Topic
Spools, welding, NDT, hydrotest and flushing.
Every new piping system is pressure tested before it goes into service. Water is the default because it stores little energy; gas testing is allowed only when water is impractical, and with extra precautions.
Most piping is built in a shop as spools and welded together on site. Here is the journey of a spool, and where things usually go wrong.
Three documents stand behind every weld: the procedure, the proof that it works, and the proof that the welder can do it. Here is how they fit together.
Each examination method finds different defects. Knowing what each can and can't see helps you read an inspection plan and choose the right test.
PWHT relaxes residual stress and tempers hard weld zones. Sometimes the code requires it because of thickness; sometimes the service does.