Displacement Plot

High bending stresses in elbows and tee’s

Underground Failure

ASME B 31J & B 31J Essentials: Why these are useful in Piping Stress Analysis?

Intergraph has announced an extension of Caesar II 2017 in May 2017. B31J Essentials provides a set of calculations for revised SIFs and flexibility factors, as defined in the code ASME B31J-2017, Stress Intensification Factors (i-Factors), Flexibility Factors (k-Factors) and their Determination for Metallic Piping Components.

By using these revised SIFs and flexibilities, your stress analyses produce more accurate results. B31J Essentials provides the “more applicable data” referenced in recent editions of the piping codes. If someone is current on CAESAR II maintenance and have installed CAESAR II 2017 (v.9.00), He can download the B31J Essentials installer from Intergraph Smart Support (http://smartsupport.intergraph.com) for free and install in their system. This article will try to inform what ASME B31J covers in brief.

For a long time, there was a need for a standard method to develop stress intensification factors (SIFs or i-factors) for ASME piping components and joints. At the time, the B31 Code books provided SIFs for various standard fittings and joints but did not provide guidance on how to conduct further research on existing SIFs or how to establish SIFs for nonstandard and other standard fittings or joints.

ASME B 31J is the outcome of a recent research by MDC on current manufacturing practices in the SIF and k-factor test procedures, to provide a consistent and up-to-date table of SIFs and k-factors for metallic piping components.

ASME B 31J provides a standard approach for the development of SIFs, k-factors, and sustained stress multipliers for piping components and joints of all types, including standard, nonstandard, and proprietary fittings. However, this code still does not cover fittings which have D/T ration greater than 100 for which you have to be dependent on FEA analysis.

Fig. 1: B31J Menu bars explaining the functions.

Sustained stress multipliers are used to multiply the nominal bending stress due to sustained loading and reflect the collapse capacity of the metallic piping component or joint. Where more accurate sustained stresses are needed but an equation for the sustained stress is not given in the B31 Code book, nominal stresses due to sustained moments computed using the section modulus of the matching pipe should be multiplied by the appropriate sustained stress multiplier. Where the sustained stress is needed and an equation for the sustained stress is given in the Code book as a function of the SIF and provided in lieu of more applicable data, the sustained stress multipliers developed using the method in this Standard may be substituted as more applicable data and used with the nominal stress computed using the section modulus of the matching pipe.

Broadly The code provides the following:

Fig. 2: Typical Output SIF results as calculated by B31J module of Caesar II

* Included the most applicable currently available stress intensification and flexibility factors compiled from test and analysis data for standard commercially available metallic components in a tabular format.
* Nonmandatory Appendix A provides the standard method to develop stress intensification factors.
* Nonmandatory Appendix B provides the standard method to develop branch connection flexibility factors.
* Nonmandatory Appendix C demonstrates how the new branch connection k-factors should be used in the elastic analysis of piping systems, and
* Nonmandatory Appendix D provides a standard method to develop sustained stress factors.

B31J Essentials is a FEATools (Version 3.0), but limited to only the B31J calculations (for SIFs and Flexibilities). One can access the B31J calculations by selecting the FEA Translation option from the CAESAR II Main Menu. The software starts FEATools, which provides the B31J computations for the translated CAESAR II model.

Reboiler piping Design & Stress analysis

Reboiler notes:

1- Horizontal reboilers shall be as close to the tower as practical with a minimum amount of pipe and elbows. The piping shall be stress analyzed as soon as the layout is firm. Support and anchor points shall be established at this time.
2- The following information is required by the piping designer in order to layout thermal siphon reboilers:
2-1- The elevation of the tower tangent line above grade
2-2- The elevation of the first tray and the reboiler return line
2-3- The length of the reboiler tubes and the type of outlet on the reboiler on the exchangers
2-4- The dimension from the tangent line to the tubesheet on vertical exchangers and bottom of horizontal exchangers
2-5- Most of this information is shown on the flow diagrams, vessel and reboiler specifications. The design shall review the layout with the process engineer to ensure that complete agreement is reached
3- Avoid locating the reboiler return line under the downcomer. The top of the return line shall be a minimum of 12 inches below the bottom tray or 6 inches below the seal pan if the return line must be located under the downcomer.
4- Allow sufficient room for removing tube bundles on vertical reboilers. Allow sufficient room to remove shell cover to grade.