TreeEng,
When sizing the PSV use the value 1.21(MAWP) + 14.7 for your P1 value, this will give you your 21% overpressure. You can also get sizing programs from most of the manufacturers. I believe you can download the Consolidated sizing software from the Dresser.com website.
J.
I agree with Scotsinst. CCI is VERY expensive and misapplied to applications that don't warrant the expediture. Masoneilan has many lower cost solutions.