Full scale experimental analysis of stress states in sleeve repairs of gas pipelines

Abstract

This study discusses the experimental determination of stress states in sleeve repairs of underground gas pipelines. Work was done to define the effects of the reduction of pressure during welding, the load and place of positioning clamps, the length of the repair sleeve, and the use of O'ring-based devices to prevent gas leakage. Tests were carried out in reinforcements, welded with internal pressure equal to 60, 80 and 100% of the service pressure. High stresses were generated in tests carried out with short sleeves and O'rings, and occurred once the sleeve was fully welded and the pipeline pressure re-established. Maximum stresses, up to 270 MPa, were generated after about 1 min following closing of venting valves, on tests with artificial gas leaks. From the results of these experimental studies, it is concluded that several operative aspects could be optimised, to minimise the stresses in the reinforcements and to reduce the risk of failures.