MIC 2

[macmet]

I have looked on the net and searched this site for information regarding MIC. I am trying to find what material might work best for use in a waste water sludge system.

I have not been able to find any information rating different material's resistance to MIC. I am not sure how to approach a problem involving MIC.

I think the best method is to get the sludge tested first, find out how to treat the sludge based on the test and then pick the material.

Is this a good approach? Is one material simply better than the rest? We are considering plain carbon, stainless and galvanized steel. I have found nothing to say one of these materials is significantly better. I know ss is susceptible to pitting so I am wondering if it might actually be worse than CS.

Any thoughts?

 

[unclesyd]

What is the source of the waste water and resultant sludge?
What type equipment?

As you state all three of you materials are going to be affected by MIC. Strange as it may seem SS will generally be the worst, then CS, and then the Galvanized Pipe, the Zinc can act as a bacteriostat.

 

[macmet]

Uncle Syd,

Thanks for your reply.

The only thing I know about the sludge now is that it is coming from a municipal water treatment facility. I will be getting more information later on, definitely before we have to decide which matl to use.

The application is a holding tank. The material will be fed in one end and pulled out the other at a low feed rate. Well, that's our thinking for now. I imagine if the sludge becomes stagnant it increases the possibility of MIC?

I was worried that zinc may form ZnS.

Do you know of any good online sources where I could read more on the subject? I've done a lot of googling and search some E-journals but have not had much luck.

 

[EdStainless]

In carbon steel you may well have bacterial attack of the steel. In stainless you will have under deposite corrosion. The microbes don't actually attack the stainless.
You can use standard crevice corrosion resistance ratings to rank stainless grades. In order for a stainless to be fully resistant to fouling and MIC you really need a grade that will stand up in seawater.
For what you are looking for there are a lot less expensive ways to do it.
Coated steel and lined concreat are the most common.


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[macmet]

I was thinking about some sort of coating. I'll look into it further.

Most of the information I have read talks about either CS or SS. Uncle Syd, mentioned galvanized have superior properties to both these. Does anyone else have some thoughts or somewhere to refer me to get more information.

 

[unclesyd]

I will have to take exception to EdStainless's statement that bugs don't actually attack SS. Bugs do attack all the more common grades of SS including some of the Duplexes.

I think our CTW system was the home base of the MIC problem. This was good only in one respect it allowed use to test all sorts of materials as either piping or Hx tubes.

The very first evidence of MIC attack is the appearance of very light rust stain, normally taken as iron from other parts of the system, on the SS. SEM examination of the SS at this point reveals the start of localized corrosion with the beginning of some pits. Electrochemical studies show these areas to be extremely active. This surface corrosion progresses to the point where we call the area "bug condominiums". This is an area of general corrosion in form of inner connected channels. These channels are the initial leak paths.

In the mean time I have to agree with EdStainless that you need a material resistant to sea water as Chloride induced Stress Corrosion Cracking is a failure mode when tied in with MIC. You can have each alone or the worst case both togather. Some of the alloys that have good resistance to Chlorides, like Inconel 600, 625, 2205 had extremely poor resistance to MIC. We several lost very large Hx made from these materials after testing showed them to suitable as a safe-end material for 316L tubes to prevent SCC on the upper part of the tubes.

One thing we found out early on is there is no standard enviroment for MIC and the existing enviroment is forever changing. What works today is crap tomorrow.

I mentioned Galvanizing as galvanized pipe 1" performed quite well in our test system and in a few laboratory tests. Another material, tested a tube baffles, that showed promise was Corten steel plate. I hate to mention this but an excellent material is Terne Plate.

The only two corrosion resistant materials we’ve found that offers immunity in our enviroment to MIC and SCC are Titanium and Hastalloy C.

 

[rconner]

I think quite large quantities of ductile iron piping with various sorts of joining systems for both exposed and buried service is used for various "sludge" process piping applications in most of the major wastewater treatment (and subsequent sludge processing) facilities in the United States. Per major manufacturers and DIPRA per

http://www.dipra.org/pdf/wastewater.pdf

etc., ductile iron piping is available with standard cement mortar lining, ceramic expoxy, and also glasslinings, with the specifier's choice of lining I guess dictated by the specific process/service conditions and perhaps also in some cases to no little extent by experience and operational factors (involving in some cases I suspect decades of experience with pipelines in similar or same services) as well.
You may wish to contact some of these large, and in some cases I think quite long-lived, wastewater etc. facilities to inquire directly for their experience.

 

[unclesyd]

Here is a little more on coatings and linings.

http://www.corrosion.com/index.asp

http://www.corrosion.com/index.asp

 

[EdStainless]

Syd, Well, sort of. To start the process, no microbes will directly metabolize metal from a stainless alloy. The bio-slime itself creates crevice corrosion conditions (oxygen depleation and impurity concentration). The waste products from the bug's metabolism (or decomposition) result in chemicals that will disolve metals. As metal disolves everything gets worse.

I have never seen MIC in an alloy that could withstand seawater service. This includes 6%Mo superaustenitics and super ferritics. Now poor quality welds in high alloy materials are another issue. I have seen welds in 625 and "C" alloys fail a number of times.

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Rust never sleeps
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[macmet]

I think I will look into using the 6% moly alloys (ss312?) as well as SS327.

I looked at different super ferritics, but we will require some welding and I believe that will be more difficult with these ferritics as opposed to the austenitics and superduplexes.

I hope these choices make sense, please let me know if I'm way off here.

Cheers

 

[EdStainless]

No, not 321, but alloys like AL-6XN, 1925hMo, 25-6Mo are teh superautenitics. To be honest, they are way too expensive these days.
Ductile Iron doesn't hold up too well either in a active environment.
Could you do this in concrete? With a good lining this should last a long time. Though you might want to use stainless re-bar.

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Rust never sleeps
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[macmet]

Edstainless,

If all suitable options are really expensive, concrete may be an option. If it's cheaper, it's an option. If I start thinking about concrete though, I'm worried we would need so much of it that it would become more expensive.

What about lining CS with one of the more resistant alloys? Then what happens if part of the lining gets damaged exposing the CS? I would think that would be worse.

I was also under the impression that 327 was a superduplex alloy and 312 was a superaustenitic. I am having trouble with all of these 'super' alloys and their designations, I've only been out of school for a year and I'm use to only the very basic forms of steels. I guess I'm still trying to learn what's what.

Thanks for the help

 

[EdStainless]

I am not sure that this is the right place.
Contact me and I'll send you some presentation materials describing modern stainless grades, properties and corrosion resistance.
Isn't someone writing a book about this? (wink, wink)

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Rust never sleeps
Neither should your protection

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[macmet]

Ed,

I filled out the questionnaire on the webpage in your signature.

 

[stanweld]

All of the waste water sludge tanks for large scale waste water treatment facilities that I have been involved with have been constructed of lined concrete or coated carbon steel (smaller tanks). Hardware (piping and mechanical componenets) have been constructed from type 316L, 904L, 254HMO and 6% Mo super austenitics and FRP. The higher grades of stainless have generally performed well. If your tank is small you may wish to use FRP as it has been used for small waste water treatment facilities in industrial plants.

 

[macmet]

Stanweld,

By FRP do you mean fibre reinforced plastics?

 

[stanweld]

macmet,
Yes.

 

[EdStainless]

For medium sized tanks FRP would be a good option, especially if they are in a building. Sunlight )UV) is the biggest worry with resin systems.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

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