sulfur, chloride and 304 vs 416 2

[caroley]

We are three chem students having a debate regarding the suitablility of 304 vs 416 SS for use in septic tanks. We have seen corrosion and think it is due either to chloride in the water or to excessive biofilm growth. Does anyone have any comments?
Also,
- HOW (chemically) does sulfur in SS reduce corrosion resistance? We know it forms a precipitate with Manganese (is this true always?) but don't know the direct chemistry of this.
- do chloride ions react directly with sulphur in stainless steel? Wouldn't they react with metals in SS first?
MANY MANY THANKS!!!

 

[Metalguy]

This thread will probably get pulled, but you should know that the effect of the Cl ion is to penetrate the protective Cr oxide film on SS, allowing attack of the metal itself.

MnS is formed preferrentially to FeS, which is a good thing when hot-working steels. There are ratios for the required amount of Mn vs. S, depending on the C level. But all of the sulfides which form are not metals, and are the usual site where pitting starts. There is little or no Cr in them, hence no Cr oxide and no protection.

If this thread survives we can talk about MIC later. Where do you go to school?

 

[kenvlach]

I have never heard of SS septic tanks; the traditional material is concrete, and some newer ones are plastic (probably PE).

Re corrosion of S-containing SS: any exposed sulfide (generally MnS although in some cases TiS_x or CrS) forms a galvanic corrosion cell with the adjoining matrix. For thorough explanation, see recent studies in The Journal of the Electrochemical Society, which can be searched at

http://ojps.aip.org/vsearch/servlet/VerityServlet?KEY=JESOAN&CURRENT=NO&ONLINE=YES

These are some studies on the corrosion of SS which may interest you:

'Microelectrochemical Measurements of the Dissolution of Single MnS Inclusions, and the Prediction of the Critical Conditions for Pit Initiation on Stainless Steel', E. G. Webb, T. Suter, and R. C. Alkire, J. Electrochem. Soc. 148, B186 (2001)

'Effects of Temperature and Chloride Concentration on Pit Initiation and Early Pit Growth of Stainless Steel,'J. O. Park, S. Matsch, and H. Böhni, J. Electrochem. Soc. 149, B34 (2002)

'IR Mechanism of Crevice Corrosion for Alloy T-2205 Duplex Stainless Steel in Acidic-Chloride Media,' J. N. Al-Khamis and H. W. Pickering, J. Electrochem. Soc. 148, B314 (2001)

'Electrochemical Study of Resistance to Localized Corrosion of Stainless Steels for Biomaterial Applications,' J. Pan, C. Karlén, and C. Ulfvin, J. Electrochem. Soc. 147, 1021 (2000)

'In Situ Local Dissolution of Duplex Stainless Steels in 1 M H₂SO₄ + 1 M NaCl by Electrochemical Scanning Tunneling Microscopy,' M. Femenia, J. Pan, and C. Leygraf, J. Electrochem. Soc. 149, B187 (2002)

'Pit Initiation on Stainless Steels in 1 M NaCl With and Without Mechanical Stress,' T. Suter, E. G. Webb, H. Böhni, and R. C. Alkire, J. Electrochem. Soc. 148, B174 (2001)

'In Situ High-Resolution Microscopy on Duplex Stainless Steels L. F. Garfias and D. J. Siconolfi, J. Electrochem. Soc. 147, 2525 (2000)

'Effect of Cold-Working in the Passive Behavior of 304 Stainless Steel in Sulfate Media,'A. Barbucci, G. Cerisola, and P. L. Cabot, J. Electrochem. Soc. 149, B534 (2002)

'Pit Initiation at Single Sulfide Inclusions in Stainless Steel,' Eric G. Webb and Richard C. Alkire, J. Electrochem. Soc. 149, B286 (2002)

'Pit Initiation at Single Sulfide Inclusions in Stainless Steel,' ibid., B280 (2002)

'Pit Initiation at Single Sulfide Inclusions in Stainless Steel,' ibid., B272 (2002)

'Dissolution and Repassivation Kinetics of a 12.3Cr-2.6Mo-6.5Ni Super Martensitic Stainless Steel,' Jakob Enerhaug, Unni M. Steinsmo, Øystein Grong, and Leif Rune Hellevik, J. Electrochem. Soc. 149, B256 (2002)

'Spatial Interactions among Localized Corrosion Sites,' T. T. Lunt, J. R. Scully, V. Brusamarello, A. S. Mikhailov, and J. L. Hudson, J. Electrochem. Soc. 149, B163 (2002)

'Repetitive Nucleation of Corrosion Pits on Stainless Steel and the Effects of Surface Roughness,' G. T. Burstein and S. P. Vines, J. Electrochem. Soc. 148, B504 (2001)

'Computer Simulation of Single Pit Propagation in Stainless Steel under Potentiostatic Control,' N. J. Laycock and S. P. White, J. Electrochem. Soc. 148, B264 (2001)

'Scanning Electrochemical Microscopy Detection of Dissolved Sulfur Species from Inclusions in Stainless Steel,' C. H. Paik, H. S. White, and R. C. Alkire, J. Electrochem. Soc. 147, 4120 (2000)

'Explanation for Initiation of Pitting Corrosion of Stainless Steels at Sulfide Inclusions,' David E. Williams and Ying Yang Zhu, J. Electrochem. Soc. 147, 1763 (2000)

'Corrosion Pits in Thin Films of Stainless Steel,' M. P. Ryan, N. J. Laycock, H. S. Isaacs, and R. C. Newman, J. Electrochem. Soc. 146, 91 (1999)

 

[PVRV]

1. Yes, you are correct. Both Chloride and biofilm growth
have the potential to break SS passive film. Thats what
Metalguy has outlined.

2. As for choice of materials;kenvlach is correct both
should not be considered. However, which one would
last longer 304(18-8).

3. Sulphur literally sucks chromium out of steel and
creates locations where pitting will occur. As Metalguy
suggested. However, at times sulphur is intentially
added to enhance machinability; as is the case with
the martensitic grade you highlighted 416.

4. Sulphur & Manganese interact in 304 & 416 to form
manganese sulphide which lowers resistances against
pitting corrosion. I dont think manganese sulfites
form in view of the metalurgical phases in question.
But Metalguy can address that.

5. Take a close to look to melting temperatures that should
shed some light.

6. Pitting corrosion is largely attributed to the chloride
content and aggitated by an increase in temperature.
What does sulphur do refer to item (3) and it lowers the
PRE number since it removes Cr.


References:

Chawla, S.L., & Gupta, R.K. (1993). Materials Selection for Corrosion Control. Materials Park, OH: ASM International.

Davis, J.R. (1994). Stainless Steels. Materials Park, OH: ASM International.

Dillon, C.P. (1995). Corrosion Resistance of Stainless Steels. New York: Marcel Dekker, Inc.

Marcus, P. & Oudar, J. (1995). Corrosion Mechanisms in Theory and Practice. New York: Marcel Dekker, Inc.

M/DE Special Report. (1963). Corrosion (No 202). New York: Reinhold Publishing Corp.

Schweitzer, P.A. (1983). Corrosion and Corrosion Protection Handbook. New York: Marcel Dekker, Inc.

Watkins-Borenstein, S. (1994). Microbiologically Influenced Corrosion Handbook. New York: Industrial Press.



Cheers

 

[Metalguy]

Either we scared them off or it's spring break. <g>

 

[caroley]

Thankyou all for your help!
To answer, we are first year chem uni students from Australia - sorry there is a bit of a time lag.
A friend of ours is a plumber and was using SS pumps in the septic tanks that he ended up having to replace (not SS tanks - sorry for the confusion) and we were trying to work out what went wrong over a few beers one night.
We were trying to work out from the reactivity of sulfur just what it would react with - to be honest we are still a little confused with regards to how the exact chemistry works but haven't made it through all those papers you kindly sent us. We would have thought that CrO would bind preferentially to CrS since O is more electronegative than either Cl or S. But perhaps after some more reading and alcohol it will all become clear.
As you can tell, we basically know nothing about SS - but thanks again for you help!

 

[Metalguy]

*IF* the pump problem was S related, it might have simply been a dilute H2SO4 attack. Sulfate-reducing bacteria (SRBs) are really nasty guys, and they make H2SO4 just for kicks. You can study them (desulfovibrio desulfuricans is a common one)if you want to give up some ethanol time.

I have some interesting stories about them, but I type way too slow to crank them out.