What is Stainless Steel Galling and what Causes it?
Galling can be the most frustrating part of using stainless steel hardware and can even cause the threads to completely seize,sometimes to the point of no-return!
With all the benefits of stainless steel materials, you don’t need to avoid them because of galling. Being aware of its challenges and taking precautions when using stainless steel parts, you can avoid the hours of headache and rework.
What is galling?
Galling is a form of wear due to excessive friction between two moving surfaces. This can happen when installing a bolt into a threaded hole, or a fitting into a pump housing. It is usually prevalent with stainless steel parts but can happen with any material.
Severe galling can result in the parts becoming so seized that the part is no longer removable. This term is known as “cold welding” since the materials don’t heat up very hot, but act like they have welded together.
What factors can “trigger” galling?
Friction causes galling, so any form of interference or heat build-up can cause galling. Common triggers are debris in the thread, reusing overtightened hardware, and threading soft materials together such as stainless steel.
Another common trigger is damaged threads due to shipping. The manufacturer may have protected the shipment from the outside environment, but it’s pretty common to ship multiple bolts in one bag, resulting in threads banging into each other.
It is always a good habit to inspect your hardware or fittings before installing them into your system.
Why Stainless Steel?
Stainless Steel is especially susceptible to galling because of its “sticky” properties. It may not seem like it, but stainless steel isrelatively soft compared to other common metals (such as zinc-plated steel). Once the material starts to deform and interfere with the mating material, the snowball starts. More friction means more deformation, which leads to even more friction.
Most stainless steel hardware will have a protective coating, which will provide a buffer between the thread materials, but once the coating is rubbed off, the material is exposed and will start to gall.
Here are Some Easy Tips to Follow When Using Stainless Steel Fittings or Fasteners:
Lubrication is by far the most common method for damage prevention. It provides a layer of protection between the two materials, allowing for the materials to easily slide past each other without creating friction or heat. There are multiple types of anti-seize compounds, but is usually a grease containing copper, aluminum, or calcium oxide.
Sometimes the manufacturer will send the product with anti-seize already applied to the threads but is still a good habit to apply your own anti-seize before installation.
As an added bonus, this method will help prevent corrosion, making disassembly much easier.
Differing Stainless Steel Grades
Sometimes using two different stainless steel grades will help prevent galling. By having dissimilar hardness ratings, the materials are much less likely to deform or fuse with one another.
In the worst case, the softer material will deform before damaging the other material, allowing you to remove the damaged part without affecting the other.
Even with differing materials, you should still apply anti-seize since this tip isn’t a cure-all. This is an added protection, especially suited for stainless steel hardware.
Don’t pull joints together
If you use a bolt to pull two joints together in an assembly, you run the risk of deforming the threads and damaging the bolt beyond disassembly.
By using the bolt to pull the two pieces together, you are relying on the thread face to push the material together. Standard threads are not designed for these dynamic loads and will only damage the threads unnecessarily.
Instead, use a clamp or vise to pull the pieces together and then use the bolt to retain the position. Clamps are designed for this type of force, not delicate threads of a bolt. This is a useful tip for any material, not just stainless steel.
Reducing the installation speed will help reduce friction between the materials. This also allows any heat buildup to dissipate through the part, rather than concentrating at the threads.
Plus with a slower speed, you may be able to feel the beginning of the galling and remove the part before it completely seizes.
Stop when you feel resistance
This may be obvious, but when you start to feel resistance in the thread, STOP! If you catch the galling soon enough, you may be able to remove the fitting or bolt before it seizes completely.
You should discard the damaged fitting or bolt since the threads are already deformed from the first installation. Reusing this fitting will only damage the new hole and further damage the fitting.
RG Group is here to help
If you have any questions about the tips mentioned today or have additional tips that would be helpful, feel free to contact us at RG Group.
P.S. In the unlucky situation where you didn’t read this article in time, RG Group can help you out!