Hardness Testing after PWHT 3

[zibaeng]

Hi.
I want to know why hardness testing is performed after PWHT?
Is it required or recommended (According to which standard)?
What will be happened after PWHT that make us to perform hardness testing?
And why is it important for us?
Thank you in advance.

 

[metengr]

Hardness testing after post weld treatment (PWHT) is required for certain air hardenable steels and creep strength enhanced ferritic steels in ASME Power Piping Code. There is no hardness testing requirement for PWHT in ASME Boiler and Pressure Vessel Code and Standards. Most engineering fabrication specifications for creep strength enhanced ferritic steels require hardness testing to ensure proper hardness as a means to verify PWHT has been performed correctly.

Is hardness testing a good thing to do? For creep strength enhanced ferritic steels and certain air hardenable low alloy steels, yes, it is a good thing to do. However, the hardness testing should be performed using a qualified procedure and with proper portable hardness testing equipment.

 

[stanweld]

ASME B31.3 requires hardness testing after PWHT for welds in materials indicated by metengr. One of the reasons for doing so was assure that the proper PWHT was provided.

 

[LittleInch]

In general my response would be:
Hardness testing is performed to check the hardness (brittleness) of the material.
Is it required - varies by materials and codes, wall thickness and individual company standards and specifications
What is happening - If PWHT is not undertaken correctly in terms of heat up or cool down times or to the wrong temperature, significant changes in the steel material properties can occur
It is important to check the material qualiy after PWHT and a key indicator is the hardness. This can increase or decrease excessively and hence the material can become more brittle or softer, than the original, which could cause it to fail in service.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zibaeng]

Thank you all my friends.

 

[davefitz]

Some other items to add to the above :
- Although the asme code may specify the allowable range of PWHT temperatures and minimum hold times, it does not directly specify the required hardness range or provide a tempering parameter for use in the field for ensuring the hold time vs PWHT temperature is correct. The "designer" will need to provide such a correlation or hardness parameter to ensure the welded structrure meets the assumed material properties.
-Even in cases where the weld zone is PWHT'd properly, there can be developed an over-tempered band directly under the induction heating coils unless the field follows the AWS D10.10 guidelines of placing add'l monitoring thermocouples directly under the coil. Fast heat-ups or widely spaced coils can lead to overheat under the coil.

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