REFURBISHMENT OF A 230 KM OIL PIPELINE WITH LONGITUDINAL SEAM WELD FATIGUE CRACKING PROBLEM

摘要

Recently, a Petroleos de Venezuela S. A. (PDVSA) oil pipeline, 230 Km (143 miles) in length and 660 mm (26 in.) in diameter, had a leak in the longitudinal seam weld of one of its sections. The analysis of this failure revealed that the leakage was originated in a fatigue crack which nucleated at a stress concentrator associated to a weld defect, and it propagated due to the cyclic stresses induced by the internal pressure changes. Partial external inspection of the pipeline revealed that the problem was extended to other sections. This paper summarizes the actions taken for the refurbishment of the oil pipeline which included: 1- the management plan set to face the problem; 2- the inspection of the pipeline, externally and internally; 3- the analysis of the inspection results; 4- the defect tolerance assessment / fitness-for-purpose study, to estimate both, the critical crack sizes as well as the crack propagation rates; 5- the development of repair procedures, and, 6- the determination of future inspection and maintenance recommended programs. All of it, with the main purpose of maintaining the operation of this line with complete guarantee of its integrity. Thanks to these actions, it has been possible to prevent additional failures in the same pipeline as well as to reduce in about MM$ 25 the maintenance cost associated with it.