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!

*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.

Jobs

Hot Tapping For PSV Installation

Hot Tapping For PSV Installation

(OP)
The results of a recent PSV study at one of our plants indicate that we will need to install some new PSVs on piping and Section VIII vessels. We plan to do the installations online which will require hot taps. API 520 and ASME Sec. VIII are fairly clear that the inlet piping to the PSV SHALL not have a cross sectional area less than the inlet connection of the PSV. B31.3 is less clear on the subject. Talking to the hot tap company and looking at the std ID of a ANSI 300 class flange, it doesn't appear that we will be able meet the cross sectional area requirement in API and ASME. For example the inlet of the 4" 300 Cl flange is 4.03"; with Sch 40 pipe the largest bit they can use for the hot tap is 3.938". So, in this case, to meet the API/ASME requirement, we will have to use a 1 size larger hot tap and swedge down to the PSV inlet. Unfortunately, in some cases we will be doing 4" x 4" hot taps so a 1 size larger is not an option. Granted the difference is not large and most of any increased pressure drop will be recovered, but strictly speaking we will be in violation of the code. Has anyone else run into the problem? Thoughts?

RE: Hot Tapping For PSV Installation

Djack, I may be doing this incorrectly, but I had historically assumed that as long as the nominal piping was = nominal valve inlet that all was ok. That said, I always use full port valves. I am interested in what others might post.

RE: Hot Tapping For PSV Installation

What you need to bear in mind is that the actual minimum bore area of the nozzle of the PSV is much smaller than the actual inlet nominal diameter of the PSV (well, in API full nozzle designs anyway). You may note that these designs have a tapering reducing bore from the inlet. This does not mean that you can have any inlet piping size smaller than the inlet ND. All PSV manufacturers will tell you that this inlet tapered (slope) is critical to the PSV design and has bearing on the established coefficient of discharge. Since the inlet size is a "nominal bore" the actual inlet size may differ between manufacturers. I would therefore identify the PSV OEM and ask the question.

Per ISO, only the term Safety Valve is used regardless of application or design.

RE: Hot Tapping For PSV Installation

Yes I faced a similar situation few years ago with an operating company i worked with. However it was understood that at alltimes the mating relief valve inlet pipe ND would match the relief valve inlet ND..irrespective of what the internal diameter of the relief valve inlet or the nozzle would be (avalveman is right). Hence your hot tapping connection should be adjusted accordingly to suit the said pipng configuration.
That said however the operating company's policy was not to do hot tapping on any relief valve connections in the plant since for them it was a safety issue (for example there could be a process upset at the time of the actual hot tapping work on the very relief valve on which a relief demand is placed).

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


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close