Inspecting Buried Pipelines from the Air


When many imagine aerial pipeline inspections, they picture epic missions with low-flying helicopters tracking meandering, shiny pipes over rough terrain while taking high-resolution photographs in the hopes of finding the beginnings of a cracks before the pipe bursts, spewing oil into nature.

Trans Alaska Pipeline Credit: Michael Baker International

While some pipelines require this regular heroism, such as those crossing across Alaska, the majority of US pipelines are actually buried underground and pass under urbanized land of all densities, private property and infrastructure.

So how does aerial inspection benefit the operators and stakeholders of buried pipelines?

The reason for burying the pipeline is to keep it well out of the way of the activities and movements of humans, vehicles and animals and to protect them from the above and the elements with a thick barrier of compacted dirt.

A coated steel pipe being buried Credit: Mothership Aeronautics

Pipes are structurally relatively simple. A steel barrier keeps high pressure fluids inside, and everything else outside. Therefore, the prevention and detection of the degradation of the steel wall of the pipe and any contributory factors is the prime directive of pipeline maintenance.

The three prime evils of the pipeline world are corrosion, uneven thermal expansion, and impact or abrasion from external factors. Burying the pipes helps to combat each of these evils.

Corrosion

Corrosion of the steel pipes can be caused by a wide variety of factors, but in all cases requires an oxidation agent, such as atmospheric oxygen or an acid, to contact the steel. Corrosion can be mitigated with a barrier, such as a coating.

Pipeline coatings only work so long as they are a complete barrier: any small gap or scratch in the coating can allow corrosion to spread like a disease in the pipe, ‘infecting’ large areas of pipe surrounding it.

The layers of Earth covering a buried pipeline serve as both a physical and chemical buffer, preventing physical damage to the coating from impact and abrasion and from ionization caused by solar ultraviolet. Additionally, the soil serves as another layer on top of the coating limiting access of oxidation agents to the pipe.

Thermal Expansion

As steel pipes expand upon heating, and contract upon cooling, there occurs a fatigue on the pipe caused by daily and seasonal temperature fluctuations that the pipe can be exposed to. Similarly to a how a paperclip bent back and forth too many times snaps, harsh, frequent temperature cycles can cause cracks in the welds between pipes.

The soil layer eliminating wind and air flow over the pipe, preventing heat transfer by convection. It also blocks heat transfer by radiation, both from the sun to the pipe, and from a warm pipe to its surroundings. Therefore, buried pipes exchange heat primarily through conduction through the soil. While ambient air cools and heats rapidly between day and night, the soil only heats slowly during the day and cools slowly at night, and thus acts as a thermal buffer. This temperature equilibrium gets even more interesting if the pipes are carrying warm or hot contents, such as steam.

Physical Factors

Finally, consider the physical factors:

  • Hail falling on the pipe

  • Acid rain corroding the pipe

  • Avalanches or mudslides pushing rocks into the pipe

  • Birds perching on the pipe, scratching the coating with their talons

  • Rebellious teenagers grinding along the pipelines on their skateboard

  • A foolish bull decides to sharpen his horns scraping on the pipe

  • A tractor or road vehicle mistakenly scraping or impacting the pipe

  • Saboteurs or terrorists with power tools or explosives

  • Godzilla

The risks of any of the above are greatly reduced by burying the pipe, especially considering that much of US pipeline runs through private property under specific long-term land-use contracts called ‘easements’

Why aerial?

Now if buried pipelines are so well protected, why do we need to inspect them? The primary thing we look for when we perform aerial inspection of pipelines is to ensure that they are still buried!

Directly above the pipeline at the surface, pipeline demarcation flags create a centerline that shows where the pipe is buried. Twenty feet on either side of this centerline is considered the pipeline’s right-of-way and is protected by an easement contract with the landowner. These arrangements usually require that the entire right-of-way be kept clear of all objects and vegetation, and manicured such that the pipeline ‘scar’ can be clearly observed.

With aerial inspections we track over the right-of-way taking regularly spaced pictures to detect anomalies or disturbances over a length of pipeline.

  • Trees spotted in the right of way can be identified and quickly removed before their roots grow to impact the pipe.

  • Harsh rain or changing water levels in nearby rivers or lakes can uncover and expose buried pipes.

  • Stories of landowners trying to dig a pool over the pipeline in full violation of their easement terms and at extreme risk to their lives are abundant. Early detection of improperly placed construction projects can prevent environmental disaster.

  • Farms or industrial facilities illegally storing corrosive chemicals over a pipeline can be identified and notified.

  • Discolored or dead grass in the right-of-way can indicate the presence of a leak.

There are 2,500,000 miles of energy pipeline running across the continental United States. Almost 40% of US pipelines were laid before World War II, older pipes become more likely to experience corrosion, and be forgotten or overlooked by changing landowners. Frequent, high quality aerial inspection of pipelines is more important than ever.

Inspection of pipelines by manned helicopter can be very dangerous as helicopters must track the centerlines close to the ground, and expensive, often reaching $15,000 per mile per year. Additionally, helicopters and airplanes require appropriate facilities for takeoff, landing and fueling, which may not be located conveniently close to the pipeline sections to be inspected.

Pipeline Inspector Before Takeoff Credit: S Bjoralt

Often, high costs of aerial inspections forces operators to perform the minimum aerial inspection requirement imposed by the government regulatory agencies. This does not encourage a regular investment into a higher quality and frequency of data.

Our Earth sustains so many diverse and rich ecosystems. Preventing damage to it by conducting frequent, high-quality aerial inspections is so important.

In part two, we discuss the modern alternatives to pipeline inspection by helicopter, such as satellites and unmanned aircraft, such as planes, rotorcraft and lighter-than-air dirigibles and airships.

To contact the author, please e-mail jon@mothership.aero

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