Pre and Post 1978 PSV calculation

[engrpiper]

I am told that the relief calc in sect VIII changed in 1978. I have been asked to investigate this due to that fact that a safety on a boiler steam drum needs to be replace in the furture. The vendor's quote for an identical replacement valve at the original design inlet conditions now has an increase in the outlet capacity of ~20%.

I am looking to understand the details of the change in calc. The code of the day was 1970 and I do not have access to a copy of this code. Any and all help would be greatly appreciated.

Also, does anyone have experience with this situation.

Thanks!

 

[insult2injury]

Section VIII or Section I?

I2I

 

[engrpiper]

Section I

 

[engrpiper]

I assume it is Section I however I am not sure. Were is the relief capacity calculated to take the reaction forces back to the steam drum?

 

[insult2injury]

Nonmandatory Appendix II in B31.1 deals with the calculation of relief valve reaction forces.

I2I

 

[engrpiper]

I2I,

Thanks for your reply. I am familar with the B31.1 reaction forces calc. I am looking to understand the revisions for the relief capacity calc. The new "identical" valve has ~20% increase in capacity. The argument being made is "this is not a rerate to the drum, the valve has always has a 1.20xrelief capacity."

Thanks!