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topic 4496

Hydrogen Embrittlement Testing


(2000)

Hello-

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.

KA

Kamal A.
- New York, New York


(2000)

Notch bar testing is the most common method and use to be cross referenced in the spec.

James Watts
- Navarre, Florida


(2000)

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.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota





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