December 2021, Vol. 248, No. 12


DIMP-Related Pipe Replacement Work Continues in Full Force US

Pipeline & Gas Journal staff report  

While the amount of work to replace cast-iron and bare-steel pipe has declined in volume since the implementation of the Gas Distribution Integrity Management Program (DIMP) in 2009, there is still plenty of construction left to be done.   

The federal Department of Transportation (DOT) estimated that at the end of 2019, 21,771 miles (35,037 km) of cast-iron and wrought-iron pipelines were still in service in the United States. The majority of that is in older eastern cities, such as New York, Boston, Washington, D.C., and Philadelphia. This represents quite a headway since 2015, when there were 3,342 miles (5,378 km) still in the ground.  

Among individual states, New Jersey led the way with 3,412 miles ( 5,491 km) of cast-iron and wrought-iron pipe, or 9.6% of its total; followed by New York’s 2,773 miles ( 4,462 km), 5.6%; Massachusetts’ 2,713 miles (4,366 km), 12.4%; Pennsylvania’s 2,284 miles (6,675 km), 4.7%; and Michigan’s 2,057 miles (3,310 km), 3.4%.   

Further DOT data indicate that replacement work, while progressing steadily for more than a decade now, is far from complete. In 2015, there were still 27,771 miles of wrought- and cast-iron gas distribution lines in service in the U.S., down from 39,342 miles (63,315 km) since 2005, a decrease of almost 30%.  

According to the Pipeline and Hazardous Materials Safety Administration (PHMSA), about 97% of natural gas distribution pipelines in the U.S. were made of plastic or steel at the end of 2020. The remaining 3% is primarily cast-iron pipe.  

Cast- and wrought-iron pipelines were originally constructed to transport manufactured gas beginning in the 1870s and 1880s, with cast iron becoming more popular in the early 1900s. 

In 1970, PHMSA began collecting data about gas pipelines mileage categorized by pipe material type. In 1983, gas distribution pipeline operators reported 61,536 miles of cast iron and 4,371 miles of wrought iron pipe. Operators began submitting merged data for the two beginning in 1984. 

In late 2009, PHMSA implemented pipeline safety regulations for managing the integrity of gas distribution pipelines. Operators were required to create DIMP by August 2011. Operators are required to know the specific characteristics of their system and operating environment to identify threats, evaluate the risk, and take measures to reduce the risk.  

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