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April 29 - May 5, 2013

What type of generic coating is required to protect the inside of a tank containing liquid with pH ranging from 2 to 13 and operated at 65-80°C? Why?



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Selected Answers

From William Slama of International Paint/Ceilcote Products on May 2, 2013:
     This is a correction to what I submitted previously First, it is important to realize that the pH range of 2-13 is generally considered moderate with regard to chemical aggressiveness to most polymers. For a pure acid solution, concentrations of about 0.1% sulfuric or hydrochloric acids would have that pH, although in buffered solutions, a higher concentration would be found to have that pH. Lime juice is about ph 2. Similarly, a pure alkaline solution of sodium hydroxide or potassium hydroxide would register pH of 2 at 1 to 2% concentration. So just knowing the pH alone doesn’t tell the story with regard to selecting a good lining. Some organic acids or other organics can be aggressive to polymers within that pH range. That being said, a vinyl ester or novolac vinyl ester or novolac epoxy system would probably withstand that range well. A bis A epoxy may even suffice. So, as said above, the pH range isn’t enough information for a confirmed lining recommendation. The other factor is, of course, the temperature. A singular issue with pH over 12 at temperatures over 120 F is the potential aggressiveness of the alkaline material to silica or silicatious filler content within the lining. In those cases, a barrier layer of the resin with a synthetic veil or carbon- or graphite-filled top (shield) coats are generally used. Independent of pH, for temperatures in that range, the lining must protect from water permeation in aqueous environments. For metallic substrates, a combination of external insulation and good permeation resistance of the film must be provided to avoid underfilm corrosion and subsequent blistering (cold wall effect). In many cases, large glass flake reinforcements are used to enhance permeation resistance. Concrete substrates are easier to protect in that regard since some water permeated through the lining will not cause corrosive degradation of the concrete, and permeated water can pass through the concrete porosity without much underfilm pressure buildup.

From William Slama of International Paint/Ceilcote Products on May 1, 2013:
     First, it is important to realize that the pH range of 2-13 is generally considered moderate with regard to chemical aggressiveness to most polymers. For a pure acid solution, concentrations of about 0.1% sulfuric or hydrochloric acids would have that pH, although in buffered solutions, a higher concentration would be found to have that pH. Lime juice is about ph 2. Similarly, a pure alkaline solution of sodium hydroxide or potassium hydroxide would register pH of 2 at 1 to 2% concentration. So just knowing the pH alone doesn’t tell the story with regard to selecting a good lining. Some organic acids or other organics can be aggressive to polymers within that pH range. That being said, a vinyl ester or novolac vinyl ester or novolac epoxy system would probably withstand that range well. A bis A epoxy may even suffice. So as said above, the pH range isn’t enough information for a confirmed lining recommendation. The other factor is, of course, the temperature. A singular issue with pH over 12 at temperatures over 120 F is the potential aggressiveness of the alkaline material to silica or silicatious filler content within the lining. In those cases a barrier layer of the resin with a synthetic veil of carbon- or graphite-filled top (shield) coats are generally used. Independent of pH, for temperatures in that range, the lining must protect from water permeation in aqueous environments. For metallic substrates, a combination of external insulation and good permeation resistance of the film must be provided to avoid underfilm corrosion and subsequent blistering (cold wall effect). In many cases large glass flake reinforcements are used to enhance permeation resistance. Concrete substrates are easier to protect in that regard since some water permeated through the lining will not cause corrosion.

From Per Gabrielsson of Free Lance Consultations and Inspections on May 1, 2013:
     APC say their MarineLine is perfect for that - but be careful! It does not come cheap - and why should it?!

From richard d souza of stoncor middle east llc on April 30, 2013:
     Use epoxy novolacs or novolac vinyl esters, but primers are required depending on whether the substrate is concrete or steel.

From Saulo Ventura of Ventura Coatings Technologies Inc. on April 29, 2013:
Novolac

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Tagged categories: Coating types; Coatings technology; Tank interiors


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