Decrease the Height of Hex Nut 2

[ripaldee]

During installation of a SS control valve it was found that the hex nut is in contact with the body of the control valve. This happened because an insulating gasket (i.e. dissimilar material and raw water service) is used in the flanged connection; thereby, it increased the bolt length causing the hex nut to clash with valve body. Now, is it possible to decrease the height of the hex nut (i.e. by grinding or machining, for example)? Does the industry code/standards allow this practice?

 

[racookpe1978]

What pressure service?
What temperature?
What dia valve?
What industry and to what reg's are you going to (try to) work at?

 

[ripaldee]

Water service x 630 psig/205 deg F x 8" dia. x ASME B31.4.

 

[Duwe6]

Under ASME, "if you can engineer it, you can build it" meaning that you would have to calculate the reduced strength of the flanged joint and compare it to the relief pressure, and the impulse generated when your PRV 'kicks'. At 630 psig, thrust from a PRV is not insignificant.

Also, just use a thinner insulating washer. A thick micarta washer with a steel washer on top is not your only choice. If you don't mind "hillbillying" it, cut some plastic washers from milk jugs. Verify their installation by testing for [lack of] continuity between the stud and flange.

 

[Eltron]

I'd say that as long as you still have three threads in the nut you are OK. Generally speaking after more than three threads you reach a point of diminishing returns.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[Eltron]

I'd say that as long as you still have three threads in the nut you are OK. Generally speaking after more than three threads you reach a point of diminishing returns.

Dan

http://www.eltronresearch.com

Dan's Blog

 

[Duwe6]

"3 Threads" 'Taint so with piping flanges. Yes, the math should work out. But somebody has to do the calc's, and sign them.

 

[ripaldee]

@ Duwe6: 1.5 mm thk Micarta insulation sheet is available in the storehouse; we are using it to insulate SS piping resting on clamped shoe supports. Can we use the said insulation sheet as substitute to the thick Pikotek washers?

 

[Duwe6]

Absolutely. Micarta is what we usually get in an Insulating Flange kit.

 

[ripaldee]

As far as I understand, industry code/standards allows up to one-thread less to consider flange bolt & nut to be fully engaged.

Thank you for all the inputs.

 

[Duwe6]

1-thread; actually no. What is allowed is 'flush at a minimum' on new work.

The 1-thread minus it the maximum underengagement allowed during an on-stream inspection. And, yes, this implies that being 1 thread short of full engagement is inconsequential.