Pipe Joining and Fabrication Methods
What this domain tests
This domain tests joining methods: welding, brazing, threading, and flanging. The exam focuses on procedure control, fit-up, filler selection, purge, and the defects that cause rejection.
Core rules
- Welding must follow a qualified WPS; the welder must be qualified for the process, position, and material.
- Stainless-steel GTAW requires an inert purge on the inside to prevent sugaring and loss of corrosion resistance.
- Carbon-steel electrodes and filler metals must be stored and dried according to the manufacturer’s instructions.
- Brazed joints need correct clearance and flux removal; threaded joints are generally limited to small-bore utility services and require suitable sealant.
- Flanged joints need parallel faces, correct gasket, and controlled torque in a crossing pattern.
Worked example
A 2-inch 316L stainless line is to be joined by GTAW. Confirm the WPS covers 316L and the welder is qualified. Purge the inside with argon, tack in at least three places, and check alignment. Weld the root with a suitable filler, then fill and cap without overheating. Clean with a stainless wire brush dedicated to stainless, and record the joint. Reasoning: purge prevents oxidation on the inside, and dedicated tools prevent iron contamination that would cause rust.
Traps
- Welding stainless without purge and calling the discoloration acceptable.
- Using carbon-steel grinding wheels or brushes on stainless.
- Mixing NPT and BSP threads.
- Over-torquing a flanged joint and crushing the gasket.