Post-Weld Heat Treatment (PWHT) — D1.1:2025 Requirements
D1.1:2025 Clause 5.9 defines when PWHT is prequalified. Clause 7.8 governs stress-relief procedure: holding temperature 1100–1200°F [600–650°C], heating rate not exceeding 400°F/hr above 800°F, entry temperature not exceeding 800°F, cooling rate not exceeding 500°F/hr above 800°F.
When Is PWHT Required Under D1.1:2025
PWHT is not automatically required by D1.1. It must be specified in the contract documents. When specified, it may be prequalified under Clause 5.9 or it may be a Clause 7.8 stress-relief requirement applied outside the prequalified WPS framework.
The Engineer specifies PWHT when residual stresses from welding must be reduced — typically for applications where dimensional stability, stress corrosion cracking susceptibility, or material service requirements demand it. D1.1 does not define the service conditions that trigger PWHT; that judgment belongs to the Engineer of Record. D1.1 defines the procedure when PWHT is required.
Clause 5.9 — PWHT Prequalification
A WPS using PWHT is prequalified under Clause 5.9 only when all five conditions are met:
(1) Yield strength — The minimum specified yield strength of the base metal does not exceed 50 ksi [345 MPa].
(2) Steel type — The steel is not quenched and tempered (Q&T), quenched and self-tempered (QST), thermomechanically controlled process (TMCP), or cold-worked to produce enhanced mechanical properties. These metallurgical conditions are sensitive to elevated temperature and PWHT may degrade them.
(3) CVN requirements — The WPS is not required to meet Charpy V-notch (CVN) notch toughness requirements. PWHT may alter the toughness of the weld metal in ways that require specific qualification testing.
(4) Weld metal data — Weld metal mechanical property data is available for the post-PWHT condition from the filler metal manufacturer or from prior qualification testing.
(5) Procedure compliance — PWHT is conducted in accordance with Clause 7.8.
If any of these five conditions is not met, the WPS must be qualified by testing per Clause 4.
Clause 7.8.1 — Steels Not Recommended for PWHT
Q&T, QST, precipitation-hardened (PH), and TMCP steels are not recommended for PWHT under Clause 7.8.1. The elevated temperatures of PWHT can alter the metallurgical condition these steels were manufactured to achieve, reducing yield strength, tensile strength, or impact toughness below minimum specified values.
If PWHT is required on any of these steel types, the procedure must be developed in accordance with the steel manufacturer's recommendations and is subject to approval by the Engineer. The prequalified Clause 5.9 route is not available for these steels — a qualification test is required.
Clause 7.8.2 — PWHT Procedure Requirements
The PWHT procedure must be written and shall include the following elements per Clause 7.8.2:
| Parameter | Requirement |
|---|---|
| Entry temperature | Furnace shall not exceed 800°F [430°C] when weldment is loaded |
| Heating rate above 800°F | ≤400°F/hr ÷ maximum metal thickness (in) [≤560°C/hr ÷ cm]; minimum 100°F/hr [55°C/hr] |
| Holding temperature | 1100–1200°F [600–650°C] per Clause 7.8.3.2 |
| Holding time | Per Clause 7.8.3.2 (minimum time based on thickness) |
| Cooling rate above 800°F | ≤500°F/hr ÷ maximum thickness (in) [≤700°C/hr ÷ cm] |
| Cooling below 800°F | Cool in still air |
| Thermocouple locations | Must be specified in the procedure |
| Heating method | Must be specified in the procedure |
Thickness note: The heating and cooling rate formulas use the maximum metal thickness in the weldment section being heat treated. For a 2 in thick plate, the maximum heating rate above 800°F would be 400 ÷ 2 = 200°F/hr. The formula automatically produces slower rates for thicker sections, reducing thermal gradients and the risk of distortion or cracking during the heat treatment cycle.
Alternative PWHT (Clause 7.8.3.3)
Lower temperatures with longer holding times are permitted per Table 7.3. This provides flexibility when the standard 1100°F [600°C] holding temperature is not achievable or would be detrimental to the material. The alternative temperature-time combinations in Table 7.3 must be followed exactly — the holding time increases as the temperature decreases below the standard range. This route may be useful for field heat treatment where furnace temperature precision is limited.
Frequently Asked Questions
D1.1:2025 does not automatically require PWHT — it must be specified in the contract documents by the Engineer. When specified, PWHT is used to relieve residual welding stresses. Clause 5.9 defines conditions under which a PWHT WPS is prequalified: minimum yield strength not exceeding 50 ksi, steel not Q&T/QST/TMCP, no CVN toughness requirements, weld metal data available for post-PWHT condition, and the procedure conducted per Clause 7.8.
Per D1.1:2025 Clause 7.8.3.2, the PWHT holding temperature shall be 1100–1200°F [600–650°C]. The weldment must be placed in a furnace not exceeding 800°F [430°C] per Clause 7.8.2.3. Above 800°F, the heating rate shall not exceed 400°F/hr divided by the maximum metal thickness in inches, with a minimum of 100°F/hr. Cooling above 800°F shall not exceed 500°F/hr divided by maximum thickness; below 800°F the weldment may be cooled in still air.
Per D1.1:2025 Clause 7.8.1, quenched and tempered (Q&T), quenched and self-tempered (QST), precipitation-hardened (PH), and thermomechanically controlled process (TMCP) steels are not recommended for PWHT. The elevated temperatures of PWHT can alter the metallurgical condition of these steels and reduce their mechanical properties. If PWHT is required on these steels, the procedure must be developed per the steel manufacturer's recommendations and approved by the Engineer.
D1.1:2025 Clause 7.8.3.3 permits alternative PWHT using lower temperatures with longer holding times per Table 7.3. This provides flexibility when the standard 1100–1200°F [600–650°C] holding temperature is impractical or potentially harmful to the material. The alternative temperature-time combinations in Table 7.3 must be followed exactly — the holding time increases as the temperature decreases below the standard range.