General Pipeline Leaks. Most pipeline leaks are caused by interior or exterior corrosion. Less frequent causes of leaks include cracked welds, split seams and joints, separation at collars, buried flanges, and threaded pipe. Initial repairs can be made by placing clamps over the damaged area and using sealing epoxy components or gaskets to seal the leak. These repairs are usually temporary and modern practice is to weld all leaks (API RP 1107). The LFM should make sure that schematics are annotated to show where major breaks and leaks have occurred in the pipeline.
Pits and Small Leaks
Pits on the exterior of a pipeline are caused by corrosion. If discovered before a leak develops, repair them by arc welding. Welding a circular patch over the hole may repair small leaks.
Large Punctures and Holes
Large holes in pipelines usually create a welding safety hazard because of the spills that have saturated the ground. Clamping a steel plate of the same curvature as the pipe over the damaged area, using petroleum-resistant rubber for a seal, makes temporary line repairs; the area may then be cleared of all hazards. The steel plate clamped over the leak can be permanently welded to the pipe. For most welding operations, the pipeline can stay in service during repairs; however, if there is danger of the arc penetrating the pipe (thin wall or badly corroded pipe), the system should be shut down during repairs. All hot work must be approved by the command fuels engineer, base safety, base bioenvironmental engineer, and base fire department.