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Cast and Wrought Iron Inventory

The inventory opens in a new window and contains three reports about each state with cast or wrought iron pipe.

In the first report, you can rank states by either gas distribution main miles or service line counts. Distribution mains are natural gas distribution pipelines that serve as a common source of supply for more than one service line. Service lines are the pipelines that transport gas to a customer's meter or piping. The table is initially sorted by the number of miles of cast or wrought iron gas distribution main but can be sorted by any of the columns.

The second report shows the change in main miles and service line counts over the years. Nationally, cast and wrought iron distribution main mileage has decreased by 60 percent from 2005 to 2023. The number of cast or wrought iron service lines has decreased by approximately 80 percent over the same time period. The third report shows data for each operator reporting iron pipelines since 2005.

All of the reports can be limited to a single state by using the state prompt at the top. Any state not included in the drop-down either never had cast and wrought gas distribution pipelines or all were removed before 2005. 24 States and 1 territory have completely eliminated cast and wrought iron gas distribution pipelines: AK, AZ, AR, CO, HI, IA, ID, KS, MS, MN, MT, NM, NC, ND, NV, OK, OR, PR, SC, SD, UT, VT, WA, WI, and WY.

Cast/Wrought Iron Gas Distribution Pipeline Inventory Reports

Recent Incidents Involving Cast Iron Pipelines

Even though the amount of cast iron pipelines is declining, there have been a number of recent incidents caused by cast iron gas distribution main failures, resurging attention to the risks associated with cast and wrought iron pipelines.

  • November 22, 2022 – A natural gas explosion occurred at a residential building, injuring 3 people in Baltimore City, Maryland. Baltimore Gas & Electric Co determined after the incident that a 4" cast iron low-pressure gas main installed in 1904 experienced a full circumferential break which allowed natural gas to migrate underground.

  • January 27, 2022 – Gas from a leaking cast iron joint ignited causing a manhole cover to lift striking a Baltimore city welding contractor, resulting an injury that required in-patient hospitalization. Baltimore Gas & Electric Co determined leaks at joints of a 12" cast iron main, installed in 1920.

  • January 10, 2020 – A gas fire and explosion at a private property in Jersey City, NJ, resulted in an injury requiring in patient hospitalization. Public Service Electric & Gas Co determined leaks at joints of a 36" cast iron main, installed in 1952, migrated through a 4" electrical conduit coming from the street and extended into the basement of the structure.

  • December 19, 2019 – Philadelphia Gas Works (PGW) crews responded to three properties on fire on South 8th Street in Philadelphia, PA. A 6" cast iron gas main had circumferential break where a large underground cavity caused ground movement and resulted in the rupture of the main installed in 1928. There were 2 fatalities. PGW evacuated approximately 60 people during the event.

  • June 16, 2018 – A Baltimore Gas and Electric (BGE) contractor paving crew was injured, requiring overnight hospital stay while installing thermoplastic marker traffic lines using a heat torch in Baltimore, MD. A gas main leak was identified and a 1903 installed cast iron joint was repaired.

  • January 20, 2018 – A gas fire at a two story residential building in Brooklyn, NY injured four with one person requiring overnight inpatient hospitalization. The building suffered moderate structural damage. The 6 inches cast iron main was installed approximately in 1927 and was operating at 0.3 psig. Apparent cause of incident was reported as frost heave.

  • July 31,2016 - Release from a cast iron main resulted in 1 fatality and 1 injury in a residence in Shreveport, LA. There is no definite cause of the incident but a combination of washout/erosion, leaking liquid from sewer manhole, improper backfill and compaction contributed to an overload even that resulted in gas leak. The 4 inch pipe was installed in 1911 and was operating at 0.5 psig.

  • March 5, 2015 - After getting notified of a gas leak in a residence in Detroit, MI, utility crew found a circumferential crack in the 6-inch cast iron main. The frost depth was 48 inches, causing the main to break. Consequence included 1 fatality and 1 injury. The cast iron main was installed in 1923 was operating at 2 psig.

  • January 27, 2015 – A home exploded on McCrory St in Cordova, AL while gas utility employees were responding to a natural gas leak. Consequences included one fatality and three injuries. Earth movement near the cast iron main caused the pipe to crack. The cast iron distribution main was installed in 1952 and was operating at 22 psig.

  • January 9, 2012 – A home exploded on Payne Ave in Austin, TX, resulting in one fatality and one injury. The leak originated at a break in a four-inch cast iron gas main installed in 1950. The cast iron main break occurred after rainfall that followed extended drought conditions.

  • February 9, 2011 – A tragic explosion occurred on North 13th Street in Allentown, PA. Local emergency responders worked to limit the spread of the fire while the operator cut through reinforced concrete to access the gas main. A preliminary investigation found a crack in a 12-inch cast iron main that was installed in 1928 and was operating at less than 1 psig at the time of incident. As a result of the explosion and ensuing fire, five people lost their lives, three people required in-patient hospitalization, and eight homes were destroyed.

  • January 18, 2011 – An explosion and fire caused the death of one gas utility employee and injuries to several others while gas utility crews were responding to a natural gas leak in Philadelphia, PA. A preliminary investigation found a circumferential break on a 12-inch cast iron distribution main that was installed in 1942 and was operating at 17 psig.

Incident and Consequence Analysis
PHMSA regulations require gas distribution operators to submit incident reports when a leak causes an injury or fatality, property damage exceeding the regulatory threshold as per §191.3, or the unintentional release of three million standard cubic feet, or more of gas. Gas distribution incident reports (excluding those caused by leaks beyond the customer meter) for 2005 through 2023 show the following:

  • 9 percent of the incidents occurring on gas distribution mains involved cast iron mains. However, only 1 percent of distribution mains are cast iron.

  • 38 percent of the cast/wrought iron main incidents caused a fatality or injury, compared to only 19 percent of the incidents on other types of mains.

  • 34 percent of all fatalities and 16 percent of all injuries on gas distribution mains involved cast or wrought iron pipelines.

What Causes Iron Pipe Leaks?
The biggest threat to cast or wrought iron pipe is earth movement. If these pipelines are disturbed by digging, seasonal frost heave, or changes in ground water levels, leakage may occur.

Another serious threat called graphitization is a natural process in which iron degrades to softer elements, making iron pipelines more susceptible to cracking. The extent of graphitization depends on many factors, but gas may leak from the joints or through cracks in the pipe if graphitization has occurred.

When leaks occur on low-pressure systems with cast or wrought iron distribution lines, the volume of gas escaping through the failure point is much less than what might escape through the same size failure in a system operating at higher pressures. However, even a relatively small volume of natural gas leakage can have catastrophic consequences.

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.

Wrought iron pipelines were joined end-to-end using either threaded or compression couplings, while cast iron pipelines were linked using bell and spigot joints with packing material stuffed in the bell to form a gas tight seal. Since these pipelines transported wet, manufactured gas, the packing material absorbed moisture and generally did not leak.

As dry, natural gas began supplanting manufactured gas use in the mid-20th century, the packing material sealing the joints dried out, causing leaks. A variety of clamping and encapsulation techniques have been implemented over the years to repair the joints.

Distribution Integrity Management Programs
In late 2009, PHMSA implemented pipeline safety regulations for managing the integrity of gas distribution pipelines. Operators were required to create and implement Distribution Integrity Management Programs (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.

Specifically for cast/wrought iron, operators must have knowledge of the specific characteristics of the pipe and environments where graphitization could be severe. Evaluating past leak history and monitoring cast/wrought iron pipe during excavations are also key components of maintaining integrity.

National Transportation Safety Board Recommendations
The National Transportation Safety Board is an independent federal agency that conducts investigations to determine the probable causes of transportation accidents.

In 1986, the NTSB investigated an explosion at a restaurant in Derby, Conn., that killed six people and injured 12. The NTSB issued recommendations for corrective action only to the pipeline operator. In 1990, a natural gas explosion and fire killed one person, injured nine, destroyed two homes, and damaged two adjacent houses in Allentown, Pa. The NTSB report found that a water main leak eroded support under a 4-inch cast iron gas main. This ground disturbance results in a circumferential crack in the gas main. Natural gas migrated through the soil and into the basement of one of the homes where it ignited, exploded, and burned. The cast iron gas main was significantly weakened by graphitization.

In 1991, the NTSB recommended that PHMSA – then called the Research and Special Programs Administration – require pipeline operators to implement a program to identify and replace cast iron pipelines that may threaten public safety. PHMSA issued two Advisory Bulletins related to cast iron replacement programs.

RSPA Alert Notice 91-02 Encourages operators to develop procedures to identify segments of cast iron pipe that may need replacement. Reminds operators that pipeline safety regulations require generally graphitized cast iron pipe to be replaced and protect excavated cast iron pipe from damage.

RSPA Alert Notice 92-02 Reminds operators that pipeline safety regulations require operators to have a procedure for continuing surveillance of pipeline facilities to identify problems and take appropriate action concerning failures, leakage history, corrosion, and other unusual operating and maintenance conditions. This procedure should also include surveillance of cast iron to identify problems and take appropriate action concerning graphitization.

PHMSA Advisory Bulletin ADB-2012-05 In 2012, PHMSA supplemented the two RSPA alert notices asking operators and state pipeline safety representatives to monitor cast iron replacement programs, establish accelerated leak surveys, focus safety efforts on high risk pipe, incentivize pipeline rehabilitation, repair and replacement programs, strengthen inspection, accident investigation and enforcement actions, and install home methane gas alarms.