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


Allowable Stress in Creep Condition

Allowable Stress in Creep Condition

Allowable Stress in Creep Condition

Dear All


(b) At temperatures in the range where creep and stress rupture strength govern the selection of stresses, the maximum allowable stress value for all materials is
established by the Committee not to exceed the lowest
of the following:
(1) 100% of the average stress to produce a creep rate of 0.01%/1 000 h
(2) 100Favg% of the average stress to cause rupture at the end of 100 000 h
(3) 80% of the minimum stress to cause rupture at the end of 100 000 h

Can you please help me understand what the difference is between average and minimum stresses in cases 2 and 3 above?

RE: Allowable Stress in Creep Condition

You get a scatter of results when testing material rupture strength NOT just a single value for multiple specimens. Maybe that gives you a clue.

RE: Allowable Stress in Creep Condition

So this is about the number of the specimens that are tested?
how many tests has to be done and based on which standard or spec those tests are performed?
Do they use extrapolation methods like Larson-Miller?

RE: Allowable Stress in Creep Condition

DSB123 is pointing to the correct answer. Creep curves (stress v log t) are often presented as bands, which incorporate the natural scatter in test results. These provide minimum and mean values.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: Allowable Stress in Creep Condition

When ASME B&PV code cases are developed, as part of the submittal there are three (3) heats required, which means multiple data points for creep and stress rupture tests. So, you need to determine the average as stated above for each test temperature and the scatter band for the lowest test values. This is basic engineering statistics.

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!


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