Evaluation of Composite Sleeve Repair in Kinked Dent in Natural Gas Pipeline

The Code ASME B31.8 is well established as a safe Code for all life phases of Natural Gas Transmission and distribution pipelines, like: design, construction, operation and maintenance. In the case of mechanical damage, such as dents, the Code contains maintenance provisions for field acceptance or repair of dent and dents combined with other defects consisting of stresses raisers such as gouges, arc burns and welds. Dents, sometimes, are found in sensitive areas due to urban sprawl upon pipeline right-of-way or environmental concerns. In addition dents shapes, sometimes, are not smooth or plain like the code defines as criteria of acceptance. This paper presents and describes some full scale pipeline test’s results in samples containing kinked dents, reproduced in laboratory, in recent vintage pipelines. This type of defect is usually caused by rock puncturing, unauthorized excavation or soil-pipeline interaction in an inservice pipeline. The damaged pipeline samples were repaired by composite reinforcing sleeves before being submitted to the tests. The dimensions of the defects were detected and sized by Geometric and MFL PIG, and compared with field measurements. The studies were conducted concerning internal pressure fluctuations, which can be covered by fluctuations in the principal stresses in the pipe wall. The analyses also considered the plastic strain around the damaged area and effects of rerounding or spring back in case of the defects were generated in conditions of normal operation or in condition of out of service pipeline.