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Guidance on material compatibility

Guidance on material compatibility

Guidance on material compatibility

Hi Friends,
Hope you all are doing good. I am a piping engineer and this is my first post on this forum. I am currently working on a RO plant to treat industrial waste water.

The project consist of a RO plant with many chemicals and their strengths as listed below

Item No. Chemical Concentration (by Wt.) Chemical Form

90-X9004 Sodium Hypochlorite- NaOCl 12% Liquid
90-X9009 Coagulant (FeCl3) 40% Liquid
90-X9003 Non Oxidizing Biocide 100% Liquid
90-X9002 Antiscalant 100% Liquid
90-X9010 Magnesium Chloride ( MgCl2 ) 30-40% Liquid
90-X9005 Citric Acid 50% Liquid

The above chemicals will be used during the various stages of the RO purification process as dosing and cleaning in place. However the spent cleaning in place solution, accidently contaminated water and any spillage of the above acids (from their diked area washdown) will be sent to the pit. The chemical water in the pit will then be neutralized with the below mentioned chemicals.

90-X9007 Hydrochloric Acid - HCl 33% Liquid
90-X9001 Sodium Metabisulfite - Na2S2O5 33% Liquid
90-X9008 Caustic - NaOH 38% Liquid

However the Material selection diagram specifies the material in contact with the chemical water (even though diluted with water inside pit) to be cPVC (non metallic). My problem here is that there is a jet mixer placed inside the pit for optimum mixing. The material of the mixer is not a problem as it is as well of cPVC MOC. However the supports to support this mixer is of Carbon steel. I strongly believe that the CS material is not compliant with the chemicals and water inside the pit and will corrode rapidly (after referring to some chemical compatibility charts). Hence, I would like to get some expert opionion on :

1) If CS can be used in the pit (as my standard supports only have CS material of construction)
2) If any coating is available in the market to protect the CS pipe support material from corrosion when continuously exposed to the worst case scenario of the above acid concentrations (not just for a brief period of time as most coating do).
3) If any alternate compatible material can be used and what material would that be.
4) Any other alternate ideas from any of your past experience or expertise.

your help would be very much appreciated. thanks in advance.


RE: Guidance on material compatibility

I would consider an epoxy coating of the carbon steel supports.

RE: Guidance on material compatibility

Or build the support structure out of fiber reinforced non-metallic.

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P.E. Metallurgy, Plymouth Tube

RE: Guidance on material compatibility

Thanks for the response guys. However I failed to mention that MSD specifies the pump casing to be SS316L. So I guess using SS316L for supporting instead of CS would be fine?

@metengr - what kind of epoxy coating would I have to look at, I mean is there a particular type? I am no coating expert but I believe that coatings are designed to last for a limited period of time @ a given worst case scenario concentration. Is that right?

@EdStainless - Any FRP support companies you aware of?

RE: Guidance on material compatibility

Beware of crevice corrosion between the 316L support and the 316L casing.

RE: Guidance on material compatibility

There are a few producers of FRP structural shapes and decking, google it.
It has been 20 years since I used any.

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P.E. Metallurgy, Plymouth Tube

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