Energy companies are gradually reducing the national inventory of iron and bare steel gas distribution main pipelines, although nearly 100,000 miles of these older lines were still in place as of 2012.  This and much related data are now being made available in an annually updated inventory placed online by the Department of Transportation’s (DOT) Pipeline and Hazardous Materials Safety Administration (PHMSA).  

Gas distribution lines comprise mains, which generally run underground along streets and highways, and smaller service lines, which carry gas to individual customers.  Incidents typically result from leaks from older casr/wrought iron and bare steel distribution mains that have corroded over time.  In 1971, the federal government mandated protective coating for newly installed inter- and intrastate transmission pipelines and distribution pipelines.  But failures of older distribution mains are still occurring with tragic consequences. 

In 2011 alone, failures of two cast iron pipelines in Philadelphia and Allentown, Pennsylvania, led to explosions and fires, the deaths of six people, injuries, and the destruction of homes. 

Following those events, PHMSA issued a Call to Action to accelerate the repair, rehabilitation, and replacement of the highest- risk pipelines.  Also, the Pipeline Safety, Regulatory Certainty, and Job Creation Act of 2011 directed the DOT to conduct a state-by-state survey on the progress of cast iron pipeline replacement. 

Inventory highlights

Data from the latest (2012) inventory include the following:

• Nationally, there are 32,430 miles of cast/wrought iron gas distribution mains, compared to 40,696 miles in 2004. 
• States that have completely eliminated cast/wrought iron distribution lines within their borders include Alaska, Arizona, Hawaii, Idaho, Montana, Nevada, New Mexico,  North Dakota, Oregon, South Carolina, Utah, Vermont, Wisconsin, and Wyoming.
• The 10 states with the most cast/wrought iron distribution main mileage account for 81 percent of all such mileage.  The cast/wrought iron distribution main mileage in these states decreased 10 percent between 2004 and 2011.  The four states with the most mileage are New Jersey (5,044 miles, 15 percent of total main miles), New York (4,417 miles, 9 percent), Massachusetts (3,792 miles,      18 percent), and Pennsylvania (3,221 miles, 7 percent).
• Nationally, cast iron comprises only 2.6 percent of distribution mains.  However, 11 percent of distribution main incidents involve cast iron.
• 37 percent of cast/wrought iron main incidents caused a fatality or injury, compared to 21 percent of incidents involving mains made of other materials.
• 67 percent of cast/wrought iron service line incidents resulted in a fatality or injury, compared to 32 percent of the incidents involving service lines made of other materials.
• There are 61,328 miles of bare steel gas main distribution pipelines, compared to 73,953 miles in 2004. 
• Between 2004 and 2011, bare steel service line miles decreased by approximately 28.9 percent.
• The four states with the most bare steel gas distribution mains are Ohio (9,043 miles, 16 percent of total main miles), Pennsylvania (8,086, 17 percent), New York (6,902, 14 percent), and Texas (6,099, 6 percent).
• No state has eliminated bare steel distribution mains, although five states have 10 or fewer miles (Maine, Utah, Alaska, North Dakota, and South Carolina).

PHMSA’s cast/wrought iron and bare steel pipeline inventories