Stud Bolt & Heavy Hex Nut Standard

[DGrayPPD]

Can somebody answer this question for me? Let's say for this example we are using two 4" NPS 150# RFWN flanges.

Once the flanges are bolted together is it standard for the the nuts to be flush with the edge of the bolt? Or should the threads of the bolt protrude the outer edge of the nut by a couple threads?

Reason I am asking is because a client is requesting longer stud bolts with their projects because they say installation is more difficult with standard size bolts because once everything is mounted together, the nuts and bolts are flush. I have looked at the charts in ASME B16.5 for bolt lengths and ASME B18.2.2 for thickness of nuts and done the math with an 1/8" gasket in between the flanges, and the found that the stud bolts are indeed flush with the nuts. Just trying to figure out if this is standard or if there are supposed to be stud bolt threads protruding out on either side of the nut.

Thanks for the help.

 

[david339933]

It is usually standard practice to have some threads extending beyond the nut, however not required in many instances.

ASME Sec VIII Div. 1 - UG-13: "they shall engage the threads for the full depth of the nut".
ASME B31.3: 335.2.3 - "Bolts should extend completely through their nuts. Any that fail to do so are considered acceptably engaged if the lack of complete engagement is not more than one thread."

 

[XL83NL]

We've made a table in which we, per B16.5 flange pound class rating and diameter combination, list the B16.5 stud bolt length and our own calculated preferred length. All B16.5 lengths then are too short, were we have applied a standard to have 2 to 3 full threads Protrude the heavy hex nut. The calcs include all tolerances and factors that influence the length. Next, we rounded all lengths to steps of 10 mm.

You dont want it to be flush, though it's not incorrect. The threads after the nut however still experience bolt assembly stress, and for certain size/pound class combinations (warren brown has written a nice PVP article on this 2013) this is more important than others. Too big of a length is not incorrect as well but esthetically not preferred.