Yield Stress Values at Temperature

[rjstephens]

Hi all, I am a piping eng in RSA and am required to perform some calcs on hot-tapping into some API 5L grd B pipework. The spec. that I am using requires a stress calc. using the Yield stress at the ope. temp & press. I cannot find any tables in B31.3 & would like some input if any one can help.

 

[JohnBreen]

Hello,

Actually the value are in Appendix A of B31.3 but you will have to "back them out" of Appendix "A", Table "A-1". You will notice when reading B31.3, paragraph 302.3.2 (d), that the allowable stress "at temperature" is the lower of 1/3 ultimate strength or 2/3 yield strength. For API 5-LGrade B it will be 2/3 yeild up to the temperature where creep would define the allowable stress. With that in mind, if you multiply the allowable value "at temperature" from Table "A-1" by 3/2, you will have the tield stress at temperature. Pressure will not affect this calculation. So, for this material, up to 400 degrees F. the yield is 30 ksi, up to 500 degrees F. it is 28.35 ksi, up to 600 degrees F. it is 25.95 ksi, up to 650 degrees F. it is 25.50 ksi, up to 700 degrees F. it is 24.75 ksi, up to 750 degrees F. it is 19.50 ksi, and up to 800 degrees F. it is 16.20 ksi, (if I have got my sums right). Don't use this material above 800 degrees (see Appendix "A", note 57).

Best regards, John.

 

[rjstephens]

Thankyou for your reply, that makes life easier.