Hardness Values Before and After PWHT on P11 Pipes

[zengx]

We have ASTM A335 P11 pipes that were post weld heat treated per ASME B31.3. We took the hardness values before and after PWHT for some reason. The resulting hardness values are below.

I noticed that the average hardness value of the four readings in the weld zone is higher after the PWHT. My understanding is that this is a stress relieving and we should not expect a substantial decrease in hardness values, however it should not go up.

Is my understanding correct and there is something wrong here or am I missing something?

Before PWHT: WELD-190/203/215/199 BHN (Avg. 201.75)
After PWHT: WELD-209/197/208/198 BHN (Avg. 203)

 

[weldstan]

What hardness test method did you use? The as welded values are quite low and highly unlikely. We once had values like yours (as welded < after PWHT) when using a MIC10 tester and found out that it was reading erroneously due to a component malfunction.

 

[zengx]

We used the Telebrinell.

 

[weldstan]

Expected as welded hardness of P22 is approximately 225 BHN to 300 BHN depending on thickness and preheat/interpass conditions.
I have certainly seen numerous erroneous Telebrineller results as well. How thick and what diameter is the pipe.

If the as welded hardness is true, the PWHT will produce M23C6 carbides which could provide the increased hardness.

 

[Chumpes]

hello
honestly, what difference do you see between the 2 numbers you provide ?

in my opinion, 201.75 = 203 taking into account the uncertainties and so your hardness did not move significantly due to PWHT.

regards