FOR IMMEDIATE RELEASE: February 11, 2003 SB-03-04
NTSB DETERMINES THAT NEW MEXICO PIPELINE RUPTURE AND FIRE WERE CAUSED BY
INTERNAL CORROSION
Washington, D.C. - In a report adopted today, The National Transportation Safety Board determined that the cause of a pipeline rupture in Carlsbad, New Mexico was the significant reduction in pipe wall thickness and severe internal corrosion due to El Paso Natural Gas Companys (EPNG) failure to prevent, detect, or control internal corrosion within the companys pipeline. Contributing to the accident were ineffective Federal inspections of the companys internal corrosion control program that did not identify deficiencies.
On Saturday, August 19, 2000, a 30-inch-diameter natural gas transmission pipeline operated by El Paso Natural Gas Company ruptured adjacent to the Pecos River near Carlsbad, New Mexico. The released gas ignited and burned for 55 minutes. Twelve persons who were camping under a concrete-decked steel bridge that supported the pipeline across the river were killed and their three vehicles destroyed. Two nearby steel suspension bridges for gas pipelines crossing the river were extensively damaged.
During the investigation, NTSB investigators found that the rupture was a result of severe internal corrosion that caused a reduction in pipe wall thickness to the point that the remaining metal could no longer contain the pressure within the pipe. Furthermore, the corrosion was likely caused within the pipeline by the combination of microbes and such contaminants as moisture, chlorides, oxygen, carbon dioxide, and hydrogen sulfide, the report notes.
One of the major issues of this investigation involved the use of cleaning pigs. A pig is a mechanical device that is used to clean the pipeline. These devices, which may include scrapers or brushes on the pig body, are inserted in a pipeline, or launched, and traveled downstream with the gas flow.
In its report, the Board noted that periodic use of cleaning pigs could remove water and other liquid and solid contaminants that may cause corrosion in a pipeline. However, because the section of pipeline that ruptured could not accommodate pigs, cleaning pigs were not run in this section.
Another related issue the Board emphasized in the report was the partial clogging of the drip. The drip is a stub line that branched off the bottom of the gas pipeline. Its purpose is to collect liquids and solids that may have built up in the pipeline during normal transportation of gas or after pigging operations.
The investigation revealed that as a likely result of the partial clogging
of the drip upstream of the rupture location, some liquids bypassed the drip
and continued through the pipeline to the eventual rupture site. At the rupture
site, a bend in the pipe had created a low point in the pipeline where liquids
and other residue accumulated and caused corrosion.
Consequently, the Board found that because of the configuration of the piping,
including the location of the pig receiver and the design of the drip, cleaning
pigs could not run in the section of pipeline that ruptured and therefore removal
of substances was incomplete. The Board also concluded that if the accident
section of pipeline had been able to accommodate cleaning pigs, and if cleaning
pigs had been used regularly with the resulting liquids and solids thoroughly
removed from the pipeline after each pig run, the internal corrosion that developed
in this section would likely have been less severe.
The Board stated in the report that before the accident, EPNG did not have
in place an internal corrosion control program that was adequate to identify
or mitigate the internal corrosion that was occurring in its pipelines. Had
EPNG effectively monitored the quality of gas entering the pipeline and the
operating conditions in the pipeline and periodically sampled and analyzed the
liquids and deposits for corrosivity that were removed from the line, it would
likely have detected the potential for significant corrosion to occur within
the pipeline, the
Board determined. Overall, the Board found that the current Federal pipeline
safety regulations do not provide adequate guidance to pipeline operators or
enforcement personnel in mitigating pipeline internal corrosion.
As a result of this accident investigation, the Board made the following recommendations to the Research and Special Programs Administration (RSPA) and NACE, International (formerly known as National Association of Corrosion Engineers). These include:
Research and Special Programs Administration
· Develop the requirements necessary to ensure that pipeline operators
internal corrosion control programs address the role of water and other contaminants
in the corrosion process.
· Evaluate the Office of Pipeline Safetys pipeline operator inspection
program to identify deficiencies that resulted in the failure of the inspectors,
before the Carlsbad, New Mexico, accident, to identify the inadequacies in EPNGs
internal corrosion control program. Implement the changes necessary to ensure
adequate assessments of pipeline operator safety programs.
NACE, International
· Establish an accelerated schedule for completion of an industry standard
for the control of internal corrosion in steel pipelines that will replace or
update NACE standard RP-01-75.
A summary of this report is available now on the NTSB Web site at <http://www.ntsb.gov/default.htm>,
under "Publications." The complete report will be available on the
website in about one month. Printed copies of the report may be purchased later
this spring from the National Technical Information Service (NTIS) (800) 553-NTIS.
Media Contact: Keith Holloway
(202) 314-6100
NTSB Home | Contact Us | Search | About the NTSB | Policies and Notices | Related Sites