NTSB Safety Recommendation Letter P-83-028

Page 1Official PDFNATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D.C. ISSUED: September 7 , 1983 ,? -,J35-- Forwarded to: \ Mr. Phillip Lathrop I "7 Chairman- American Society of Mechanical Engineers I SAFETY RECOMMENDAT I ON (S) Gas Piping Standards Committee c/o Pacific Gas and Electric Company 77 Beale Street Room 2883 San Francisco California 94106 -------------r_-----____________________ i P-83-28 -- A t 12:15 p.m., c.d.t., on October 1, 1982, a 1/4-inch-thick steel plate, which had been welded by a work crew to cap temporarily the open end of a section of a 22-inch-diameter gas transmission pipeline which had been isolated by closing a gate valve and then gas freed, blew off under an initial pressure of possibly 260 psig. Rapidly escaping natural gas from the pipeline, which had accumulated due to a leak in the gate valve, ignited almost immediately and the entire work area and a portion of US. Route 65 were momentarily engulfed in flames. Seven persons who were working to r e p h e a section of the pipeline under the road about 2 miles south of Pine Bluff, Arkansas, were burned and hospitalized. Resultant property damage was minimal. &/ Work at the site had begun on September 13, 1982, when materials and equipment were moved to the job site and new 22-inch-diameter, heavy wall pipe lengths were welded together for installation under the crossing. The Mississippi River Transmission Corporation's (gas company) division superintendent, four other gas company personnel, and four persons from an independent pipeline contractor with whom the gas company had contracted were assigned to the project. During the next several days the original pipeline was excavated and totally exposed for a distance on each side of the road. One escape route, a sloping ramp out of the ditch, had been provided approximately halfway along the east side of the ditch; no ladders or other means of rapid escape were available. A similar excavation had been dug on the south side of the road. After the excavations were made, road boring equipment was set up, the passage under the road was "slick bored," and the new pipe was installed. On September 28, 1982, a 10-mile section of the pipeline which included the section being replaced, was taken out of service by closing a 22-inch-diameter gate valve at milepost 94 (9.8 miles south of the road) and another 22-inch gate valve at milepost 104 (approximately 600 feet north of the road). Gas was transferred from the isolated section t o adjacent looped lines using a portable compressor which reduced the pressure from 260 psig to 14 psig. The remaining 14 psig was vented to the atmosphere, leaving the isolated section of pipeline still full of gas at atmospheric pressure. - 1/ For more detailed information read Pipeline Accident Report-"Mississippi River Transmission Corporation Natural Gas Flash Fire, Pine Bluff, Arkansas, October 1, 1982" (NTSB/PAR-83/03). 3758#

Page 2-2 .- On September 30, 1982, the remaining gas in the isolated pipeline section evacuated, and 20-foot-long sections of pipe were removed from the pipeline on each sid of the roadway. The workers installed a temporary cap on the open end of the remainin pipeline using a round, l/4-inch-thick steel plate welded with one pass because the ea was intended only to keep water and debris out of the pipeline pressure. The blowdown valve at milepost 94 was left ope building in the section of the pipeline that was then isolated the end cap at the excavation site. All valves within the locked. Nevertheless, pressure would build up in the isolated the closed gate valve. By that afternoon, the new road crossing had been in had been abandoned, and a pipeline section composed connecting the new road crossing with the existing pipeline of the workday (approximately 5 p.m.), the gas comp company maintenance man to the gate valve site at said he told the maintenance man "to close his air m venting out of the 6-inch blowdown." The maintenance m closed the air mover valve, and also closed the blowdown valve. The maintenance m said that he closed the blowdown valve, even though he was not so instructed, because did not want rain to get into the pipeline. On the morning of October 1, 1982, when the crew resumed wo valve and the blowdown valve a t milepost 104 were still closed. The e also closed, and no pressure gauge had been connected to it. This sh been in effect since about 5 p.m. the evening before. their correct open or closed positions, nor was the cap between the gate valve at milepost 104 and the exca buildup. The crew was welding on the road crossing alignment section the road when the accident occurred about 12:15 - p.m. Even though the gate valve at milepost 104 had been closed abo accident and the isolated 500-foot section of pipe w a s made gas free at that tim must have been leaking through the valve continuously, but it woul accumulate in the isolated section until sometime after the pipe was any gas leaking through the valve would have vented safely throug valve until the blowdown valve was closed at 5 p.m. on September 3 t h a t time, the gas leaking through the valve and entering the isola would have begun to build up pressure. The leakage of gas throu U M O t i C e d because no means for monitoring the internal atmo section had been provided and because no inspections or periodic checks were made t o ensure that the isolated section remained gas free. A s gas continued to leak through the valve, pressure within the 500-foot section increased for 19 hours until the single-weld bead on the end cap was abruptly ruptured, the end cap blew area, and the accumulated gas was rapidly released. The superintendent recognized the potential for valves, but he neither installed pressure gauges for m isolated sections nor checked to ensure that any gas leaking being vented safely. The 2-inch valves installed on each e prevent any water t h a t might accumulate in the excavation from entering the pipe. pressure gauge had been installed on the valves in the end caps, pressure buildup could#

Page 3-3- have been detected visually by anyone in the work area. Even if pressure gauges had not been installed, the 2-inch valves could have been opened periodically throughout the day, and any gas under pressure would have been released making an audible sound; such a gas release would have initiated a search for the leak source, would have revealed the closed blowdown valve, and would have prompted its opening. Therefore, the National Transportation Safety Board recommends that the American Society of Mechanical Engineers, Gas Piping Standards Committee: Develop guidelines for monitoring gas pipeline segments that have been isolated from gas under high pressure solely through the use of valves. Establish the conditions under which the monitoring should include an automatic means for alerting employees to the presence of gas within the isolated section and the timing and frequency of inspections that should be made to determine the presence of gas when an automatic alerting means is not incorporated within the monitoring equipment. (Class E, Priority Action) (P-83-28) BURNETT, Chairman, GOLDMAN, Vice Chairman, McADAMS, BURSLEY, and ENGEN, Members, concurred in this recommendation. Chairman /#