NTSB/PAB-01/03 

National Transportation Safety Board 

Washington, D.C. 20594 

Pipeline Accident Brief

Pipeline Accident Number: DCA-00-MP-005 

Type of System: Hazardous liquid 

Accident Type: Pipe failure and leak 

Location: Greenville, Texas 

Date and Time: March 9, 2000, at 10:20 p.m., central standard time 

Owner/Operator: Explorer Pipeline Company 

Fatalities/Injuries: None 

Damage/Clean Up Cost: $18 million 

Material Released: Gasoline 

Quantity Released: Approximately 564,000 gallons 

Pipeline Pressure: 705 pounds per square inch, gauge, (psig) 

 at site of failure 

Component Affected: 28-inch-diameter, American Petroleum Institute 

Specification 5LX, Grade X-52, 0.281-inch-wallthickness, DSAW (double seam submerged-arc 

welded) steel pipe 

The Accident 

On March 9, 2000, about 10:20 p.m., central standard time,1 a 28-inch-diameter 

pipeline owned and operated by Explorer Pipeline Company (Explorer) ruptured and 

released 13,436 barrels (about 564,000 gallons) of gasoline. The pipeline was buried 

about 4 feet 6 inches under ranch land. The release site was near Greenville, Texas, about 

45 miles northeast of Dallas. 

Explorer’s Greenville pumping station on the 28-inch pipeline was about 

10.3 miles south and upstream of the rupture site. This station automatically shut down its 

two running pumping units when the rupture occurred. Before the failure, the pipeline had 

been in steady-state operation, and its flow rate was approximately 20,000 barrels per 

hour. About 2 minutes after the rupture and the automatic shutdown of the Greenville 

pumping station, the pipeline controller (located in Tulsa, Oklahoma) started a different 

pumping unit at the Greenville pumping station in an effort to keep the entire pipeline 

balanced and operating. Meanwhile, the operator of the Greenville pumping station 

attempted to determine the cause of the automatic shutdown of his pumping units. The 

pumping unit that the controller had started also shut down automatically after about 

2 minutes. The controller shut down the entire line. After a few minutes, thinking that the 

 1

 All times reported are central standard time. 
NTSB/PAB-01/03 

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cause of the initial shutdown had been a control valve problem, the controller restarted 

the line at a reduced rate. About 13 minutes later (around 10:49 p.m.), the controller shut 

the entire line down for evaluation. 

Leak Reporting and Response 

Individuals near the rupture began calling 911 soon after the pipeline failure. Other 

residents who detected the odor of gasoline called Explorer personnel because they were 

aware that the Explorer pipeline passed through the area. 

The released gasoline flowed a few hundred feet across the surrounding terrain and 

into a dry creek bed, which was a tributary to East Caddo Creek. From the tributary, the 

gasoline flowed downstream into East Caddo Creek. The banks of the tributary and creek 

contained the escaping gasoline as it flowed away from the ruptured pipe. 

Explorer closed remotely operated valves at pump stations about 10:59 p.m. to 

isolate the ruptured section of pipeline. By 11:05 p.m., Explorer personnel were on the 

scene and meeting with emergency responders. About midnight, a local contractor arrived 

on the scene to construct dams across East Caddo Creek to stop the flow of gasoline. 

About 1:30 a.m., Explorer personnel manually closed a mainline valve to further isolate 

the rupture area. 

By morning, three dams had been constructed across the East Caddo Creek. The 

leading edge of the escaping gasoline was eventually contained about 2 1/2 miles from 

the rupture site. Then, about 8:30 a.m. the morning after the rupture, heavy rains began to 

fall. The rain lasted throughout much of the day. An estimated 1.5 to 2 inches of rain fell 

in the area, and East Caddo Creek rose about 12 feet. The rising waters destroyed the 

three dams that had been constructed in the night and allowed the gasoline to move 

further downstream. 

Work continued during the day, and the leading edge of the gasoline appeared to 

have been stopped about 15 miles from the rupture site, about 7 miles upstream of Lake 

Tawakoni. The lake is a major water supply for Dallas and numerous smaller 

communities. After the accident, the chemical MTBE (methyl tertiary butyl ether), a 

component of the gasoline, was found in Lake Tawakoni. 

Preaccident Information 

The line pipe was 28 inches in diameter, with a wall thickness of 0.281 inch. The 

double seam submerged-arc welded pipe had been manufactured in 1970 by the Steel 

Company of Canada to conform to American Petroleum Institute Specification 5LX, 
NTSB/PAB-01/03 

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Grade X-52. The pipeline had been constructed in 1970. The soil in the area of the 

rupture consisted of “gumbo” clay and limestone marl. Koppers Bitumastic pipe coating 

was applied during construction to this section of the line. 

An in-line inspection tool (“smart pig”) was run through this section of line in 

1997. Anomalies meeting Explorer criteria were excavated, evaluated, and repaired. No 

anomalies meeting Explorer’s 1997 criteria were reported in the area of the March 2000 

failure during the in-line inspection, so the pipe was not visually examined at this location 

before the failure. 

Postaccident Examination of the Failed Pipe Segment 

Postaccident laboratory examination of the failed pipe segment showed that the 

rupture area had a typical “fish-mouth type” crack; when one looked north along the 

pipeline, the crack was at about the 1 o’clock position on the pipe. The crack was about 

50 1/2 inches long, and its maximum width was about 6 3/4 inches. The ends of the crack 

were located off the edge of the longitudinal seam weld, and about the middle one-third 

of the crack was directly adjacent to the pipe’s longitudinal seam weld. 

The surface of the main fracture was examined. In the middle region, where the 

crack was located directly adjacent to the longitudinal seam weld, a portion of the fracture 

surface appeared relatively smooth, and crack arrest marks typical of fatigue were 

observed. Crack arrest lines appeared to nearly intersect the inner edge of the main 

fracture surface, but the fracture plane was at an angle of about 45 degrees, consistent 

with high-stress, low-cycle fatigue. In another region of the fracture surface adjacent to 

the outer edge, fracture features were obliterated by corrosion. 

The pipe coating in the rupture area appeared wrinkled and torn. The coating bore 

meandering cracks, ranging up to 2 1/2 inches wide, which exposed the pipeline surface. 

Corrosion pits were observed on the outer surface of the pipe in areas where the coating 

was cracked. The corrosion pitting was generally isolated, except in the area adjacent to 

the failure, where zones of continuous corrosion pitting were observed. Pitting was found 

on the longitudinal weld, and crack-like features were observed at the longitudinal weld 

boundary in some of the pitted areas. The crack-like features were typical of a weld 

defect, such as incomplete fusion. No crack-like features were observed in any pits not on 

the longitudinal weld. (Upon examination after the accident, Explorer noted that, during 

initial construction of the pipeline section surrounding the failure site, the pipe and 

coating may have been backfilled before the coating had cooled sufficiently. This could 

have caused extensive wrinkling in the coating, as well as pulling and tearing the coating 

materials.) 
NTSB/PAB-01/03 

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Postaccident Activities 

Before Explorer restarted the pipeline, it established a testing plan, which it gave 

to the U.S. Department of Transportation’s Research and Special Programs 

Administration (RSPA) for review and approval. The plan established repair procedures, 

required a pressure reduction to 20 percent below the calculated failure pressure of the 

pipe at the rupture location, set a refilling and startup procedure, and mandated a pipeline 

incident review that addressed controller training and SCADA2 design improvements, 

including simulation training. Additional in-line testing was conducted, and several 

repairs to the pipeline were made. On December 15, 2000, RSPA gave Explorer 

permission to return pipeline operation to the operating pressures that had been in effect 

before the accident. 

Probable Cause 

The National Transportation Safety Board determines that the probable cause of 

the pipeline failure was corrosion-fatigue cracking that initiated at the edge of the 

longitudinal seam weld at a likely pre-existing weld defect. Contributing to the failure 

was the loss of pipe coating integrity. 

July 6, 2001 

 2

 Pipeline controllers use SCADA (supervisory control and data acquisition) systems to remotely 

monitor and control movement through pipelines. Using a SCADA system, controllers can monitor flow 

rates and pressures along the lines, control valves, and pumps to adjust the flow at pump stations and other 

locations throughout the pipeline system.