crude oil Tank Vent

[saliba11]

We have dia: 92 m, heigth:16 m floating roof crude oil storage tank.

Oil has escaped from the vents (located on roof) during filling and emptying operation of the tank. At first oil starts to pass from the vents, then after oil passing stops.

Could anyone indicate a reason for this.

Have you ever come accross such a problem.

Thanks in advance

saliba

 

[khardy]

Do you mean oil is escaping from the vacuum vent on the floating roof? If so, I would suspect the floating roof is hanging up somewhere. Maybe the shell has a deformity?

What is the tank level when this happens?

 

[0707]

In addition of what Khardy said, check the wheels of the roof ladder may be during the filling and the emptying of the tank they got stuck on wheel guides impeaching or creating resistance to the normal roof movement.


luis marques

 

[saliba11]

yes oil is escaping from the vacuum vent on the floating roof. we check that, the roof is not hanging or stuck anywhere.

escaping occurs at first movements.

 

[0707]

For sure you must have any prison impeaching the free tank roof movement, due to lack of flexibility of pipe drain, gage pole prison, or leaking pontoons. If you are real confident that the tank roof is not stuck anywhere, another possibility is bad vacuum vents design. Please note:


“Filling and emptying a storage tank creates positive and negative pressures inside the tank. To fill a tank, air and vapors within the tank must be pushed out developing an internal tank pressure slightly above atmospheric pressure. For this reason, tanks are designed to withstand an internal pressure of 2.3 kPa. To empty a tank, the reverse occurs requiring air to enter the tank, developing an internal tank pressure slightly below atmospheric pressure. For this reason, atmospheric tanks are designed to withstand a vacuum of 0.689 kPa. Ambient pressure and temperature changes may also produce a slight pressure or vacuum within the tank. To accommodate this air movement, vents are provided to prevent the tank from exploding or imploding. Normal vents are sized in accordance to Article 4.3.4.1. or API Standard 2000, "Venting Atmospheric and Low Pressure Storage Tanks," Table 1, but in no case should the vent size be less than 30 mm nominal inside diameter”


Luis marques

 

[JoeTank]

Luis,
From where did the quoted text come? It looks like a project spec statement. I do not recognize it as coming from an API document.

Joe Tank

 

[0707]

JoeTank

The quoted text is from Canadian Guide Lines, according API Standard 2000.

For your information go to the site bellow.

http://www.ofm.gov.on.ca/english/Publications/Guidelines/part4/4commen5.asp

regards

luis marques