Stainless Grade for High PH in Industrial Wastewater
Stainless Grade for High PH in Industrial Wastewater
(OP)
I would like to spec a stainless steel column in an industrial wastewater tank. The column would be partially submerged 99% of the time. The water is extremely basic w/ a ph around 10 and has a CaOH content of 700ppm. I am attaching the latest lab report for mineral content in the water. The column needs to be around a HSS6x6x3/8. Can you please advise me on what grade of stainless would provide the best corrosion resistance?





RE: Stainless Grade for High PH in Industrial Wastewater
For Aerated water: Stainless Steel would not be a good choice. It is recommended to use carbon steel/cast-iron with some organic /non-metallic coating else use copper alloys.
As I understand, there is no separate criteria for material selection for saline water and sea water is used as a basis to characterize behaviour of metals.
RE: Stainless Grade for High PH in Industrial Wastewater
Will there be any scale formation? If so then I would use coated CS.
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P.E. Metallurgy, Plymouth Tube
RE: Stainless Grade for High PH in Industrial Wastewater
2205 is better than 300 series SS but generally faces crevice corrosion problems.
Super Duplex SS (25% Cr) and 6Mo can be used for sea water but for lower temperatures only (below 25-30degC).
For materials permanently submerged in sea water, NORSOK M-001 gives Alloy 625/Titanium/GRP as options for Materials of construction. However, it assumes room temperature of North Sea (6-17 degC).
Titanium and GRP can be easily used for up to 70-75 degC. I am not sure for Alloy 625.
Refer below link which I found addresses similar issue:
http://www.eng-tips.com/viewthread.cfm?qid=249509
RE: Stainless Grade for High PH in Industrial Wastewater
316 would be marginal, at high pH it would be OK, but in the splash zone I would worry about pitting and possible SCC.
There is no reason to go to higher alloy grades unless you are working above 70C.
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P.E. Metallurgy, Plymouth Tube