Microbiologically - Influenced Corrosion Riviera Park Case Study

摘要

As part of a pipeline integrity management (PIM) assessment of the Riviera Park line north of Amarillo, Texas, we were performing an internal corrosion direct assessment (ICDA) dig to determine if internal corrosion was present due to this location being identified as a critical angle. A critical angle is an area that could be a possible water hold up region. The pipe being examined was immediately upstream of a suspended creek crossing, and MIC was discovered on the external surface of the east leg of the crossing. Finding microbiologically influenced corrosion (MIC) in this particular area was highly unexpected. The dry soil and moderately high soil resistivity in the Texas Panhandle typically are not conducive to the growth of corrosive bacteria. The line was installed in 1946 and was coated with coal tar. The pipeline is cathodically protected using the 100 mV criteria. In 2009, the close interval survey (CIS) indicated that the line was not adequately protected at this location to meet the requirements of this criterion. We now know that the current was being shielded by the MIC. The dig results determined wet, sandy soil with a slightly acidic pH of 5.5. It is likely that the deterioration and disbonding of the pipeline coating contributed to circumstances that allowed bacterial growth. Large areas of corrosion features were discovered at the 3:00 to 9:00 location for 40 feet along the line. MIC analysis, using quick test kits, confirmed that both anaerobic and acid producing bacteria were present in the pits. Due to the bacterial damage, 65 feet of the pipe was replaced. A new deepwell was installed to ensure that the system is in compliance with the criteria and that the pipe is adequately protected. Subsequently, the pipe has been uncovered while installing a valve and shows no evidence of corrosion as of May 2012.