×
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

DESIGN PRESSURE FOR PIPING CLASS
3

DESIGN PRESSURE FOR PIPING CLASS

DESIGN PRESSURE FOR PIPING CLASS

(OP)
Hi every body.
I would like to know if for the elaboration of a piping class for a main station where the working pressure is about 60 psig I should design using the maximum pressure in the system or I should use the maximum pressure of the flange ( 275 psig to 200 ºF). And if the last is true where can I get that information.

RE: DESIGN PRESSURE FOR PIPING CLASS

Don't know what your codes applicable to this specific station/application say, but of course "a chain is only as strong as its weakest link" (meaning from a practical standpoint you probably should consider everything in the system, including practical bolting/gasket selections and also at any applicable pressure conditions that might include additive surge).  [On the surface, however, a "60 psi working" system would not appear overly demanding on a 275 psi rated flanged piping system.]   

RE: DESIGN PRESSURE FOR PIPING CLASS

3
Engineering is the art of balancing cost, quality, and time.  We sometimes confuse quality as being better in ways ways that do not mean anything.  Hence, some engineers say if 60 psi is good, the 600 psi is better in designing a piping system.  

I'd say design for what you need.  If you need 60 psi and the fluid is not corrosive, then plug 60 psi in the design and add a small value for corrosion (round up to nearest standard).  As for flanges, you can not get standard flanges les than 150 ANSI (they do have a 125 ANSI flat face, but mostly for water service).

The reason some engineers go ahead and make the pipe match the flange ratings is because "internal standards" say so, no more no less.  The internal standards are usually set to minimize design work and make sure there are fewer errors during install.  I had an engineering firm tell me they had to use SCH 80 4" on a skid because SCH 40 was not rated to the ANSI 600 flange (1480 psi)and that met their "internal standards".  All the vessels and relief valves were rated at 1000 psig.  Now what did the engineering firm save me by making the piping good to2270 psig?

You get to set your "internal standards". So have some fun, be an engineer.

RE: DESIGN PRESSURE FOR PIPING CLASS

One other reason to design and test to the flange limit is that if the system needs to be rerated in the future another pressure test would not be required.

EJL

RE: DESIGN PRESSURE FOR PIPING CLASS



One step is often forgotten in engineering.

When you have checked or designed what you actually need, you also have to check for cost and time against what is actually commercially readily and cheapest available!

Typical example is the 150LB flanges mentioned above, probably cheaper than 125LBS. What about piping size and material?

RE: DESIGN PRESSURE FOR PIPING CLASS

gerhardl is correct- in a refinery or chemical plant, the long term purpose of a piping system may change, so rating teh piping system for the max consistent with flange rating is often appropriate. Also, you reduce the need to add relief valves or perform casualty flow analyses for that specific overdesigned piping system.

RE: DESIGN PRESSURE FOR PIPING CLASS

I always spec "minimum required wall thickness".  That way, the vendors are free to propose whatever they have available that meets or exceeds the spec.  You find out what the most economical wall thickness is from the currently available selection as soon as you sort the quotations.

http://virtualpipeline.spaces.msn.com

RE: DESIGN PRESSURE FOR PIPING CLASS

Consider instruments etc. that may connect via stainless steel or other flange materials.  Avoid setting the design pressure based upon the maximum pressure and temperature for flanges in predominent steel piping and equipment material as it would exceed the flange class for other materials.  If they set the piping design pressure for the carbon steel piping you might require class 300 stainless steel flanges for the 60 psig system.

RE: DESIGN PRESSURE FOR PIPING CLASS

There is nothing stopping you designing flanges to suit the pressure and end up with thinner flanges. This is routinely done in the water industry where spiral wound stainless steel and thermoplastic pipe uses stub ends and backing rings.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng
www.waterhammer.bigblog.com.au

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