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Bolting for Hydrotest

Bolting for Hydrotest

Bolting for Hydrotest

(OP)
Hi,

I understand that the design stress for bolting during a hydrotest can be multiplied by 1.5

Does this mean that I can use bolts that have 2/3 the root area of the service bolting for a one off hydrotest?

Would there be any problems or risks with this ?

RE: Bolting for Hydrotest

Why would you even consider using bolts that have a smaller root area that could result in possible leakage during hydrotesting? Size the bolts based on maximum force to sustain 1.5X MAWP. Very simple approach.

RE: Bolting for Hydrotest

(OP)
We are making a one off item, the standard bolt size is 3 inches, we have to buy 128 of them.

The cost is considerable for something that will not be used again.  

RE: Bolting for Hydrotest

One of the main risks would be that the joint leaks.  Of my many hydro's, the primary source of leaks is in the mechanical joint (which only ever required re-tightening).  While reducing the bolt size will be cost effective upfront, there is always the possibility that these bolts may need to be replaced with slightly larger ones and then the cost and schedule will be truly affected.  

In the event that there was leakage, someone else in your team or an independent will never concur with the smaller size bolts.  They will always go with the minimum specified by the code of design.  Then you will have a lot of explaining to do.

But if you do your sums and the numbers work out and you feel confident, then for sure go with the most economical alternative.    

RE: Bolting for Hydrotest

And use VERY thick washers to compensate for the oversize hole.
If this vessel cannot have ALL the air vented out, don't hydro anywhere near people.  Flange may just leak, but there have been catastrophic failures due to undersize bolting.

Hope for the best, plan for 'What If' the flange goes ballistic.

RE: Bolting for Hydrotest

"Hope for the best, plan for 'What If' the flange goes ballistic."

What steps to take next ?  .... Big ones.  
 

RE: Bolting for Hydrotest

(OP)
Thanks for the advice guys,
We have decied to downsize to 2 3/4" bolts, it saves some money (which keeps the Project happy) and stops us worrying too much.
Cheers
 

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