Abstract: Modern chemical enterprises are featured by large-scale unit and continuous production. If there is a leak in the steam and condensate pipelines, online repair welding is required when energy isolation and release is impossible and risk is controllable. In order to prevent the uncontrolled rupture and leakage of the steam and condensate pipelines during repair welding, in addition to the macro inspection of pipelines, the cold and hot state inspection of supports and hangers, the thickness measurement, the out-of-roundness measurement of bends, the hardness test and the creep test, stress calculations are required if necessary to determine the minimum wall thickness and the electrode diameter of the weld. After the welding conditions are met, it is also necessary to pay attention to the fact that the fire work should not be carried out at the same time during the welding with pressure. Only after the blocking and welding of a hot part is completed can the next hot part be blocked and welded.

Key words: steam and condensate pipeline, thinning；, repair welding with pressure