Vacuum resistance of two similar vessels
Vacuum resistance of two similar vessels
(OP)
Hi another question on resistance to external pressure
If I have water two storage vessels, one marked 'atmospheric' and protected at 100 mbarg and one rated at 1 barg, of a very similar shape, size and diameter and the same material (stainless steel), and having been in the same service conditions (fluid, temperature etc) can I assume that the one with the lowest vacuum resistance rating is the one with the lowest pressure rating?
In other words, if I ask the vessel fabricator of the atmospheric vessel to determine by calculation the vacuum rating I can protect them both at this setpoint? Or is it imperative to remeasure the wall thickness of the other vessel.
Thanks
If I have water two storage vessels, one marked 'atmospheric' and protected at 100 mbarg and one rated at 1 barg, of a very similar shape, size and diameter and the same material (stainless steel), and having been in the same service conditions (fluid, temperature etc) can I assume that the one with the lowest vacuum resistance rating is the one with the lowest pressure rating?
In other words, if I ask the vessel fabricator of the atmospheric vessel to determine by calculation the vacuum rating I can protect them both at this setpoint? Or is it imperative to remeasure the wall thickness of the other vessel.
Thanks





RE: Vacuum resistance of two similar vessels
And get a competent mechanical engineer well-versed in pressure vessel design and fitness-for-service to perform the evaluations.
RE: Vacuum resistance of two similar vessels
If it was my money I wouldn't hesitate but this site is mean with money. I suppose I need to make the case that the consequence might be that we have to change quite drastically their operating mode to avoid any slight underpressure.
I have found an engineer from the vessel fabricator who is willing to do the work so he should be competent.
RE: Vacuum resistance of two similar vessels
RE: Vacuum resistance of two similar vessels
However if the pressure rating or relief rating of the atmospheric tank is only 100 mbar, I can't see the vacuum rating being anything higher than 20-30 mbar. At the sort of level the risk is very low so although you really should find out what the wall thickness is it won't in reality collapse.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Vacuum resistance of two similar vessels
Excellent! Competence tends to be a good thing.
You could always suggest to the client that they proof test the external pressure capability. Maybe replace the vacuum breaker with one with 1/3 the capacity, then drain the tank. That'll give you an opportunity to help them procure a new tank!
RE: Vacuum resistance of two similar vessels
Try hiring a certified API Inspector with 510 & 653 cert's. What is being discussed [and agonized over] is a typical day in the tank farm for an API. Tank or Vessel? What Code, if any? What thickness, and where? Any features to give vacuum support? All pretty simple IF you have ever evaluated a vessel [tank?] of unknown origin.
You need an API evaluation. So you need an API Inspector who is ready to do some calculations. The engineer you found might be able to get this done, but if he didn't correct your idea of stripping off all the insulation, probably not.
RE: Vacuum resistance of two similar vessels
RE: Vacuum resistance of two similar vessels
In both API-650 and API-620, they have a statement that tanks built to those codes can be used up to some nominal vacuum rating (I think 1" water column) without any additional vacuum design. If the tanks were built to one of those codes, that could save a lot of work if you can furnish vacuum protection within that limit.