Make adjustments during testing
When welders are tested for in-service pipeline work, they test with water running through the pipe to mimic welding on a pipe filled with oil or gas. Don’t put a sleeve on the pipe during testing. This helps operators see how quickly the puddle cools — so they understand which amperage levels are necessary for these welds. It often takes 40% to 50% higher amperage for in-service welds, so operators must understand how to adjust the amperage enough that they can fuse the metal but not burn through it.
Understand the parameters for the wall thickness
The ultrasound testing (UT) of a pipe’s wall thickness is critical for in-service repairs. If the wall thickness in the weld area is too thin, the operator must extend the sleeve area on the pipe. The ability to safely weld the pipe also depends on the pressure the line is running; pressure is often lowered for repair work. Pipeline owners have different protocols for different wall thicknesses. They have predetermined the interpass temperatures and pipeline pressure measurements and what wall thicknesses can be safely welded.
Focus on butter passes
For in-service pipe welding, a butter pass is used in place of a root pass. Buttering is a term that refers to adding weld material to build a part up. A butter pass adds a layer to an in-service pipe to help prevent burn-through. This builds up the pipe wall, making it thicker so the operator can add more weld metal to it. It’s best to carry a light puddle for the butter pass. Running two butter passes should allow the welder to tie-in to the sleeve under the long seam. Operators may prefer different angles for this pass. A butter pass is required as part of the in-service weld test, which helps operators hone technique.