NTSB Safety Recommendation Letter P-79-020 through P-79-021

Page 1Official PDFp - / 3 y k-4 WASHINGTON, D.C. I S S U E D : August 8, 1979 M r . L.D. Santman 1 Director \ SAFETY RECOMMENDATION(S) Materials Transportation Bureau Department of Transportation Washington, D.C. 20590 A t 12:20 p.m., c . s . ~ . , on A p r i l 18, 1979, a 24-inch n a t u r a l gas transmission p i p e l i n e owned by t h e Natural Gas P i p e l i n e Company of America (gas company) pulled out of a compression coupling during a line-lowering p r o j e c t under Iowa S t a t e Highway 181 i n a r u r a l a r e a near Dallas, Iowa. Within seconds, t h e n a t u r a l gas i g n i t e d and burned a 900- f o o t by 400-foot area. Five of t h e e i g h t i n j u r e d workers were hospi- t a l i z e d . Two cars, a pickup truck, and a trailer housing construction equipment were destroyed. A backhoe w a s p a r t l y damaged, and windows were broken i n a nearby farmhouse. The n a t u r a l gas p i p e l i n e system, which includes three lines con- s t r u c t e d p a r a l l e l t o each o t h e r (24, 26, and 36 inches i n diameter), extends 980 m i l e s from West Texas through New Mexico, Oklahoma, Kansas, Nebraska, Iowa, and I l l i n o i s , and serves approximately 1 2 m i l l i o n customers. The 24-inch p i p e l i n e , t h e o l d e s t of t h e three, w a s i n s t a l l e d i n 1931 by welding two lengths of pipe together on top of t h e trench and then j o i n i n g t h e double lengths of pipe i n t h e trench with compression couplings. There are approximately 51,700 couplings on t h i s l i n e , and 15,135 couplings are located i n t h e S t a t e of Iowa. Two days before t h e accident, in preparation f o r t h e l i n e lowering, a gas company crew closed mainline valves which were 8.7 miles a p a r t , thereby i s o l a t i n g a s e c t i o n of t h e pipeline. Crossover valves on e i t h e r s i d e of the s e c t i o n were opened so t h a t n a t u r a l gas could continue t o flow around t h e i s o l a t e d s e c t i o n without i n t e r r u p t i n g customer s e r v i c e beyond. The p r e s s u r e in the i s o l a t e d s e c t i o n w a s then lowered from 635 p s i g to 5 p s i g and w a s t o have been monitored while a c o n t r a c t o r ' s crew 2676#

Page 2lowered and replaced a segment of t h e p i p e l i n e under Iowa S t a t e Highway 181. A pressure gauge, which had been i n s t a l l e d on the i s o l a t e d line s e c t i o n t o monitor t h e pressure, apparently was removed sometime before the accident. There were no w r i t t e n company procedures f o r t h e pressure monitoring; t h e orders were given o r a l l y . The contractor exposed t h e f i r s t compression coupling on t h e e a s t s i d e of t h e highway t o v e r i f y t h e l o c a t i o n of t h e p i p e l i n e and the coupling. The contractor did n o t i n s t a l l a welded s l e e v e on t h i s coupling because i t was included i n t h e s e c t i o n t o be replaced. The excavation was then b a c k f i l l e d and a compression coupling was uncovered 80 feet east of t h e first coupling. A welded sleeve was i n s t a l l e d on t h i s coupling t o r e i n f o r c e it a g a i n s t p u l l o u t , and a trench exposing t h e p i p e l i n e was dug t o within 10 feet of t h e f i r s t coupling. A 13-degree bend i n t h e p i p e l i n e was exposed j u s t west of t h e second coupling. While t h e c o n t r a c t o r w a s exposing t h e p i p e l i n e and welding t h e s l e e v e s on, t h e gas company d i d n o t monitor t h e pressure; therefore, t h e construction crew was unaware t h a t gas at some pressure up t o a maximum of 635 p s i g had leaked by one of t h e closed valves and had increased the pressure i n t h e i s o l a t e d section. The pressure apparently increased t o a p o i n t where t h e axial f o r c e , a c t i n g on t h e 13-degree pipe bend, exceeded the p u l l o u t r e s i s t a n c e of t h e f i r s t coupling. The 80-foot-long exposed s e c t i o n of 24-inch pipe pulled o u t of t h e f i r s t coupling t h a t had been exposed but n o t sleeved. The p u l l o u t f o r c e caused t h e pipe t o rise straight up i n t h e a i r and then slam down t o the ground, causing it t o c r i m p and f i n a l l y break i n the middle of t h e 80-foot s e c t i o n . The gas company's accident records indicated t h a t this 24-inch p i p e l i n e had experienced 1 2 previous f a i l u r e s s i n c e it w a s constructed; 9 of these involved compression coupling pullouts. Five of t h e s i x f a i l u r e s t h a t occurred i n Iowa were coupling p u l l o u t s . On March 3, 1979, i n M i l l s County, Iowa, t h e 24-inch p i p e l i n e pulled o u t of a compression coupling where t h e p i p e l i n e extended over a h i l l (overbend). On March 4, 1979, i n Washington County, Iowa, more than 200 miles away, t h e same l i n e pulled o u t of another compression coupling i n an overbend. Both ruptures occurred i n open f i e l d s , a n d no i n j u r i e s were reported. Five of t h e 10 coupling p u l l o u t s were located e i t h e r a t a sidebend o r a t an overbend. The causes of t h e s e p u l l o u t s are s t i l l under investigation.#

Page 3- 3 - The 26-inch p i p e l i n e was completed i n 1948, and the 36-inch p i p e l i n e was completed i n 1963. In both of t h e s e p i p e l i n e s , a l l of t h e j o i n t s were welded and, t h e r e f o r e , n o t s u s c e p t i b l e t o p u l l o u t f a i l u r e s . Over t h e years the gas company has welded sleeves over 4,800 compression couplings on t h e 24-inch p i p e l i n e where those couplings were exposed f o r various p r o j e c t s . The sleeve welding is done t o prevent f u t u r e p u l l o u t of t h e pipe from the coupling. Gas transmission p i p e l i n e s constructed i n the 1920's and very e a r l y 1930's were o f t e n i n s t a l l e d with compression couplings. These couplings were dependable and capable of holding high pressures; however, they were n e i t h e r designed f o r nor intended t o r e s t r a i n l o n g i t u d i n a l pipe movement. Therefore, t h e National Transportation Safety Board recommends t h a t t h e Materials Transportation Bureau of t h e Department of Transportation: Coordinate with t h e appropriate S t a t e agencies, by f i e l d test r e p o r t s and on-site inspection, i n monitoring t h e excavation of t h e compression couplings on t h e 24-inch transmission p i p e l i n e t o i n s u r e the i n t e g r i t y of the p i p e l i n e . (Class I, Urgent Action) (P-79-20) Coordinate with t h e appropriate S t a t e agencies i n t h e monitoring of t h e 24-inch transmission p i p e l i n e t o determine i f t h e problem of compression coupling p u l l o u t s p e r s i s t s . I n the event of a continuing p u l l o u t problem, consider t h e reduction of pressure o r the shutdown, i n s e c t i o n s or i n t o t a l , of t h e p i p e l i n e u n t i l t h e problem can be corrected. (Class I, Urgent Action) (P- 79-21) K I N G , Chairman, DRIVER, Vice Chairman, McADAMS and GOLDMAN, Members, concurred i n these recommendations.#