How cathodic protection prevents lightning from causing corrosion in pipelines
April 16, 2021 •Corrosion CONTROLLED, Corrosion Essentials, CP
Lightning-resistant remote cathodic protection (CP) monitoring devices are able to communicate potential problems with corrosion specialists in a timely manner.
Can lightning cause corrosion? It’s a question people don’t often consider; however, when it comes to pipelines, it’s a legitimate concern. While lightning itself does not cause corrosion, the damage it creates to a pipe’s walls, coatings, and cathodic protection (CP) system can leave a pipeline vulnerable.
“If we get a direct strike to an exposed piece of pipe, there’s a potential that it could cause a burst in the covering of that pipeline somewhere down further, which is not visible,” says Tony da Costa, VP of Engineering at Mobiltex Data (Calgary, Alberta, Canada). “Then, that exposed area would be susceptible to corrosion after that event.”
Because there are over 2,000,000 mi (3,218,688 km) of oil and gas pipelines in North America, the likelihood of a lightning strike to a pipeline can be high. According to a Mobiltex white paper, this is especially true in areas with a vast concentration of oil and gas pipelines, or areas more prone to lightning storms. Of even greater concern are areas in which both of these circumstances are true, like Texas. “Lightning strikes are very dependent upon the geographical region,” notes da Costa.
Numerous pipelines, along with the CP systems protecting them, are still inspected physically, as opposed to being remotely monitored. Technicians must perform inspections at specific intervals to determine the health and performance of the systems. Since a time lapse occurs between such inspections, the pipelines and equipment are left vulnerable to damage and the longer this amount of time is, the higher the risk. These time periods can be anywhere from several weeks to several months. Should a rectifier suffer a failure during the time between inspections due to lightning, there is no way anyone would know. Additionally, it’s nearly impossible to ascertain when the failure occurred, how much downtime has elapsed, or estimate the extent of possible corrosion.
Describing pipeline damage from lightning
The cathodic protection current in different parts of the pipeline is separated using flange inserts. Furthermore, they divide underground and aboveground pipes, i.e., pipes utilized at pipe stations. If a pipeline is directly hit by lightning, or even if lightning simply strikes nearby, the dielectric strength of the flange is customarily surpassed by the electrical energy. It is especially damaging to the pipe wall and insulation when this high voltage arcs across these pipe flanges or when it escapes to the ground.
Fortunately, ways to prevent this from happening exist in order to protect both the equipment and the workers. To guide the lightning’s energy away from the pipeline toward the ground, decouplers, cathodic isolators, and isolating spark gaps are used. They also aid in the protection of rectifiers in CP systems in much the same way. These protective devices can fail when a lightning strike overwhelms the rectifier, causing a great deal of damage.
Another issue occurs when lightning strikes nearby powerlines. “Usually when you get a lightning strike on a high voltage power line…there is an ionization of the air, essentially turning it into almost like a plasma, which becomes a low-resistance path,” explains da Costa. “It’s possible then that the high-voltage power line continues to feed an arc to the ground or another structure. So you can end up with periods of time where a significant amount of current is flowing beyond the initial lightning strike and that current can cause serious damage to the pipeline or structure that this flashover is occurring to.”
Because flashovers occur for a longer length of time than a lightning strike, they can cause significant damage to equipment, including pipelines and rectifiers. When the equipment is physically inspected, rather than remotely monitored, several weeks might pass with the pipeline left unprotected. The pipeline is then at risk for even further damage, such as corrosion.
Evaluating lightning impact
Remote cathodic protection monitoring systems gather real-time data from CP rectifiers and notify the operators of failures or changes in performance almost instantly. “To evaluate the impact there would essentially be an analysis of the data that’s being provided by the remote monitoring unit [RMU],” explains da Costa. “It’s looking for changes in the operational parameters, so if there is damage to a pipe, then the CP sources could be providing more current that is now exiting through that break in a coating. You could also be looking at the potential on a pipe—see if that’s changed as well. Now, with that break in the coating, the potential at a nearby test could be indicating that it’s no longer within the protection criteria.”
An RMU works by utilizing either satellite or cellular networks to gather performance data, which is transmitted to a cloud-based platform. Technicians have the ability to set normal operating parameters and receive notification when the equipment is not operating within optimal range. “They can be set up to send out automated alerts when parameters do change in the operation of the system,” says da Costa. “So they’re definitely an early indicator that something has happened. That can be followed up with more assessment—perhaps on site.”
Lightning-resistant remote CP monitoring devices are able to communicate potential problems with corrosion specialists in a timely manner. While some devices only send data at specific times, those equipped with two-way communication allow data to be accessed as needed. The information received, such as an undetectable amount of CP current or an amount of current that does not fall into the set parameters, can quickly alert operators to potential damage.
Additionally, these monitoring devices can provide data about the coupons located in the pipeline. If a change in current density were to occur, that could alert experts of an issue with the coating causing the current to leak into the adjacent ground. All of this knowledge, provided in a timely manner, supports well-informed decision making and a quicker response to repair.
The image below shows Mobiltex Data’s RMU3 remote monitors installed in rectifiers that were damaged by lightning strikes and continued to transmit data to the CorView platform. Due to their two-piece design, the RMUs are still able to function after a lightning strike and the damage is simply cosmetic and, once refurbished, can be used well into the future.
IMAGE: A cathodic protection, remote monitoring unit (RMU) damaged by lightning. Photo courtesy of Mobiltex.
Protecting cathodic protection equipment
The design helps to obtain a high level of immunity against lightning, and increase the chance that equipment not only endures a strike, but also continues to operate. Remote cathodic protection monitoring devices are in danger of lightning strikes when installed on the outside or inside of a CP rectifier and powered from the AC line power by a step-down transformer. Ensuring the RMU is able to absorb transient currents and is not bonded to the earth, alleviates the lightning’s effect.
“The CP systems would be in the form of coupling units that would be used to bleed energy off of the pipe in a controlled manner to a grounding system,” says da Costa. “Beyond that, there isn't much protecting the CP sources, so a rectifier and so forth could get easily damaged by lightning. As far as the monitoring units for CP, there are different techniques to try to minimize the impact of a lightning strike on the unit operation. In our case, we focus on using isolated ground systems and also energy-absorbing devices on our front ends to try to limit the damage.”
The bottom line, according to da Costa, is although nothing can be done to prevent the lightning from occurring, there are steps that can be taken to mitigate the risk of damage to this valuable infrastructure.
Find and/or validate certified Cathodic Protection professionals for your next project. Visit NACE International Institute’s Certificate Registry.
Source: Originally appeared on materialsperformance.com, authored by Rebecca A. Bickham, editor Materials Performance.
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