Pinholes in epoxy coating submerged in potable water
Pinholes in epoxy coating submerged in potable water
(OP)
I remember reading that pinholes in the epoxy coating is all it takes to seriously corrode the underlying material and that the epoxy coating is basically useless when the coating is scratched up.
I'm thinking this might be true for galvanic corrosion between two dissimilar metals in contact. But what about in submerged applications? Will a small pinhole in the coating of a submerged steel plate be the cause of a serious corrosion failure? I thought it was the wetted area that matters.
I'm thinking this might be true for galvanic corrosion between two dissimilar metals in contact. But what about in submerged applications? Will a small pinhole in the coating of a submerged steel plate be the cause of a serious corrosion failure? I thought it was the wetted area that matters.





RE: Pinholes in epoxy coating submerged in potable water
RE: Pinholes in epoxy coating submerged in potable water
RE: Pinholes in epoxy coating submerged in potable water
I thought when you have a small anode and large cathode, it should be fine. For example, using stainless steel bolts in a galvanized steel frame is not much of a problem, but if you're using galvanized steel bolts in a SS assembly, you will have a huge problem.
Also, how would carbon steel fare when continuously submerged in potable water without any coating?
RE: Pinholes in epoxy coating submerged in potable water
RE: Pinholes in epoxy coating submerged in potable water
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Plymouth Tube
RE: Pinholes in epoxy coating submerged in potable water
We always used a coating that could be repaired if there were breaches in the coating. We checked our water tanks with a "bird dog" prior to commissioning and during periodic inspections.
Anything is better than the coating that was used when I started in industry. The coating was pure Lanolin applied by hand. Lots of fun in elevated water tanks. All the girls were envious of the applicator's hands from working with Lanolin all day,smooth as baby's butt.
RE: Pinholes in epoxy coating submerged in potable water
Corrosion rate for carbon steel in potable water is a function of several factors like: velocity of the water, temperature, oxygen content, carbonate content... usually the velocity of corrosion in potable water is not constant but decrease with time due to formation of protective scale.
a corrosion rate of 0.1-0.3 mm/y can be a realistic value..
S.
Corrosion Prevention & Corrosion Control
RE: Pinholes in epoxy coating submerged in potable water