Analysing as per 31.1 or 31.3 which are fittings/transitions where the SIF considered by Caesar by default can be inaccurate and therefore the user must examine them closely?

Hello,

The requirements for the structural analysis of piping systems is generally defined by Codes and Standards. The Caesar II software incorporates the Stress Intensification Factors that are prescribed by the applicable Codes. These SIF's were developed by testing a limited number of manufactured or fabricated piping components.

You will note that the B31 Pressure Piping Codes provide SIF's that are appropriate for specific types of piping geometries (e.g., fabricated components, fittings, etc.); those which testing derived data is available. However, the B31 Codes also tell the piping engineer that if he/she has more appropriate SIF's for specific fittings they are to have the latitude to use these data. The Caesar II software provides the piping engineer with the capability to override the Code prescribed SIF's by specifying alternate data. It would be prudent for the piping engineer to peruse B31.1 and/or B31.3, Appendix "D" to determine the details of the specific component geometries for which SIF's are provided. For example, the piping engineer may specify that B16.9 Welding Tees (fittings) be used, but the "crotch radii" and general wall thickness of these fittings varies greatly from manufacturer to manufacturer. If the piping engineer determines that the component to be used in the design is significantly different from thoses described in Appendices "D", it may be appropriate to develop alternate SIF data.

There is information available in the literature (and in some of the Codes) regarding the development if SIF's. The Welding Research Council has published the following:

Developing Stress Intensification Factors: (1) Standardized Method for Developing Stress Intensification Factors for Piping Components, by E.C. Rodabaugh and (2) Effects of Weld Metal Profile on the Fatigue Life of Integrally Reinforced Weld-on Fittings, by G.E. Woods and E.C. Rodabaugh, June 1994 (26 pp) (ISBN #1-58145-391-4) ─ $64.00

To obtain this document, go here:

http://www.forengineers.org/pvrc/wrcpvrcbulletin.htm

Regards, John.

Mr.Basu,

B16.9 weling tees is a typical case, where if the requirements pertaining to crotch ridius and thickness are not met, user has to override the Caesar default values at least till version 4.3 . Second, 31.3 does not consider the effect of a reduced intersection and in order to be conservative, user can use the Schneider option in the Caesar Configure set up where if the d/D ratio is in the range 0.5 to 1, the out of plane Sif gets multiplied by a factor ranging between 1 and 2.

But Schneider's work was rather given a solid footing by Rodabaugh's work which is documented in WRC 329.Particularly for reduced intersection, the user who wants to be conservative, can use the WRC 329 option.

Anindya Bhattacharya

Stress analyst

Bechtel Corporation