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Modification of Welded Boss Inside Dive Chamber

Modification of Welded Boss Inside Dive Chamber

Modification of Welded Boss Inside Dive Chamber

Morning all, first time poster, long time lurker.

Quick question regarding the modification of a welded boss inside a sat dive system. Current boss has threaded holes which are severely corroded, plan is to re-drill and tap. My question is regarding how to classify these bosses, they severe no functional purpose in the pressure boundary and are only used to attach items inside the chamber. By gut tells me these are not part of the pressure vessel boundary and that I will not have mess around with LR or DNV.

I am looking for a something perhaps from PD5500 or something similar that deals with the classification of welded on attachments inside a pressure vessel and the modifications to these items?

Cheers in advance,

RE: Modification of Welded Boss Inside Dive Chamber

I'm not familiar with pressure vessels for human occupancy as they are not covered by ASME B&PV codes but rather ASME PVHO-1. I'm also not familiar with the European codes either (PD5500).

You could try looking in ASME PVHO-1 for a possible solution to your issue or hopefully someone with experience in this area can chime in!

Michael Hall, PE (TX) PMP - President
Engineering Design Services LLC

RE: Modification of Welded Boss Inside Dive Chamber

I managed to get my hands on PVHO 1 and 2 and I think trawling through them might give me the correct answer I am looking for. I will update this thread if I get anywhere with it!



RE: Modification of Welded Boss Inside Dive Chamber

If PD5500 is the design and fabrication standard then that is what you would have to conform to. If it is only re-drilling and tapping, with no increase in design load applied to the boss then I don't see any issue with this repair. Since it is welded to the pressure boundary any hot work would need to be assessed by a suitably qualified engineer. You could also check with NOPSEMA for guidance.

RE: Modification of Welded Boss Inside Dive Chamber

From memory you won't find anything in PVHO.

If they are simply attachments welded to the surface of the unpearced pressure shell, then you can do anything to them as long as you don't touch the attachment weld or pressure vessel shell. I assume they are for fastening the piping control panel or something similar and don't experience much in the way of applied loading.

If they are NPT couplings which penetrate through the shell, then they are nozzles and obviously a Pressure Vessels engineer would need to re-run the nozzle reinforcement calculation.

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