How to Prevent Thread Galling in Stainless Steel Hardware

When a nut and bolt engage friction generates heat which increases the chances of galling. Slowing down wrench installation speed can help reduce the chance of galling. Coarse threading and cold rolled threads also offer smoother surfaces that reduce friction.

Poor shipping and haphazardly tossing of fasteners in storage can nick or dent threads creating a trigger for galling. It is important to specify quality Stainless Steel fasteners and lubricate them with an anti-seize.

Thread galling affects all industries using stainless steel fasteners — including marine, aerospace, oil and gas, chemical processing, energy, defense, pulp and paper, construction and general engineering. While the most severe cases of galling can lead to catastrophic failures, it is possible to prevent the problem by choosing premium quality stainless steel fasteners, following torque specs and lubricating the threaded surfaces with an anti-seize compound.

Fasteners like stainless, aluminum and titanium typically have thin protective oxide films on their exposed surfaces that reduce friction. But under excessive pressure during installation, these films can rub off bringing the relatively soft metals into direct contact and creating friction that eventually fuses the materials together resulting in galling. Slowing down the wrench speed during installation will help eliminate this issue.

Thread galling results from friction between the mating threads. Friction causes heat that fuses and locks the fastener components together, often making it impossible to separate them. Poor handling of fasteners (dropping or haphazard tossing) and high tightening torque can also generate a lot of friction and heat.

One of the best ways to lower the chance of galling is to use a lubricant (often referred to as anti-seize). There are many varieties of lubricants available, some specially formulated for particular alloys and environments. These lubricants drastically reduce the friction between the fastener surfaces. However, be sure to take into account that using a lubricant will alter the torque-tension relationship. In some applications lubrication is not an option (for example, powder processing equipment) and other steps must be taken to prevent galling.

Many fasteners made of stainless steel, aluminum or titanium self-generate an oxide surface film to protect against corrosion. Under certain conditions during installation or use this layer can wear off putting the mating surfaces in direct contact with one another, causing thread galling. When threads gall they clog, shear and lock together, producing friction and heat that eventually destroys the fastener.

Understanding what causes thread galling and how to overcome it can save you time, money and headaches. Some easy tips include using a proper anti-seize, lower your wrench speed during fastener installation and opting for coarse threads instead of fine (Unified Thread Standards recommend a 2A-2B fit). Coarse threads offer a larger thread allowance and are more tolerant to abuse during handling. Also using materials of different hardness for the nut and bolt will reduce galling by giving them a harder surface to contact with each other.

Debris can increase the friction between fasteners and cause galling. A small nick or burr in the thread can greatly impact how much force is needed to loosen or tighten the bolt. Dirty or damaged threads can also increase the friction between a bolt and nut, especially when the threads are made of soft materials like stainless steel.

The good news is that there are steps you can take to reduce the chances of thread galling. Ensure that the fasteners you’re using have clean threads and use anti-seize compounds or thread lock adhesives to help lubricate the thread surfaces and reduce friction between them. Also, avoid using power tools during installation as they generate more heat and can aggravate friction between the fasteners. If your system experiences thread galling, it may result in a seized bolt that can’t be disassembled without significant force.
Stainless Steel

Stainless steel hardware can be prone to thread galling but, with the right care, this problem can be avoided. It’s important to keep surfaces clean to exclude dirt and abrasive materials that can cause friction between mating parts. Also, proper storage can prevent nicks and dents that can trigger galling.

Using fasteners of different hardness ratings can help reduce the risk of galling. For example, pairing a type 304 stainless steel bolt with a type 316 stainless steel nut can help prevent galling because these two metals have different hardness ratings.

Using lubricants can also help reduce and avoid galling. Using high-pressure lubricants, like Never-Seez, can help dissipate heat and reduce friction between thread flanks. Slowing down installation rpm speed can also significantly reduce the likelihood of galling.

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