PSV installation by Stud Bolt with Nuts or Machine Bolt with Nuts? 3

[Nasim12345]

Dears
Can you please explain me, what are the disadvantages, if we use Machine bolt with Nuts for PSV installation. Based on one project specifications, it is clearly mentioned, we must use Stud bolt with Nuts for Safety valve installation.

Thanks
Nasim

 

[The Obturator]

I think the statement you made from the project "Stud bolt with Nuts for Safety valve installation" can be interpreted as the standard stud and separate bolt fastening. I would certainly seek clarification on it.

Disadvantages of using a machine bolt can be;-
Availability and cost - Since for all full nozzle inlet PRV's, the Flange thickness + raised face (nozzle) is always larger than specified in B16.5

You will always need to get these made for each different PRV manufacturer (this total thickness is not governed by API-526). The difference may be small but it can catch you out unless checked for all.

More potential for mixing similar looking bolts up.


Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

Most O&G companies I know of don't permit the use of what are officially called machine bolts because there is a risk ( and recorded failures) of fatigue and corrosion cracking at the end formed nut/shaft interface which cannot be seen or monitored.

Also if the end nut siezes on the bolt then it can get very difficult to remove. At least with a stud bolt and two nuts you have a chance that one of them will start to move and then you can extract the stud.

Although it shows both types ASME B 16.5 contains the following.

"6.10.3 Bolting Recommendations. For flange joints,
[highlight #FCE94F]stud bolts with a nut at each end are recommended
for all applications[/highlight] and especially for high temperature
service.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Nasim12345]

Thanks for your feedback