×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Shouldn't allowed backpressure be based on differential (CDTP) rather than set pressure?

Shouldn't allowed backpressure be based on differential (CDTP) rather than set pressure?

Shouldn't allowed backpressure be based on differential (CDTP) rather than set pressure?

(OP)
Hi all,

Yes, I know that the whole API always states that gauge set pressure should be used to check if built-up BP is within allowed limits. Still this question arises frequently and is answered differently. Most engineers I ask intuitively vote for CDTP as reference, me too. I searched the forum and couldn't find an exhaustive answer beyond "leave it to the vendor". Assume the following (extreme) example:

Vessel MAWP: 10 barg
PSV set pressure: 10 barg
Relief pressure: 11 barg
superimposed BP constant: 8 barg
CDTP: 2 bar
Built-up BP: 1 bar

From API point of view the valve will be derated acc. to backpressure ratio and everything is fine. I also have no doubt that a properly selected valve will relieve sufficient massflow at differential pressure from 11 to 9 barg and accumulation is not exceeded. I'm concerned that the valve is operating stable from the point of opening, until the vessel pressure reaches relief pressure. The inlet pressure just managed it to open the valve against a meager spring force of 2 bar and instantly an additional force of up to 1 bar is added to close, but the valve remains open?
The example is in the subcritical flow regime and the lift/flow/backpressure relation is interdependent, which may soften the increase in built-up BP. Please post your comments and which type of valve you would select.

Thanks, Smiler

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources