Oil and gas pipelines become damaged in service as a result of severe rust pitting. Salt water and other chemicals in creek beds and in the ground cause rusting on the outside of the pipe. Sulphide gas inside the pipe causes corrosion and pitting. Leaks occurring when the pits penetrate the pipe wall must often be repaired while crude oil, gas or other petroleum products are being pumped through the pipe at pressures up to 3400 kPa (500 psi). These repairs can be difficult and hazardous, especially when flammable liquids are being carried.
Sometimes a large area of pitting will be repaired by “sleeving,” in which a section from a slightly larger diameter pipe is cut to cover the pitted portion of pipe.
The edges of the sleeve are fillet welded all around to the outer surface of the pipe.
In some cases, a section must be cut out and replaced, requiring that pumps be shut down, the pipeline section be bled of any liquid, and the section to be repaired purged with inert gas. The defective section is cut out and a replacement section of the same diameter and wall thickness is welded into the line.