Nameplate MAWP Less than Design Pressure
Nameplate MAWP Less than Design Pressure
(OP)
Our customer needs an SA-516-70 pressure vessel that will operate at slightly below 1 atm. The original plan was to rate the vessel for 1 atm, and avoid needing to Code-stamp.
But now we find that the vessel must be pressurized with steam at 2 atm for 48 hours in order to cure the rubber lining that is to be applied. It seems to me that if the vessel is designed for 1.54 atm, there is nothing wrong with pressurizing it to 1.3 x 1.54 = 2.0 atm for 48 hours. Furthermore, it seems that the vessel, although designed for 1.54 atm, can still be tagged as 1 atm MAWP in order to avoid needing to Code-stamp.
Can anyone tell me if there is a flaw in my reasoning for this vessel, which is to be to be installed in the province of Sasketchewan?
But now we find that the vessel must be pressurized with steam at 2 atm for 48 hours in order to cure the rubber lining that is to be applied. It seems to me that if the vessel is designed for 1.54 atm, there is nothing wrong with pressurizing it to 1.3 x 1.54 = 2.0 atm for 48 hours. Furthermore, it seems that the vessel, although designed for 1.54 atm, can still be tagged as 1 atm MAWP in order to avoid needing to Code-stamp.
Can anyone tell me if there is a flaw in my reasoning for this vessel, which is to be to be installed in the province of Sasketchewan?





RE: Nameplate MAWP Less than Design Pressure
I think that your design pressure is 2 atm.
RE: Nameplate MAWP Less than Design Pressure
RE: Nameplate MAWP Less than Design Pressure
RE: Nameplate MAWP Less than Design Pressure
Or is it for regular production runs?
RE: Nameplate MAWP Less than Design Pressure
We deal with non-Code FRP knockout drums all the time, and declare them non-Code and designed to 100 kPag or less, even though the shop involved always hydrostatic leak tests them to 50 psig (345 kPag).
RE: Nameplate MAWP Less than Design Pressure
You might check if the difference between 1 and 2 atm really makes much difference in the design or not- I would suspect not.
RE: Nameplate MAWP Less than Design Pressure
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RE: Nameplate MAWP Less than Design Pressure
This is a complex issue to me because it is a tall vessel that must be hydrotested vertically due to logistic considerations. (40 psi static head during hydro on a vessel intended to operate empty at 1 atm.)
I will look into Snorgy's comment, but will also bear in mind that the 48 hours at 2 atm is essentially a pneumatic test. This has its own hazards, and safety is paramount.
RE: Nameplate MAWP Less than Design Pressure
RE: Nameplate MAWP Less than Design Pressure
Without getting into details, this large vessel must be assembled and tested on site. You echo my own thoughts regarding UT and RT, but I was thinking the "restricted distance" should be 500 ft and everyone should be inside cars with the engines running.
Back to my original quandry: It's hard for me to understand why we wouldn't get this vessel (designed and built for 2 atm) stamped to the level of quality proven. The only reason I can see is that the bureaucratic red tape (and fees) are unnecessary. The customer said he only needed a vessel to operate at atmospheric pressure, so it's difficult to argue that he should spend any extra time and money certifying it to 2 atm.
But it sounds like there's nothig wrong with the MAWP stamped on the nameplate being lower than the design pressure.
RE: Nameplate MAWP Less than Design Pressure
I agree that the vessel should (indeed must) be designed, built and tested to the most severe condition it will ever see - including the lining cure. After that, you can *nameplate* it to anything less severe.
RE: Nameplate MAWP Less than Design Pressure
RE: Nameplate MAWP Less than Design Pressure