Piping, Tubing, Valves, and Gaskets
Pipe and fittings
Nominal pipe size is not the outside diameter; for sizes through 12 in, OD stays constant while wall thickness changes with schedule (Sch 40, Sch 80). Know the joining methods: threaded, welded, flanged, soldered, brazed, compression, and solvent-cemented. Fittings include elbows (90° and 45°), tees, reducers, couplings, and unions - a union is the fitting that lets a line be broken without cutting.
Valves
Gate valves isolate and should be fully open or closed; globe valves throttle; ball and butterfly valves are quarter-turn and are poor throttlers; check valves allow flow in one direction only and are marked with a flow arrow; relief valves protect against overpressure and are set, sealed, and never used as controls. Know the parts: body, bonnet, stem, packing, seat, disc.
Gaskets and flanges
Selection follows service: sheet gasket for low pressure and temperature, spiral wound for high pressure/temperature and cycling, ring joint for high pressure, O-ring for special facings. Clean the flange faces, align the bolt holes, lubricate threads as specified, and tighten in a star or cross pattern in stages.
Traps
Using a gate valve to throttle; installing a check valve backwards; over-torquing one bolt and cocking the flange; reusing a spiral-wound gasket; mismatching gasket material to the fluid.
Worked example
On an 8-bolt flange, tighten in a cross pattern to about 30% of final torque, then 60%, then 100%, working around the circle. This seats the gasket evenly and prevents the spiral winding from being crushed on one side.