Post-weld heat treatment is the standard answer to HAZ hardness and hydrogen cracking risk on alloy steels — put the weldment in a furnace, hold it at temperature, let the microstructure normalize. But in-service equipment rarely cooperates. Fired heaters, operating vessels, and critical piping that cannot be shut down or removed for heat treatment create a repair problem that PWHT cannot solve. ASME Section IX addresses this with QW-290: a dedicated qualification path for temper bead welding procedures.

Understanding QW-290 matters for any QC manager or CWI working in the refinery, chemical plant, or power generation space. The requirements are specific, the PQR testing is more demanding than a standard groove weld qualification, and the essential variables are tighter than most fabricators expect.

What Temper Bead Welding Actually Does

The technique works on a metallurgical principle: every weld pass heats the material it touches plus the base metal and previously deposited weld metal immediately beneath it. That heat-affected zone can be hardened, coarsened, or embrittled depending on the chemistry and cooling rate.

Temper bead welding uses controlled bead placement so that each new pass reheats — and thereby tempers — the HAZ left by the previous pass. The result, when done correctly, is a refined, lower-hardness HAZ across the completed weld joint that approximates what PWHT would produce, without a furnace cycle.

On P1 carbon steels (A36, A516-70, A105) the technique is fairly straightforward. On P4 (1-1/4 Cr–1/2 Mo) and P5 (2-1/4 Cr–1 Mo) steels the requirements tighten considerably — higher preheat, narrower heat input windows, and mandatory CVN testing in many applications.

QW-290 Qualification Scope

QW-290 establishes a separate qualification track within ASME Section IX. It does not replace or modify the standard WPS/PQR qualification process in QW-200 — it supplements it. A WPS written to QW-290 must also comply with the applicable process variables in QW-250 through QW-280.

The qualifying test weld is called a temper bead mock-up. Unlike a standard groove weld coupon, the mock-up must represent the actual repair geometry — typically a buttering layer over a simulated defect cavity on a plate or pipe section that matches the P-Number, Group Number, and nominal thickness of the production material.

Test Weld Requirements

The mock-up must be welded using the exact technique specified in the WPS: the same bead width-to-depth ratio, the same overlap between adjacent beads, the same number of layers before the temper pass, and the same interpass temperature controls. Spot-checking these parameters during PQR qualification is not optional — they drive the hardness result.

After welding, the mock-up is allowed to cool completely before any PWHT (which, in the typical application, means no PWHT at all). Then the test specimens are removed.

Hardness Testing

QW-290 requires a traverse hardness survey across the weld cross-section. Hardness readings are taken at the weld metal, the fusion line, and across the HAZ at defined intervals. For most P1 applications the acceptance criterion is 200 HV10 maximum HAZ hardness. For P4 and P5 materials, check the applicable construction code (ASME VIII, B31.1, B31.3) — the limit may be lower and may reference Brinell rather than Vickers.

The hardness survey catches two failure modes: inadequate tempering (the final pass did not sufficiently reheat the underlying HAZ) and over-heating (excessive heat input produced an overtempered zone with reduced strength). Both show up in the traverse.

CVN Impact Testing

Where the construction code requires it — or where the engineer specifies it — CVN Charpy specimens are taken from the HAZ of the mock-up. The QW-290 HAZ toughness requirement is separate from the weld metal CVN requirement. HAZ specimens are notched at the fusion line or at the coarse-grained HAZ, depending on the specification.

This is one reason temper bead PQRs are more expensive and time-consuming than standard groove weld PQRs. The mock-up consumes more material, the hardness survey requires a precision lab, and the CVN specimens require a licensed test laboratory. Budget accordingly when pricing a repair contract that requires QW-290 qualification.

Essential Variables Specific to QW-290

Standard ASME IX essential variables (P-Number, F-Number, A-Number, thickness, position) all apply. QW-290 adds several variables that are unique to the temper bead method:

Temper bead technique. The specific sequence — number of layers before the temper pass, bead placement geometry (percentage of overlap, bead width relative to previous bead), and progression direction — is an essential variable. If you change the technique, you must requalify.

Preheat and minimum interpass temperature. Temper bead procedures typically require a higher minimum preheat than a conventional PWHT-backed WPS on the same base metal, because the elevated preheat supports hydrogen diffusion in the absence of PWHT. Dropping below the qualified minimum preheat is a requalification trigger.

Maximum interpass temperature. An upper interpass limit is often specified to preserve the refined HAZ microstructure. Exceeding the qualified maximum — even briefly — invalidates the WPS for that joint. This is a more demanding control than most FCAW or SAW operators are accustomed to.

Heat input range. Both minimum and maximum heat input are essential variables under QW-290. Too little heat input and the temper bead does not reheat the HAZ beneath it; too much and you risk overtemper or excessive grain growth. The PQR must bracket the range your welders will use in production.

PWHT. If the mock-up was qualified without PWHT (the standard temper bead application), you cannot add PWHT to the production procedure without requalification — and vice versa. A WPS with PWHT and a WPS without PWHT are two separate qualifications.

WPS Documentation for Temper Bead

The WPS for a QW-290 procedure carries the same mandatory fields as any other WPS under QW-482, plus the temper bead-specific parameters. Inspectors and CWIs reviewing a temper bead WPS should check for:

  • Explicit bead sequence diagram or description — not just "stringer beads" but a dimensioned layout showing the overlap and the temper layer placement
  • Preheat maintenance requirement (often stated as a minimum time at temperature before welding resumes, not just a minimum preheat at start)
  • Maximum interpass temperature with a measurement method (contact pyrometer, tempilstick, or calibrated IR gun — and the acceptable range for each)
  • Heat input formula and limits, with the process parameters (voltage, amperage, travel speed) that produce the qualified range
  • Hydrogen control requirements — low-hydrogen electrodes, baking requirements, or shielding gas purity specifications as applicable

The "co-pilot" principle applies here as much as anywhere: a CWI or welding engineer must review the WPS before any temper bead repair goes into production. The technique is sensitive to execution. A welder who cuts corners on preheat maintenance or bead placement can produce a HAZ that looks sound on visual inspection but fails hardness criteria — or, worse, cracks in service.

ASME IX vs. AWS D1.1: Different Codes, Different Repair Paths

QW-290 is part of ASME Section IX, which is the welding qualification standard referenced by pressure vessel codes (ASME VIII Div. 1 and 2), ASME B31.1 power piping, and ASME B31.3 process piping. For a deeper dive into how ASME IX and AWS D1.1 qualification requirements compare, see D1.1 vs. ASME Section IX: key WPS differences.

Structural steel repairs under AWS D1.1 take a different path — repair procedures must be qualified per Clause 7 and supported by approved WPS documentation. See repair weld WPS documentation under AWS D1.1 for the structural side of this picture.

If your shop handles both structural and pressure-boundary work, you will need separate WPS libraries for each code family. Qualification under ASME IX does not qualify you under AWS D1.1, and vice versa. See WPS vs. PQR vs. WPQ: what each document does for a grounding in how the documentation layers fit together regardless of governing code.

Practical Notes for Fab Shops

Most structural fab shops will never need QW-290 — it is a specialty path for repair contractors, maintenance organizations, and EPC firms working on in-service pressure equipment. But fab shops that diversify into vessel repairs, heat exchanger maintenance, or piping modifications will encounter it, and the cost of discovering the requirements mid-contract is significant.

If you are pricing a repair job that specifies temper bead welding, budget for:

  • PQR mock-up fabrication (the mock-up often costs more than a standard groove weld coupon due to geometry and material requirements)
  • Certified test laboratory for hardness survey and CVN testing
  • WPS review by a welding engineer or CWI with ASME IX experience
  • Welder training on interpass temperature control and bead placement — this is not a procedure most production welders have executed

A digital WPS management system helps keep temper bead WPS documents current and accessible to the inspector at the repair site. See pricing and plan features to evaluate whether a software-managed WPS library fits your shop's repair workflow.

Rule library based on AWS D1.1:2025; verify against your governing edition. ASME IX requirements cited reflect the current edition — verify against the construction code revision specified in your contract.