Introduction and Background
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Introduction and Background IntroductionTo illustrate the progress pipeline operators are making in their efforts to replace aging gas distribution pipelines made of cast or wrought iron, PHMSA will now provide the public access to an annually-updated online inventory that lists high-risk pipeline infrastructure mileage by state. The online inventory allows users to view up-to-date information detailing replacement efforts from 2004 to the present, including the amount of cast or wrought iron pipe in use per state or pipeline operator. Cast and wrought iron pipelines are among the oldest energy pipelines constructed in the United States. Many of these pipelines were installed over 60 years ago and still deliver natural gas to homes and businesses today. However, the degrading nature of iron alloys, the age of the pipelines, and pipe joints design have greatly increased the risk involved with continued use of such pipelines. Transportation Secretary Ray LaHood issued a Call to Action in March 2011 urging states to promote pipeline safety awareness and pipeline operators to accelerate efforts to repair, rehabilitate, and replace higher-risk pipeline infrastructure – including cast iron pipelines, which have been at the heart of several recent tragic incidents that caused injuries and claimed lives. In January 2012, President Obama signed the Pipeline Safety, Regulatory Certainty, and Job Creation Act of 2011, which called for the DOT to conduct a state-by-state survey on the progress of cast iron pipeline replacement. For updates on the states’ progress, contact information and incident and mileage data, the public should visit PHMSA’s state pipeline profiles.
The amount of cast and wrought iron pipeline in use has declined significantly in recent years, thanks to increased state and federal safety initiatives and pipeline operators’ replacement efforts. Some states have completely eliminated cast or wrought iron natural gas distribution lines within their borders, including Alaska, Arizona, Hawaii, Idaho, Montana, North Dakota, New Mexico, Nevada, Oregon, South Carolina, Utah, Vermont, Wisconsin, and Wyoming. Approximately 97 percent of natural gas distribution pipelines in the U.S. were made of plastic or steel at the end of 2011. The remaining 3 percent is mostly iron pipe.
History 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.
Incident and Consequence Analysis
What Causes Iron Pipe Leaks? 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.
Recent Incidents Involving Cast Iron Pipelines January 9, 2012 – A home exploded on Payne Ave in Austin, Texas, 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.
Distribution Integrity Management Programs 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 In 1991, the NTSB recommended that PHMSA – then called the Research and Special Projects Agency – 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. |