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
