orrosion is the deterioration of a metal surface because of an electrochemical process between it and the surrounding
environment. Here we will demonstrate why this is a problem for springs. Interestingly, corrosion is not usually the sole
cause for failure. Rather, it creates pits on the surface, which act as stress concentration points, resulting in a premature fatigue failure. Corrosion can also lead to embrittlement of the material, causing catastrophic failure.
When we receive a broken spring, we visually examine it by eye for any signs and clues of a failure method. Corrosion is usually easy to
see, as there is typically discolouration of the wire’s surface. Corrosion is also identifiable by surface pitting. Pits are holes created on the surface of the wire by a corrosive substance. Pits can be small or large, depending on the length of exposure, the amount, and the strength of the corrosive substance present. Once the initial examination is done, it’s time
to move to the microscopes for a more detailed view. Initially, the microscope allows us to look at the surface of the spring under low magnification. The entire spring is examined, and this will indicate if the corrosion is widespread or localised. We also check to see if there is any substance left on the spring or damage to the region. Residual substances could be from oil to cleaning products, and both could give us an idea of why the corrosion started. Localised damage, scratches, etc., are also identified – these could remove any corrosion protection. After the severity of pitting has been
identified, close-up images, especially around the initiation, are taken so our final report can be as informative as possible. Next, we mount and polish samples cut from
Image 1: Example of pitting
the failed spring; one piece is cut and mounted in the transverse orientation, the other being longitudinal. Once polished to a one micron level, the sample is examined under a second microscope. Focusing on the edge of the specimen, we are looking for surface pits, again determining the extent of the corrosion. These look like tree branches initiating from
8 Image 2: Corrosion under amicroscope
the outside diameter, moving inwards. Final examinations include SEM and EDX
analysis. These will help us give our final determination on whether corrosion has occurred. SEM imaging allows us to get highly magnified images of the initiation, and EDS analysis tells us if any contaminating elements are consistent with corrosion.
The most common reason corrosion occurs is the storage of either the material or the springs themselves. If raw material or a spring is stored in a humid area with significant temperature variations, condensation can form, reacting with the surface, causing oxidisation. Something often overlooked is highly
corrosive cleaning solutions, such as bleach and floor cleaning agents. If a storage area is cleaned using these solutions and they come into contact with the spring material, it could cause the material to start corroding. A spring’s surrounding atmosphere, such as
coastlines, can also cause accelerated corrosion rates because the atmosphere holds salt from the sea. Springs can be designed to operate in corrosive environments. But, corrosion will still occur without proper materials and manufacturing methods or coatings tailored for the environment in which they will be working. Even springs working within an oil environment
can corrode if the working oil is contaminated with another solution, such as water. To summarise, it's essential to consider
storage, working environments and protective coatings when designing and working with springs. Reducing exposure to contaminants will help reduce failures and improve a spring’s life cycle. Understanding how to keep your springs
safe against corrosion is just one aspect of spring health. The design, material choice, correct manufacturing processes and proper testing all play a vital role in ensuring safe and reliable springs. If you have any concerns about the health
of your springs, talk to us. With nearly eight decades of experience under our belt, there’s nothing we don’t know about springs!
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