By Michael J. Humphries, Ph.D.
Carmagen Engineering, Inc. recently conducted a study for an overseas client to identify the risk associated with a change in quality of gas fed to a natural gas pipeline. The corrosion impact of the change in gas composition was evaluated using published data and gas compositions and operating data supplied by the client. The resultant change in risk was assessed considering a range of damage scenarios according to the methodology defined in ASME B 31.8S. This standard covers managing integrity of onshore pipelines that handle nominally dry gas.
The method was based on evaluation by an experienced Subject Matter Expert, and considered damage scenarios covering the anticipated service life of the line. Our experience base includes reliability assessments on overseas pipelines ranging from 2 to 500 miles in length and 6 to 48 inches in diameter, on land and under water. The analysis identified cases where the damage scenario showed a potentially increased risk of an incident due to the change in operation. The various damage scenarios were plotted on a risk matrix to illustrate their criticality and the need for corrective action.
A range of mitigation measures were considered and evaluated to assess the level of risk reduction which each would accomplish. The effect of each mitigation measure in reducing the risk was then plotted on the risk matrices to clearly identify the benefit of each remedial measure. Using this approach, a mitigation measure was chosen that resulted in reducing the risk of damage to an acceptable level, similar to that of the current operation. The client was able to show to local authorities that the change in gas composition could be accomplished without an increased risk of damage to the pipeline.