Preinstallation Verification Test – Tension Contol (TC) Assemblies
The Preinstallation Verification Test is required by RCSC/AISC specifications. This test must be conducted on site to ensure that all bolt assemblies, lubrication, and installation tools can achieve minimum bolt tension prior to installation.
Pre-Installation Verification testing does not pass or fail fastener assemblies. This testing is designed to uncover possible issues between fasteners, tools and installers, before installation begins.
In this video, we tested a one inch tension control, or TC, bolt. TC bolt assemblies function by calibrating the torque needed to twist off the spline manufactured into the bolt shank. Once the pretension is above the minimum requirement, the bolt’s spline will twist off.
TC Bolt Preinstallation Verification Testing Steps
To perform the preinstallation verification test, ensure you have a properly calibrated Skidmore Wilhelm device, also called a Bolt Tension Measuring Device. Gather three bolt assemblies for each length, diameter, grade, and lot.
Put the bushing for the TC bolt onto the device, then put the bolting assembly, including nut and washer, in place.
Tighten the nut from the nut side with a hand wrench or non-impacting gun. This test does not permit the use of an impact gun.
Tighten the bolt with your non impacting wrench to the required load weight. The spline must break off at or above the minimum tension.
Repeat this test two more times and record results.
For the TC bolting assemblies to pass the test, the results must meet 105% of the value. If this doesn’t occur, first check your tool and try again with three new bolts. TC bolts cannot be altered with lubricants except by the manufacturer. However, if a hex assembly first fails the test, a stick wax lubricant can be applied before retesting.
Why TC Bolts Fail Preinstallation Verification Testing
There are a few common reasons bolting assemblies fail the preinstallation verification test:
One is lubrication. Without proper lubrication, the nut can spin and strip out the bolt.
Another common issue we see in the field is the internal socket on the TC gun being worn down. This makes it unable to grip the spline correctly and causes the bolt to strip. To avoid this, ensure your tools are in good condition prior to installation.
Another common problem resulting in failure is using the incorrect plate, incorrect direction of the plate, or incorrect bushing. Be sure you have the correct size plate installed as well as facing the plate in the correct direction. The plate or bushing can become warped overtime, so it’s equally important to inspect items before use. When testing Tension Control Bolts, wiping the plate clean of oil from previously tested bolts will reduce the risk of failure caused by additional lubrication in the assembly.