Stress corrosion failure of high-pressure gas pipeline F. Hasan * , J. Iqbal, F. Ahmed Department of Metallurgical and Materials Engineering, University of Engineering and Technology, Lahore 54890, Pakistan Received 28 October 2006; accepted 19 November 2006 Available online 10 January 2007 Abstract Incidents of failure due to corrosion/stress corrosion cracking of high-pressure gas pipelines in Pakistan have been observed to occur after about 15–20 years of service. The present paper constitutes the failure analysis of an 18-inch diam- eter electric resistance-welded gas pipeline. The failure was characterized, on the basis of all the available evidence and the metallurgical examination carried out on the ruptured pipe, as a stress corrosion failure that had initiated at a longitudinal ‘stress raiser’. This stress raiser, which was essentially a manufacturing defect, constituted a longitudinal ‘step’ on the pipe surface that had resulted from the faulty trimming/shaving of the weld flash. The findings of this study, thus, emphasize the need for the care that must be taken during the shaving-off of the weld flash. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Stress corrosion cracking; Cathodic protection; Inter-granular 1. Introduction Pakistan has large reserves of natural gas in the southern part of the country. Accordingly, it also has a sizable network of high-pressure gas transmission pipelines. The gas company that supplies the gas to the northern part of the country is called Sui-Northern Gas Pipelines Limited (SNGPL), and the one which supplies the gas to the southern side is the Sui-Southern Gas Company (SSGC). The present paper describes the failure of a pipe in the SNGPLs main transmission lines. The main transmission lines of SNGPL were laid down essentially at two different times. The earlier lines of 16-inch and 18-inch diameter were longitudinally seam-welded pipes, coated with coal-tar based compound for protection against cor- rosion. The more recent lines of 30-inch and 36-inch diameter are spiral-welded pipes protected with poly- ethylene tape coating. The 16-inch line suffered from a number of corrosion-related failures after about 15–20 years of service, while the only two ruptures which occurred in 18-inch line were after 22 years of service (stress corrosion cracking) and after 25 years of service (corrosion failure). The larger diameter lines, which are coated with PE-tape, have so far not exhibited any catastrophe due to aging or corrosion. 1350-6307/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2006.11.002 * Corresponding author. Tel.: +92 42 6814059; fax: +92 42 6822566. E-mail address: drfaiz@uet.edu.pk (F. Hasan). Engineering Failure Analysis 14 (2007) 801–809 www.elsevier.com/locate/engfailanal