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If one is to develop an audit checklist for PWHT activities on a project site, what should be the critical areas to look after other than temperatures/graphs, the final hardness values etc?

The checklist shall include the following:
1. Verification of qualified PWHT operators present at the machine
2. Same joint as mentioned on the chart is being post weld heat treated
3. Adequate number of thermocouples are installed
4. Calibration certificates are in place
5. Attachment of thermocouple made by attachment unit (capacitor discharge welding)
6. Wrapping of weld joint and HAZ area with elements shall be adequate
7. Material of the weld joint being heat treated versus the chart being followed (heating rate, holding temperature / time and cooling rate)
8. Delta between different thermocouples is within acceptable range normally ~ 40 - 50 deg C
9. All safety measures are in place
10. Before signing off the graph, hardness reading shall be witnessed
11. Ensure that the weld joint is heat treated again if hardness is still out of the range
12. Dig out the reasons as to why hardness is not coming in the acceptable range despite following the correct curve

Hope this would help.