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Corrosion in dermacoat coated caron steel
3

Corrosion in dermacoat coated caron steel

Corrosion in dermacoat coated caron steel

(OP)
Dear All

I am facing some issues related to the corrosion of dermacoat coated carbon steels bolts with grade astm a490m. These bolts are installed in an ammonia plant with 1 year in service. At the same time i have some bolts which are coated with hot dip galvanized coating the grade of the bolts is astm a325m but they are not corroded. Only dermacoated bolts got corroded. Corrosion seams to be like rust with only those surfaces corroded which are exposed to the environment. Any idea why this is happening.

RE: Corrosion in dermacoat coated caron steel

Can you provide any information about dermacoat? Organic, inorganic, metallic, ?????

RE: Corrosion in dermacoat coated caron steel

(OP)
Metallic coating with thickness 10 micron

RE: Corrosion in dermacoat coated caron steel

Googling (from the US) for dermacoat returns skin lotion for dogs.

Perhaps a link to the product datasheet...

RE: Corrosion in dermacoat coated caron steel

Can you measure the thickness of the coating on the hot dipped galvanized bolts and compare it to the thickness of the dermacoat coating? I suspect that your dermacoat coating may be substantially thinner.

Maui

RE: Corrosion in dermacoat coated caron steel

You have not provided enough details to determine the true root cause. One possibility is that the thin Dermacoat (never heard of this before, could not find information on the Internet either) is not suitable for your environment. Hot dip galvanizing usually is around 40 micrometers thick, so it can provide higher performance.

RE: Corrosion in dermacoat coated caron steel

I believe that the OP is referring to Dacromet coating for ASTM A490 bolts. If so, a potential cause of poor performance is poor adhesion of the coating. Provide some bolts to the fastener supplier and an independent lab for further evaluation.

RE: Corrosion in dermacoat coated caron steel

Well, if it is Dacromet then...

Dacromet contains Chromium 3 (Cr3+)

Ammonia reacts with chromium(III) ion to precipitate gray-green chromium(III) hydroxide:

Cr3+(aq) + 3NH3(aq) + 3H2O(l) <==> Cr(OH)3(s) + 3NH4+(aq)

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