What grade Stainless Steel for De-Ionised Water ?

[awemawson]

I'm making some new fittings for my Wire EDM machine. Electrolyte is de-ionised water which can be quite aggressive. What grade should I choose (or avoid) to minimise corrosion ?

Pictures are of parts of the machine when I was re-building it showing significant stainless corrosion - some parts were like swiss cheese!

I have no idea what grade those parts are. (Machine is 1984 Fanuc Tapecut Model M)

 

[Agroshield]

Interesting question.

Some links below.

The problem seems to be not one of corrosion per se but of the water dissolving the metal.

Answer seems to be 316 (I think 'L' for low carbon) and passivated/electropolished. Or plastic...

https://www.finishing.com/306/29.shtml
https://www.corzan.com/blog/what-is-deionized-water-and-which-piping-materials-convey-it-effectively
http://hghouston.com/resources/technical-faq/corrosion/316ss-and-deionized-water-corrosion
https://www.finishing.com/286/30.shtml
https://www.eng-tips.com/viewthread.cfm?qid=29596

 

[awemawson]

Thanks for those interesting links.

The other complication is of course that it is supporting (but not connected to) the brass 0.25 mm cutting wire, that carries a complex waveform switching voltage that at times can approach 100 volts.

 

[voipio]

Deionised water by itself is no more aggressive than ordinary tap water. It's the dissolved substances from the EDM process that creates the corrosive liquid that you end up with after machining.

I remember an experiment at school. Two bright steel nails in tubes of deionised water. One tube was sealed tight and the other left open to the air. The nail in the sealed tight tube remained shiny bright, whilst the tube left opened, to allow oxygen to dissolve, ended up with a nail that became rusty.