Shane,
You are exactly right.
NDTIII,
Look, you're obviously a smart guy, and I don't think I've ever disagreed with you before, but I think you're confusing design requirements with service requirements. A system hydrotest is not meant to test the max integrity of every single part. The part manufacturers are responsible for that.
The goal of a hydrotest is to ensure that the system or portion of a system has been designed and fabricated in a manner that ensures system function and integrity. In order for the hydrotest to prove effective, it only has to be performed at the max operating pressure of the system. Hydrotests are performed above this pressure, mostly 1.5 times above, just to provide a safety factor in the advent of a pressure surge. The Engineer for one reason or another often changes this excess safety factor.
Now, if a spool or system segment has components rated for different pressures i.e. 150# and 300#, then that throws up a red flag that something is wrong. Maybe the guys on the shop floor ran out of 150# flanges and used a 300# substitute. That's no big deal really as long as it fits, its just wasting money. It does not mean that you have to increase the hydrotest pressure. Even though, it should still be approved by the Engineer. If a spool has been designed to require a 150# flange on one end and a 300# on the other, this is a design error. If there is any chance a 150# rated component may be subjected to pressure greater than it's rating, even if the only way it may happen is due to the failure of a pressure reducing valve or some other unplanned error, the spool should be designed to the max possible pressure that it hypothetically could be subjected to. Any other design is simply the result of a designer placing cost above safety and system integrity.
Tim
Let's not forget that 150, 300, 600, etc are not the pressure ratings of the flanges but are instead the class of flange. Working pressures/temperatures are listed in B16.5. Maybe everyone already knows this but, from what I've been reading, it sounds like there are at least a few here who don't.
FWIW, I agree with Tim and Shane.
Jeff
before the hydro test, the Inspector will be asked to perform the line checking and you will be supplied with the test package for review.
If you have a doubt on test pressure to be used, then why not write your comments in the punch list. I believe the rigth person will be called to solve and close the punch list items prior to the hydro test.
Ariel D C
Piping Spools with different pressure ratings shall have different design pressure and therefore required to be hydrotested at different test pressure. Such piping spools are therefore required to be hydrotested separately.
If flange ratings are different due to some other reason such as piping spec break (design pressure is same), hydrotest shall be based on design pressure of piping spool and not on flange with higher rating.
mdk
