Stainless Grade for High PH in Industrial Wastewater

[dodson]

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?

 

[nickypaliwal]

For de-aerated water: Chloride content is not high (223ppm) and SS316 /316L should be fine. (This is the case generally claimed for underground water)

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.

 

[EdStainless]

It wouldn't bother me to see 2205 used in this (aerated or not).
Will there be any scale formation? If so then I would use coated CS.

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P.E. Metallurgy, Plymouth Tube

 

[nickypaliwal]

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

 

[EdStainless]

CaHO can be resisted by any grade of stainless, and for this Cl level 2205 would be the best option.
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