Resin used to seal pipe flanges against leaks in the nation’s largest district steam system, Manhattan’s 105-mile-long network, instead is a culprit in a pipe explosion last July that killed one person, severely burned two others and cost nearby businesses millions of dollars, says a new report probing the event.
Steam-pipe explosion last summer is pushing New York City utility to change its materials and approaches.
The report by two outside consulting firms commissioned by New York City-based utility Con Edison says remnants of the epoxy used by a pipe-repair contractor months earlier had migrated from flange locations to adjacent steam traps, apparently clogging their ability to release water that had built up from heavy rain. Con Edison, which released the report several weeks before executives had intended when its conclusions were published in local media, has replaced the system’s 1,654 steam traps and promises other major fixes through 2009.
According to the consultants’ findings, the July 18 accident in midtown was caused by internal pressure seven times greater than usual that sent boiling water shooting nearly 400 ft into the air, pouring mud and debris onto pedestrians and carving a 37-ft-wide crater. The “waterhammer” condition ruptured the pipe, although the pipe itself was found to be in good condition, say the consultants. They are ABS Consulting Inc., a Stratham, N.H., firm that did the technical analysis investigation and Lucius Pitkin Inc., New York City, the metallurgical consultant. The firms were believed to have earned a total of $1.3 million for the report, which was presented to Con Edison on Dec. 18.
The probe findings were accompanied by a utility “action plan” that spelled out remedial steps it has already taken to prevent similar incidents and new design approaches and technologies it may implement over the next year to improve the overall system that generates 10 million lb per hour of steam at winter peak.
“We are committed to operating the steam system in a safe and reliable manner,” says William G. Longhi, senior vice president of central operations. “We are also committed to applying what we’ve learned to enhance the safety of our equipment in a complicated underground environment.”
Among other things, Con Ed complied with the report’s recommendations to replace old steam traps with ones that have improved debris-handling capabilities and to change its procedures for dealing with heavy rains and injecting leak-sealant.
The utility, already criticized for poor response to a major power outage in 2006, also agreed to stepped-up “vapor patrols,” including closer inspection of manholes and blow-off valves. Con Ed also promises more frequent inspections of the steam traps, “now requiring that the trap assembly sediment pocket be cleared every time a trap test is performed,” the utility says. Previously, that had been done only once a year, according to its action plan.
Con Ed says it will also now mandate “additional levels of management approval” when pipe-leak sealants must be used and contractors hired. “When the injection process is completed, the new protocol calls for an extended period of purging of the steam main and enhanced testing of nearby steam traps,” the utility says.
The utility also is exploring options to increase trap capacity for condensate load, noting that the investigation found that it had been exceeded on the day of the explosion, triggering the waterhammer. But Con Ed cautions that a high- capacity trap may create operational problems by introducing excessive steam into the city’s sewer system, which could then be released as steam vapor to the street through the catch basin.
The utility says it is now testing various thermodynamic, float and thermostatic trap technologies that can allow larger debris in without affecting trap performance. It expects to complete a feasibility study on the new approaches by September and to begin testing prototypes by June 30, 2009. It is also exploring improved wireless communications and new ways to remotely monitor system conditions.