"Re-rating" a non-pressure vessel
"Re-rating" a non-pressure vessel
(OP)
Hi all,
I've got an induced air flotation device to skim oil from our waste water. It's a standard design, almost like a skid, installed about 30 years ago. There is no documentation save for a drawing, no stamp, and no data sheet. I asked the OEM if they had any calculations or anything and they've come up empty. It does have an MAWP but it looks like it was written in. 1/2 oz. per inch squared, which is like .031 psig. We're guessing it used to be rated for atmospheric, but some peripheral piping was upgraded that required a higher MAWP of the IAF. Maybe. I've been asked to evaluate if we can re-rate this IAF as the operations folk are operating above the prescribed MAWP anyway. However, as this thing was built to no code and no calculations exist, I'm not sure where to start. It's not even circular or rectangular. The cross section has multiple vertical/horizontal sections and corners. I looked at API 510 section 7.7 but even then it says "3) Perform design calculations based on applicable codes and standards." Can't do that since I don't know what code to go by. We could do an FEA analysis if we contract it out I guess. Does this thing even need to have a rating? Anybody have any advice?
Thanks for reading my ramble!
I've got an induced air flotation device to skim oil from our waste water. It's a standard design, almost like a skid, installed about 30 years ago. There is no documentation save for a drawing, no stamp, and no data sheet. I asked the OEM if they had any calculations or anything and they've come up empty. It does have an MAWP but it looks like it was written in. 1/2 oz. per inch squared, which is like .031 psig. We're guessing it used to be rated for atmospheric, but some peripheral piping was upgraded that required a higher MAWP of the IAF. Maybe. I've been asked to evaluate if we can re-rate this IAF as the operations folk are operating above the prescribed MAWP anyway. However, as this thing was built to no code and no calculations exist, I'm not sure where to start. It's not even circular or rectangular. The cross section has multiple vertical/horizontal sections and corners. I looked at API 510 section 7.7 but even then it says "3) Perform design calculations based on applicable codes and standards." Can't do that since I don't know what code to go by. We could do an FEA analysis if we contract it out I guess. Does this thing even need to have a rating? Anybody have any advice?
Thanks for reading my ramble!





RE: "Re-rating" a non-pressure vessel
RE: "Re-rating" a non-pressure vessel
RE: "Re-rating" a non-pressure vessel
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P.E. Metallurgy, Plymouth Tube
RE: "Re-rating" a non-pressure vessel
RE: "Re-rating" a non-pressure vessel
Yes you can get instruments to measure inches WC. All pressures are guage so it doesn't matter what the atmospheric pressure is, its the difference to atmospheric pressure that you're measuring.
Or just not bother.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: "Re-rating" a non-pressure vessel
You can do it with a ruler. I'm no longer surprised to meet young engineers who do not know what a manometer is or how to read one. Manometers are why we use inches of water as a pressure unit. Bear in mind that if your tank is one foot tall and full of water, the pressure at the bottom of the tank is 12 inches of water. Understanding small details such as this is what leads to "good engineering judgement". For future reference it would be good to always remember that 1 psi is roughly 24 in. H2O, and when you think this there should be a picture in your head of something full of water 24" deep, not a picture of a number written on paper.
https://en.wikipedia.org/wiki/Pressure_measurement.