API 650 tanks minimum design temperature and hydrocarbon sensing valves

[Sawsan311]

Dear All,

For tanks operating above ambient temperature, minimum design temperature typically considered is the lowest mean ambient temperatue.

IF tanks operate below ambient temperature, what is the typical rule for specifying the minimum design temperature. As per API 650 also, impact testing is required for tanks with minimum design temperature of 13 C and less. Hence , by all means, it seems usually impact testing is required.

Additionally, is there any criteria on when to provide hydrocarbon sensing valves on the roof top and would close in case of a leak. If a tank is fixed roof tank, how would the roof drain valve be opened during normal operation.

Appreciate your views.

 

[LittleInch]

Define which bot of APi 650 you're referring to.

Fig 4.1 shows temperatures lower than this.

Setting min design is a function of external temperature or fluid temperature, whichever is the lower.

What valves on a roof top?

you can't close the vents because API 650 is for atmospheric pressure tanks.

Normally for fixed roof tanks the roof is sloped so that the water drains off the side. External Floating roof tanks have a roof drain which is normally open otherwise the roof sinks.

Have you ever seen a large API 650 storage tank before because these are very basic questions here.

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Also: If you get a response it's polite to respond to it.

 

[mk3223]

For a fixed roof tank, it's normally fabricated with a cone or doom types of roof. there is roof drain valve needed.

What's the purpose to have a "sensing valve" on the roof top if there is a tank leak? Do you mean the sensing valve on the process inlet line to the top of the tank roof?

 

[LittleInch]

Mk3223, I think you missed a "no" out of your post. ....

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

 

[Sawsan311]

Dears, I made a typo mistake, I didnt mean to say roof drains for fixed roof tanks, I was enquiring about hydrocarbon sensing valves installed on roof drains for external floating roof designs. some guideline stated these sensing valves will close in case a hydrocarbon leak is detected possible due to a leak in the normally opened roof drain.

Going back to the question of minimum design temperature, what would be the criteria for refrigirated tanks?

For non refrigerated we consider the lowest day mean ambient temperature.

 

[Sawsan311]

Dear All

for floating rood tanks, some guidelines calling for a minimum 0.7 SG for the design of the roof accounting for the Bouyancy, can you explain the rational behind that, is it because of setting of the rood towards the bottom of the tank?

Thanks

 

[LittleInch]

The problem with closing the roof drains is where does the water go on the roof?

If you let it pond on the roof the roof can sink.

So it should be an alarm and then doggie out how much product is coming out. A full rupture yes you need to close it but usually these lines leak.

Or yes close it but then have a plan B for the roof drain or drain the tank as quick as you can. Or have two drains.

The 0.7 SG refers to the density of the fluid in the tank which is probably as low as you can go for an EFR tank. That's the SG of gasoline. The lower it is the bigger you need to make your pontoons to carry the weight of the roof.

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