Galling in Stainless Steel

You’re tightening a stainless steel eye bolt on a rigging assembly and … nothing. The bolt doesn’t budge. Worse, it seems fused in place.

What happened to the rigging hardware?

In these cases, it is likely Galling has occurred.

Galling is a type of adhesion caused by the heat and friction produced between two sliding forces. It is common in the application of fasteners and turnbuckles where threads contract as they are tightened into place. The resulting pressure causes the threads’ coating to break down into small metal filings that often fuse together with the resulting heat and increased friction of the installation. The process can be nearly instantaneous.

The result is an often expensive, welded mess that cannot be taken apart. Generally, the fasteners must be split or cut in order to dismantle the rigging.

Stainless, aluminum, titanium and hot dipped galvanized fasteners – while crafted to prevent corrosion – are most susceptible to Galling, due to their protective coatings. Though this coating protects against every-day friction and elemental wear, it is no match for the intense heat created when adjusting threaded fasteners under load.

Locknuts are also especially prone to Galling because they are designed to produce friction with mating threads in order to prevent loosening.

Since Galling feeds off friction and heat, the best way to reduce this form of wear is to starve it. These are the most effective ways to prevent Galling:

• Reduce installation speeds

Galling most commonly occurs with the use of a high-speed driver, given the greater presence of heat and friction. Do not use power tools when installing?stainless, aluminum, and titanium fasteners.?Tools with slower installation speeds will greatly reduce the amount of friction built up on the fastener.

• Be mindful environmental conditions

Examine the threads to see if they are damaged or dirty. Both can create unnecessary friction in the installation process.

Though most instances of Galling occur due to the friction and heat generated by driver installs – Galling can still occur if a wrench, bolt or turnbuckle is left out in the sun. Before installation, keep stainless, aluminum, and titanium fasteners, as well as wrenches out of direct sunlight to reduce the risk of Galling.

• Do not over torque

torqueing a nut, bolt or turnbuckle can damage the threading, creating a greater likelihood that Galling will occur.