Hardness on P11 and P22 welds

[kamran]

There are a number of welds available with us that have been heat treated twice or even thrice but their hardness continues to remain above the upper limit. Some of these lines have already gone live.

Material: P11 and P22
Service: Steam

Assuming the worst case scenario i.e. we cannot bring down the hardness level, what should be the final course of action? Re-welding?

Please comment.

[ben]

I would recommend to look into the PWHT procedure you are following.

[mechcolor]

Kamaran,
Before I answer your queries, provide these details.
1. Tell me what are the hardness readings before and after PWHT?
2. How have you taken these welds in service if hardness was not in acceptable range?
3. PWHT temperature, holding time, weld thicknesses and the way you are performing PWHT? Conventional or Induction?

Right now, I can only advise you to look into the following things:
1. Calibration of PWHT machines
2. PWHT procedure being followed and the applicable code requirements
3. Correct holding time
4. Heating and cooling rates
5. Conduct PMI of welds (whether correct filler metal was used)
6. Perform a demo with the same PWHT machines in presence of qualified QC guys

[kamran]

Kamaran,
Before I answer your queries, provide these details.
1. Tell me what are the hardness readings before and after PWHT?
2. How have you taken these welds in service if hardness was not in acceptable range?
3. PWHT temperature, holding time, weld thicknesses and the way you are performing PWHT? Conventional or Induction?

1. Before - 330 After 2 heat treatments - 260 and not going any lower.
2. Welds were taken into service after hardness values were taken and found to be ok. It dawned upon the inspection team later that the device had been calibrated for Aluminium rather than Fe. Joints falling outside the allowable hardness values are being treated again to salvage the situation.
3. Conventional and temperatures, holding times etc. are all being monitored and controlled.

Right now, I can only advise you to look into the following things:
1. Calibration of PWHT machines
2. PWHT procedure being followed and the applicable code requirements
3. Correct holding time
4. Heating and cooling rates
5. Conduct PMI of welds (whether correct filler metal was used)
6. Perform a demo with the same PWHT machines in presence of qualified QC guys

Already under control.

[mechcolor]

The first thing I would say is:
"Do not take those welds as acceptable"
2- What's the cooling rate? If its 200-250 deg C/hr, reduce it further like 150 deg C/hr
3- I assure you that the hardness of these low alloys do come in an acceptable range after proper PWHT procedure followed as per code. Re-organize your procedures and re-audit the parameters I mentioned in my earlier post. I hope you would get the right acceptable values this time.
4- Re-welding is not an option to work upon if PMI shows the correct welding material.
5- Just for your information, these alloy are hardenable steels and only to taken in service when in acceptable hardness limits. Otherwise, failure is likely to occur any time under service.

[kamran]

Thanks for the response.
Lowering the cooling rate is an option not explored as yet and could be the key.
Kamran