4 replies to this topic

[sunil_chemical]

Dear All,

Can anybody tell me about Cold Defferntial test pressure? And why It is required.
Actualy I gone through the API-520, in which it is mentioned that the CDTP is required for Test stand.

Further for Convetional Valve API-521 paragraph 4.2.3.3 A convetional PRV Operating with a constant superimposed back pressure normally required a correction factor to compensate for the back pressure. In this case the required set pressure minus superimposed back pressure is equal to CDTP. This change account for the addtional closing force exerted on the valve disk by back pressure.

Now, we have to add this pressure for back pressure consideration or valve is tested based on CDTP, But if we tested based on CDTP than this is less that the set pressure as CDTP is Set Pressure - Superimposed back pressure.

Can anybody Clarify me regarding the CDPT term in API.

Thanks

[fallah]

CDTP is to be specified for adjusting the set pressure of a PSV on the test stand.
Considering actual operating conditions ,temperature and pressure correction should be considered.

Supposing the back pressure on the test stand would be 0.0 barg, the differential pressure (set pressure-back pressure in operating condition) should be multiplied by the temperature correction factor to specify CDTP.

In actual coditions, the PSV experiences existing net pressure that would be pressure difference between set pressure and back pressure.

While on test stand, set pressure of a PSV is adjusted based on CDTP, it could be supposed that PSV is nearly subjected to actual operating conditions and won't have any problem in predifined operation.

[sunil_chemical]

Hello Mr.Fallah,

Thank you very much, after long i am gettting the Ans,

As per your ans I understand that, During the test stand for PRV, the back pressure is zero so that we have to add correction factor for temp and pressure as operating condition is different.

Can you tell me from where this correction is obtain means this value we are getting from the vendor or we have to calculate this value, fi we are calculating this value than how this value is calculating?

thanks.

Dear All,

Can anybody tell me about Cold Defferntial test pressure? And why It is required.
Actualy I gone through the API-520, in which it is mentioned that the CDTP is required for Test stand.

Further for Convetional Valve API-521 paragraph 4.2.3.3 A convetional PRV Operating with a constant superimposed back pressure normally required a correction factor to compensate for the back pressure. In this case the required set pressure minus superimposed back pressure is equal to CDTP. This change account for the addtional closing force exerted on the valve disk by back pressure.

Now, we have to add this pressure for back pressure consideration or valve is tested based on CDTP, But if we tested based on CDTP than this is less that the set pressure as CDTP is Set Pressure - Superimposed back pressure.

Can anybody Clarify me regarding the CDPT term in API.

Thanks

CDTP is to be specified for adjusting the set pressure of a PSV on the test stand.
Considering actual operating conditions ,temperature and pressure correction should be considered.

Supposing the back pressure on the test stand would be 0.0 barg,the differential pressure (set pressure-back pressure in operating condition) should be multiplied by the temperature correction factor to specify CDTP.

In actual coditions,the PSV experiences existing net pressure that would be pressure difference between set pressure and back pressure.

While on test stand, set pressure of a PSV is adjusted based on CDTP,it could be supposed that PSV is nearly subjected to actual operating conditions and won't have any problem in predifined operation.

[fallah]

Can you tell me from where this correction is obtain means this value we are getting from the vendor or we have to calculate this value, fi we are calculating this value than how this value is calculating?

For pressure if the back pressure in actual conditions is above ATM,then in test stand it should be subtracted from set pressure to obtain the differential pressure.
CDTP is calculated by multiplying the calculated differential pressure by temperature correction factor that should be obtained from PSV manufacturer.

[sunil_chemical]

Hi,

Thanks for the Clarification.

Can you tell me from where this correction is obtain means this value we are getting from the vendor or we have to calculate this value, fi we are calculating this value than how this value is calculating?

For pressure if the back pressure in actual conditions is above ATM,then in test stand it should be subtracted from set pressure to obtain the differential pressure.
CDTP is calculated by multiplying the calculated differential pressure by temperature correction factor that should be obtained from PSV manufacturer.