×
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

B31.1Stress due to sustained loads

B31.1Stress due to sustained loads

B31.1Stress due to sustained loads

(OP)
Dear all,

As you know, ASME B31.1 states that stresses due to sustained loads are lower than Sh. When calculating longitudinal stress due to sustained loads only moments and pressure effect is taken into account but not stress due to axial loads (for example Bourdon effect). Does anybody know the reason? Or perhaps anybody knows, at least, where I can fing the explanation? (perhaps an ASME paper).

I don't really understand it....

thanks for any help

RE: B31.1Stress due to sustained loads

Not sure, but certainly axial loads must be considered  for the effect of gravity loading, espescially if the pressure part is used to support itself or another pressure vessel.

RE: B31.1Stress due to sustained loads

It is a simplification in the rules.  Remember, the rules were developed when folks were doing hand calculations for these stresses.  The justification for the simplificiation is that the effect of axial loads other than pressure is generally insignificant.  

RE: B31.1Stress due to sustained loads

Hello,

Just my opinion.

BVI is correct, Pure axial stresses "seldom" are significant in real world systems.  We did at one time (maybe 25 years ago) have a term in the equation for  sustained longitudinal stress (aka -"additive stresses").  That term was simply the axial tensile or compressive force divided by the cross sectional area of the pipe (F/A). It was removed because the committee thought it was a needless complication.

Some of the current stress analysis computer programs either give you the option of including this term or (TRIFLEX) they put the term in regardless.

Thanks for bringing up the topic, it is nice to know folks out there think about this stuff.

Regards, John.

RE: B31.1Stress due to sustained loads

Longitudinal stresses are often insignificant compared to hoop and radial stresses.  The most significant of course, is the hoop stress.

Depending on your exact setup, longitudinal stresses are often constricted, i.e. the component is not free to lengthen due to endcap reaction to bore pressure.  This IS NOT the case when external loading induces components of stress in the longitudinal direction, you need to be very aware of this important fact.

Therefore the piping is modelled as a biaxial state of stress and not triaxial.  On occasion this is not the case, the ASME B31.1 specification seems to be slightly misleading or at least, confusing, as you have correctly pointed out.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

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