Many industrial complex managers take fastener corrosion for granted, including expensive change out of weakened systems that become corroded. Several alternative systems have been used in industry to address fastener corrosion as follows:

Paint or Coating

Painting or coating fasteners is an inexpensive protection method, both for installation and use. This method of protection is easily damaged or can simply wear away with time. Corrosion readily occurs at sites of coating damage from normal make-up procedures.

Grease or Wax

Coating fasteners with grease or wax is an inexpensive protection method, but it is also time consuming and messy. Any areas left unprotected can easily corrode. Grease can allow moisture penetration and accumulation of dust, dirt, or other impurities in the grease resulting in corrosion. Grease can also absorb corrosive gases such as SO2, CO2, H2S, that can accelerate corrosion of steel nuts and bolts.

Corrosion Resistant Alloys (CRA)

Properly selected, corrosion resistant alloys provide excellent corrosion protection, but selection of the wrong alloy can result in rapid failure. Corrosion of an improperly selected CRA can occur as crevice corrosion, pitting, dealloying, chloride stress corrosion cracking or hydrogen cracking. Galvanic corrosion can be a problem if the fastener is used with a more noble base metal or an active metal such as aluminum alloys. This is the most expensive protection method.

Electroplating (Cd, Zn, Zn-Ni)

Electroplating offers minimal corrosion protection with added cost. At elevated temperatures, liquid metal embrittlement and hydrogen embrittlement can be a problem. Corrosion readily occurs at sites of coating damage from normal make-up procedures.

Hot Dip Galvanizing

Hot dip galvanizing offers good, long term corrosion protection with added cost. The galvanized surface is rough, and nuts for galvanizing must be tapped over-size to allow proper make-up. The high coefficient of friction due to the surface roughness make multiple make-up and break out very difficult.

Fluoropolymer Coating

Fluoropolymer coating systems, e.g., Teflon, are very effective in reducing make-up and break out torque. Because of limited coating thickness, i.e., <1.5 mils (38 µm), corrosion protection is limited. Corrosion occurs at sites of coating damage that results during normal make-up procedures.