What is the fatigue limit for copper pipe with a factor of safety of 5?

[MysticDream]

TL;DR Summary

Trying to estimate the fatigue limit for very low stress.

I’m wanting to estimate the fatigue limit for copper piping that has a factor of safety of about 5 (yield FOS). All I can find online is graphs of curves that go to about 100 million cycles, but I need more. Obviously for these materials that don’t have a distinct fatigue limit like steel, the slope of the curve goes more horizontal as stress levels decrease, but I want to know what the slope is up to a billion cycles if possible. This piping will be subjected to external gas pressure cycles of 300 cycles per min, 24/7. That means after one year, it will have gone through about 157,680,000 cycles. I need to have a reasonable estimate of how long these would be in service before they fail from fatigue. If anyone has any insight into this, I’d greatly appreciate any assistance.

 

[hutchphd]

I would think electrical conductors see 50 Hz continuously (in UK at least) for many decades. Perhaps there is some data about any mechanical degradation evidenced from this. How big is the pressure and the pipe?

 

[MysticDream]

I would think electrical conductors see 50 Hz continuously (in UK at least) for many decades. Perhaps there is some data about any mechanical degradation evidenced from this. How big is the pressure and the pipe?

Yeah, that’s a good point, but that max stress is probably way lower than the max stress in my design with a FOS of 5. Electrical conductors probably have a FOS of 100 or more given that the stress it’s subjected to is so small.

The pipe is .625” OD with a wall of .028”. The min and max external pressure in the cycle is from 300 to 350 psi. An FEA showed a yield FOS around 5 for that max pressure of 350.