NTSB Safety Recommendation Letter P-79-022 through P-79-025

Page 1Official PDFp- t.70 TI T SP TI s Y D WASHINGTON, D.C. M r . S.M. Salvino President Natural Gas P i p e l i n e Company of America 122 S . Michigan Avenue Chicago, I l l i n o i s 60603 ......................................... 1 SAFETY RE OMMENDAl O N ( S ) P-79-22 through -25 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 o u t of a compression coupling during a line-lowering p r o j e c t under Iowa State 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 c a r s , a pickup truck, and a trailer housing construction equipment were destroyed. A backhoe was 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 t h r e e l i n e s 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 12 m i l l i o n customers. The 24-inch p i p e l i n e , the o l d e s t of t h e three, was i n s t a l l e d i n 1931 by welding two lengths of p i p e together on top of t h e trench and then j o i n i n g t h e double lengths of p i p e i n the 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 the accident, i n 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 p i p e l i n e . Crossover valves on e i t h e r s i d e of t h e s e c t i o n were opened s o t h a t n a t u r a l gas could continue t o flow around the 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 service beyond. The pressure i n t h e i s o l a t e d s e c t i o n was then lowered from 635 p s i g t o 5 p s i g and was 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 t h e i s o l a t e d l i n e s e c t i o n t o monitor t h e pressure, apparently was removed sometime before t h e accident. There were no written company procedures f o r t h e pressure monitoring; the 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 the highway t o v e r i f y the l o c a t i o n of the 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 w a s 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 i t against p u l l o u t , and a trench exposing t h e p i p e l i n e w a s dug t o within 10 f e e t 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 contractor was 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, the gas company did n o t monitor the pressure; t h e r e f o r e , t h e construction crew w a s unaware t h a t gas a t 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 t h e p r e s s u r e i n t h e i s o l a t e d s e c t i o n . The p r e s s u r e apparently increased t o a p o i n t where t h e a x i a l force, a c t i n g on the 13-degree p i p e bend, exceeded t h e 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 the f i r s t coupling that had been exposed b u t not sleeved. The p u l l o u t f o r c e caused t h e pipe t o rise s t r a i g h t up i n the air and then slam down t o t h e ground, causing it t o crimp 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 t h i s 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 t h e s e 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 pullouts. 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 out of a compression coupling where the 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, the same l i n e pulled o u t of another compression coupling i n an overbend. Both r u p t u r e s 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 these p u l l o u t s a r e still under i n v e s t i g a t i o n .#

Page 3- 3 - The 26-inch p i p e l i n e w a s completed i n 1948, and the 36-inch pipeline w a s completed i n 1963. I n both of these 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, therefore, 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 pullout of t h e pipe from the coupling. Gas transmission p i p e l i n e s constructed i n t h e 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 Natural Gas P i p e l i n e Company of America: Include i n its w r i t t e n procedures t h e designation of s p e c i a l company personnel who w i l l continuously monitor pressures during p i p e l i n e maintenance work similar t o this p r o j e c t . (Class I, Urgent Action)(P-79-22) Review with its construction crew and others t h e hazards of exposing any p i p e l i n e i n s t a l l e d with compression couplings without monitoring t h e pressure i n the l i n e , e s p e c i a l l y a t l o c a t i o n s where overbends or sidebends e x i s t . (Class I, Urgent Action)(P-,79-23) I d e n t i f y contour areas where v e r t i c a l o r h o r i z o n t a l bends i n t h e p i p e l i n e may e x i s t , and excavate, on a random b a s i s acceptable t o t h e appropriate S t a t e agencies, t o determine i f compression couplings located adjacent t o these bends have experienced excessive a x i a l f o r c e s t h a t could cause a coupling f a i l u r e . I n s t a l l s u i t a b l e strappingor sleeving on couplings which do n o t pass reinspection because of leakage, corrosion, o r evidence of p a r t i a l pullout. (Class I, Urgent Action)(P-79-24)#

Page 4- 4 - Determine what effects soil conditions have on this pipeline where changes in the land contour could cause shifting or movement of the soil. As a result of this determination take steps to correct the condition. (Class 11, Priority Action)(P-79-25) KING, Chairman, DRIVER, Vice C concurred in these recommendations.#