×
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

TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

(OP)
The note no T8 of Table 1A of ASME II Part D mentions "Allowable stresses for temperatures of 750F and above are values obtained from time dependent properties". How this will affect the vessel design?

RE: TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

In time dependant material properties Creep failure is an additional concern. When you are in time dependent properties a detailed fatigue analysis is required. That anaylsis is time consuming and can be expensive. Depending on design temperature like say 800F, it is generally easier to just change the material from carbon steel (SA516 Gr70) to a CrMoly with a higher limit for time-dependant properties.

RE: TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

Quote (muld0020)

When you are in time dependent properties a detailed fatigue analysis is required.
That's an interesting claim. Care to provide a reference to that?

brkmech1234 - It means that that allowable based on the lower of:

Quote (ASME Section II, Part D, Mandatory Appendix 1, Paragraph 1-100(b))

(1) 100% of the average stress to produce a creep rate of 0.01%/1,000 hr
(2) 100*Favg% of the average stress to cause rupture at the end of 100,000 hr
(3) 80% of the minimum stress to cause rupture at the end of 100,000 hr
(Where Favg is defined as: At 1500°F and below, Favg=0.67. Above 1500°F, it is determined from the slope of the log time-to-rupture vs log stress plot at 100,000 hr such that Favg=1/n, but it may not exceed 0.67.
What this means from a design perspective is, in my opinion, the following:
a) Not much - vessels are designed in the creep regime all the time without much difficulty. However, the life will be limited, depending on the OPERATING stress levels and OPERATING temperature.
b) A fatigue analysis to ASME Section VIII, Division 2, Part 5 is not permitted, as the current rules are explicitly in the non-creep regime. If you will be cycling pressure or temperature or both, then I would recommend that you contact someone with creep-fatigue evaluation experience.
c) Evaluation of nozzle loads may or may not be more complicated. If you stick with WRC 537 (previously WRC 107), and the allowable stresses then, based on my experience, you'll be fine.

RE: TIME DEPENDENT PROPERTIES -EXAMPLE SA 240 316

(OP)
Thank you TGS4.

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