FTM 198 – how do I know if a bolt has been properly tightened?”

Fastener Training Minute 198 - How do I know if an installed bolt has been properly tightened?

This edition of the Fastener Training Minute with Carmen Vertullo was originally published March, 18th 2024 as “how do I know if an installed bolt has been properly tightened?” during episode 198 of Fully Threaded Radio.

Well hello everyone, this is Carmen Vertullo with your Fastener Training Minute,  coming to you from Fastener Training Institute and Carver Labs in beautiful El Cajon California.

Today’s topic, like many, came from an email inquiry and the question was sort of like; how do I know if an installed bolt has been properly torqued? Torqued was the actual word but tightened might be a better word. How can we tell after the fact, after an assembly has been put together, whether or not the fasteners were properly tightened? Well one of the ways we can do that is with the process called a torque audit, and when we return I’m going to tell you all about the torque audit and maybe a few things that most people don’t know.

Welcome back to the Fastener Training Minute this is Carmen Vertullo, and today we are talking about the torque audit. The torque audit is a method by which we can ascertain if already installed fasteners, that is nuts bolts and screws, have been properly tightened. There are three different basic types of torque audits.

The first one in the most popular one, and is called the first movement tests and basically if we know the fastener was supposed to be tightened to a certain torque, (let’s say 30 ft lb) we will take an indicating torque wrench, not at clicker torque wrench. An indicating torque wrench has a dial and a memory needle, so it remembers the torque, or some sophisticated electronic version of it, which are far easier to come by and cheaper than they used to be. We put that torque wrench on there and we tighten it and see when it moves. Now if it moves at less than 30 ft lb, we can say that it probably was not tightened to 30 ft lb. It should move just above 30 foot pounds because it takes a little bit more torque to get a Fastener started than it took to get it where it was torqued to, That’s the first movement test. Now it doesn’t necessarily mean the part was improperly torqued, because sometimes you can have relaxation of the joint, and so this test would indicate one of two things: either we had some relaxation in the joint if the torque was low, or it was not torqued to the right amount if the torque was low, or if it was over tightened if the torque was too high.

The second type is called the loosening test, and this is similar to the process we just described called the first movement test, except this time we move the fastener in the loosening direction and we see where it breaks loose. This also should be slightly higher than the specified tightening torque. These are the two most popular tests.

The third test is called the marking test, and we take the tightened fastener and we clearly mark the surface of the fastener, (the nut, the bolt, the washer or whatever) and the clamped surface for a reference. We just put a mark there, and then we loosen the fastener, and then we re-tighten it until the marks line up again. And we see what that torque was. If that torque is similar to the required torque, we can presume that the fastener was most likely tightened properly in the original installation.

Now one of the things that most people don’t understand about this process, is that it’s much more powerful if you know what the original torque was, and then you’re coming back and saying; okay I knew that was properly torqued at the time, now I’m checking to see if it actually was properly torqued. If you know what the proper torque is in the beginning and you know that torque was applied, then this process has a much better chance of indicating that the torque is correct. If you’re just walking up upon a situation, and you don’t know what was done to it initially, then you don’t know, Another powerful thing about it is that if you know what the original torque is is, you now know okay it was properly torqued at 30 ft lb and it’s breaking loose at 35 ft pounds. So I know when I’m doing the torque audit that I should get a 35 ft lb break loose if it was properly torqued, or I know I will get a 40 ft lb requirement to get the fastener in motion in the tightening direction.

So, those are essentially the three choices that we have. The first movement test, the loosening test, and the marking test. I think the first movement and loosening tests are easier and simpler to apply, especially if we have reason to know what that loosening should be based on the part having been properly tightened in the first place. If you want more information on the birth

work audit you can email me, or you know how to get a hold of me when you see me. I have a couple of documents that will help you  to put this process into practice.

This has been Carmen Vertullo with the Fastener Training Minute, thanks for listening.



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