QW-407.2 2

[WE.MetE]

I understand how the 80% of PWHT time applies when the PWHT is stress relief. But if your PWHT is Quench and Temper, how does the does the 80% rule apply, possibilities are:

PQR - 4 hrs above upper critical (Austenitizing), followed by 4 hrs below lower critical (Tempering)

1) Treat the above upper and the below lower separately (PQR of 4 hrs Q & 4 hrs T, would qualify for up to 5 hrs of Q, and up to 5 hrs of T).

2) Combine (a total of up to 10 hrs, applied to Q&T, this could be 2 hrs Q & 8 hrs T or 8 hrs Q & 2 hrs T or any other combination that does not exceed 10 hrs total).

3) The time only applies to the PWHT of below the lower (Quench could be any time, including exceeding the 5 hrs, but the Temper must not exceed 5 hrs, the 80% rule).

 

[Mr168]

Have a look at interp IX-81-40. IMO, they make it clear that the intent is to simulate the PWHT for the given "temperatures". By the use of "temperatures" plural, they are referring to the ranges which would warrant separate qualifications. There is also an ASME III interp that uses the words "aggregate times at temperature(s) as stated in QW-407.2", which I believe reinforces this intent.

I think based on your options presented above, #1 is the only option I could defend.

 

[metengr]

I am not sure I would agree with #1, none of the above applies. If your PWHT is a normalization and temper heat treatment, which is always performed above the lower critical transformation temperature, it is a separate heat treatment performed to eliminate the heat affected zone, and reset weld and base material properties. Why would time at temperature be tracked other than it is performed once using an hour per inch of thickness for austenitizing, rapid cool and temper under the same conditions. 80% of aggregate time for a normalization heat treatment makes no sense and would not apply for a separate heat treatment. You screw up the N&T heat treatment, you can re-do again to reset the material with a quench and temper. Each time your doing a N&T, you have coupons to measure and ensure mechanical properties are above the minimum per the material specification.

For subcritical PWHT absolutely agree that exposure time makes sense because of successive temper cycles.

 

[WE.MetE]

Metengr, that is exactly the issue I was questioning. Clearly the 80% applies to all PWHT below the lower, such as tempering and stress relief.

But does it apply to PWHT above the upper, for quenching or normalizing, for the reasons you mentioned?

Normally it would not even be an issue as the PQR times are typically longer than what is done in production, but occasionally something stays in longer than expected for various reasons.