While statistically pipelines remain the safest method to transport natural gas and liquids, growing demands on the aging infrastructure has increasingly pointed to the need for upgrades--sometimes tragically so.
Despite federal Department of Transportation (DOT) statistics that show pipeline incidents resulting in serious injury or death have dropped nearly 50% over the last 20 years, sporadic high-profile events, including the deadly incident in New York's East Harlem* this year and the Allentown, PA** explosion in 2011, have highlighted the need to hasten the repair and replacement of the most at-risk lines.
A report from the federal Pipeline and Hazardous Materials Safety Administration (PHMSA), which sets national policy on hazardous materials transportation, shows inroads have been in the last decade. Nationwide, total miles of cast-iron distribution mains have decreased almost 24% since 2004. Meanwhile, the number of cast- or wrought-iron (less brittle, more resistant to corrosion than cast iron) service lines was reduced by 73% during the same period.
"It is important to realize that it is just not logistically or economically feasible to replace all the cast-iron or bare-steel pipe at once nor does it all need to be replaced right away," said Lori Traweek, senior vice president and chief operating officer of the American Gas Association (AGA).
Still, several recent news articles have concentrated on the "worsening condition" of older pipe as a major threat to public safety. This, despite PHMSA data going back to 2004, which points to only a relatively small percentage of "reportable incidents" being caused solely by infrastructure deterioration.
A recent USA Today article, "Look Out Below: Danger Lurks Underground From Aging Gas Pipes," for example, uses an interactive map based on PHMSA "reportable incidents" in citing what it calls pipelines "prone to failure." A feature of the online version of the article bears the heading, "There is a destructive gas leak every two days in the USA," and allows readers to enter local zip codes, which then purport to display a map showing incidents dating back over 10 years.
In the case of ZIP code 77006 (central Houston), for example, a plethora of leaks for the area appears on the screen, but most took place in the ocean or well outside of Houston itself. Additionally, the majority of these "destructive incidents"--both in the Gulf of Mexico and on land--did not cause injury, and most of the incidents causing injury involved one person. Reasons for leaks varied but third-party excavation, vehicular accidents and operator error were the dominant causes --not pipe deterioration.
"No state has experienced more major gas leak incidents  or more gas leak deaths  than Texas," an accompanying voice recording warns those entering the Houston zip code. But a closer look at the expansive greater Houston area itself showed the city had experienced four leak-related deaths since 2004; the causes listed were excavation, miscellaneous, explosion and unknown.
"I'm not sure what can be done to quell public concerns," said John Erickson, vice president of operations for the American Public Gas Association (APGA). "The recent USA Today articles sensationalized the issue far beyond the actual degree of risk to the public."
Erickson also cited the example of a TV station in Washington, DC that obtained a redacted version of the local utility's federally required Distribution Integrity Management Plan (DIMP), and then "mischaracterized" it as a "secret list" of dangerous gas pipe.
"Relative risk is a difficult concept to explain to the public, when in fact, the highest relative-risk segments in a utility does not mean the pipe is unsafe," he said.
While the natural degrading of iron, or graphitization, makes cast-iron pipelines more susceptible to leaks from joints or cracks, by far the biggest threat to cast- or wrought-iron pipe is earth movement caused primarily by groundwater fluctuation, seasonal frost or digging.
In fact, effects of excavation and damage by other outside forces accounted for over 60% of all reported pipeline incidents between 19952004, according to statistics by the federal Office of Pipeline Safety which has since been re-organized as PHMSA. Additionally, research by utility software provider Opvantek, Inc. found that since 2010, over 75% of unintentional gas releases were caused by something other than aging infrastructure alone. Excavation damage was faulted in 29% of the incidents.
It is this type of distinction that AGA and others in the industry try to make: The age of the pipe, while certainly a factor, is not the primary characteristic...