Sent: Wednesday, December 31, 2025 5:52:24 pm
To: materials-welding@googlegroups.com <materials-welding@googlegroups.com>
Subject: Re: [MW:35939] PWHT for Piping weld joint | heating & cooling rate
Sent: Wednesday, December 31, 2025 4:56:22 PM
To: materials-welding@googlegroups.com <materials-welding@googlegroups.com>
Subject: Re: [MW:35939] PWHT for Piping weld joint | heating & cooling rate
Dear Hai,
As you confirmed, overall, the PWHT cycle appears satisfactory, meaning that the work was completed according to the approved WPS and within the target temperature achieved, the holding time was completed, and temperature stability was maintained. However, a concern is that local fluctuations were observed in the heating phase above 315°C, which we address below.
As I understood, two PWHT charts were provided, referred to here as Chart A and Chart B for clarity.
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Chart A: Thermocouple TC-1 (Blue) deviated briefly from its normal trend during the heating stage at approximately 590°C and rejoined the main curve at around 620°C.
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Chart B: Thermocouple TC-1 (Blue) showed a similar brief deviation during the cooling stage at approximately 590°C and rejoined the main curve at around 520°C.
These fluctuations are considered acceptable based on the following technical rationale:
It is important to note that a longer chart time corresponds to a lower heating/cooling rate, while a shorter chart time corresponds to a higher rate. In Chart A, the deviated TC-1 (Blue) traveled above TC-2 (Green) and required a longer duration to rejoin its original path, indicating that the effective heating rate remained below the maximum allowable limit of 335°C/hr. Therefore, this deviation does not represent a violation of para. 331.1.4 and is acceptable.
The same principle applies to Chart B during the cooling stage. Had TC-1 deviated below TC-2, it would have indicated a faster cooling rate and could have raised concerns regarding compliance. Since this is not the case, the observed fluctuation is acceptable.
I trust the above explanation clarifies the observations and acceptance rationale.
Suggestions or additional comments from other experts are also welcome.
Dear Experts,
Please help review and advise on the acceptability of the attached PWHT record against ASME B31.3 clause 331.1.4 (Heating and Cooling).
From the chart, the overall PWHT cycle appears satisfactory (target/hold achieved and stable). However, there is one localized segment during the HEATING stage (T > 315°C) where the temperature ramp is steep and the heating rate appears to exceed 335°C/h (local/short-duration excursion). All other portions of the cycle look compliant.
Could you please advise:
Whether this single local heating-rate exceedance can be accepted as-is (engineering disposition/justification), or
If not acceptable, recommended corrective actions (e.g., re-PWHT, additional NDE/metallurgical evaluation, etc.).
Best Regards.-------------------------------------------------------------------Name : Le Dinh Hai (Mr Hai)Mobile : Vietnam: +8497 397 1597Email : Dinhhaibkdn@gmail.com--
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