ASME B31.3 APPENDIX V 1

[pegus]

Good day,

I am currently developing a pipe system design that needs to be aligned to ASME B31.3 code. As this pipe line will be under high temperature (1200F), I need to use the APPENDIX V (Allowable variations in elevated temperature service), which uses the Linear Life Fraction Rule to get the rupture life and usage factor, however I have a few doubts regarding this method:

-What does exactly the usage factor represents?
- is there any equation that gave us 0.5% or 1% creep strain time besides rupture life time? (The equation that is included in the standard for rupture life is tri=10^a, where a depends of the Larson miller parameter)

Thanks in advance!

 

[NRP99]

Answer to first question-Usage factor (or you can call it as damage factor for simplicity) represents ratio of actual service life in creep condition/calculated creep life based on long term stress-high temperature condition and based on design dimensions. For example, usage factor of 0.7 means that the 70% of the actual life will be consumed(or damage happened to) by the component under given stress and creep range temperature. Similarly usage factor of 1 means 100% of actual life is consumed(or damage happened to) by the component under given stress and creep range temperature.

Answer to second question- Don't know exactly. But I think you need to use creep power law equations. You can refer any textbooks on the creep design. I guess code gives life in terms of time-day/hour and not in terms of strain rate.