[en] A test program was conducted to evaluate the effectiveness of commercial leak repair services, with respect to the requirements of nuclear power plants. Three companies commercially engaged in on-line leak sealing demonstrated their sealants, fixtures and techniques on an evaluation matrix of leaking pipes, flanges and valves. Repaired test specimens were left on-line at full internal fluid pressure and temperature of approximately 2200 psi and 600₀F (15.2 mPa, 316₀C) initially for 48 hours. Selected specimens were left on-line at pressure and temperature with thermal and pressure cycling for as long as 14 weeks to determine longer-term repair durability. Sealant samples were thermally aged, irradiated, and analyzed for the presence of reactive components such as sulfur, heavy metals and halogens