3 replies to this topic

[Nagarajan K]

Dear All,

 

I want to find out how should i decide Vacuum Design Pressure for Storage Tank (API 650)

 

As per API 650 it says Max. Design Pressure of 2.5 Psig or 0.17 Barg.

 

So i can keep my Maximum Internal Operating Pressure below 0.17 barg so that My PVRV can operated due to Overpressure based on set pressure provide.

 

Now say my tank Design Temperature is 150 Deg C,i have kept Max. Design pressure as +20 m barg.

 

Now, How to i decide the Vacuum Design Pressure?and on what Temperature whether Ambient say 40 or Minimum design Temperature of 5 deg C or 150 Deg C.

 

One of My datasheet said Vacuum Design Pressure of  -6m barg @ 150 Deg C? How it would have be defined and why at 150 Deg C,

 

Regards,

 

Nagarajan K

[TS1979]

This topic belongs to mechanical engineer category. Vacuum design pressure is determined by cost, experience and code. You can design higher vacuum pressure by increasing the wall thickness but the equipment cost will be high. There must be a minimum wall thickness for API 650 tank.

 

When you decide wall thick and roof thickness, you can calculate the maximum allowable vacuum based on formula in API 650 (I guess) or ASME code.

 

As to the design temperature, for any material, there is a maximum allowable stress and temperature chart. Higher temperature normally means lower maximum allowable stress.

 

At very low temperature, metal may become brittle and this will also reduce the maximum allowable stress.

 

Therefore, once the wall thickness is determined, you can calculate the maximum allowable operating pressure and vacuum based on applicable code. The pressure and vacuum will be your PVRV setting points.

[fallah]

 

One of My datasheet said Vacuum Design Pressure of  -6m barg @ 150 Deg C? How it would have be defined and why at 150 Deg C,

 

 

Hi,

 

The 150 C probably is the temperature of steam in "steam out" operation of the storage tank during which the tank may be subject to a high vacuum due to steam condensation following to a sudden raining... Please check and let's know...

[Nagarajan K]

HIi fallah Sir,

 

I doubt the same but steam out operation was not mentioned any where in the Datasheet.

 

or i shall raise a TQ to Client for which we are bidding

 

so if it is not assumed to be Steam out operation.

 

vaccum generate at 40 deg will be more i guess then that of -6mbarg at 150 Deg C due low temp concerning.

 

Regards,

 

Nagarajan K