PREN 3

[Corgas]

Colleagues:

Can PRE numbers be applied to predict resistance to MIC (Microbiologically Induced Corrosion)? After all, Mo improves the passive layer. Is there a published relationship between PREN Vs resistance to MIC?

Thanks,

Corgas

 

[metengr]

No, I would not consider PREN as a reliable means for quantifying susceptibility to MIC attack because other than Ti, metals will be susceptible to MIC attack. MIC is a complex phenomenon because you have living organisms that can thrive and produce by-products which attack material under various conditions.

 

[brimmer]

None that I know of. Part of the issue is there are many different kinds of bacteria causing the MIC, depending on evironment, food source different bacteria will be there, which will have different corrosion rates. Sometimes it will take one species to establish itself, to allow a different species later come in, etc. So it is very difficult to predict rates and resistance of metals.

 

[Corgas]

Thanks both metengr and brimmer.

Cladded vessel (separator) has shown extensive pitting due to MIC (sample already taken to id type of bacteria). Material is 304L and damage is confined to below water level (between 4 and 8 position).

What material would you recommend to repair existing cladding with weld overlay? Logic tells me that I should aim for a higher PREN material. Also, a biocide treatment is going to be put in place but it needs to be repaired.

 

[metengr]

I would repair using either 308 or 316L filler metal. There would be no need to use a material with high PREN because this will not guard





























































































































































































































































































































































































































































































































I would recommend using either 308L or 316L filler metal to weld repair the 304L cladding. Using a higher PREN filler metal is not going to help against MIC. Using a biocide treatment will be effective.

 

[EdStainless]

Only in a very general way is there a relationship.
If you select an alloy that is suitable for seawater service (6%Mo superaustenitic, superferritic, super duplex) then you will have MIC resistance. At any level less than that all bets are off.

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Plymouth Tube

 

[Corgas]

EdStainless,

Agreed. The only publication that I've seen that shows some correlation is B.J.Little, P.A. Wagner and R.I. Ray, "An Experimental Evaluation of Titanium's Resistance to Microbiologically Influenced Corrosion", paper presented at NACE Corrosion/92, Preprint No 173, 1992 . They tested AL6XN in various MIC environments.

Reference was given by A.John Sedriks


Thanks,

Corgas