Recent changes in ASME B31.3 and their implementation in CAESAR II

This presentation is prepared by Mr. Deepak Sethia (working in Imagegrafix software) who has extensive experience in using Caesar II software and troubleshooting. The points that will be covered in this article are:

  • Allowable Displacement Stress Range
  • Expansion Allowable Stress Change
  • Longitudinal stress due to sustained loads
  • Appendix P
  • B31J

Allowable Displacement Stress Range (SA)

  • SA is defined in equations (1a) & (1b) of ASME B 31.3 (Reproduced below)
  • SA is a function of the cyclic factor f
Allowable Displacement Stress Range

The definition of f has changed over the years.

Stress Range Reduction Factor

Sc and Sh each limited to 20 ksi when calculating SA allowable displacement stress range.

Sc-Sh

Expansion Allowable Stress Change

Process Piping

CAESAR II Has Always Determined & Used the “Maximum Value”.

But What Does “Considering All Support Conditions” Mean?

Alt Sustained (formerly Hot Sustained approach)

nonlinear stress

“… All Support Conditions (Positions) of The Pipe …”

  • Each Operating Load Case (For Particular Support Condition) Could Produce a Different Sustained Stress Distribution.
  • The Expansion Allowable Must Be Based on The Maximum Sustained Stress, Considering All of These Operating Load Cases.
  • Consider the following Example:
  • Only 2 of The Branch Lines are Hot.
  • One Branch Line is Cold.

System Has Three “Real” Operating Conditions, All Producing a Different Primary (Sustained) Stress State Due to Different Nonlinear Support Condition.

How Can This Be Achieved, Automatically In The Software?

New Load Case Template Recommendations

Load case
load case changes

ASME B31J

  • Standard Test Method for Determining Stress Intensification Factors (i & k Factors) for Metallic Piping Components
  • Scope of this standard has recently been revised to add the ability to update new i & k Factor information as it becomes available
  • B31J provides a set of calculations for revised SIFs and flexibility factors, as defined in the revision to ASME B31J. By using these revised SIFs and flexibilities, your stress analyses produce more accurate results. B31J provides the “more applicable data” referenced in recent editions of the piping codes.

What 319.3.6 is saying……

load condition

i-factor requirement as per the Latest Code

As shown in Figure the previous code (Appendix D) you had SIF(i) and SIF(o) which were valid for both Expansion Stress and Sustained Stress. Now you can find the following.Not only the SIF are different for the primary and secondary stress but in addition you have to consider SIF for Tortion and axial effect!

  • SIF is valid for Expansion Stress (SIF)and Index(SSI) is valid for Sustained Stress.
SIF entries

Do you know that the i & k factors from ASME B31.3/ASME B31.1 can be calculated according to B31J and it is freeware available with CAESAR-II software?

B 31J calculations in CAESAR II…..

B 31J result for Flexibility (k) & SIF (i)…..

CAESAR-II model with “more applicable data”….

We open the translated model in CAESAR II using B31J option

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Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

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