Customizing a Lattice Tower Structural Health & Corrosion Assessment Program

Corrosion damage is one of the more pervasive threats to the structural integrity of steel poles, lattice towers, and other utility transmission assets.  For a material type that was once considered relatively maintenance free compared to wood structures, the industry is now realizing that steel structures do, in fact, require proactive inspection and remediation. 

One of Exo’s utility clients recently acquired an aging transmission line that was built way back in the 1960s.  In doing so, they expanded their capacity to serve more customers and grow their revenue base. But they didn’t perform a conditional assessment of the newly acquired line as part of their due diligence, which posed some challenges for their long term asset management program.  They turned to us to assist them with a comprehensive, holistic inspection program which would determine the true health of the line, and make practical repair or replacement recommendations to be incorporated into their long term operations strategy.

Visual inspections can be helpful in situations like these, but utility linemen, construction crews, and others may not have the appropriate qualifications and experience necessary to properly diagnose potential structural risks that could lead to catastrophic failures, collapse, and service interruption. Exo was able to develop and execute a plan that helped ensure the structural stability of some of our client’s most vulnerable lattice towers. Here’s how we did it. 

Structural  Health and Corrosion Assessment  

To help the utility establish the most appropriate and optimal O&M strategy moving forward, we tackled two central questions: 

• What is the current condition of the line?
• What immediate maintenance needs exist and what is the remaining life expectancy of the asset?

The Problem: Potential Corrosion of Lattice Tower Legs

After conducting a thorough review of the line and its history, Exo found potential corrosion of lattice tower legs at the ground line as an area of concern, making corrosion assessment a key priority for the overall inspection. 

Because the effects of corrosion on lattice towers are usually at or below grade, and can slowly progress unnoticed, excavation is necessary to determine the true extent of any degradation present before catastrophic failure and service interruption threatens a transmission line’s safety and operability. 

In this case, there wasn’t the time or budget to fully excavate and inspect every single structure on the line, which numbered several hundred structures and spanned a large area. But safety was still paramount, so that meant inspection remained a top priority to stay ahead of any necessary field service and repair. 

The Solution: Data-Driven Risk Management

We needed a cost effective and time sensitive solution for the overall assessment of this line.  To achieve this, Exo employed a data-driven strategy. Rather than conducting a purely random sampling of the towers, we developed a method of rating and ranking structures according to their overall risk of corrosion.

In this case, we used soil conditions to better pinpoint high risk areas since various chemical and physical properties considered together can highlight areas of increased corrosivity potential. 

1. We used publicly available data to create a composite soil corrosivity map. 
2. We then plotted the transmission line over this map to see which structures fell in critical areas whose soil conditions put the lattice towers at high risk for corrosion. 
3. From this data set, Exo selected those structures to be excavated and inspected.

With this new information in hand, it was time to execute the field inspections and assess the overall structural health of the line. This phase of the project included:

• Excavating around each of the four lattice tower legs to provide access for evaluation
• Cleaning dirt and scale off of the members to get an clear look at the state of the lattice tower legs
• Completing visual inspections to check for any observable signs of discoloration, deterioration, and other structural damage associated with corrosion
• Measuring the thickness of the tower legs to determine if there was section wall loss due to corrosion

Our analysis determined that there was, in fact, no significant loss in thickness or visual damage, meaning corrosion degradation was minimal even on the higher-risk, aging structures. A simple coatings upgrade would suffice for proper life extension of the asset. This was great news for the utility asset owner. Had we excavated to find significant corrosion on our sample set, a much more expansive inspection, field service, and repair solution would’ve been required, at a substantial cost to the client. 

Our customized approach to asset management gave our client peace of mind that the rest of the structures on this line were likely to be free from corrosive damage, saving them the significant time and resources otherwise required to maintain and operate the line.

Partnerships for Longevity and Stability

If you’re a utilities leader, you know the cost of leaving your steel pole or lattice tower line vulnerable to rust, corrosion, and other structural damage. Exo offers alternatives to steel pole and tower replacement whenever possible. And when it is time to replace, we help you customize a plan for a smooth transition that optimizes cost savings. If you think you may be facing similar challenges with corrosion or other structural deficiencies, don’t wait. Act now!

Talk to us today about how we can optimize steel pole and tower performance and eliminate unnecessary service interruption of your transmission lines for your valued clients.

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