OK, how corrosive is this stuff? 1

[PeterCharles]

We're looking to handle some sludge cake from a water treatment plant. The specification makes a specific reference to Chloride Concentration, and quotes it as
Average 486 mg/l
Maximum 2000 mg/l

I have to hold my hand up and say I've no idea what is really means. How corrosive is this? We can fabricate contact parts from mild steel, 1.4003 (3CR12) corrosion resistant steel, 304 or 316 stainless steels.

Any advice would be appreciated.

 

[micalbrch]

With 486 mg/l it is slightly corrosive. 2000 mg/l corresponds to 0.2 % which is not good for mild steel but fore sure for 1.4003, 304 and 316. So, you are save with one of the those. I would not choose mild steel if 2000 mg/l could really occur. Check rubber lined steel instead of stainless steel. Depending upon the part it might be cheaper and is excellent for your chloride concentrations.

 

[PeterCharles]

Micalbrch,

Thanks for the prompt response, we'll go with 1.4003 (which is what we've used before).

 

[ash9144]

You also need to check temperatures. High temperature plus chloride can result in SS cracking.

 

[PeterCharles]

This is delivered by lorry, no more than 30 deg C.

 

[strider6]

chloride concentration is just one factor that you've to consider to assess the corrosion performance of a material.. the chemical composition of the sludge cake, water content, if the water is oxygenated or not..
regarding the Stainless Steel, usually 304 is used for Cl conc up to approx 200-500 ppm while 316 for conc up to 1000 ppm.

Stainless Steel properties



Vitt

Corrosion & Rust Prevention Control

 

[PeterCharles]

Is 200-500 ppm the same as 200-500 mg/l ??
There isn't really any free water in the sludge cake, as to whether any water in the cake is oxygenated, who knows.

 

[micalbrch]

Yes, 200-500 ppm corresponds to 200-500 mg/l.

 

[EdStainless]

Don't use 304 or 316, there is no chance that they will ever hold up in 2,000 ppm Cl.
Look at duplex stainless grades, 2003 or 2205 would be good options.
What is going to happen is you sludge is not going to be real dry. Then you will have a high chloride mud stuck to the surface. It is crevice corrosion under this mud that you need to be concerned about.

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