Chloride limits for stainless steels 3

[JasonLouie]

We are chosing materials for a multistage sump pump for the retention pond for the hot lime softener blowdown. The normal operating temperature is 5C with upsets to 98C (cannot quantify how often there will be upsets). Chlorides are 4800-22000ppm and there is 5% lime sludge (i.e. erosion from magox crystals). pH is 9.5 and the water is oxygenated.

1) 12Cr is an option, although I do not know how 12Cr reacts to 22000ppm Cl-. We also do not know how severe the pitting will be.

2) Hard chrome plating could be used, but again I do not know how severe the Cl- pitting would be.

3) Would super duplex (e.g. 2507) stand up to this environment assuming the worst case of 98C and 22000ppm Cl-?

4) Any other options for materials (other than Hastelloy/Inconel)?

Thank you very much for any help you can provide!

 

[EdStainless]

You have a grasp of the keys.
Low temp helps, higher hurts.
Higher ph helps.
Abrasion hurts.

In pumps I like to think of the parts in an order of how critical thy are. First is the shaft, it must survive. A cold worked "C" alloy (C276, C22, 59 or 686) would be a good place to start. Then the impellers, a super duplex will offer good pitting resistance and the high strength will offer at least some abrasion resistance.
The bowls are the least critical parts. If anything goes wrong you want them to corrode first and provide galvanic protection to the other parts. You might look at a 6% Mo superaustenitic grade.
You can't make all of the parts last forever, but you can control how it fails.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[strider6]

why the pH is so high? there is something else in the fluid?

S.

http://www.corrosionist.com

 

[JasonLouie]

The hardness in the water is removed by the hot lime softeners. Lime, Magnesium oxide and soda ash are added to remove the majority of the hardness. This softened water is used as BFW.

 

[TVP]

EdStainless gave you excellent advice. Neither option 1) nor option 2) are suitable in my opinion.

 

[castmet13]

I concur with some of the information you have already. I think that the Superaustenitic grades (6Mo or higher) would be a great stepping stone. A concern will be critical crevice temperature and I do not know how you would work to avoid it at 98C - high, obviously.

I would look into CK3MCuN (6Mo), CN3MN (6Mo), or a patented alloy Alloy 31 (7Mo). Of all of the alloys, the Alloy 31 has the highest numbers for PRE and CCT, without getting to the Hastelloy / Inconel range.

The patent holder is MetalTek International in Wisconsin, if you have trouble finding them.

 

[0707]

At chloride levels environments as low as 10ppm stainless steels are susceptible to SCC. At your service chloride levels, stainless steels should not be used.

In complement to others suggestions I would add SEA-CURE S44660 and also AL-6XN

For more information about this subject go to:

http://www.seacuresolutions.com/pdf/PerformanceofSuperferriticinHighChloride.pdf

luismarques

 

[SJones]

Since the conditions are not a million miles away from seawater, the wealth of experience in this environment, particularly in MSF desalination, can be drawn upon. The original poster has a slight dilemma in that upset conditions have to be catered for but they may be so infrequent as to be negligible.

I would have a troll through the hits in the following:

http://www.google.co.uk/search?hl=e...ection++pumps++desalination&btnG=Search&meta=

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[JasonLouie]

SJones is correct...normal operating conditions will be at the lower ends of the described process limits, but I have to mitigate the upset conditions of high chlorides and high temperature.

Thank you very much to SJones for the Google hits. I read through the desalination papers/info and it looks like 254SMo and superduplex are frequently used. I could not find process information regarding what temperatures and chloride concentrations are typical in desalination plants. I do not have experience specifying superduplex for 22000ppm and 98C...I guess I don't have that "warm fuzzy feeling" due to my lack of experience.

Can superduplex (such as 2507) be used successfully as a pump impeller at 98C and 22000ppm chlorides? I looked in MTI 27 and MTI 15, but only 2205 is on the graphs (although I wouldn't use 2205 in this case).

 

[strider6]

The "NIDI ref 11004 - materials for saline water , desalination and oilfield brine pumps". is a good paper to select materials for pumps in saline water. 98°C for a duplex SS is high in terms of pitting and crevice corrosion and if you look at this data:

http://www.sandvik.com/sandvik/0140/internet/se01598.nsf/cdatas/98A6DA5240941BAF41256618006F4439

you see that the limit is approx 90°C.
In terms of Stress Corrosion the limit is well above and it's not a concern.
the problem at this point is not only the impeller, which materials will you select for the rest of the plant to work at 98°C with something very close to seawater? you should go to a nickel alloy to withstand such a conditions in my opinion.
regards
S.

http://www.corrosionist.com

 

[metengr]

JasonLouie;
I have a suggestion regarding corrosion information for stainless steels and duplex steels. Go to the web site below and request the Corrosion Handbook by contacting Outokumpu directly. They have an on-line version, however the hard copy is what you need because it contains more comprehensive information. I had received it in the mail some time ago.

http://www.outokumpu.com/applications/documents/start.asp

 

[SJones]

JasonLouie,

Go for 25Cr super duplex with a minimum PREN of 40 - peanuts difference in price.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[EdStainless]

Your pump shaft is critical and must be totally immune to corrosion. I can't see using less than a Ni alloy, either a "C" type NiCrMo or maybe a Monel K=500.
The impellers must be tough, a superduplex or superaustenitic would work.
You do not want to use the same material for all parts of the pump. The service is enough different that you would suffer early failure of impellers if all parts were the same.

The bowls could be a lesser material, maybe even a type 2 NiResist would work.
Don't use a 12%Cr for any parts and don't rely on plating.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[joeswoes]

...or you could simply install a fiberglass pump.