Letter 26053

Rust problem on cooling tower tubular fan shafts  

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Hello,

We service Cooling Towers, I'm a service mechanic who is having trouble with tubeular steel fan shafts. Rust is appearing.We start with preping the fan shaft by removing the old rust with wired wheel, and wipe with mineral spirts.Then we brush on Z.R.C ( cold galvanizing compound [link is to product info]) Rust will start to appear within few months. Any suggestion?

Thank you,

James Dale Horton
Service Manger, - Los Angeles, CA, USA

James:

Let me take a stab at this one with you. The shafts are mechanically finished to remove red corrosion products. Then you wipe them down with a kerosene type material. Next, you apply a zinc rich coating, and finally you see red corrosion in a few months.

I propose we try removing all traces of the kerosene or other sulfur based oily compounds prior to applying the zinc rich compound. It has been seen that zinc and zinc alloys degrade incredibly fast to red rust when they have any sulfonated oils or sulfur containing organics applied to them (even when a hexavalent chromate passivate is applied.) Removal of the sulfur compounds should return you to a long service life for the parts.

Ed Budman
- Pennsylvania

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