Dropping Pipe Hydrotest to Suit Vessel

[Berndt]

I have a vessel which cannot be isolated from the piping since the vessel nozzles have welded connections in stead of flanged connections. After a modification to the piping which increases the minimum required hydrotest the following becomes pertinent:

Reading B31.3 345.4 carefully seems to indicate that I can't reduce the hydrotest pressure (As per 345.4.2 (b)) to cater for yielding components (As per 345.4.2(c)) and then on top of it drop the hydrotest pressure further to allow combined pressure testing with a vessel (As per 345.4.3 (b)). This is due to the fact that 345.4.3(b) refers specifically to 345.4.2 (b) and makes no mention of 345.4.2 (c).

Is this view too obtuse? Or is this actually the intent of the code?

 

[MJCronin]

Hydrotesting is specifically the main reason why there are flanges on tanks and vessels.

Insert flanges on your nozzels. Blank the new flanges. Test the tank in accordance with the code of record. Test the piping in accordance with B31.3

 

[moltenmetal]

A couple options to consider:

1) Hydrotest pipe and vessel to 1.3x MAWP x ratio of stresses if applicable, to suit the vessel, and as owner, call that good enough.

2) Hydrotest pipe and vessel together to 1.3x MAWP, then if it can be done safely, pneumatically test both to 1.1x MAWP without the ratio of stresses. After a 1.3x hydrotest, this should be safe for both, correct?

3) If 1) or 2) is not an option, do 1) and then do additional inspections (sensitive leakage testing, full radiography etc.) to further assure yourself.

This of course assumes that flanges were deleted for good reasons. If so, clearly putting flanges back in solely to serve the needs of the test would be a bad idea!