Local collapse of gas pipelines under sleeve repairs

Local collapse of the pipe wall under full encirclement sleeve reinforcemen ts is associated with breaks and blow outs that cause large gas losses and abrupt depressurisation in gas pipelines. Although these defects do not rep resent an imminent risk of failure, they should be eliminated because they impede the normal passage of the "instrumented pig" for internal inspection . Four failed repairs were experimentally evaluated, and the effects of dif ferent geometric factors were numerically assessed via non-linear numerical modelling of fluid how and pipe response. All possible causes of the appea rance of these defects and measures to minimise their occurrence were evalu ated. The position of the repaired portion with respect to the blow out, lo cal geometry of the repair and previous defects, and the amount of gas caug ht in the interstice between the pipe and the reinforcement, have an import ant part in the event. The measures for the prevention of this problem invo lve the use of fillers and improved construction of repair sleeves. (C) 200 0 Elsevier Science Ltd. All rights reserved.