Dear All,
What is the safety margin for stresses in the bolts during hydrotest (with reference to bolts' yield strength?). In what case bolts should be replaced after hydrotest. What the code and engineering practice say?
Thanks.

Malyl.

90% of the yeld is reasonable. Bolts which make part of the Code designed item (e.g. joining sections of p.v. or applied on blind flange) shall not be overstressed. Hydrostatic test shall be made using the "definitive" ones and cannot be substituded after. Not by the stampholder otherwise pressure test shall be repeated. Mauro

Mauro,
I'm not familiar with NBIC, maybe there's an answer, but could you say something more about removing bolts during in-service? Is there something that the manufacturer should do or make the user aware to ensure that he (mfgr) will not be responsible for consequencies of switched main bolts after the pressure equipment has been despatched? Maybe they should be marked somehow? Are there some clauses in contracts practicable?

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Konrad Anikiel

Hi Konrad, The manufacturer has to record material, size and number of removable bolts on the MDR. I suggest all manufacturer to record all bolts including those used on manhole and all blind flanges within the pressure boundary, and nuts as well.
More than 10 years ago in a NB bulletin it was reported an accident happened to a US Navy ship making engine repairs in India, after the Bush Senior Gulf War. They stripped down the main steam valve and put wrong material nice new nuts. When the valve was opened wide the bonnet released cathastrophically and the massive steam output killed all in the engine room. I was Navy Engineer and I cannot forget it: I verify bolts and nuts specified stamping and I verify bolts and nuts are correctly described in MADR. I have not NBIC available now, but, as far as I know there is no special provision. I will verify asap and refer.