Chemical analysis is a complicated thing. When a customer calls and says, ‘I need to know what material I have’, I know that I want to use our OES machine. When another customer calls and says, ‘I want to know what gunk could be causing porosity in my welds’, I know I would rather pop it in the SEMand check with EDS before exploring further options. What I don’t know, is what to say when a customer calls and says, ‘This can’t be right. I checked it with my EDS and it said that it was XYZ!’
While both methods have their advantages (OES has good accuracy and is fast, EDS can give you a surface analysis), you need to be careful which one you choose to analyze your part. OES is great for weld metal qualifications, base metal qualifications, and identification of an alloy, while EDS is great for screening of surface impurities and first checks on particles stuck in microstructures.
In the end, both methods are good for specific tests, but be sure you know what you want your end result to be prior to requesting either of these tests.