Local collapse of gas pipelines under sleeve repairs

Abstract

Local collapse of the pipe wall under full encirclement sleeve reinforcements is associated with breaks and blow outs that cause large gas losses and abrupt depressurisation in gas pipelines. Although these defects do not represent 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 different geometric factors were numerically assessed via non-linear numerical modelling of fluid flow and pipe response. All possible causes of the appearance of these defects and measures to minimise their occurrence were evaluated. The position of the repaired portion with respect to the blow out, local geometry of the repair and previous defects, and the amount of gas caught in the interstice between the pipe and the reinforcement, have an important part in the event. The measures for the prevention of this problem involve the use of fillers and improved construction of repair sleeves.