August 28, 2019

How to use ASME B31J-2017 and FEM for SIF and k-factors for Stress Analysis

By Alex Matveev

How to use ASME B31J SIF and k-factors in PASS/START-PROF

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 ratio greater than 100 for which we have to be dependent on FEA analysis.

So in nutshell, The code ASME B31J-2017 offers us revised, more accurate SIFs and flexibility factors for tees, bends and reducers. By using these revised SIFs and flexibilities, the stress analysis results become more accurate.

Now the question is How to use it in START-PROF Software?

Very easy. No additional software or model convertion is needed. Just turn on this checkbox:

Click to enlarge

If “ASME B31J” option is activated then all tees are automatically modeled with simultaneous use of run and branch springs with flexibilities and stress intensification factors calculated according to ASME B31J code requirement:

Tee model

Start-Prof software allows activating “ASME B31J” option for ASME B31.1, B31.3, B31.4, B31.5, B31.8, B31.9 and EN 13480 codes. If some of k-factor becomes less than 1.0 Start-Prof assumes this spring as rigid:

ASME B31J covers only standard straight tees and D/t less than 100. For nonstandard tees, for example lateral and tees with D/t greater than 100 Nozzle-FEM software can be used. It can calculate SIF and k-factors which can be used in START-PROF software using nonstandard tee.

In the next version 4.84 the NOZZLE-FEM software will be embedded into START-PROF and allow to calculate using FEM methods SIF and k-factors for tees. Also embedded NOZZLE-FEM will allow to calculate nozzle flexibility and check nozzle stresses using FEM.

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