Over Torquing bolts

If you over torque a bolt can you back it out and torque it properly and use it?

For example if a bolt requires 70 ft. lbs and you accidentally go to 90 ft lbs, can you loosen it and re torque it to 70 ft lbs and all is well?

Or does over torquing require the bolt to be replaced?

thanks

Replace

Replace. The bolt strength is compromised.

Check the torque chart published in AC 43.13-1B, as it has a Maximum Allowabled Tightening Torque value. If you exceeded that torque value, throw away the fasteners. If you did not exceed that value, loosen it off, and retorque.

As Kevin's document shows, most recommended torque values are well below the fastner's yield. This is done so that the bolt, once torqued, still has more elongation available before it's yield strength or where the fasteners strength is compromised and is therefore less likely to break when additional stress or force is applied from the parts held in tension. If all of your bolts were torqued to the point where they could not stretch further, you would find most fasteners broken after an impact like an accident.

Ultimately torquing a bolt is really all about elongation and some engine builders even use bolt stretch gauges instead of torque for key fasteners, such as connecting rod bolts.

Larry

I second what others have said, if the max torque wasn't exceeded carry on, if so replace. However, if you have the spare bolt around I personally would replace it anyways as bolts are mega cheap (most of the time).

Over Torquing Bolts

lr172 said:

This is done so that the bolt, once torqued, still has more elongation available before it's yield strength or where the fasteners strength is compromised and is therefore less likely to break when additional stress or force is applied from the parts held in tension. If all of your bolts were torqued to the point where they could not stretch further, you would find most fasteners broken after an impact like an accident.

Click to expand...

Not quite true. In critical one time use applications it is not uncommon to torque the bolt to 90% of its yield strength. In a tension application, it's a little counter intuitive, but in order to put additional stress on the bolt (and potentially break it), the joint has to open so the bolt sees additional elongation. It's a little more complicated than this, and the relative stiffness of the bolt(s) and joint materials must be considered, but in general this is true.

I agree with other comments to the OP, if the bolt was torqued beyond recommended torque for that size fastener, replace it.