4 replies to this topic

[arvind]

Hi All,

 

I am working for the shell projects and wanted to clarify the requirement given in sell DEP 80.45.10.12-Gen. (EMERGENCY DEPRESSURING AND SECTIONALIZING) for the following statement:

 

“Depressure the equipment to 7 bar (ga) (100 psig), or 50 % of design pressure, whichever is lower, within 15 min.”

 

Is it mean if my equipment design pressure is 100 barg then it can be depressurized to 50 barg in 15 minutes or 7 barg in 15 minutes.

 

This make me confused because in the statement given in Shell DEP it says "whichever is lower" is it mean lower between 7 barg and 50 barg (50% of design pressure), then 7 barg will be final pressure in 15 minutes or

 

whichever achieve first between 7 barg and 50 barg, in this case 50 barg is can be achieve first.

 

Thanks in advance.

 

Regards,

Arvind

 

 

[shvet]

Hi

 

Shell practices are more stringent then those in API 521. For more information see API 521 4.6.6 "Depressuring rates". Shell DEP provides both criterions:

- vessel wall temperature versus stress (50 % / 15 min)

- vessel leak or failure (100 psig / 15 min)

In your case  it means 7 barg within 15 min.

[fallah]

 

Hi All,

 

I am working for the shell projects and wanted to clarify the requirement given in sell DEP 80.45.10.12-Gen. (EMERGENCY DEPRESSURING AND SECTIONALIZING) for the following statement:

 

“Depressure the equipment to 7 bar (ga) (100 psig), or 50 % of design pressure, whichever is lower, within 15 min.”

 

Is it mean if my equipment design pressure is 100 barg then it can be depressurized to 50 barg in 15 minutes or 7 barg in 15 minutes.

 

This make me confused because in the statement given in Shell DEP it says "whichever is lower" is it mean lower between 7 barg and 50 barg (50% of design pressure), then 7 barg will be final pressure in 15 minutes or

 

whichever achieve first between 7 barg and 50 barg, in this case 50 barg is can be achieve first.

 

 

arvind,

 

In your case the final pressure will be 7 barg and depressuring should be done within 15 min...but now the criteria, per new editions of API 521 has been changed to:

 

"...reducing the equipment pressure from initial conditions to a level equivalent to 50 % of the vessel design pressure within approximately 15 min."

 

Then in new editions 7 barg will be considered as final pressure of depressuring just when depressuring system is designed to reduce the consequences from a vessel leak.
 

[arvind]

Thanks Fallah for your response.

 

So did you mean no benefit of vessel thickness to be considered now (as per both shell DEP and API)?

As per old API 521, if vessel thickness is equal or more than 1", then final depressuring pressure could be 50% design pressure i.e. 50 barg (50% of 100 barg) in this case (for taking credit of wall thickness) in first 15 min of time interval .

 

Regards,

Arvind

[fallah]

 

So did you mean no benefit of vessel thickness to be considered now (as per both shell DEP and API)?

As per old API 521, if vessel thickness is equal or more than 1", then final depressuring pressure could be 50% design pressure i.e. 50 barg (50% of 100 barg) in this case (for taking credit of wall thickness) in first 15 min of time interval .

 

arvind,

 

If thickness would be lower than 1", depressuring should be done faster than 15 min with the same final pressure i.e. 50% of the vessel design pressure...