The Office of Pipeline Safety has posted an advisory bulletin to Owners and Operators of Gas Transmission Pipelines concerning Internal Corrosion in Gas Transmission Pipelines. The bulletin advises owners and operators of natural gas transmission pipelines of the need to review their internal corrosion monitoring programs and operations. This action follows a review of incidents involving internal corrosion, some of which resulted in loss of life, injuries, and significant property damage. OPS' preliminary investigation of a recent gas transmission pipeline incident found internal wall thinning on damaged pipe associated with the incident. The wall thinning is consistent with that caused by internal corrosion. Gas transmission owners and operators should:
- Review procedures for testing to determine the existence or severity of internal corrosion associated with their pipelines. Some methods for monitoring internal corrosion are weight loss coupons, radiography, water chemistry tests, in-line inspection tools, and electrical, galvanic, resistance and hydrogen probes.
- Give special attention to specific conditions, including flow characteristics, pipeline location (especially drips, deadlegs, and sags which are on line segments that are not cleaned by pigging or other methods, fittings and/or "stabbed" connections which could affect gas flow, operating temperature and pressure, water content, carbon dioxide and hydrogen sulfide content, carbon dioxide partial pressure, presence of oxygen and/or bacteria, and sediment deposits.
- Review conditions in pipeline segments downstream of gas production and storage fields.
- Review conditions in pipeline segments with low spots, sharp bends, sudden diameter changes, and fittings that restrict flow or velocity, and segments in unusual terrain. These features can contribute to the formation of internal corrosion by allowing condensates to settle out of the gas stream.
The full advisory bulletin is available on the OPS website at http://ops.dot.gov/advisory082500rev2.htm.