Hardness test and PWHT

[tonnesen]

Hi,

In my company we have a internat standard that recommends to do a hardness test after PWHT in the HAZ and in the weld, obviously to evalute the PWHT, but we have to compare these values with some standard value of maximum hardness after PWHT. I only found this kind of rereference in ASME B31.3 but not for P-number 1 materials which I'm interested in. Do you know any literature or standard where I could find this information?

Thanks a lot.

 

[Engdoitbetter]

Usually hardness is measured in order to ensure that there is no martensitic, or generally hard and brittle phases, in the welded/HAZ area.
I don't know hardness limits related to this kind of requirement. However, in case this item must undergo NACE MR0103 or MR0175 prescriptions against Sulfide Stress Cracking (often refereed to as SSC), it is usually prescribed that hardness does not exceed 22 HRC (about 240 Brinell Hardness.)

Hope it helps.

Stefano

 

[stanweld]

Unless you have a service (SCC) need to perform hardness testing on welds of P-No.1, low carbon steel as indicated by Stefano above, there is no real need to perform hardness testing. Whereas your standard states "recommends", it is not mandatory. Having said that, a number of Owners have required hardness testing with maximum hardness of 200 BHN.

 

[metengr]

As mentioned above, hardness testing of P-No 1 base materials is typically unnecessary because this classification of base materials are not typically as air hardenable as low alloy steels. Second, the primary purpose of PWHT for P-No 1 base materials is to reduce residual stresses from welding with a secondary benefit of tempering any transformation products from the heat of welding.

As a cautionary note even under service requirements for SCC, hardness testing of base metal heat affected zones in-situ is problematic. Instead, in-situ hardness testing is used for qualitative purposes, at best.

 

[jbeckhou]

It would be good to know the specification your parts must meet. Most of the time when checking hardness areas of welds, HAZ and the weld its self is due to H2S service, and has nothing to do with SSC. SSC will only affect certain types of material, called out within NACE. Typical SSC only affects parts loaded in tension, if the parts are loaded in compression, SSC will not affect the material. SSC typical affects, stems, hangers, etc. NACE states different max hardness results for different materials, 4130 and Inconel have different max hardness values.

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