8 Welding Challenges in Steel Pole Transmission Structures
Constructing a steel pole transmission structure typically requires a series of welded assemblies. These include folding the pole shafts and plates and joining the edges of the plates with seams. The resulting tubular shafts are then welded to flanges or other brackets to join them together, and insulators are attached to some type of plate welded to the arms or pole shafts.
What makes all of these welding connections challenging is they can either perform as they were designed, or they can be at risk for catastrophic failure. Welding is considered the most significant quality element in steel pole maintenance and manufacturing, but it can be hard to understand.
So instead of risking public safety and relying on in-field weld repairs, we’re here to help make some of it clearer.
What Is Welding?
According to the American Welding Society, welding is defined as a joining process that produces coalescence of materials by heating them to the welding temperature, with or without the application of pressure or by applying pressure alone with or without the use of filler metal.
When it comes to steel poles, most welded connections use processes that add filler metal, which results in deposited weld metal consisting of a dilution of the base metals and the external filler metal. Welding processes must be properly engineered to produce consistent welds that meet the expected quality and mechanical properties. Additionally, it’s important to understand the strength of the deposited weld metal and its effects on the adjacent base metal, also referred to as the Heat Affected Zone (HAZ).
Common Welding Challenges
Challenge #1: Proper Certification
First and foremost, the engineers welding your connections must be properly certified for the welding process and positions the joint requires. The skill required for the individual welders will vary based on the positions used, whether flat, horizontal, vertical, or overhead.
Challenge #2: Appropriate Process
You’ll need to ensure that the pole supplier’s welding process is appropriate for the type of connection/joint being welded. All four of the major welding processes—Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), Submerged Arc Welding (SAW), and Flux Cored Arc Welding (FCAW)—are used to varying degrees in the fabrication of tapered tubular steel poles. The two most common processes are FCAW and GMAW.
Challenge #3: Joint Assembly
The joint must be assembled as designed, and all tolerances for fit-up must be properly met to prepare the connection/joint for welding. There are joint tolerances provided on a typical welding procedure specification (WPS) for root opening, bevel angles, weld capsizes, etc., that need to be carefully followed.
Challenge #4: Material Specifications
The materials being welded must be the ones specified and consistent in mechanical properties with the materials used for the WPS and the tested procedure qualification record (PQR). When you develop a very specific WPS for welding a particular joint and the subsequent testing of the WPS with a PQR, you can ensure the weld performs as it was intended to perform.
Challenge #5: Heat Distortion
You want to assemble welded plate connections so that distortion caused by heat doesn’t create quality issues. With this, you need to consider whether the joint is a highly constrained weldment or a non-constrained weldment. The more highly constrained it is, the higher the residual stress as the weld cools and shrinks.
Challenge #6: Inspectability
Be sure that the quality of your welding will pass the necessary inspections. These inspections will depend on the type of welds and welded joints. Complete Joint Penetration (CJP) welds are expected to have 100% fusion of the plates in the joint and are tested by either ultrasonic or radiographic methods. Partial Joint Penetration (PJP) welds, on the other hand, are only expected to have a partial depth of fusion and are visually inspected for workmanship-related deficiencies.
Challenge #7: Heat Monitoring
It’s important to closely monitor pre-heat, heat input during welding, interpass temperatures, and post-weld cool down temperatures. Heat input from welding influences the cooling rate, which may result in undesirable effects on the mechanical properties and the metallurgical structure of the deposited weld and HAZ.
Challenge #8: Hot-dipped Galvanizing
The effects of hot-dipped galvanizing need to be monitored both during welding and after galvanizing. Shaft side, HAZ “toe cracks” can develop within these types of welded connections due to various residual stresses; be sure to watch for these so you can maintain high weldment quality.
Preserve Your Welding Connections
As demonstrated above, it is challenging to ensure high-quality welds when fabricating connections in steel transmission poles. But, most of these challenges can be minimized by paying attention to industry standards, the skill of your welders and quality of your materials, and a properly implemented transmission line maintenance plan.
Ready to Work with Us?
Our team would love to talk to you, so we can learn about your company’s welding 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.