I took and passed the examination (both the Material Selection/Design and Corrosion Specialist) more than 10 years ago. I found the examination (and the lead-in requirements) to be basically equivalent to a PE examination (which I passed almost 30 years ago).
Is it useful? Hard to tell. I list it on my resume (although I'm not currently job seeking), but can't say it's provided any tangible benefit.
OPINION - NACE is an organization, just like any organization, that needs to maintain an income stream. In the past 20 years, NACE has, IMO, found it more beneficial to push & support inspection type certifications (CP inspector, coating inspector, etc) than the "higher level" COrrosion Specialist type certification.
//mjs
