Microbiologically Influenced Corrosion Failure of a Crude Oil Pipeline

Premature failure due to severe internal corrosion was encountered in a 24-inch, API 5L Grade-B Sch-20 carbon steel pipeline used for carrying light crude oil (LCO) from a wet tank to a common header.  The failure occurred after about 6 years of service.  A detailed investigation was conducted consisting of material analysis, hardness tests, optical microscopy, scanning electron microscopy (SEM), and fluid analysis, which indicated that the failure was due to microbiologically induced corrosion (MIC).  
The failure morphology was typical of corrosion damage caused by sulphate reducing bacteria (SRB) which manifests as extensive localized corrosion, resembling large terraced pits.  Fluid analysis indicated that bacteria are present in all the fluids and coupon scrapings in the related process circuit.  The high H₂S encountered in the fluid downstream of the LCO wet tank compared to that found in the LCO wet tank is an indication that the excess H₂S is most likely the result of SRB activity.  The severe type and rate of corrosion observed in the pipeline is supported by previous coupon data obtained in the same facility.
Keywords: Failure Analysis, Light Crude Oil, MIC, SRB, Localized Corrosion