Welding Inspection & Metallurgy API ICP Self Study Notes

11.2 HOT TAPPING AND IN-SERVICE WELDING
API Publ 2201 provides an in depth review of the safety aspects to be
considered when hot tapping or welding on inservice piping or equipment.
Prior to performing this work, a detailed written plan should be developed and
reviewed.
The following is a brief summary of welding related issues. Two primary
concerns when welding on in-service piping and equipment are:
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burn through and
cracking.
Burn through will occur if the un-melted area beneath the weld pool can no
longer contain the pressure within the pipe or equipment. Weld cracking
results when fast weld-cooling rates produce a hard, crack-susceptible weld
microstructure. Fast cooling rates can be caused by flowing contents inside
the piping and equipment, which remove heat quickly.