DIAGNOSTICS OF GAS MAINS SUBJECT TO EXTERNAL CORROSION CRACKING

We consider the results of diagnostics of the condition of buried gas mains performed by testing the gas line at elevated pressure and by me ans of inline flaw detection by passage of the UltraScan-CD flaw detec tor. We show that by testing the gas pipeline, we can detect only thos e cracks found in a critical state for the pressure level attained. In this case, the depth of the remaining defects might increase during t he testing. The uncertainty of the data on the dimensions of the remai ning defects and the negative consequences of the testing connected wi th crack growth substantially reduce the possibility of determining th e actual condition of the gas pipeline after using this diagnostic met hod. Inspection of the gas pipeline with the help of inline flaw detec tion made it possible to accurately determine the location of all defe cts containing cracks longer than 30 mm and deeper than I mm. In this case, the information obtained on the depth and length of the defects corresponds well to the results of local flaw detection in test excava tions (up to an 86% match between depth data) and is sufficient for ma king estimates of the residual useful life of the damaged section.