Some pipelines used to transport high pressure gas to long distances are made from carbon steel plates by spiral welding. There are instances in which such pipelines gave a long service in sour atmospheres. But when they failed they failed catastrophically and sometimes repeated failures occurred.In one such instance the pipeline in the subject case gave a service life of about 12 years in sour gas service. In year 2012 the pipeline failed suddenly by cracking along the heat affected zone of the spiral weld. Onwards frequent failures began to occur in identical fashion at different locations. This prompted for a failure investigation to be carried out. Mechanical metallurgical and chemical tests and analyses have been carried out to understand the natures of the failures.The paper presents the findings and a discussion on the correlation of mechanical metallurgical and chemistry parameters to the type of failure that has occurred.Keywords: Spiral weld pipelines sour gas cracking.