joints or other discontinuities in live gas pipelines are sealed by spraying the joint or discontinuity with a coating material by means of an explosion - resistant coating device , capable of traversing long lengths of pipe . the coating device is inserted into the pipe and uses an explosion - resistant camera for locating joints or other discontinuities in the pipe . the preferred coating material is a high build epoxy - type elastomeric polyurethane , which quickly cures in the presence of pressurized flowing gas . several joints or discontinuities , spanning several hundred feet of pipe , may be coated using a single excavation .