FTM 121: ROCAP Testing

Fastener Training Minute 121: ROCAP testing for structural nut and bolt assemblies

This edition of the Fastener Training Minute with Carmen Vertullo was originally published October 30, 2017 as “ROCAP Testing” during episode 121 of Fully Threaded Radio.

Hello everybody. This is Carmen Vertullo with the Fastener Training Minute coming to you from the Fastener Training Institute and the Carver FACT Center here in beautiful downtown. El Cajon, California.

Today’s topic is ROCAP testing. Now. You probably have heard the word ROCAP and you don’t know what it means or maybe you do. If you’re in the structural bolt business you absolutely positively should know what it means and you absolutely positively should know all about it. But the other side of the coin is even if you’re not in the structural bolt business, ROCAP testing is a very interesting principle that informs us about how nuts and bolts work in general. So it’s a good thing to know about it. When we come back, I’ll tell you what the ROCAP test is and why it matters to you.

Well, welcome back everybody to the Fastener Training Minute And today you’re going to talk about the ROCAP test. ROCAP is short for ROtational CAPacity. Sometimes called the RC test as well. It’s a peculiar test in that it only applies to one type of Fastener. And that is the structural bolt that is used for bolting steel together. Generally. This is a requirement for ASTM A325 hot dip galvanized fastener assemblies. When we say an assembly. that’s an important word, because it means that we have a nut a bolt and a washer as an assembly. The object of the game with the rotational capacity test is to ensure that when we put these components up in the steelwork, we know that they’re going to function properly.

So before we do that we do this test on the ground or in the lab to make sure that the nut actually is able to work in conjunction with the bolt and the washer to achieve the tension that’s desired within a safe margin. Now one of the reasons why this applies in particular to hot dip galvanized fasteners is because with hot dip galvanized structural bolting there is a very high friction in the joint because of the hot dip galvanizing on the threads of the bolt. Now the nut is over tapped, it doesn’t have any hot dipped galvanized zinc in the threads, but it’s dry. Generally there may be a little bit of lube left over from the tapping process, but that’s not enough. So what we do is we put wax on those nuts and sometimes the wax is visible. It will be a blue color or red color or a green color, depending on the manufacturer’s process. It is not required to have that color unless specifically asked for. There’s a general feeling that it should be colored but it’s not required.

So the object of the game with the rotational capacity test is to ensure that the lubrication which is on the nut, in the threads of the nut, and on the bearing surface of the nut, provides us a relief of the friction. That is a lubrication that will enable, with a certain number of turns and a certain amount of torque, to give us the tension that’s available as well as to ensure that the bolt has good ductility.

So the rotational capacity test works like this. Well actually there two different types of rotational capacity test, so let me start with the old type or the simpler type. That used to be under ASTM A325. We simply installed the bolt in some steel similarly to how we would do it in the structure. We snug the nut down and then we put a mark on the nut, and we also put a mark on the socket that goes on the nut, and we also mark the steel. Then we would rotate the nut to a certain number of degrees, well beyond what it’s normal tension would be, then we would disassemble it and make sure that there was no damage to the threads in the nut. The bolt is actually allowed to stretch, its allowed to yield but we are not allowed to damage the threads. We do same test with three assemblies. We have a good test.

Now as time rolled on certain entities particularly our transportation department (DOT), and other state transportation departments, and people like us, the state architecture departments developed a more sophisticated rotational capacity test in which not only did we measure the amount of turns on the nut and determine that we didn’t fail with a certain number of degrees of rotation. By the way, the longer the bolt is, the more the degrees it is required to turn. It’s generally somewhere between a third of a turn, and a turn and a third, that’s more than one full turn. That’s a lot of turns even for a long bolt.

And so now with the newer test under ASTM F3125, we need to not only measure the number of turns, but we’re also going to put this in a device called a Skidmore-Wilhelm Bolt Tension Calibrator. We’re going to measure the load and we’re also going to measure the torque. There are some interesting formulas that go into this. Essentially want we want to make sure is that with a given amount of tension applied, we achieve that tension before we exceed a certain amount of torque. Likewise as we go to further turn the nut to the maximum number of turns, we want to make sure we get there before we exceed a given amount of torque, while also achieving a certain amount of tension. So it’s a relatively complicated test and it used to apply only to ASTM A325 Grade hot dip galvanized assemblies. Now it can apply to anything if the end-user asked for it.

So there are two instances when we need a rotational capacity test. One is; if we have an ASTM F3125 grade a325 hot dip galvanized structural bolt assembly, it doesn’t matter whether it’s asked for or not, it must be done. The other instance is, whether we have ASTM A325, ASTM A490, tension control bolt, whether it has a coating or not, if the end user requests it, then we have to do the rotational capacity test. These tests sometimes pass, sometimes they don’t. There’s no guarantee that just because all of the components of the assembly, the nut, the bolt, the washer, and the coating all meet their specific requirements, there’s no guarantee that when we marry those all those four things together, that we’re going to get an assembly that will pass the ROCAP.

So just beware that there’s some risk involved as a structural bolt supplier. You should know all about the ROCAP test, as even someone who’s not supplying structural bolts, I think it’s kind of a cool thing to know about because it informs us regarding fasteners.

And once again, if you need some training on this subject contact the Fastener Training Institute. The Fastener Training Institute provides training on structural bolting, and you’ll learn all about the ROCAP test there, maybe even get to do one in person.

This has been Carmen Vertullo for the Fastener Training Minute. Thanks for listening.

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