Fretting Corrosion: Causes, Effects and Prevention Methods

Fretting corrosion happens when two metal parts touch and rub against each other in tiny steps, over and over. That rubbing can come from vibration, shifting during heating and cooling, oscillation, machine forces, or the way equipment runs. Even when the motion looks minor, it can wear the surface little by little. After enough cycles, corrosion can start and the damage can grow.

In process plants and other industrial sites, vibration and stress are common. You may see fretting corrosion at bolted joints, on shafts, in bearings, and where tubing is held in place. It can also show up around heat exchanger parts and other points where metal meets metal. Over time, the surface can suffer from both rubbing and corrosion at the same time. This can lead to metal loss, roughening of the surface, cracks, and then system failure.

Knowing what drives fretting corrosion, and catching it early, supports reliable service. Good checks, the right material choices, control of vibration, protective coatings or surface treatment, and routine upkeep all lower the risk.

What Is Fretting Corrosion?

Fretting corrosion is a kind of wear that shows up where two materials touch.  

It happens when the parts shift by a very small amount, then move back the same way.  

Those tiny back and forth motions can thin or break the thin oxide film. That film normally acts like a shield for the metal. Once it is disturbed, the metal is left more open to the surroundings.  

With the shield gone, fresh metal is exposed to air and to any nearby liquid.  

If moisture is present, along with oxygen, salt, or other harsh chemicals, rusting can start at the exact contact point.  

The rubbing motion can also make tiny particles of metal and oxide. Some of these bits can stay trapped between the two surfaces. When they sit there, they can make the damage grow faster.  

Over time, small holes or pits may appear. Those pits can later support the start of cracks.  

In short, fretting corrosion is driven by both rubbing damage and chemical attack. 

How Does Fretting Corrosion Occur?

Fretting corrosion usually develops through several stages.

First, two metal surfaces are held together under a certain contact load. Small movements then occur between the surfaces because of vibration or other mechanical forces.

The repeated movement damages the protective surface film. This exposes fresh metal to the surrounding environment.

At the same time, small particles are generated because of mechanical wear. These particles can oxidise and form debris between the surfaces.

As the process continues, the damaged area becomes rougher. Localised corrosion can develop, and small pits may form. These pits can act as stress concentration points.

If the condition continues for a long period, cracks may develop and grow. In severe cases, the affected component can lose its structural integrity and experience premature failure.

Common Causes of Fretting Corrosion

Several operating and design conditions can contribute to fretting corrosion.

1. Ongoing vibration  

Vibration is a frequent driver. Spinning gear, pumps, compressors, motors, fans, and other equipment can push two touching parts to shift back and forth.  

Even if the motion looks small, time on the job can still wear down the outer layer.

2. Weak or wrong fit  

If parts do not seat correctly, they can move when they should not.  

Loose joints, the wrong gap size, or sloppy assembly can raise the chance of fretting.  

A part that was meant to stay still may creep a little in use, which can set up the damage.

3. Cyclic force from operation  

Loads that rise and fall over and over can create tiny slip at the contact faces.  

This often appears in machines working under repeating operating cycles.

4. Hot and cold size change  

Metal parts grow when they heat up and shrink when they cool.  

When two connected parts change at different rates, they can shift at the joint.  

After enough cycles, those small shifts help fretting corrosion grow.

5. Water and harsh surroundings  

Wear can happen from motion by itself.  

But damp conditions or corrosive agents make the problem worse.  

In chemical works, you may find humidity, chemical vapors, salt, or wet process streams. All of these raise the corrosion risk. 

Where Does Fretting Corrosion Commonly Occur?

Fretting corrosion can occur in many industrial components where two surfaces remain in contact and experience repeated movement.

Common examples include:

• Bolted and clamped connections

• Shafts and couplings

• Bearings

• Heat exchanger components

• Tubing and pipe supports

• Mechanical joints

• Flanges and contact surfaces

• Rotating machinery

• Electrical connectors

• Fasteners

• Engine and turbine components

• Support brackets

In chemical processing facilities, areas exposed to continuous vibration should receive particular attention during inspection.

Effects of Fretting Corrosion

Fretting corrosion can create several problems if it is not identified and controlled.

Surface Damage

The first visible effect is often surface wear. The contact area may develop scratches, grooves, discolouration, or deposits of corrosion products.

Material Loss

Repeated movement can gradually remove material from the contacting surfaces. This may change the dimensions and fit of the components.

Pitting

Localised corrosion can create small pits. These pits may become deeper with time and act as stress concentration points.

Crack Formation

Fretting damage can contribute to crack initiation. When cyclic stress is also present, cracks may grow and eventually cause component failure.

Equipment Malfunction

Damaged bearings, shafts, connections, or supports may affect equipment performance. In rotating machinery, even small changes in component condition can lead to vibration and operational problems.

Premature Component Failure

Severe fretting corrosion can reduce the service life of components. A failure may occur earlier than expected, resulting in unplanned maintenance or production interruptions.

Fretting Corrosion and Corrosion Failure

Fretting corrosion can become an important contributor to a wider Corrosion Failure. A component may initially have adequate strength and corrosion resistance, but repeated surface damage can gradually reduce its condition.

For example, a small fretting mark can become a local stress concentration. If the component is also exposed to cyclic loading, a crack may initiate at the damaged location.

This is why failure investigations should consider both corrosion and mechanical operating conditions. Looking only at the corrosion product may not reveal the actual reason for the damage.

Prevention Methods for Fretting Corrosion

Preventing fretting corrosion requires attention to both mechanical and environmental conditions.

1. Reduce Unnecessary Vibration

Controlling vibration is one of the most effective approaches. Rotating equipment should be properly aligned and balanced.

Loose components, damaged bearings, and other sources of excessive vibration should be identified and corrected.

Regular vibration monitoring can also help identify developing problems before serious damage occurs.

2. Improve Component Fit

Components should be properly fitted to minimise unwanted relative movement.

Correct clearances, suitable contact pressure, proper alignment, and appropriate fastening methods can reduce fretting risk.

3. Select Suitable Materials

Material selection should consider the operating environment as well as mechanical loading.

Materials with suitable wear resistance, corrosion resistance, and mechanical properties may provide better performance in applications where fretting is expected.

A Corrosion Expert can help evaluate material compatibility and environmental conditions during the design or assessment stage.

4. Improve Surface Finish

Smooth and properly prepared surfaces can reduce friction and localised damage.

Where required, surface treatments or engineering modifications can be considered to improve resistance to repeated contact movement.

5. Use Protective Coatings

A good protective coating can add another layer between the metal and the air or moisture around it.

Pick a coating by looking at the actual job conditions. That means the operating heat, the chemicals it may touch, any movement or vibration, and the overall service setting.

If you are unsure, ask a coating specialist. They can help you judge whether a specific coating setup will work for your use. 

6. Use Lubricants Where Appropriate

In suitable applications, lubricants can reduce friction and limit direct metal-to-metal contact.

The lubricant should be compatible with the operating temperature, process environment, materials, and equipment requirements.

Lubrication should also be included in the maintenance program where applicable.

Conclusion

Fretting corrosion happens when small, repeated motion meets a wet or corrosive setting. Over time, this mix can wear down the surface. It may form tiny pits and cracks. It can also thin the material. The result is higher risk of early equipment failure.

To reduce fretting corrosion, you need more than one fix. Good equipment design matters. Picking the right material helps. Vibration control is key. Use surface coatings or other protection. Then keep checking the condition with regular inspections. Condition monitoring should be part of the routine too.

With a clear plan for corrosion review and failure checks, you can narrow down the real driver. That makes it easier to stop the same issue from coming back.

CorroSafe Consultant offers help with corrosion review and failure investigation. They also support metallurgy based root cause analysis. Training on corrosion is available as well. Asset integrity management services are offered too. Reach out to the team to look at your equipment, spot corrosion threats, and set workable steps to improve reliability and extend asset life.