Inspection

How Exo Remediated Severe Corrosion on Aging Steel Transmission Poles Without Disrupting Service

August 11, 2021

Everyone wants reliable power. Our homes, businesses, and all of society can’t survive without it, and reliable power relies on overall grid resiliency. One of the biggest threats that we see with the steel poles and lattice towers that make up the grid is corrosion. 

Historically, utility owners were told these assets would last forever after installation. At Exo, we know that is clearly not the case. After years of wear and tear, there could be an extensive amount of damage depending on service territory, age, and type of asset. And unfortunately, needed repairs are often overwhelming for an asset owner’s budget and timeline. But if remediations don’t take place, corrosion can degrade the structural performance of steel poles and towers, lead to catastrophic failure, cost the asset owner a lot of money, cause liability and safety issues for the public, and lead to unplanned outages.

These catastrophic outcomes could have happened to our client, Westerville Electric, a public power provider in the suburbs of Columbus, Ohio. But luckily, due to their partnership with Exo, we were able to remediate and maintain their assets with no disruption to the grid resiliency. 

What to Know About Corrosion of Aging Steel

What Was the Issue With Westerville Electric’s Steel Poles?

Westerville Electric owns a 69kv transmission line that was built in the early 1970’s. This structure was built with “Cor-Ten” steel, which was, at the time, thought to be “maintenance free”. Naturally, Westerville Electric didn’t implement much proactive “structural” maintenance for years due to the way this steel was billed to asset owners in the 70s. However, in 2018, they noticed a crack in one of the steel poles.

 

They learned that the crack was caused by pack rust, a type of corrosion that occurs due to atmospheric conditions within restricted spaces. The damage had occurred near the groundline where conditions made it difficult for the “self-weathering” patina to form and protect the pole. Because of the location, corrosion at the groundline can be difficult to discover and repair. 

They knew it was likely that other poles in the transmission line had issues, so Westerville Electric decided to conduct a comprehensive structural inspection and corrosion assessment of the remaining 109 steel poles. Severe degradation that significantly reduces the wall thickness of the shaft can be measured accurately using a VWAC gauge or an ultrasonic thickness gauge. From there, a structural engineer can determine the remaining load capacity of the pole and evaluate its current strength in relation to the original load cases the structure was designed for. 

Since these poles were located near a popular recreation trail and in residents’ backyards, they had to be repaired as soon as possible. Westerville Electric began the repair process on the cracked pole to keep it standing but knew it was a serious risk to pedestrians. After excavating the ground around the poles and performing nondestructive testing methods to understand the severity of the corrosion across the pole, Westerville Electric knew they had a big problem on their hands. They had to make repairs fast, and they knew it would be difficult to find a partner who offered turnkey solutions to mitigate the corrosion issues without turning off service to their customers. 

Luckily, they contacted Exo to execute the needed repairs. We offered them turnkey solutions from structural engineers and technicians with experience specific to steel poles and lattice towers.

What Solutions Did Exo Implement?

Our inspection program was completed in June of 2019 and brought to light the problem that was facing the utility. 70 of the 109 poles required some level of intervention, ranging from coatings application to full structure restoration or replacement. Twenty nine of those poles suffered significant wall loss but it was imperative that power keep running throughout the transmission line at all times; so tearing them down and rebuilding wasn’t an option. To remediate these issues, Exo designed, fabricated, and installed splints to the base of the steel poles at the groundline where the corrosion had been discovered. 

The splint solution was equally robust as it was flexible. A series of interlocking channels that, when bolted together, would form a collar around the pole. The splint was adjustable and could latch onto the poles with a range of diameters, tapers, and even ground sleeves. Combined with a barrier protective coating on the pole/components and cathodic protection in some cases, the splint offered corrosion mitigation, prevention, and full structural restoration.

How Is Westerville Electric Doing Now?

Westerville Electric was able to restore the poles to their original design capacity, and under budget. They now have peace of mind knowing that the transmission line corrosion remediations are effective. Because of their diligence and partnership with Exo, their reputation as a power company who puts their customers first was also protected.

Ready to Work With Us?

If you need corrosion remediation services on your steel poles, work with a partner who offers turnkey solutions on budget and time. Our team would love to talk to you so that we can learn about your company’s goals and primary areas of concern. Contact us today, and we’ll help you take the first step in creating a comprehensive asset management program. Give us a call at 281-259-7000.

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