Baker & O'Brien, Inc.

Case Studies

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Rapid System Depressurization Leads to Operator Injury

Litigation, North America

July 1, 2015

Compressors are used throughout the natural gas industry to provide the motive force needed to transfer natural gas from the point of production to downstream distribution systems. When the main compressor at a natural gas production facility shut down unexpectedly, a smaller compressor feeding the main compressor also shut down due to high pressure in the discharge line.  The maintenance contractor was called out to investigate.  The contractor tried to restart the smaller compressor by opening a “blowdown” valve to vent any hydrocarbons in the system and reduce the discharge pressure.  However, opening the valve caused the blowdown piping to fail, injuring the contractor’s employee.  Baker & O’Brien was engaged to look into the incident to determine whether the “root cause” of the blowdown pipe failure was defective equipment, operator error, or some other factor.

Our investigations revealed that the compressor, the blowdown valve, and the failed blowdown piping all appeared to have been properly maintained and exhibited no inherent defects or excessive deterioration prior to the incident.  When the failed blowdown piping was replaced, the compressor operated satisfactorily with no modifications.  However, we learned that the attempt to purge the discharge line had resulted in very rapid depressurization.  When this occurs, the resulting pressure surge can damage pipe fittings—particularly at “elbows” and “tees” where there are changes in flow direction.  Another potential cause was the presence of liquids in the line.  These liquids were likely formed by condensation following cooling of the compressor discharge system.  This would have greatly increased the force that resulted from depressurization.  Our findings were presented in a report that assisted the parties in eventually settling the case.