Weld Repair Procedure: ASME Code Requirements for Fabrication and In-Service Repairs

Category: Quality & Management  |  Reading time: ~20 min

A weld repair is not simply a matter of grinding out a defect and rewelding. Under ASME codes, every repair to a pressure-retaining weld is a controlled engineering activity with defined procedural requirements, documented authority chains, and mandatory verification steps. Cutting corners on any part of the process — removing less than the full extent of the defect, using an unqualified WPS, skipping PWHT, or omitting post-repair NDE — can leave a component in a worse condition than before the repair attempt, potentially with a camouflaged flaw that passes a visual examination but fails in service.

This guide consolidates the weld repair requirements from the four ASME codes most relevant to pressure equipment fabrication and maintenance: Section VIII Divisions 1 and 2 (pressure vessels), Section IX (welding qualifications), B31.3 (process piping), and PCC-2 / NBIC Part 3 (in-service repair). It is structured as a practical reference for welding inspectors, welding engineers, and QC managers who need a single consolidated document covering the full repair cycle from defect identification through to final documentation.

1. Overview — What Constitutes a Weld Repair Under ASME

Under ASME codes, a weld repair is any operation that removes unacceptable weld metal or base metal affected by welding and deposits replacement weld metal to restore the joint to a condition that meets code acceptance criteria. This is a broader definition than many practitioners assume. It includes:

• Excavation and rewelding of a weld containing cracks, porosity, slag inclusions, lack of fusion, or other rejectable discontinuities found by NDE during original fabrication.
• Weld overlay or build-up to restore wall thickness lost to corrosion, erosion, or mechanical damage on a previously accepted pressure-retaining component.
• Repair of a crack or leaking joint discovered during in-service inspection, hydrostatic testing, or after a service incident.
• Removal and replacement of an unacceptable weld seam (cut-out and reweld).
• Seal welding of a previously mechanical-sealed joint where leakage has occurred.

Importantly, adding a cosmetic weld bead to improve weld surface appearance — without excavating to the defect — does not constitute a repair and will not remove the underlying discontinuity. This “cap-over” practice is a code violation and may mask a rejectable flaw that would otherwise be detectable by surface NDE.

1.1 Regulatory authority — who must approve a repair

The authority chain for approving weld repairs differs between new construction and in-service scenarios:

New construction (original fabrication): The manufacturer’s written Quality Control (QC) System — required for ASME Code stamp holders — must describe the repair control process. The Authorised Inspector (AI) from the Authorised Inspection Agency (AIA) must be notified of all unacceptable NDE indications and must concur with the proposed repair method before work begins. The AI is not required to physically witness every repair weld but must review the repair documentation and be satisfied that the repair meets code requirements before the component proceeds to final inspection.

In-service repairs: Repairs to existing stamped equipment in service fall under the National Board Inspection Code (NBIC) Part 3 and must be performed by an organisation holding an ASME ‘R’ Certificate of Authorisation. The owner, the Authorised Inspector, and the Jurisdiction (state/local authority) must all be notified per the applicable jurisdiction requirements. Form R-1 (Report of Repair) is completed and submitted to the Jurisdiction and the National Board after completion.

2. Classification of Weld Repair Types

ASME codes do not use a single universal classification for repair types, but three broad categories describe the range of repair scenarios encountered in practice, each with different procedural implications.

2.1 Minor weld repairs (weld metal only)

The most common category: a weld discontinuity (porosity cluster, slag line, lack of fusion indication) is found by NDE, excavated, verified clean by PT or MT, and rewelded. The repair weld is confined entirely within the original weld cross-section. No base metal is involved. PWHT requirements are the same as for the original weld. Post-repair NDE uses the same methods and acceptance criteria as the original examination. This type of repair can usually be completed within the original WPS and does not require a new procedure qualification if the essential variables are unchanged.

2.2 Major weld repairs (involving base metal)

The excavation extends into the base metal — for example, when a toe crack extends into the parent plate, or when a weld is found to have gross lack of fusion that necessitates removal of a significant portion of the weld and adjacent base metal. Base metal involvement changes the P-Number grouping considerations for the repair WPS and may affect the PWHT requirement. Mechanical property testing of the repaired region may be required if the base metal heat-affected zone has been significantly altered by multiple thermal cycles.

2.3 Complete weld removal and replacement

In cases where a weld seam is found to contain pervasive, deep, or extensively distributed defects — particularly in high-pressure service or fracture-critical applications — the most technically sound solution is complete removal of the weld by machining or arc gouging, followed by a fresh joint preparation and rewelding. This is treated as a new weld for code purposes, with full production weld NDE requirements applied to the replacement weld. This approach avoids the complexity of PWHT exemptions for partial repairs in thick-section vessels and gives the inspector confidence that no residual defects remain from the original weld.

3. WPS and Welder Qualification Requirements

ASME Section IX governs welding procedure and welder qualification for all ASME-coded pressure equipment, without distinction between production welding and repair welding. The qualification rules are identical: a repair weld is performed under a WPS supported by a PQR with test results demonstrating that the procedure produces welds with the required mechanical properties.

3.1 Using an existing production WPS for repairs

In most cases, the welding engineer can use the existing qualified production WPS for the repair weld, provided that the repair does not involve essential variable changes that would take the repair outside the WPS qualification range. The following checks must be made before approving an existing WPS for repair use:

• P-Number: The base metal P-Number of the repair area must fall within the WPS-qualified base metal range.
• F-Number and A-Number: The filler metal must match the qualified F and A numbers.
• Heat input range: The repair weld heat input must fall within the qualified range. Repair welds in restricted-access cavities often use lower current and slower travel speeds — verify that the procedure covers this range.
• PWHT: If the original WPS was qualified with PWHT and the repair will receive PWHT, this is satisfied. If the repair cannot receive PWHT (see Section 6), a procedure qualified without PWHT is required.
• Position: The repair position may differ from original production welding (e.g., overhead repair in a vessel that was originally welded in flat position). Verify that the WPS covers the required position.
• Preheat: Repair welds in thick sections or after prior thermal cycles may require a different preheat than the production WPS specifies. If preheat is increased beyond the WPS limit for non-qualified welding, a supplementary PQR may be required.

3.2 Qualifying a new WPS specifically for repair

A new WPS and supporting PQR are required when the repair involves essential variable changes that take it outside all existing qualified procedures — for example, repair of a crack in a P-5B (Cr-Mo) vessel using a lower-hydrogen process not previously qualified, or repair without PWHT on a vessel that was originally constructed with mandatory PWHT. Qualifying a new repair WPS follows exactly the same Section IX process as qualifying any other WPS: test assembly, mechanical testing (tensile, bend, impact if required), and documentation of the PQR.

3.3 Welder and welding operator qualification

Welders performing repairs must be qualified for the process, position, and filler metal type of the repair weld per ASME Section IX QW-300 series. A welder qualified for production welding is not automatically qualified for all repair scenarios — if the repair requires a different position, process, or filler metal outside their current qualification range, a new welder qualification test is required. Welder qualification records (WQR or WPQ) must be traceable to each repair weld through the repair record documentation.

4. Defect Removal — Excavation Methods and NDE Verification

Complete removal of the defect is the non-negotiable first step of any weld repair. Partial removal — grinding down until the indication disappears from the immediate surface — is not acceptable for cracks, lack of fusion, or other planar discontinuities. The excavation must remove all defective material and extend into demonstrably sound metal.

4.1 Excavation methods

Grinding: Suitable for shallow surface defects (porosity, surface slag, surface-breaking cracks). Angle grinders with abrasive discs remove material progressively while allowing visual monitoring. The cavity profile should be dressed to a smooth, tapered shape with a minimum 4:1 length-to-depth ratio to avoid stress concentration at the base of the excavation.

Arc air gouging (CAC-A): The most common method for removing significant depths of weld metal in carbon and low-alloy steel. A carbon electrode with compressed air blast removes molten metal rapidly. Produces a carburised surface layer (~0.5–1mm) that must be removed by grinding before repair welding — failure to do so increases the risk of cracking in the repair weld due to elevated carbon at the fusion interface. Not suitable for stainless steel or nickel alloys without careful subsequent grinding.

Mechanical gouging (chipping, routing): Used where arc gouging is impractical (tight spaces, in-service environments with flammable vapours). Slower but produces no carburised surface. Required for repair of stainless steel pressure vessels in food, pharmaceutical, or cryogenic service where contamination from the carbon electrode is unacceptable.

Plasma gouging: Produces a cleaner cut than arc air gouging with less carburisation, suitable for stainless and nickel alloys. Higher equipment cost but preferred for thin-section or austenitic alloy repairs.

4.2 NDE verification of the excavated cavity

Before repair welding begins, the excavated cavity must be examined by MT or PT to confirm that the defect has been completely removed. This is a mandatory hold point — not a recommended practice. The code basis is ASME Section VIII UW-38(a) for pressure vessels and ASME B31.3 345.2.3 for piping.

• MT (magnetic particle testing): Used for ferromagnetic materials (carbon steel, low-alloy steel, ferritic stainless steel). Wet fluorescent MT is the most sensitive method for crack detection at the base of the excavation. After arc air gouging, MT must be applied after the grinding step to avoid false indications from the magnetic field distortion caused by the carburised surface layer.
• PT (liquid penetrant testing): Used for non-magnetic materials (austenitic stainless, nickel alloys, aluminium) and as an alternative to MT for ferromagnetic materials. Visible dye PT is the minimum; fluorescent PT provides higher sensitivity and is preferred for crack removal verification.
• Cavity geometry: Before beginning PT or MT, visually verify that the cavity profile is smooth, without sharp corners or undercuts at the edges. Sharp corners concentrate stress in the repair weld root and may mask crack indications during NDE.

5. Repair Welding — Parameters, Technique, and Controls

5.1 Joint geometry and access

Repair excavations rarely have the ideal geometry of a production weld joint. Cavities are often asymmetric, narrow, and deep, with limited torch access. These conditions make lack of fusion the primary repair weld quality risk. The welding engineer must assess the cavity geometry before specifying repair welding parameters and may need to widen or reshape the cavity to ensure adequate electrode or wire access and fusion at the cavity walls.

Minimum recommended cavity geometry for successful repair welding: width at least 1.5× the electrode diameter plus the required manipulation room; minimum wall angle of 10–15° from vertical on each side to allow torch access to the fusion faces; smooth radius at the cavity base of at least 3mm to avoid notch effects. Cavities that cannot meet these geometry requirements should be widened before repair welding begins, even if this removes additional sound material.

5.2 Preheat for repair welds

Preheat requirements for repair welds are governed by the same code provisions (ASME Section VIII UCS-56 tables; AWS D1.1 Table 4.5; EN ISO 13916 for European codes) as for production welds, with the additional consideration that repair welds are typically deposited into material that has already experienced one or more thermal cycles. Repeated heating and cooling raises the residual hydrogen content of the surrounding material and may have created hardened microstructures in the original HAZ. As a minimum, apply the preheat required by the WPS for the relevant P-Number and thickness. For crack repairs, additional preheat — typically 25–50°C above the production minimum — is advisable as a precaution against HACC in the repair weld root.

5.3 Bead sequencing and heat input control

Repair welds in pressure-retaining joints are held to the same heat input limits as production welds — typically specified in the WPS as a maximum kJ/mm value. In thick-section repairs, heat input control is particularly important because successive passes reheat the previous HAZ repeatedly, and cumulative thermal exposure can degrade toughness if interpass temperature or heat input limits are exceeded.

For repairs in sections thicker than 25mm, a temper-bead sequencing approach (even if formal temper-bead PWHT exemption is not being claimed) is good practice: each bead is deposited to overlap the previous bead’s HAZ by approximately 50%, providing thermal refinement of the coarse-grained HAZ. Butter layers are used on the cavity walls in dissimilar material repairs to prevent dilution effects.

5.4 Interpass cleaning and inspection

Between each pass, the repair weld must be cleaned of slag (SMAW), spatter, and surface oxides by grinding or wire brushing. Each pass must be visually inspected before depositing the next. Any surface cracks, porosity, or unfused edges visible between passes must be reported to the Inspector, who must decide whether the interpass condition is acceptable or whether additional excavation is required before proceeding.

6. Post-Weld Heat Treatment for Repairs

PWHT requirements for repair welds are derived from the same code tables that govern PWHT for production welds, with additional complexity arising from situations where the repair cannot practically receive the same PWHT as the original joint.

6.1 When PWHT is mandatory for repairs

ASME Section VIII UCS-56 mandates PWHT for P-Number 1 carbon steel welds above specific thickness thresholds (typically >38mm for P-1 Group 1 materials), and for all welds in P-4, P-5, P-6, P-7, P-8 (when impact tested), and P-15 materials. These mandatory requirements apply equally to repair welds as to production welds. There are no blanket exemptions for repair welds from mandatory PWHT in ASME Section VIII — each case must be evaluated against the applicable UCS/UHA/UNF/UHT paragraph for the material and thickness involved.

For ASME B31.3 process piping, PWHT requirements are stated in Table 331.1.1 by P-Number and wall thickness. Repair welds in P-4 (Cr-Mo) and P-5 piping, for example, require PWHT regardless of wall thickness under the standard process fluid service category.

6.2 PWHT of in-situ repairs — practical challenges

Local PWHT of a repair area is technically and practically complex. Furnace PWHT of large assembled vessels or piping systems in service is rarely feasible. Local PWHT using electrical resistance heating blankets (most common), induction heating, or gas ring burners must achieve the minimum holding temperature uniformly across the repair area and a surrounding zone at least as large as the minimum specified by the applicable code (typically the greater of 1× the weld width or 25mm on each side of the weld fusion line, and extending through the full wall thickness).

Thermocouple placement must be controlled and documented: a minimum of one thermocouple per 900mm of weld length, with additional thermocouples at the edge of the heated band to verify that the temperature gradient does not cause thermal shock. ASME Section VIII UW-40 and B31.3 331.1.3 specify the maximum heating and cooling rates that apply during local PWHT.

7. Temper-Bead Welding — Avoiding PWHT on Repairs

Temper-bead welding (also called controlled deposition welding or controlled thermal severity welding) is the most widely used technique for performing code-compliant repairs on pressure equipment when furnace or local PWHT is impractical. It is particularly common for in-service repairs to large vessels, piping systems, and rotating equipment where cooling to the required PWHT temperature, then reheating, then rehydrostatic testing would be prohibitively disruptive.

7.1 Metallurgical principle

As discussed in the context of grain growth, the HAZ of any fusion weld contains a coarse-grained zone (CGHAZ) immediately adjacent to the fusion line where austenite grain growth has occurred and where hard, potentially brittle transformation products may form on cooling. In production welding, PWHT tempers these hard microstructures and reduces residual stress. Temper-bead welding achieves a similar microstructural improvement without PWHT by using a precisely controlled bead placement pattern in which each new bead reheats the previous bead’s CGHAZ into the fine-grained austenite temperature range (Ac3 to ~1100°C), causing grain refinement and partial tempering of the coarse prior-austenite microstructure.

7.2 ASME Code Cases for temper-bead repairs

ASME has issued several Code Cases that formally authorise temper-bead welding as an alternative to PWHT for specific material groups and situations:

7.3 Qualification requirements for temper-bead procedures

A temper-bead WPS requires a dedicated PQR demonstrating that the procedure produces HAZ hardness values and Charpy impact toughness equivalent to those of a PWHT’d weld. The qualification test assembly must replicate the repair geometry as closely as possible. Post-qualification hardness surveys (HV10 across the HAZ) typically demonstrate that the peak hardness in the as-welded temper-bead HAZ is within the ASME-permitted hardness limit (typically ≤248 HV10 for P-1 steels under most process codes). Charpy impact tests on sub-sized specimens from the HAZ at the design minimum temperature must meet the minimum absorbed energy requirements specified by the code for the material group.

7.4 Limitations of temper-bead welding

Temper-bead welding does not fully replicate the residual stress reduction achieved by PWHT. Residual tensile stresses in the repair weld remain at or near the material yield stress until PWHT is applied. This is a consideration in environments susceptible to stress-corrosion cracking (SCC) — temper-bead repairs in SCC-sensitive service (wet H₂S, caustic, amine) should be evaluated by a corrosion engineer, and the owner may specify full PWHT as the only acceptable option regardless of code allowances for temper-bead.

8. Post-Repair NDE Requirements

Post-repair NDE is the final technical verification step before a repaired weld is accepted for return to service or continuation of fabrication. The fundamental rule across all ASME codes is that the post-repair examination must be at least as stringent as the examination required for the original weld. In some cases — where the repair has involved base metal, crack removal, or repeated thermal cycles — additional examination methods may be specified by the AI or the engineering authority.

8.1 Minimum NDE after repair — by code

8.2 Timing of post-repair NDE

For repairs involving crack removal in hardenable steels, PT and MT must not be performed immediately after welding. Delayed cracking (hydrogen-assisted cold cracking) can initiate up to 48 hours after weld completion in higher-carbon and Cr-Mo steels. ASME B31.3 and many owner specifications therefore require a minimum 48-hour delay before post-repair PT or MT on P-4, P-5, and P-6 materials when no PWHT has been applied. RT and UT may be performed at any time after weld cooling but should not replace the mandatory surface examination at the 48-hour hold.

8.3 Acceptance criteria

Acceptance criteria for post-repair NDE are identical to those applied to the original weld. For ASME Section VIII Div. 1 full radiography, this means UW-51(b) acceptance criteria for RT and UW-52 acceptance criteria for spot RT. There is no relaxation of acceptance criteria for repair welds. If the post-repair NDE reveals further unacceptable indications, the repair cycle begins again: notification to AI, additional excavation with NDE verification of the cavity, re-welding, PWHT if required, and post-repair NDE.

9. In-Service Repairs — NBIC, PCC-2, and API 510/570

Repairs to pressure equipment already in service involve a regulatory and technical framework that overlays the original construction code requirements. The primary additional considerations are fitness-for-service assessment, regulatory notification, and the involvement of a certified repair organisation.

9.1 NBIC Part 3 — National Board Inspection Code

The NBIC Part 3 is the primary code governing repairs and alterations to pressure-retaining items in the United States. It requires that:

• The repair organisation holds an ASME ‘R’ Certificate of Authorisation.
• A repair plan is prepared and approved by the Owner and the Authorised Inspector prior to commencement of work.
• Repair welding is performed using procedures and welders qualified per ASME Section IX.
• Form R-1 (Report of Repair) is completed by the repair organisation and countersigned by the AI; a copy is submitted to the Jurisdiction and the National Board.
• A pressure test equivalent to the original code test (hydrostatic or pneumatic) is performed after the repair, unless a written exemption is approved by the Jurisdiction and AI.

9.2 ASME PCC-2 — Repair of Pressure Equipment and Piping

ASME PCC-2 provides engineering guidance for repair methods beyond conventional welded repairs, including weld overlay and cladding, hot tapping, composite sleeve repairs, and bolted clamps. For weld-based repairs, PCC-2 Article 2.1 covers weld repair of pressure equipment and references ASME Section IX and the original construction code for procedure and qualification requirements. PCC-2 is particularly useful for fitness-for-service decisions when the extent of corrosion or damage is such that a direct weld repair is not feasible.

9.3 API 510 (Pressure Vessel Inspection Code) and API 570 (Piping Inspection Code)

API 510 and API 570 govern the inspection, rating, repair, and alteration of in-service pressure vessels and piping respectively. Both codes require that repairs be performed to the original construction code standard (typically ASME Section VIII or B31.3) and that the repair be reviewed and approved by a pressure vessel or piping inspector certified per API 510/570. Key provisions relevant to weld repairs include: fitness-for-service assessment per API 579-1/ASME FFS-1 before deciding whether repair is necessary; classification of repairs versus alterations (the distinction affects regulatory notification requirements); and risk-based inspection (RBI) considerations for scheduling post-repair inspection intervals.

10. Documentation Requirements

Documentation is the paper record that proves a repair was performed correctly — it is the inspector’s primary tool for demonstrating code compliance and the owner’s evidence that the equipment is fit for continued service. Inadequate documentation is itself a code non-compliance, regardless of the technical quality of the repair weld.

10.1 Required documentation for fabrication repairs (new construction)

10.2 Required documentation for in-service repairs (NBIC)

In addition to the manufacturing repair documentation above, in-service repairs require:

• Form R-1 (Report of Repair): Completed by the ‘R’ Certificate holder; signed by the AI; submitted to Jurisdiction and National Board. Describes the item repaired, the repair method, the materials and procedures used, and the result of the post-repair inspection and pressure test.
• Fitness-for-Service (FFS) assessment: Required when the repair involves a flaw that has been evaluated but not fully removed, or when the decision to repair (versus replace) was based on remaining life calculations. Performed per API 579-1/ASME FFS-1 and retained as part of the equipment file.
• Pressure test record: Hydrostatic or pneumatic test report documenting test pressure, medium, duration, temperature, and result.
• Updated equipment inspection record: The equipment’s inspection history file (API 510 or API 570 file) must be updated to reflect the repair, the nature of the defect found, the probable cause, and any changes to the inspection interval or remaining life calculation resulting from the repair.

10.3 Record retention

ASME Section VIII and the NBIC require that all records associated with the original fabrication — including the Manufacturer’s Data Report and all supporting documentation — be retained for the life of the equipment. In-service repair records (Form R-1 and supporting documents) must similarly be retained by the owner for the life of the equipment. Electronic records are acceptable provided that they are backed up, access-controlled, and reproducible in legible printed form on demand. Inspectors reviewing a vessel’s service history should expect to find complete documentation for every repair performed since original fabrication — missing repair records are a significant compliance concern.

11. ASME Code Reference Summary

12. Recommended Reading

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13. Frequently Asked Questions

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