NTSB Safety Recommendation Letter P-79-028

Page 1Official PDFm. C. L. Neaves President Lone S t a r Gas dompany 301 South Harwood Street Dallas, Texas 75201 SAFETY RECOMMENDAT I O N (S) P-79-28 A t 1:lO a.m., c.s.t., on January 19, 1979, i n North Richland H i l l s , Texas, an accumulation of natural gas i n a house was i g n i t e d by an unknown source. The resulting explosion and f i r e destroyed the house. One resident w a s killed and another was c r i t i c a l l y injured. The houses i n the accident area were connected t o a &inch Lone S t a r Gas Company gas main by 1 1/4-inch service lines. The service connection was made with two 90-degree elbows t o allow for both hori- zontal and vertical movement of the line as the s o i l moved. This "swing connection" did not prevent the fracture of the pipe. Investigators have determined that gas escaped from a circumferential fracture a t the threads of a 1 1/4-inch nipple above the service tap on the main. The w e t clay soil at the accident site retarded the upward movement of the leaking gas. The gas moved l a t e r a l l y along the pipe; through the d r i e r , more permeable clay; and into the house. On November 27, 1978, a leak occurred on the Lone Star system in Arlington, Texas. This leak w a s also a t the threaded section of a mainlservice l i n e connection. The leak resulted in an explosion in which one person was killed. The conditions a t the January 19, 1979, accident were also similar t o those which existed on October 4, 1971. when a connection failed i n North Richland H i l l s . I n a l l three cases, the pipelines were located i n dense clay soil that swells when it is w e t . The movement of the s o i l applied force t o the pipes which in turn induced stxesses which concentrated a t the threaded connections of the 1 1/4-inch nipple at the service tap. The continued stress eventually - 1/ For more detailed information read "Pipeline Accident Report-- Lone S t a r Gas Company, North Richland B i l l s , Texas, October 4, 1971" (NTSB-PAR-72-3). 2718-A#

Page 2- 2 - caused the threaded areas t o crack. I n the 1971 accident, the e f f e c t s of the stress were heightened because of b r i t t l e n e s s caused by the hydrogenation of the galvanized pipe used at that connection. Investi- gators determined that the 1978 leak w a s also induced by a combination of stress and corrosion. The pipe involved i n the January 19, 1979, accident w i l l be tested by Metallurgical Consultants, h c . , of Houston, Texas. The type of pipe--plain steel or galvanized steel--has not yet been determined. The Board has requested t h a t the t e s t i n g be expedited. As a result of its investigation of the 1971 accident, the Safety Board recommended that Lone S t a r make random inspections of its m a i n / service line connections t o determine conditions and initiate corrective action as necessary. Lone S t a r r e p l i e d t h a t the leak was due t o the corrosion action on the galvanized pipe rather than stress. Lone S t a r stated that its construction standards "have never permitted the use of galvanized pipe underground. Galvanized pipe has been utilized i n the past for above ground connections. Construction records on work in t h i s area indicate that black steel pipe was used. Any use of galvanized pipe was inadvertent and unusual. Since the date of t h i s occurrence, a l l of our warehouses have been purged of galvanized pipe of any type. 'Its use has been prohibited. Since the date of t h i s accident, we have followed closely a l l repairs on our system. Excavations number in excess of 1,000 a month i n the Fort Worth system of which North Richland H i l l s is a part. These excavations have failed t o reveal a single similar installation. 'In addition, immediately following the accident several services were dug up in the immediate area. These w e r e not determined t o be galvanized pipe." Failure of pipe a t the main/service l i n e connection with threaded couplings on the Lone Star system appears t o be a recurring problem. After the 1971 accident, Lone S t a r only addressed the galvanized pipe/ hydrogenation corrosion problem and not the stress problem. The short time between t h e November 1978 and the January 1979 accidents has caused the Safety Board concern as t o the safety of the entire Lone Star system. Therefore, the National Transportation Safety Board recommends that the Lone Star Gas Company: Determine through sample inspections, the extent of the problem of circumferential cracking on its service line/gas main connections similar t o that#

Page 3- 3 - a t the accident locations. Take appropriate action to reduce the probability of the recurrence of similar accidents. (Class I, Urgent Action) (P-79-28) A similar letter and recornendation was issued t o the U.S. Department of Transportation, Research and Special Programs Administration on September 6 , 1979. KING, Chairman, DRIVER, Vice Chairman, WmS, GOLDMAN, and BURSLEY, Members, concurred i n this recommendation.#