Felt to caution people who prescribe the bolt coating.
In an inhouse test of Polymer coated bolt of of a reputed Japanese vendor, which was to perform 4000 hours of salt spray test as per B 117, did not meet the requirement though the vendor's test certificates prooved so. The inhouse test was performed as in one of the plant it was used and has peeled off while normal wrenching and never stood even 1/4 of the life period gauranteed by the supplier. Literally all bolting of the plant had to be replaced by the client.
The final recommendation is that it is ideal to have a phosphating coat and a galvanizing or zinc coat and the final coat to be fluorocarbon polymer coat which really stood well in acc. with B117 in the inhouse test and has been proven in few operational plants.
So as a caution note, it would be a good practice to go for multiple coat rather than single coat for the general call for such coating requirements.
I do not want to name the companies explicity in this list for obvious reason.
Readers' experienced views are welcome.
With regards,
Kannan.
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