A company in the Netherlands fabricates exacting offshore pipework using several automatic TIG and MIG welding installations, each having a turntable with two sets of adjustable roller beds. For 100 mm diameter pipes, manual TIG is used for the root pass and automatic TIG with wire feed for filling and capping passes. For 300 mm diameter pipes, the same procedure is used for the root pass and automatic TIG with cold wire feed for filling and gapping passes: For 300 mm diameter pipes, the same procedure is used for root pass, and automatic MIG with a flux-cored wire is used for subsequent passes. Table 11.4 shows a procedure for C: Mn pipe in which two types of flux-cored wires can be used for the MIG passes, one for temperatures down to 25°C and the other for temperatures below -25°C. The latter deposits a 2.5% Ni steel weld­metal with Charpy-V notch value of 47 J minimum at -60°C which also meets the COD test requirement.

Reducing tee

Concentric reducer

Table 11.4. Procedure for offshore pipework welding

Material Root pass Filling/capping Welding position Preheat temp. (°C) Interpass temp. (°C)

Pipe dia. (in.)

Wall thickness (mm) Joint preparation Root pass TIG wire type Wire dia. (mm)

Welding current (amp)

Filling/capping MIG wire type Wire dia (mm)

Gas type Gas flow (1/min)

Welding current (amp) Welding voltage Wire-feed speed (cm/min) Welding speed (cm/min) Total welding time (min)

Joint preparation and runs