Hydrogen Embrittlement Testing(2000)
What's a good test to establish whether or not the failure is due to Hydrogen Embrittlement (for fittings)?
Is a sustained load test for 72 hrs with 85% max. allowable load a good criterion?
Fittings are made from 8740 steel, Heat treat to 170-190 ksi and CAD plated per QQ-P-416 [link by ed. to spec at Defense Logistics Agency, dla.mil] and subsequently baked for 23 hrs.
- New York, New York
Notch bar testing is the most common method and use to be cross referenced in the spec.James Watts
- Navarre, Florida
James is correct. A sustained load test on a notched tensile bar is the preferred method for testing for hydrogen embrittlement. I am not up on the current requirements, but the test used to be 200 hrs minimum at a sustained load of 75% of the ultimate tensile strength of the material. I do not believe that 72 hours or a load of 85% of max allowable is adequate. Assuming that the max allowable is probably only 25% of yield, this load is less than 1/4 of the typical sustained load test criterion.
Without a machined notch, the effective stress is even less.
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