Saturday, June 16, 2018

Natural Gas Pipeline Explosions: Can They Be Prevented? Can Risk Be Minimized?


Natural Gas Pipeline Explosions: Can They Be Prevented? Can Risk Be Minimized?

The recent explosion of a TransCanada pipeline on Nixon Ridge in Marshall County, West Virginia begs some obvious questions and answers. When the pipeline was first placed in service less than 6 months ago, a TransCanada spokesman stated:

“We’re looking forward to generations of safe operations,” he added. “This is truly a best-in-class pipeline and we look forward to many years of safe, reliable, and efficient operation on behalf of our customers.”

-TransCanada Scott Castleman, 6 months ago in January.

The pipeline exploded in the first week of June just after 4 AM in a fireball fed by pressurized gas that could be seen for up to 20 miles away. Although that pipeline was shut-in as soon as possible the fire in the surrounding countryside burned for another hour or so, singing several acres of forest. What happened? The cause of the explosion is of course still under investigation. Corrosion is often the culprit in pipeline leaks and explosions in old pipelines, but this is a new pipeline presumably with standard anti-corrosion measures built in.

Chemist Richard Peekema notes that although the National Transportation Safety Board (NTSB), which investigates pipeline explosions, has determined that many are caused by mechanical failure of defective pipe, one might also conclude that they are caused by “explosive ignition of accumulated gas leaks from pipeline defects into surrounding air spaces.” This assumes that the pipes leak first then explode. An explosion requires two things: a leak of gas and an ignition source or spark. Other potential causes are improper installation (usually ineffective welding), excavation that disturbs a pipeline, and ineffective safety equipment. An explosion can become far worse if safety valves to shut off compromised pipelines are not there or are defective. Adequate leak detection and repair (LDAR) is very important for preventing potential explosions.

Newer high volume and high-pressure pipelines may cause larger explosions, higher flames, and larger ‘incineration zones’ around the explosion. This is one argument environmentalists use against these large high-pressure pipelines. If the zones of incineration from a potential explosion are larger then this suggests that setbacks from homes and other structures should be larger as well. I live about 500-600 ft from a transmission pipeline, so I wonder what the incineration zone would be here. Explosions may lead to fatalities, injuries, property damage including houses and structures burning down, and forest and brush fires. Often people are evacuated during an incident.

Statistics from the Pipeline and Hazardous Materials Safety Administration (PHMSA) show that in the U.S. in the last 20 years (1998 through 2017) there have been 807 serious pipeline incidents (+40 per year on average), 306 fatalities (+15 per year on average) and 1262 injuries (+63 per yaer on average). Although the number of incidents has dropped slightly over the time span the number of fatalities and injuries has remained fairly constant. Thus far, there is no evidence that there are more incidents, fatalities, or injuries since the advent of “fracking” and with more high-pressure, high-volume transmission pipelines. Some pipeline incidents are caused by third party excavation so this does not just reflect just natural damage or leaks due to faulty installation or welding. Both the PHMSA and the National Transportation Safety Board (NTSB) investigate pipeline ruptures and assess fines.

Wikipedia has an extensive list of pipeline leak, spill, and explosion incidents in the U.S. The U.S. has by far the largest network of natural gas, oil, gasoline, natural gas liquids, and jet fuel pipelines in the world. They count about 3200 significant or serious pipeline accidents since 1987. That averages to over 100 per year. These include oil and other liquids pipelines, compressor-station incidents, excavation damage, and distribution lines (distribution lines are small but urban ones can be extremely old and unsafe - some made of cast iron – many currently being replaced) so do not reflect just natural gas events. According to Wiki the causes of pipeline leaks and ruptures include bad welding, foreign material contamination into a weld, cracked pipe due to manufacturing defects, cracked pipe at a bend in pipe, external corrosion, internal corrosion, a corrosion crack at a weld, gasket failure, valve failure, external bacterial corrosion in wet shale, environmental cracking, dented pipe, excavation, mismatched pipe, landslides, and even pipe thought to be damaged in transport. Contributing factors have included rocky backfilling, not enough inspection and pigging, lack of external coating on old pipes, inadequate past repair, landsliding, and other earth and soil movement. Pressure testing with nitrogen can also cause pipe bursts but not explosions.

Pipeline “smart pigs” are used to inspect internal and external irregularities in pipes and welds. They can measure degree of internal or external corrosion and corrosion pitting. Some old pipes do not have external coating that protects against corrosion. Some of those have been ordered to be replaced. These days there is cathodic corrosion protection on new pipelines and some older lines are dug up and equipped with it. Pigging operations can also be dangerous if a pipe has a pre-existing leak and people have been killed during pigging.

If a pipeline accident were to occur resulting in significant loss of life due to the line being to close to people and habitations then public outcry might change and setback requirements (which may vary by state but I’m not sure) would likely be increased. There seems to be no indication thus far that high-pressure lines and those with larger volumes are more likely to explode. The bigger pipes have thicker walls and are pressure tested before being placed in service. Environmentalists against pipelines have jumped on the danger of big high-pressure lines carrying “fracked gas” (as if it were different from non-fracked gas – anyway most gas is now fracked gas and that will increase).

I wonder what the likelihood would be of say a mile section of pipeline exploding. One might simply divide the number of explosions by the number of miles of pipeline. The PHMSA lists that there are 300,635 miles of transmission pipelines in the U.S. (as well as 927,011 service miles, 18,358 gathering miles, and 1,308,665 distribution miles – so 2,554,668 miles overall) and we assume about 50 transmission line explosions per year (guesstimate – probably less actually), then there is about a 1 in 700 chance that a pipeline will explode in a given year within about a mile from anyplace. If incineration zones are 500-1500 on avg. (another guess – say 1000ft avg) then that means that about 1/5 or 20% of the section within each mile will be in an incineration zone. This suggests that the risk of a section of pipeline being in an incineration zone is about 1 in 3600 in a given year. If we extrapolate that to a 30-year period that would be 1 in 120 so less than a 1% chance that a given section of pipeline will be part of an incineration zone in a 30-year period. So, the overall risk is small, but the results could be catastrophic. One might say that the risk of getting in a car accident is greater, probably much greater, than having an explosion occur nearby and certainly very far greater than getting hurt in one. Even so, it is possible. These explosions happen and can be disconcerting and possibly horrific to experience close up. People do die and get injured. Houses and barns burn down, Forest and brush land is burned – even if the risk of it happening to a certain person or place is small.

Addendum – I also see from the PHMSA site that about 10-12 % of the incidents were transmission lines and 15% of the fatalities – that means that my numbers over-estimate the risk by more than triple. Meanwhile over 80% of the incidents and over 70% of the fatalities are from distribution lines. This means that even though environmentalists call transmission lines “buried bombs” they are far less likely to explode and one is far less likely to die due to on exploding than for distribution lines. Thus, if they are truly interested in saving lives and lessening incidents they would be better off promoting replacement of old distribution lines than protesting against transmission lines. Graph below shows that transmissions pipeline explosions have not increased in the last 20 years (and through the advent and normalization of “fracked gas”) nor have fatalities.





References:

Causes of Natural Gas Pipeline Explosive Ruptures (Abstract) – by Richard M. Peekema, Ph. D., in American Society of Civil Engineers - Journal of Pipeline Systems Engineering and Practice, Vol. 4, Issue 1, Feb. 2013

Pipeline and Hazardous Materials Safety Administration 2018 (website/portal)




List of Pipeline Accidents in the United States in the 21st Century, in Wikipedia


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