The Importance of Proper Manufacturing, Design, and Installation of Slip Splices

At a Glance:

• Tubular steel poles’ sections are most commonly joined by slip splices which are the easiest method to manufacture, but they’re not without their flaws.
• Proper manufacturing, welding, and installation are crucial components in the longevity of these slip splices and the assets they hold together.
• Exo will protect these assets and their components with proactive detection and remediations.

 Tubular steel poles are made in multiple sections. These sections are joined by utilizing flanges or slip splices. There are design and cost considerations for each, but slip splices are by far the most common way to make connections between tapered tubular pole sections. Like any other component of steel poles, slip splices rely on proper manufacturing, welding, and installation to carry out their intended purpose. As an owner of steel assets, understanding each of the components that hold your steel poles together is imperative to avoiding catastrophic failure and liability issues.

What to Know About the Components of Your Steel Assets

What Asset Owners Should Know About Their Slip Splices

The telescopic slip splices that hold steel assets together are by far the easiest method for a manufacturer to fabricate, but there are some key design, manufacturing, and installation details that need to be considered to ensure the proper fit and function of the joint. The moment transfer occurs between the sections cause very large shear forces and hoop stresses across the joint. These stresses can lead to the splices becoming compromised which will weaken the steel structure as a whole.

Luckily, there is a standard in place to ensure proper measures are taken so that structural engineers and all involved in the electric power transmission industry are guided during the designing and building of electrical transmission lines. This standard is called ASCE/SEI 48-19 Design of Steel Transmission Pole Structures addresses many of these requirements, so that  a simple oversight in the manufacturing, installation, or design doesn’t lead to a catastrophic failure.  

How ASCE48 Affects Every Detail of Tubular Steel Assets

Understanding the importance of ASCE48 can allow the asset and its components to reach their full intended lifecycle. Field issues can be minimized by ensuring the sections of tubular steel poles are properly fabricated during the manufacturing process and fit properly in the field without gaps to avoid issues from corrosion. 

ASCE/SEI 48-19 Design of Steel Transmission Pole Structures directly guides affects these processes and standards:

• Slip Length
• Welding
• Installation

 Slip Length: ASCE48 section 6.4, ensures that the minimum slip length between the sections shall be not less than 1.5 times the maximum inside diameter. The ability to achieve this minimum length is a combination of manufacturing tolerances (diameter variation, flat widths, bend radius, the squareness of sections, cutting method), installation practices (alignment and application of sufficient force across the joint), and workmanship (clean welds, minimal slag). 

The 1.5 times the maximum inside diameter measurement is a general practice that was developed years ago through testing. Since then, changes in the size, scale, tighter design margins, and design practices have changed, including the increased use of the thinner plate, increasing w/t ratios, which result in noncompact sections in slip joints. These sections are hyper-sensitive to any slight mis-fabrication, which in turn may not fully develop the strength of the joint upon installation, making the pole vulnerable to unpredicted local buckling. With the proper precautions in place, slip lengths will be measured every step of the way, allowing for proactive testing and insight of these vital assets. 

 Welding: Per ASCE48 Section 6.4, “The outer section longitudinal seam weld in the area of the splice shall have full fusion through the section thickness and complete joint penetration.” This requirement allows the tube to resist the large hoop stresses that can be present in a joint of this type. Improper fusion, porosity, or positional alignment issues in the section can cause the seam to separate and the pole joint to fail. Additionally, failure to properly clean up this weld after fabrication can cause fitment issues in the field that can compromise the joint. By holding welders and manufacturers accountable for the precision of the weld, an asset owner will have a comprehensive handle and understanding on every part of their structure. An asset management program for slip splices is essential to obtain this kind of actionable data.

 Installation: The pole joints must be installed per the manufacturer’s recommendations. This typically requires the sections of the steel pole to be properly aligned and pulled together to the minimum length mark and the specified load. Any gaps or slip lengths below the minimum required should be reviewed by the manufacturer’s engineer to determine if the joint is acceptable. Doing so can avoid major liability issues and catastrophic failures once the steel asset is in the field. 

The Exo Difference 

Identifying manufacturing and design issues early allows preventative or corrective measures to be taken before there are installation issues or pole failures. Doing so limits risk, extends the life of assets, and prevents damage to other equipment. In-plant inspection and oversight can eliminate issues before they reach the field, saving time and money and helping to ensure the proper fit and function of your new pole structures.

Exo offers many solutions for steel poles. From our vendor surveillance services to our Ex-Tend program, we offer the actionable data you need to understand every detail of your tubular steel poles and their components. An asset management program with Exo should be your first step in ensuring your transmission assets reach their full intended lifecycle, enhancing your reputation as a reliable power source and promoting overall grid resiliency.

Get Started with Exo

Ready to Work With Us?