It’s only a matter of time before someone in a power plant is killed by a preventable catastrophic failure of a buried natural gas pipeline. The danger posed is less the result of willful negligence than of the temptation to ignore an invisible problem.
Safety has long been a primary concern of U.S. industry, particularly in the power generation sector. Today, on a tote board at their entrances, many plants proudly display a running count of the number of work days accumulated without a lost-time accident. All employees must attend numerous safety training seminars, not only because the U.S. Labor Department’s Occupational Safety & Health Administration (OSHA) requires it, but also because most companies have come to realize that safety is good for business.
Despite this attention, major threats still escape detection by the risk radars of plant workers and managers. One such threat is external corrosion of underground natural gas pipelines at all plants, not just those that convert the fuel to electricity. According to decades of statistics compiled by the U.S. Department of Transportation’s Office of Pipeline Safety (OPS), the leading cause of pipeline failures is external corrosion of buried pipe.
The threat is so significant that the OPS insists that pipeline operators take extensive steps to minimize it. Such steps include installing sophisticated corrosion-prevention systems (Figure 1), regularly maintaining and testing those systems, and reporting the results to regulators—a process the industry calls “pipeline integrity management.” An army of specialists, consultants, and service providers supports the pipeline companies in their efforts to mitigate corrosion.
1. Laying pipe. This segment of a natural gas pipeline is being installed to serve a power plant. Operators are required by law to protect their pipelines from corrosion that could compromise pipe integrity and lead to an explosion. But their responsibility for corrosion protection ends at the isolation flange, where the line enters the plant through a metering station. Courtesy: Matcor
This process does much to protect the public from the devastating effects of a ruptured pipeline, but it does little to protect plant workers. That’s because pipeline operators’ responsibility for integrity management ends at the metering station, where the pipeline enters the plant. There, the pipeline company installs a flange that electrically isolates its regulated portion of the line and its corrosion system from the final unregulated segment of pipe. The isolation flange marks the physical and legal transfer of responsibility for pipeline safety from the pipeline operator to the plant owner.
Pipeline companies’ corrosion-prevention measures take three forms: coating the pipeline during its construction, installing what’s known as a cathodic protection (CP) system to keep stray currents from fostering corrosion as the coating deteriorates, and regularly testing the integrity of the pipeline and the performance of the CP system. The tests include monthly inspections of the system’s key components—rectifiers (Figure 2), annual testing to ensure that the operating environment hasn’t changed, and intense surveying every seven to 10 years to validate the pipeline’s physical integrity. If any defects detected in the system are not reported to regulators and fixed promptly, the pipeline operator is fined.
2. Rectifying the problem. The key components of a pipeline’s cathodic protection system are rectifiers like these. Courtesy: Matcor
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