Nearly two years after the fatal explosion on El Paso Natural Gas, the National Transportation Safety Board (NTSB) issued a series of factual reports last Thursday that appeared to confirm federal investigators’ initial suspicions of substantial internal corrosion as the cause, or one of the causes, of the blast that killed 12 members of an extended family in August 2000.
A materials/metallurgical examination of pipe components recovered from El Paso’s Line 1103, which ruptured and exploded near Carlsbad, NM, revealed that there was “severe corrosion damage” on the bottom of the interior of the 1950s-vintage natural gas pipeline, according to the NTSB, which began its investigation of the explosion — the deadliest pipeline blast ever — within hours of the accident on El Paso’s South Mainline system on Aug. 19, 2000. The corrosion damage extended over a 21-foot area near the point of fracture, the board said.
As a result of the internal corrosion, the pipe near the origin of fracture “showed significant reduction in wall thickness,” the NTSB noted. In the severest case, the pipe’s original nominal wall thickness of 0.335 inch was reduced by 72%, it said.
The internal corrosion was most prominent at the “bottom half of the circumference” of the El Paso pipeline near Carlsbad, where liquids and condensation tend to gather, according to the board’s report. Federal investigators also said they found evidence of “pitting corrosion” — localized corrosion that takes the form of cavities — in several areas of the interior of the pipeline. “Many of the corrosion pits were interconnected that resulted in an area of significant reduction in wall thickness,” the NTSB said, adding that some of the corrosion pits were as deep as 0.15 inch.
In addition, the wall of one of the pipe segments “contained a 1.3 inch long through-the-wall crack…This crack coincided with pitting corrosion damage at the internal surface,” the board noted. It also said it found evidence of “deformation stretch marks” on the exterior of the pipeline closest to the point of fracture. “The severity of the deformation stretch marks increased in areas of the pipe that displayed more severe corrosion at the internal surface. Deformation stretch marks were found in other segments in areas adjacent to the fracture.”
While federal investigators noted that the wall thickness of the El Paso pipeline had receded significantly in some areas, they found no segments where corrosion had penetrated completely through the wall of the pipe.
The metallurgical and materials findings were contained in more than 2,000 pages of documents that were released by the NTSB last Thursday. The reports primarily presented the facts surrounding the deadly explosion and the board’s subsequent investigation, along with a number of interviews. The NTSB has not yet ruled on the cause of the blast, which killed seven adults and five children of an extended family who were camping and fishing along the banks of the Pecos River near the New Mexico-Texas border. They were consumed in the blast and fireball that ripped open a 113-foot long, 51-foot wide trench, and left a mass of twisted metal pipe in its wake. The NTSB is expected to rule on the cause later this year.
At the time of the explosion, El Paso came under attack for failing to inspect the pipeline with a pigging tool, a state-of-the-art device used to detect damage to pipe wall. The NTSB confirmed that the segment of the El Paso line that ruptured and exploded, as well as the two parallel pipes, had not been inspected by any in-line tool, let alone a pigging device, in the two years leading up to the blast. “The portion of the pipeline that contained the rupture did not have a pig launcher and receiver, and had not been inspected by a pig,” the board concluded. The configuration of the pipe at the river crossing precluded the use of a pig. In addition, El Paso did not inject any inhibitors in Line 1103 or looping pipelines to prevent corrosion, the NTSB reported.
Records revealed that El Paso had last conducted an in-line inspection of the affected Line 1103, and adjoining Line 1100, in 1998 between the Guadalupe and Cornudas Compressor Stations, located about 58 miles downstream of the accident site, the board said. El Paso conducted the inspection (using a low-resolution magnetic flux leakage internal inspection tool) following a blowout on Line 1103 near the Guadalupe Station on Jan. 27, 1998, in which corrosion was found on one remnant of the blasted pipe.
In the year following the Carlsbad accident, El Paso reported to NTSB it had identified 60 pipeline sites that contained characteristics similar to the rupture site — that is, they were crossings that could not be traversed by an internal cleaning tool (pigging device), or areas of no flow such as dead-end pipe stubs, valved-off crossovers, low spots and other sections where liquids could settle.
The company completed integrity testing and remedial work on those 60 sites, telling NTSB it had identified internal corrosion on the ruptured Line 1103 in two other places near the rupture spot. It also found five areas of internal corrosion on its Line 1107 and indications of slight internal scaling or slight internal wall loss on two other lines. The inspection also turned up several instances of external corrosion. El Paso also said it has reconfigured numerous pipeline segments to increase “pigability,” including installing temporary pig launchers and receivers. El Paso has run cleaning pigs, smart pigs, caliper pigs and tethered pigs, as well as x-raying, conducting ultrasonic testing, hydrostatic testing, bellhole testing and visual inspections.
The NTSB provided reports from Carlsbad-area residents who had smelled natural gas at the explosion site the day prior to the accident. Sgt. Danny Kiper of the New Mexico State Police said he had followed up one of the incident reports, and “found that the El Paso Natural Gas pumping station nearby was venting gas during [that] day.” He said he believed the resident “had smelled the vented gas, and stressed that an odor of natural gas was not unusual in the area.” Another area resident, Eric Sager, and his friends also told the NTSB that they had smelled gas that day. Both Kiper and Sager had confirmed that an El Paso employee had been working at the site the day before the explosion, Aug. 18.
Significantly, the NTSB said El Paso had placed signs at the site, where the victims were camping, identifying Line 1103 and the two parallel pipelines as “high pressure pipelines.” Moreover, it noted that the land was privately owned.
Seismographs that were conducted on the morning of Aug. 19 revealed that there was more than one explosion — three, to be exact. The strongest blast occurred at 5: 26 a.m., was preceded seconds before by a weaker one, and was followed by a moderate explosion, according to the NTSB. “The data are consistent with at least three significant separate explosions occurring within a time span of approximately 40 seconds, the first being much smaller than the subsequent two. Other smaller explosion events are also visible later in the recording.”
The NTSB’s review of the timeline of events following the fatal explosion seem to show that El Paso personnel, both those on and off duty, immediately were aware that something was wrong at the Carlsbad site, and quickly reacted by shutting off valves and taking other actions. It was not until later, however, that they learned that people had been camping near the pipelines. The board also reported that key El Paso personnel tested “negative” for alcohol and/or drug use, and did not appear to be over-worked.
The NTSB indicated that El Paso personnel had been trained in corrosion detection and control, satisfying National Association of Corrosion Engineers (NACE) guidelines, but it noted that most of their expertise was with external, rather than internal, corrosion control. It reported that El Paso had three corrosion coordinators, who provided technical support to field corrosion technicians. The corrosion coordinators were based in Albuquerque, NM; Tucson, AZ; and El Paso, TX, but the company did not have a coordinator in its Midland (TX) Division, which had responsibility for the segment of the pipeline on which the blast occurred, the board said. The six corrosion-related employees in the Midland Division were not trained in internal corrosion until after the accident, it noted.
This seems to square with the Department of Transportation’s Office of Pipeline Safety (OPS) finding that El Paso’s internal corrosion control program was seemingly inadequate. In a “notice of probable violations” issued against El Paso in June 2001, the OPS cited this as one of the violations in the wake of the fatal Carlsbad explosion. It proposed a $2.52 million fine against the pipeline, which has yet to be settled. It was said to be the largest civil penalty ever imposed against a pipeline operator for federal safety violations.
The NTSB publicly released El Paso’s written response to the OPS allegations. While El Paso accepted “full responsibility for what happened at Carlsbad,” El Paso said it was “quite a different matter from whether there is evidence that the company broke any rules or did anything wrong in connection with maintaining its pipelines prior to the rupture.”
The explosion and its “tragic human consequences do not by themselves justify finding the company at fault where the company scrupulously followed both applicable regulations and its own procedures,” El Paso told the OPS.
Both the NTSB and OPS also seem to agree that internal corrosion played a major role in the explosion. Even El Paso has not completely discounted this as a possibility. “If indeed the rupture at Carlsbad resulted from internal corrosion, it did so in circumstances not foreseen or reasonably foreseeable by OPS or [El Paso],” the pipeline said.
It pointed out that the OPS did not issue its advisory on internal corrosion until after the explosion at Carlsbad. “No similar advisories had been issued previously. This is because prior to Carlsbad, neither [the] OPS nor the industry viewed internal corrosion in onshore transmission pipelines as among the most significant threats to pipeline integrity or pipeline safety.” Due to corrosion concerns on the affected Line 1103, it was nearly a year after the accident before the OPS permitted El Paso to reopen the pipeline — at reduced pressures.
El Paso spent nearly $7 million repairing and restoring the damaged lines to service.
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