NTSB Safety Recommendation Letter P-76-001

Page 1Official PDFT S WASHINGTON, D.C. FOR RELEASE: 6:30 A,", E,D,T,, JANUARY 23, 1976 (202) 426-8787 ISSUED: January 23, 1976 __----_--______-_I______________________- Forwarded to: \ M r . N . P. Chesnutt President Southern Union Gas Company 1507 P a c i f i c Avenue Dallas, Texas 75201 SAFETY RECOMMENDATION (S) P-76-1 About 3:45 a.m. on March 15, 1974, the Southern Union Gas Company's 12-inch n a t u r a l gas transmission pipeline ruptured in a desert near Farmington, New Mexico. Natural gas a t almost 500 psig pressure escaped, i g n i t e d , and burned s e v e r a l hundred f e e t high. An 8-foot s e c t i o n of the 12-inch p i p e l i n e had blown out, digging a c r a t e r 40 feet long, 1 7 f e e t wide, and 10 f e e t deep. Three persons driving down a road adjacent t o t h e p i p e l i n e died and the e a r t h within a 300-foot diameter w a s charred. A t 5 a.m., t h e valves on both s i d e s of the break were closed, i s o l a t i n g the f a i l e d s e c t i o n within 8.9 miles. The longitudinal f l a s h w e l d of t h e A. 0. Smith pipe, manufactured i n 1948, showed severe crevice corrosion i n t h e fusion l i n e . Metallurgical examination showed t h a t t h e b r i t t l e f r a c t u r e i n i t i a t e d along t h e longi- tudinal seam on t h e bottom of t h e pipe and propagated i n both d i r e c t i o n s from t h e o r i g i n area along t h e w e l d . The corrosion i n t h e f l a s h weld reduced t h e o v e r a l l s t r e n g t h of the pipe by reducing t h e w a l l thickness; t h i s resulted i n higher-than-normal s t r e s s e s i n t h e weld l i n e u n t i l t h e f a i l u r e occurred. T h i s uncoated p i p e l i n e had been under hot-spot protection s i n c e 1965. Although i t had experienced many corrosion leaks, t h e r e had never been a rupture of t h i s type i n t h e past. The pressure at t h e time of f a i l u r e was below t h e maximum allowable operating pressure of 565 psig. After t h e accident, a s p a r t of an uprating process, t h e p i p e l i n e was t e s t e d t o pressures of 660 psig and up. These t e s t s would have located any other f l a s h welds t h a t had been weakened by crevice corrosion to such an extent t h a t f a i l u r e was imminent. Since none were found, and t h e l i n e 1722 -75-3#

Page 2will only be operated to a maximum pressure of 565 psig, it no other severely weakened flash welds existed at the time of the but since crevice corrosion could continue, despite efforts, failures could result in the future. Experimental work has been conducted by several ) develop an internal inspection tool which could detect longitudi While this tool has been perfect the excess metal left in the weld area in A. 0. Smith flash weld pip so great that it has a tendenc cate a defect. Additional test 1 indi- n a tool which may be able to de the flash weld failure. Therefore, the National Transportation Safety Board the Southern Union Gas Company: Work with developmental manufacturing firms to determine if an internal inspection tool could be utilized to detect defective flash welds in its Farmington-Albuquerque pipeline system. If a tool is found effective, it should be used in areas where crevice corrosion could be expected. (Recommendation P-76-2) (Class 11, Priorit Followup) REED, Acting Chairman, McADAMS, THAYER, BURGESS, concurred in the above recommendation. THIS DOCUMENT IS TO BE RELEASED TO THE PUBLIC ON THE NO PUBLIC DISSEMINATION OF THIS DOCUMENT SHOULD BE MADE BEFORE THAT DATE.#