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Tips January - March 2001
Joint Efficiency Factor and Material Allowable Stresses
Question: I am using ERW pipe (Electric Resistance Welded, not Seamless pipe) from the piping code (B31.1/B31.3) that has a joint efficiency factor of 0.85. In CAEPIPE, when I changed the joint efficiency factor input under Materials, the material allowables did not change. Why? (B31.1 lists different allowable stresses for different joint factors/materials).
Reply: The material allowables are not joint efficiency factor dependent. The allowable stresses in Caepipe for different materials are as published in B31.1, Appendix A, (and B31.3, Appendix A). All of the materials have a joint factor of 1.0. So, if you have a material (such as ERW) with a different joint factor, 0.85, you could input that under the material input screen. The only resulting change CAEPIPE will make will be to the calculation of the Allowable pressure (refer equation eqn.4 of para 104.1.2). But, the allowable stresses should not and will not change owing to the different factor.
Same applies to B31.3 Appendix A. B31.3 does not list the same grade material with different joint factors like in B31.1. So there is no confusion. There is only one set of allowable stresses (in CAEPIPE) for each material entry which is what the code contains. Any change to the joint factor will affect only the calculation of Allowable pressure (refer para 304.1.2).
Note: We strive to provide accurate data for the material properties. Sometimes, typographical errors do creep in. It is recommended that you verify the properties before using them.