Help on choosing suitable stainless steel

I would use the 303 only if the required machinablity of the part justified it.
The stainless steel groups regardless of specific alloy choice requires do care during fabrication to prevent iron (from carbon tool steels) contamination. Solution alloy treatment after welding (if possible), passification using nitric acid (or other oxidizing acid to remove free iron particles), and argon sheilding inside pipes for welding are fabrication steps often missed.
Stainless steels are suscepitble to pitting and crevice corrosion occuring from iron metal contamination.
Ed

Your water analysis is missing the chloride content. Since it is one of the important factors controlling selection of a stainless steel to resist crevice corrosion, I cannot tell you whether 304 will be acceptable or if you will need 316. Typically 304 will work to about 50 ppm, and 316 to 250 ppm.
There is a detailed 20 page reference booklet on =93Fabricating stainless steels for the water industry=94 that you can get for free from the Nickel Institute. It is Nickel Development Institute publication No 11026. See Appendix C. You might also want to look at some of the other references shown in this publication.
Go to: On the top of the page is a box labeled =93Nickel & Its Uses=94. Click on it. On the right side of the page is a column with a box labeled =93Technical Literature. Click on it. Change the search box under Technical Literature Locator to be by Catalogue No., and put in 11026. Then you can download the book. (You may have to register if this is the first time at the site).
Stainless steels also are discussed on the Corrosion doctors web site. Rouging is discussed at:
Pittsburgh Pete
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