cut by mechanical or plasma cutter processes. It shall not be cut using an oxy-acetylene torch. A minimum of 1.0 mm shall be removed from the pipe by grinding to eliminate any trace of carbon that may have been deposited by plasma cutting.
6.4.3 Materials that are being welded shall be carefully fit, aligned, and retained in position during the welding operation. Adequate and proper tack welding will be considered acceptable. Tacks shall not obstruct a full-penetration weld. Before starting to weld, tacks must be thoroughly cleaned.
6.4.4 The inside surfaces of piping components to be joined by butt welding shall be aligned so that the misalignment at any point on the inside circumference does not exceed 1.5 mm (1/16 in) or 1/4 of the nominal thickness of the component with the thinner wall, whichever is smaller.
6.4.5 The longitudinal seams of welded pipe in adjoining pipe sections shall be staggered.
6.4.6 Branch connections shall not intersect the longitudinal seam of welded pipe.
6.4.7 The fabricator shall ensure that the seams of any prefabricated piping spools do not coincide with the seams in fabricated miters.
6.4.8 Fabricated tees and mitered bends DN450 and above shall be back welded on the inside of the fittings (reference Company document 4WPI-FWAB01).
6.4.9 Material provided for the fabrication of miters, pipe fittings, or pipe shall not be provided with any weld preparation unless specifically advised by Company. The fabricator shall allow for making the required weld preparation.
6.4.10 All socket-weld joints shall have a 1.5 mm (1/16 in) gap between the pipe end and socket bottom of the fitting.
6.5 Material Specific Welding Requirements
6.5.1 Welding Requirements for Carbon Steel, Stainless Steel
6.5.1.1 The fabricator shall perform all welding according to the applicable code. The following welding processes are permitted for making one-sided groove welds:
- Stainless steel welded to carbon steel: For Schedules 5 and 10, only GTAW shall be used for the root bead and the balance of the weld. For heavier piping, the root bead shall be made with GTAW; the balance of the weld may be made using another Company- approved welding process. All welding shall be made using an internal gas purge of either argon or nitrogen gas. The use of backing rings is not permitted except for final closure welds when approved by the Company representative on a case-by-case basis. Final closure welds are those welds where prefabricated piping is installed to a fixed component in the piping system resulting in positional welding where the ability to obtain a uniform root pass is impaired and/or extensive purging would be required to weld successfully. Typically, these should be less than approximately 15% of the total number of welds. Locations where backing rings have had to be used must be recorded in the construction records.
- Carbon steel: Root bead welding will be made by either (1) GTAW, (2) on carbon steel only, SMAW using backing rings, for girth joints (not including branch connections), (3) GMAW – short circuit if automated and rolled, (4) GMAW – short circuit semi-auto on joints that cannot be rolled, but have access for visual inspection and grinding of the internal bead, as needed. The balance of the weld may be made using another approved welding process.
Note: GMAW – short circuit is permitted only for making the root bead. If FCAW is used, supplemental gas shielding must be provided.
6.5.1.2 Piping designated for oxygen service shall have the root pass welded using the gas tungsten arc welding (GTAW) process with argon backing purge. Following the root pass, subsequent welding may be completed by another Company-approved process.
6.5.1.3 The use of backing rings is not permitted for carbon or stainless steel classified for oxygen service.
6.5.1.4 For carbon steel welding, each welder shall identify the welder’s specific production welds by stamping the welder’s regularly assigned identification number on the pipe adjacent to the welds made in all carbon steel material. Stamps shall be low-stress type with a round or “U”-shaped cross section.
6.5.1.5 For stainless steel welding, each welder shall identify the welder’s specific production welds by etching (with an electric pencil) the welder’s regularly assigned identification number on the pipe adjacent to the welds made in all stainless steel material.
6.5.2 Welding Requirements for Aluminum: Refer to Appendix D, Aluminum Welding.