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Multiple tank vents to prevent roof corrosion?

Multiple tank vents to prevent roof corrosion?

(OP)
Hello,

I have a project to install a new storage tank. A question came up regarding the basis of several vents that are installed on existing tanks in the same service. The existing tanks have 12 vents installed all around the circumference of the roof. It was mentioned that these vents are to prevent corrosive products from forming on the inner roof, and that we should have them on the new tank. Has anyone have experience with this application, and a basis for the number of vents?

I do not believe the vents are for pressure or vacuum protection, as the number would be overkill for that purpose. The existing tank has twelve 6" diameter vents. The only inlet line to this tank is 6", and the only outlet line is 8". This is a very high boiling material at atmospheric pressure.

At this point I am thinking of taking the ratio of the cross sectional area of the existing tank and open area of its vents to use as a basis for the new tank.

Thank you,

RE: Multiple tank vents to prevent roof corrosion?

I didn't see the tank designed with 12 vents on the roof. What's the special of the liquid?
IMO, you may want to understand the property of the storage material and the real purpose of the 12 vents on the existing tank, so the new tank can be designed properly. Will the liquid caused the tank corrosion pollute the air, or be harmful to the life?

RE: Multiple tank vents to prevent roof corrosion?

Sounds like someone had a nice idea but not sure it's based on anything other than guesswork. If condensation is an issue then clearly more ventilation is a good idea but limited. Do these allow wind to blow through or simple pipe vents/U bends. ?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Multiple tank vents to prevent roof corrosion?

Interesting, would you be able to post pictures of the tanks with 12 vents and also state the contents within such tanks.

RE: Multiple tank vents to prevent roof corrosion?

(OP)
http://www.eng-tips.com/viewthread.cfm?qid=317354

Hello, the thread above describes what I am referring to. API 650 refers to Welded storage tanks, but Appendix H refers to the fixed roof portion of internal floating roofs. My tank is a fixed roof tank, so I'm not sure how it applies. This was the only reference I could find to what is installed at my facility.

RE: Multiple tank vents to prevent roof corrosion?

Yes, API-650 App.H is applied for the tank which has an internal floating roof and the fixed roof.

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