×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• 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.

# ASME B31.8 TABLE 841.1.18-1 Temperature Derating Factor

## ASME B31.8 TABLE 841.1.18-1 Temperature Derating Factor

(OP)
ASME B31.8 TABLE 841.1.18-1 has temperature derating factor for temperatures ranging from 250F to 450F with 50F increment.

GENERAL NOTE below the table says : For intermediate temperatures, interpolate for derating factor.

I noticed a graph of Temperature vs derating factor make a straight line. So why not select factors at 250F and at 450F (just 2 points) to interpolate for any temperature in between to determine derating factor? ?

Any reason why we have to iterpolate in between each 50F block?

### RE: ASME B31.8 TABLE 841.1.18-1 Temperature Derating Factor

Errors are too likely when interpolating between extended ranges.

Sure, if you treat the interpolation arithmetic as "automatically correct all the time" the same result will always result, and no one will make a mistake selecting the proper material strength for his.her pressure vessel (today, and back in the slide rule error (er, era).) However, is it not smarter to force the selection for an error band into the smallest practical upper and lower limit? And, temperatures are NOT explicit and exact across the entire vessel! Selecting from a reasonably small band forces the designer to consider the ranges of temperatures fro inlet to outlet, at exposed nozzles and deep within the heated zone of a PV that is fed hot fluid one place, and venting colder fluid elsewhere.

We see already people who "design by the pretty computer picture". No red spots = good design, right?

#### 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.

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!