TC Bolt - Spline not cut off

[PT99]

Is a TC twist off A325 bolt where the spline did not come off considered snug tight and OK (SC is not required), or does snug tight only apply to standard A325's.

 

[phamENG]

A325 does not come with a twist off spline. F1852 does, though.

You say it doesn't need to be Slip Critical...what about pretensioned? They are not the same thing. SC requires surface prep to encourage greater friction AND pretensioning, pretensioned doesn't require surface prep.

As long as the requirements of the RSCS section 8.1 are met, I would think you'd be okay...though I'm not entirely sure how you get there since that kind of bolt/nut assembly requires a special wrench. And if you go through the trouble of paying extra for a TC bolt and use the proper wrench, why stop short?

 

[PT99]

The situation is that the special inspector is noting this on his report as a non-conformance item.

So the question is, is it actually is it possible to snug tight a F1852, (no SC no pre-tension)? Or should I direct that this bolt be replaced either with a A325 to snug tight or an F1852 properly installed.

 

[phamENG]

Or should I direct that this bolt be replaced either with a A325 to snug tight or an F1852 properly installed.

This is probably what I would do in this case.

 

[Agent666]

A snug tight bolt is not fully tensioned. Have a look at the criteria for snug tight and see you meet that definition. Usually involves words like effort of one person using some form of standard spanner and simply bringing plies together. What stops anyone doing this with a tension controlled bolt and leaving the spline, how is it different from a 'normal' bolt tightened the same way. No difference to me provided the TC bolt is the same diameter and grade.

https://engineervsheep.com

 

[BridgeSmith]

There is no way to assure (or verify) even a snug tight condition on a TC bolt - the head is domed, so there's no way to put a wrench on the bolt to keep it from turning while applying the torque to the nut.

I say have them use the tool to rattle the TC bolts (torque them until the spline shears off) or replace them with a standard A325.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[JLNJ]

I supposed you could calibrate a tool to a "snug tight" equivalent if you really didn't want to go through the effort of fully twisting them off.

 

[phamENG]

Rod - they do make manual wrenches for TC bolts, but I agree it's sort of a weird place to be and best to go all the way with the chosen option.

It's important to note that they would likely need to replace the bolts either way - TC bolts require proper lubrication, and you are not allowed to lubricate them on site (has to be done under controlled, factory conditions). Once they come out of the packaging, they have a clock before they have to be fully installed. If you miss it, you replace it.

Now, here's something we should all be aware of: ASTM F3148, Fixed Spline Bolts I saw them referenced in the latest Modern Steel. Make sure this isn't what you have installed. This is a great idea, especially for limited access bolting operations, but man is it going to make field identifying TC bolts a lot harder...

 

[Agent666]

There is no way to assure (or verify) even a snug tight condition on a TC bolt - the head is domed, so there's no way to put a wrench on the bolt to keep it from turning while applying the torque to the nut.

Yeah good point.

Maybe just replacing the bolts is the easiest and cheapest way to compliance. If you still have access for the tool, just replace bolts one by one and correctly install them. Assuming you can undo the nuts somehow to get them out.

https://engineervsheep.com

 

[BridgeSmith]

If the tool to tension the TC bolts is available, I don't believe there's any disadvantage to fully tensioning them.

Rod Smith, P.E., The artist formerly known as HotRod10