Abstract
A southeastern United States oil company gathers and transports a variety of sour crude though its pipeline to the refinery. The system experienced leaks due to internal corrosion in the mid 90’s. The asset owner initiated an in line inspection (ILI) program shortly thereafter. The asset owner began a biocidal treatment program to address the microbiological induced corrosion (MIC) caused by sulfate reducing bacteria (SRB). Failures due to internal corrosion increased even with system testing showing low bacteria counts. Data collected from (ILI) runs became suspect as verification digs showed that the magnetic flux leakage (MFL) tool identified pits had larger wall loss than identified by the tool. In 2007 the company implemented a program centered on patented chemistry to address the under deposit corrosion (UDC). It was identified that the primary cause of the UDC was an iron based debris matrix harboring biomass and providing a physical barrier that prevented biocide efficacy. Additionally, ferromagnetic debris in the pits resulted in pit depth inaccuracy when measured by MFL tool. The asset owner initiated a novel chemical program to address under deposit MIC and optimize ILI accuracy. After 5 years, ILI data corroborates field corrosion data and indicates system corrosion is well under industry standards. MIC corrosion is under control and ferromagnetic debris interference negated.
Additional study needs to be done ferromagnetic debris and its role in pit growth, as well as remnant pipeline magnetism, magnetotatic SRB bacteria and pitting.
