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Bolts with corrision resistant coating for coastal applications

 

We currently use cadmium coated high strength steel bolts. I have been asked to identify an alternative non-cadmiun corrosion-resistant coating for use in industrial equipment located in coastal environments (but not in direct contact with sea water or spray. I have read about a number of Zn and Zn-alloy coatings (hot dip, electroplated, ...).

Can anyone suggest where I can get relevant information on such fasteners?.

David F. Tessier
- Ontario, Canada

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There are a number of papers published yearly on this subject in MF and P&SF; and also at the various plating conferences. You should contact a supplier of the various alloys/or straight Zn and have your parts plated and then tested in your environment. This way you would know what coating is the best for this environment.

George Shahin
Atotech - Rock Hill, South Carolina

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David,

I am not a plater and know (nearly) zilch about this subject but I have an idea which might/might not interest you.

When using fairly large bolts for plastic flanges, where the corrosion is minimal, ie. brine, salt, alkalies, weak acids ... there is one problem to consider ... that of seizing up, ie. rusting up.

The pundits will throw up their arms in dismay and talk about preferential corrosion but I'd advocate using off-the-shelf, el-cheapo galv. or cad plated bolts with stainless NUTS.

I'd recommend coating them with Molybdenum disulfide (molyslip) or with tfe tape.

I NEVER had a problem. The nuts would never come loose (but the bolt thread should extend slightly) and can always be undone simply and without the use of an acetylene torch ... which is a total no-no for PVC or any plastic flange bolts.

Cheap. Easily available. Easily undone, if needs be. The personification of the K.I.S.S. principle.

Cheers!

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).