AndrewTT
Mechanical
- Jul 14, 2016
- 261
I have a compression screw that has a conical tip that terminates in a spherical radius. In assembly the tip of this screw sits in a very shallow dimple. The assemble must pass many tests but the two I am here to discuss are a 30-day salt fog exposure (20% by weight sodium chloride) and a 500-hour boiling MgCl2 test (for stress-cracking).
Originally this screw was designed to be made from S303. The S303 screw exhibited a crevice corrosion type failure in the 30-day salt exposure test. The same screw geometry, made from Monel 400, successfully passes this test but loses material during the MgCl2 test. An Ammonia environment may be the more appropriate stress-cracking test for a Monel component, but the assembly MUST pass the MgCl2 test. Passing criteria is no cracking, no delamination, no degradation.
I am now considering Inconel 625, Inconel 718, and Hastelloy UNS-N10276 (C-276).
I am not a materials expert so any input is appreciated. Material/screw cost is not a huge concern. Thank you very much.
Originally this screw was designed to be made from S303. The S303 screw exhibited a crevice corrosion type failure in the 30-day salt exposure test. The same screw geometry, made from Monel 400, successfully passes this test but loses material during the MgCl2 test. An Ammonia environment may be the more appropriate stress-cracking test for a Monel component, but the assembly MUST pass the MgCl2 test. Passing criteria is no cracking, no delamination, no degradation.
I am now considering Inconel 625, Inconel 718, and Hastelloy UNS-N10276 (C-276).
I am not a materials expert so any input is appreciated. Material/screw cost is not a huge concern. Thank you very much.
