Pipe Welding Guide

Pipe welding is the highest-skill, highest-paying discipline in the trade. Every pipe joint combines multiple positions in a single weld because you can’t rotate the pipe to keep the puddle flat. A 6G test coupon at 45 degrees hits overhead, vertical, horizontal, and flat all in one pass sequence.

The standard pipe joint is an open-root V-groove: 37.5-degree bevel (75-degree included angle), 1/16 inch root face (land), and 1/8 inch root opening (gap). These dimensions give the TIG arc access to the root while leaving enough material to form the keyhole. Fit-up must be consistent around the entire circumference, and tack welds should be feathered or ground to blend into the bevel.

The root pass is the critical pass. TIG (GTAW) with a keyhole technique produces the cleanest root. Watch the keyhole at the leading edge of the puddle. If it’s too big, slow down and add more filler. If it’s too small, increase amperage or slow your filler rod additions. The inside reinforcement should be 1/32 to 1/8 inch. Too much internal buildup is a defect just like lack of penetration.

The hot pass comes immediately after the root, while it’s still warm. It adds heat to burn out any slag or contamination in the root toes and builds the first layer for fill passes. On TIG-root/stick-fill procedures, this is where you switch to 7018 stick electrodes and DCEP.

Fill passes build up the joint thickness. Run stringer beads, each one overlapping the previous pass by about 50%. Keep each bead flat to slightly convex. Concave fill beads trap slag and create inclusions. Watch interpass temperature with a contact thermometer.

The cap pass is the final layer and the one the inspector sees first. It should be slightly convex, extend 1/16 to 1/8 inch beyond each bevel edge, and show a uniform ripple pattern. The cap determines visual acceptance, and a rough cap invites closer scrutiny on every other aspect of the weld.