Section VIII Div.1 - drainage 1

[hhssbb2206]

The channel side of U-tube heat exchanger under corrosive service has a nozzle located at hill side. The lowest edge of nozzle is higher 0.7 inch than the lowest point.

"UG-25(f),Sec. Viii div.1, requires ' Vessels subject to corrosion shall be supplied with a suitable drain openin at the lowest point practicable in the vessel'

1) In the above case, may the bolted channel cover be considered as drain opening?
2) or does an additional drain opening have to be provided at lowest point in the channel?

Thank you.

 

[gr2vessels]

The chnnel cover cannot be drain nozzle, because cannot prevent large outflow of corrosive liquid/spillage. The drain nozzle of corrosive fluid must be piped away to prevent spillage and injury to personnel.
If you can prove that the corrosive fluid remaining in the channel can be diluted, drained again and contain the spillage when opening the channel cover, then you may use the mentioned nozzle as drain nozzle in accordance with the code. However, this is still a distortion of the intent of the code...
cheers,
gr2vessels

 

[hhssbb2206]

Thanks, gr2vessels.
I fully agree with your answer from an engineering point of view.
However, is this code violation?

Thanks.
hhssbb2206

 

[gr2vessels]

I believe it is a violation of UG-25(f), since it makes it mandatory to have either a dedicated drain nozzle at the lowest point or another nozzle with its lowest point at less than 6 mm of the vessel inside diameter lowest point.
You don't have a dedicated drain nozzle and the lowest point of your existing nozzle is at 18 mm above the vessel lowest point. Remember '..shall be supplied..'?
However, as I said, as long as you are not out to hurt someone and you can prove the user that it is safe to operate without the mentioned drain nozzle, you can ignore the code. Please note that you will not convince any halfwit AI you can deviate from the code in this matter.
Good luck,
gr2vessels

 

[trottiey]

I agree with the answer but not the reasoning here. I don't think that "vessels subject to corrosion" is necessarily related containment of dangerously corrosive fluids. A carbon steel tank with water in it would be "subject to corrosion" and requires a drain. Dilution has nothing to do with it. Conversely, a zirconium alloy tank holding nitric acid at room temperature would not require a drain, but you had better not spill that.