Topic: How much do you decrease torque values when using anti-seize on bolts?

[Tugboat]

Is there a set percent?

[donpark1086]

Good question Tugboat.

I use an anti-seize that is copper and lead fine particles dispersed in a light oil.  My guess is that bolt or stud stretch will increase a bit with anti-seize present.  But I've torqued to specification for years with this goop present with no ill consequences.

But to quantify this would be an experimental determination.

I have a 1 inch micrometer generally good for 1/10 thou.  Measure the bolt stretch without then with anti-seize.  It might take several repeats to get a good average.

It would be better if I had a 2 inch micrometer.  Do you have one?

[donpark1086]

Tugboat:

There is some information out there.

"I took a ten millimeter, grade 8.8, 1.25 thread, bolt, then put a spacer and nut on it. With the nut loose I measured the over all length of the bolt. I then torqued it to thirty five foot pounds with a torque wrench. Then I measured the it again. 3.022" to start. Then 3.026" after torquing, so we have .004" bolt stretch. Doing the same thing with the bolt threads lubricated with Molybdenum Disulfide grease. The bolt stretched to 3.027". So lubed, we have .005" stretch. That's about a 20% increase. I was surprised to find that getting an accurate, repeatable measurement was quite difficult."

http://www.dansmc.com/bolts2.htm

This came from a hobbyist and not a laboratory.

I'll see if there is a more definitive study easily found.

[SOHC Digger]

Tugboat:  it's refreshing to find someone taking this into account.  I have read articles about how lube of any kind on a fastener leads to distorted torque values, excess clamp force, and premature fastener failure.  I did find this table:  http://www.mzind.com/M_Z_Suggested_Assembly.pdf  which lists values for "Dry" and "Lubed".  I would imagine the difference in torque between a bolt lubed with Moly and one lubed with Anti-seize would be negligible, especially considering most people don't take lubing into account in the first place.

Coincidentally, the difference in values corresponds to the 20% donpark1086 refers to.

[BobbyR]

I used to teach torquing in our shop. The Industry standard is 20% for a "wet" torque. The reason is that the reduction in friction between the threads will achieve the same stretch at a lower torque effort. Plated fasteners and using Loctite are considered a wet torque.

   

[SOHC Digger]

...and one last note:

Sometimes in manuals you are directed to apply oil, loctite, etc., to threads and then you are given a torque value.  In those instances, you should NOT decrease the torque as it has already been calculated with wet threads.

[Bru-tom]

so can one use copper slip on head studs?

[rhinoracer]

Do you calibrate your torque wrench on a regular basis? Is the accuracy within the range you're torquing to? If not, it's kind of irrelevant to know the difference between wet and dry torquing as you really don't know your real torque values. Just sayin' 

[SOHC Digger]

Do you calibrate your torque wrench on a regular basis? Is the accuracy within the range you're torquing to? If not, it's kind of irrelevant to know the difference between wet and dry torquing as you really don't know your real torque values. Just sayin' 

I disagree.  Yes, you should have your torque wrench calibrated on a regular basis, but even if you don't, that's no reason to throw all other considerations out the window. 

We have a dial for verifying torque wrench calibrations at work, and the most I have seen one off was about 10%, and that is still not enough to where it would make no difference to neglect wet or dry specs.

[Rigid]

Aircraft fastener torque assumes lubricant applied.  I have read that dry or corroded fasteners can reduce applied torque by 80%.  Calibration is an issue and so is technique but most fasteners have a large torque range to accommodate such things.