HDG Bolting Thread Sizing Practice

[SnTMan]

Hello All, this is my first post in this forum, I am more usually found in Boilers and Pressure Vessels, but this seems more of a machining problem.

My company is looking into supplying HDG bolting, mostly 1/2" and 5/8" coarse thread, in our equipment, and I am researching the issue.

I am not familiar with how thread sizing is specified for HDG bolting and am looking for common practices, if they exist. Web searches have turned up little useful for me. I have also studied some of the relevant ASTM standards such as A-153 & A-563 and info from the American Galvanizers Assn, but have not found really definitive information.

The studs and nuts would be bought out. My first question is, do I have to specify thread sizes and tolerances to the vendors, or might they have standards?

The studs will be fitted to tapped holes in our equipment, and while I know the holes will have to be tapped oversize I don't know how much over. So, my second question is, again are there standards or common practices for this?

I am trying to avoid reinvention of the wheel here where I or another engineer would have to analyse the allowances, tolerances, clearances, etc. confirm the strength of the tapped holes, and so forth.

Surely this is common enough that common practices exist. Thanks in advance.

Regards,

Mike

 

[CoryPad]

You should purchase fasteners to recognized standards if possible.

For example, use ASME B18.2.2 for bolt dimensions. Specify ASTM A 307 or A 325 for bolt material, A 563 for nut material, and A 153 for galvanizing.

Here is a nice summary as a starting point for you:

http://www.portlandbolt.com/faqs/galvanized-nuts-tapped-oversize

Your tapped holes should be oversized like the nuts. There is a nice summary table here:

http://www.portlandbolt.com/technicalinformation/astm/ASTM_A563.html

 

[SnTMan]

CoryPad, thanks for the links. I am reading these materials as a 5/8-11 stud will have no special tolerances or allowances applied, the nut will be tapped 0.020" oversize, per A-563.

From these dimensions I have performed the commom thread strength calculations, disregarding the presence of the coating. Per these calculations I would need to increase engagement length slightly.

Some testing of actual shop-produced tapped holes with galvanized bolting could show whether this is necessary or not.

Testing various oversizes of taps might also show whether the full 0.020" is necessary.

This is helpful, thanks again.

Regards,

Mike