Joe,
There was no comment made of pipe caps - your initial post stated the "tank" arrived with "straight pipe outlets".
Why can you not use pipe dams or dissolvable paper dams for purging as the rest of the world does ?
Regards,
Shane
Hi Joe
I have been on a shutdown for the last month, so only reading this post in "hindsight". All the points raised sound interesting and valid, but I believe there may be more than one way to look at this problem. I find your posts are a little difficult to read, so I may be misinterpreting your explanations, but it sounds to me like the situation you are in is as follows:
1) The particular pressure vessel was produced as per drawing, (And design) which required no flanges on the nozzles, as the vessel (as is often the case for cryogenic vessels) has been designed to be welded into the piping without any flanged connections.
2) As pointed out by Shane, the code then delimits the vessel boundary at the first weld onto the attaching pipe work. (That would have been the case for all the other nozzles, from what I understand.)
3) Due to an oversight, it has come to light that at least one flanged connection will be required in the system to allow for purges. (I am not entirely clear if this is only for weld purging for attaching the piping to the nozzles, or production purging, but the precise reason is not important to the discussion.)
While I do not fully understand the legal requirements in the USA, I believe the attachment of the flange to the vessel could potentially be dealt with in three different ways:
1) The attachment of the flange is seen as a late modification by the original manufacturer, and they make the change, re-issue the as built drawing and MDR to reflect the change. (Would in all probability not be possible given that the vessel was made in India.)
2) The attachment of the flange is seen as a modification to the vessel, and the necessary National Board processes are followed for modifications to pressure vessels. (This seems to be the way it is heading at the moment.)
3) The flange is seen as part of the attaching piping, not part of the vessel. In this case the ISO for the piping would show this flange as part of the piping, and the termination point of the vessel being at the first weld onto the piping. (As was originally intended.) In this case, welding the flange using B31.3 would be appropriate.
I know that the last option above does not appear "above board", but if we ask ourselves the following questions, it may not seem quite so ridiculous:
1) If there was a 10m length of pipe welded onto the welded end nozzle before the first flange, would it be expected that the entire 10m length be part of the vessel? If not, then what about a 5m length? OR 1m length... You get the picture I am sure.
2) This weld will be no different than the other welds onto the welded end nozzles, which would all be welded to B31.3, so from a risk or technical point of view, there would be no difference between these welds.
I believe that the real issue here is how the records will be kept and applied into the future. As long as it is clear from the records that the flange welded onto this particular nozzle is not part of the vessel, but part of the piping, legally everything should be OK. If I am getting this wrong, by all means let me know.
Regards
Niekie