316 SS with Chlorides up to 10.000 ppm 1

[Jens12]

Hello,

our Contractor recommends 316 SS Agitator shafts & impellers for the use of agitating PHC Sludge in big storage tanks (Ø5000) at a temperature up to 115°C and a Chloride value up to 10.000 ppm ! The tanks are made of CS with painting. I have big concerns of using 316 SS in such an environment but the supplier of the agitators seems to be very confident.
Has anybody applicable experience for this case of operation ?

regards, Jens

 

[Metalguy]

Does the guy sell pump parts on the side?

 

[Jens12]

Hi Metalguy,

I assume you disagree with the proposal ...

 

[EdStainless]

Based on my experience, no chance.
Between pitting and CSCC you have some issues.

If this was a high pH application with lots of exposed CS to provide galvanic protection, then maybe.

I would be thinking about alloys like 2205. You will still get pitting eventually, but it would give you good CSCC resistance.

Ask for referances, with operating conditions.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Metalguy]

>"I assume you disagree with the proposal ..."<

Hmm, guess I wasn't clear enough. The combination you stated is almost sure to fail-the conditions are way beyond what 316 can resist. While it might survive for a while in operation, if the pump is shut off for a few days the pitting could be severe.

A 9% Mo SS might be able to cope.

 

[mcguire]

At this temperature and [Cl] you will need 2507 (S32750) or equivalent to avoid pitting. 316 will get you to 25C and 2205 to about 70C according to Gunn in "Duplex Stainless Steels".

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[robsalv]

IMHO, the contractor doesn't have a clue!

You can expect CSCC and pitting with austenitic stainless steels in environments where >65C, >50ppm chlorides are present. Add stress, pH variations, sulfur and all bets are off.

I think I'd even have doubts about the CS coated tank. A sludge suggests abrasives... what happens to CS where the coating chips or wears thin???

This is a curly one alright. Sounds like a job for an exotic steels.

What was the outcome??

Cheers

Rob

 

[FIF99]

Hi,

I agree mcguire and robsalv. Even Duplex isn't suitable at this temperature. Exotics are to my opinion the only possibility.
You may consider the high alloy 6Mo (SMO) steel.

Regards.

 

[Jens12]

Hi guys,

thanks for all your interesting comments. As this is obviously really a tricky problem I have now almost as much different opinions as people are involved.
Our Contractor is now proposing to use just Carbon Steel in order to avoid pitting/CSCC assuming that Corrosion on CS will be lower because consistent on the whole surface.
By the way, Supplier of the agitators also propose CS.
What is your opinion on CS ?

regards
Jens

 

[stanweld]

If the solution is deaerated, bare carbon steel could prove effective. If not the carbon steel must be adequately protected with a suitable coating. Have you thought about using Aluminum bronze or copper-nickel alloys for this service?

 

[EdStainless]

In my experience with pumps I found that you could get fair life out of systems that were 'desinged to fail' as long as you controled what failed first.

What is the oxygen level? Saturated or deairiated? If there is little or no O2 then carbon steel tanks and 2205 mixers will last a while.
With high O2 levels you will need more robust materials. What about non-metals?

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm