NTSB Safety Recommendation Letter P-81-021 through P-81-022

Page 1Official PDFNATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ISSUED: August 3 , 1981 President Missouri Power d( Light Company P.O. Box 780 P-83-21 and -22 Jefferson City, Missouri 65102 ___ A t 10:15 o.m., c.s.t., on January 8, 1981, a 2.-inch-diameter plastic gas main pulled apart at a compression coupling under an alley in downtown Mexico, Missouri. Natural gas at 43-psig pressure escaped and migrated through a sanitary sewer into a nearby building where i t was ignited by an undetermined source at approximately 10:25 p.m. The explosion md fire destroyed a commercial building, severely damaged an adjacent building, broke nearby windows, and damaged several vehicles. There were no fatalities; however, three firefighters were injured while fighting the fire. The Missouri Power & Light Comoany installed a 4-inch-diameter cast-iron gas main in the alley in 1950. Part of this gas main was later replaced by a 4-inch-diameter steel gas main. In 1975, the remaining 170 feet of cast-iron gas main was inserted with 2-inch-diameter polyethylene plastic pipe. During this installation, the length of plastic pipe needed was misjudged, and an additional 10-inch-long segment of 2-inch-diameter plastic pipe had to be added. Two standard compression couplinqs were used for the connection. The pullout resulting in this accident occurred at the upstream end of the downstream coupling. The 170-foot-long segment of plastic pipe had contracted because it was not restrained and had pulled out of the short-barreled compression coupling with a smooth steel insert which was not designed to prevent pullout. The Safety Board has issued two major pipeline accident reports 1/ involving the pullout of cornpression couplings joining polyethylene plastic pipe to-steel pipe. In each case, more than 100 feet of plastic pipe had been inserted in gas mains and the unrestrained plastic pipe had been joined to the steel pipe by a standard, short-barreled cornpression coupling with a smooth steel insert. These failures were caused by thermal contraction of the plastic pipe which exerted pullout forces on t h e compression couplings. Recommendations were made to inspect locations where comparable conditions may already exist and to properly design, install, test, inspect and anchor future installations. - 1/ Pipeline Accident Report--"Nebraska Natural Gas Company, Pathfinder Hotel Explosion and Fire, Fremont, Nebraska, January 10, 1976" (NTSB-PAR-76-6); Pipeline Accident Report--"Kansas Public Service Company, Inc., Explosion and Fire, Lawrence, Kansas, December 15, 1977" (NTSB-PAR-78-4). 3293#

Page 2The city of Mexico is served by a town border station with dual-orifice meter runs. The failure and subsequent shutdown of t h e gas main were indicated on the station's charts which record gas pressure and gas flow. The increased rate of flow that occurred when the coupling failed was also shown on the telernetered charts in the unmanned service center of the local Missouri Power & Light Company. Many gas distribution systems employ telemetry to monitor facilities to insure continuity of service and t o effect shutdown in the event of a line failure. The addition of a monitored alarm to the telemetered equipment on t h e single-feed distribution system serving Mexico would provide a prompt warning. The Safety Board also investigated a similar accident where no alarm system was installed which occurred on July 30, 1977, in Cherokee, Alabama, and in which a house was destroyed and one person died. As a result of this accident, the Safety Board recommended that t h e Gas Piping Standards Committee of the American Society of Mechanical Engineers (ASME): Develop guidelines for the installation and operation of pipeline monitoring alarms on applicable single-feed systems, such as Cherokee, which will promptly alert operators to emergency conditions such as linebreaks which are evidenced by abnormally high gas flow rates or pressure reductions. (Class III, Longer Term Action) (P-78-43) On August 3, 1978, the ASME replied that the conimittee would initiate whatever action was required. On September 6, 1978, the ASME Gas Piping Standards Committee stated that the action reconimended in P-78-43 was under review. The Safety Board has received no statement as to a n y action taken as a result of the review. Therefore, the National Transportation Safety Board recommends that the Missouri Power & Light Company: Review company records and rnaps to identify locations where compression couplings have been installed on unrestrained plastic pipe of sufficient length that thermal contraction could Cause separation from the couplings and take corrective action as necessary to prevent such separations. (Class E, Priority Action) (P-81-21) Install alarms on the existing gas pressure and gas flow telernetering equipment to promptly alert operators to emergency conditions such as linebreaks which are evidenced by abnormally high gas flow rates or pressure reductions. (Class II, Priority Action) (P-81-22) KING, Chairman, DRIVER, Vice Chairman, McADAMS, GOLDMAN, and BURSLEY, Members, concurred i n these recommendations. I#