Grooving corrosion of seam welded oil pipelines Mohamed Hanafy El-Sayed * CMRDI, Cairo, Egypt 1. Introduction An oil pipeline of 24’’ diameter was installed in the Eastern Desert 25 years ago. It has experienced many leaks. Pipeline and operating data are shown in Table 1. A recent intelligent pig inspection was conducted, revealing that the line was suffering an extensive internal corrosion. Periodic cleaning was adapted to prevent further deterioration; nevertheless, a pipe failure has taken place in the form of 2 m longitudinal crack at the 6 O’clock position. Effective actions and precautions were carried out to prevent polluting the coast. For steel pipelines, one of the most dominant forms of deterioration is corrosion which decreases the metal cross-section. This results in a reduction of pipeline carrying capacity and safety. Electric resistance welded (ERW) carbon and low alloy steel pipes may suffer preferential corrosion attack in the weld area when exposed to neutral, salt-containing waters resulting in premature leaking. The selective and localized corrosion prefers to occur in the weld, especially close to the fusion line. ERW seams in the presence of a corrosive environment are susceptible to preferential attack at the bond line. Because of alloying element mismatch existing between the base metal and the weld resulting from the ERW process, the weld generally becomes less resistance to corrosion due to the small decrease of alloying elements, as demonstrated by Zongyue et al. [1]. Chemical composition, microstructure, and the use of post-weld heat treatment can greatly affect the grooving tendency of ERW pipes, through formation of non-metallic, MnS inclusion and redistribution of sulfur by the thermal cycle of the ERW, as demonstrated by Lee et al. [2], Lee and Lee [3], and Wang [4,5]. The material at the bond line is anodic to the surrounding material and the result is a V-shaped groove with the apex of the V centered on the bond line, as demonstrated by Quickel et al. [6]. Case Studies in Engineering Failure Analysis 2 (2014) 84–90 A R T I C L E I N F O Article history: Received 24 December 2013 Received in revised form 1 May 2014 Accepted 8 May 2014 Available online 29 May 2014 Keywords: Crack at the 6 O’clock position Lack of fusion Grooving by corrosion Stress relief A B S T R A C T 24’’ pipeline carrying oil was failed in the form of longitudinal crack at the 6 O’clock position resulting in oil spill. The failed pipe was investigated to reveal the main cause of its failure. The procedure of investigation was built on studying the intact pipe, rupture area, parent material, and intact weld. Results of chemical analysis, mechanical properties, and microstructure of the pipe material were confirmed with the specified standard. Cracks were originated from weld defected sites, initiated by grooving corrosion, propagated by inertia at the normal designed pressure condition, and stopped when stress relief is attained. It is recommended to use high quality ERW pipe, with its seam weld line positioned around the 12 O’clock during installation, to minimize and decelerate grooving corrosion. It is also important to perform regular or routine inspection, on suitable intervals, determined by past experience. ß 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). * Tel.: +20 225468115; fax: +20 225010639. E-mail addresses: hanafys@hotmail.com, mohamadhanafy@yahoo.com Contents lists available at ScienceDirect Case Studies in Engineering Failure Analysis jou r nal h o mep age: w ww.els evier .co m/lo c ate/c sef a http://dx.doi.org/10.1016/j.csefa.2014.05.002 2213-2902/ß 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 3.0/).