Stainless steel service bolt not to be hydrotested

[jtseng123]

Dear all,
First time seeing a spec saying austenitic service bolts shall not be used in shop hydrotest. We have stainless steel vessel with stainless steel service bolts for manways and blinded nozzles. Any reasoning why SS service bolts shall not be hydrotested ?

 

[r6155]

This is especially likely with bolts of small diameter and with bolt materials having a relatively low yield strength. The yield strength of austenitic stainless steel can easily be exceeded with ordinary wrench effort in the smaller bolt sizes.

During pressure test retightening of the bolts may be necessary, but it must not be forgotten that the effects of repeated retightening can be cumulative and may ultimately make the joint unserviceable.

See more in ASME VIII-1 APPENDIX S

Regards

 

Austenitic SS fasteners are the most problematic to use, for reasons of low YS mentioned by r6155. Not only low YS, but potentially wide variation in strength.
For practical purposes a group of SS flanges studs is almost impossible to tighten effectively, and they certainly cannot be reused.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[r6155]

This situation can be resolved by measuring the elongation (not the torque) of the studs Personnel must be qualified to install studs, but this appears to be very difficult in the field.

Regards

 

[IdanPV]

As per ASME VIII-1, UG-99(b):
"Bolting shall not be included in the determination of the LSR, except when 1.3
times the LSR multiplied by the allowable stress of the bolt at its design temperature exceeds 90% of the bolt material specified minimum yield strength at the test temperature."

It doesn't mean you shall not used SS Bolts in hydrostatic test. Just don't include this kind of bolts for determinatin of the LSR.