Is rust on industrial power supplies a safety hazard or not? In this BLOG article we explain which type of corrosion is harmless and when you should take action. You will also learn how corrosion tests can help to prevent rust.
Why does rust arise?
Rust is one of the results of corrosive gases such as sulphur dioxide or nitrogen oxide. These gases lead to corrosion, especially in the case of metallic materials in combination with atmospheric humidity. This can accelerate the ageing of electronics and worst case result in malfunctions or in the failure of assemblies or electronics within the expected lifetime.
The corrosive gases are found in varying degrees in various environments. Some industries are more affected by corrosion than others, e.g. the processing industry, paper mills, sewage treatment plants, road traffic as well as farms.
Corrosion accelerating substances
H2S is found in petrochemical processes, the steel industry, waste water, standing water and animal farms.
H2S and chlorine bonds
H2S in combination with chlorine bonds are found in the pulp and paper industry.
NO2 and SO2
NO2 and SO2 are present primarily in the combustion of fossil fuels and in environments with heavy vehicular traffic.
Rust is typically only a visual flaw on the housings and screws. But it may also arise on the connectors of the. Components making electrical connections such as plug connectors, relay contacts and soldered joints are particularly critical. Rust formation in these areas, often causes a loss of function or even total failure.
Let's take a closer look at the two most common types of rust: white rust and red rust.
White rust and red rust: What is the difference?
To be able to assess the corrosion, knowledge of the different rust types is important. White rust forms on zinc surfaces such as galvanized steel as a thin zinc oxide layer evenly distributed across the surface. Its appearance is a whitish sheen. The layer adheres to the surface and does not drop off. If wiped with a finger, it fades a little.
White rust is generally non-critical and is merely a visual flaw. It can be hazardous in combination with salt. Salt or salt mist combines with zinc oxide and efflorescence forms that can develop into crystal formation. Pieces of these efflorescence or crystals can break off and cause short circuits in the electronics. Therefore, Zinc-plated surfaces should not be generally used in the offshore sector or for road construction equipment where salt can be expected.
Red rust is the classic form of corrosion on ferrous or steel materials when corrosion protection is insufficient. Red rust should be avoided, as it spreads and efflorescence can easily break off causing short circuits because the rust is conductive. The extent to which red rust occurs on zinc-plated steel sheets, cutting edges or screws depends on the quality and homogeneity of the zinc-plating or corrosion protection.
What can you do to prevent rust on your power supply?
The removal of rust is usually very time-consuming and needs special equipment. There are even companies that specialize entirely in cleaning industrial electronics. So the best thing you can do is to prevent rust on your power supply before it occurs.
Analyse the environment of your application:
- Is the application exposed to substances that accelerate corrosion (see box "Corrosion accelerating substances")? If yes, which gases and to what extent?
- How high is the humidity to which the application is exposed?
- Is the application exposed to salt or salt mist?
- Are there strong temperature fluctuations?
- Are electronic components, such as the power supply, protected by a control cabinet with an IP rating or not?
Ask the manufacturer about the following topics before you decide for a power supply:
- Certain materials, such as silver for soldering, accelerate the reaction with corrosive gases. Are such materials used in the power supply design? If yes, to what extend?
- Are the printed circuit boards of high quality and is good tinning used on the copper traces?
- Are the contact pins of plug connectors protected against corrosive gases by using generously proportioned and fitted housings?
- Are coatings and sealing made from silicone? If yes, this will barely help to prevent rust. Silicone and silicone coatings are gas-transparent and only provide little protection against corrosive gases.
- Are components such as potentiometers or relays used in sealed versions?
- Do the metal parts, especially screws, feature the best corrosion protection?
How can corrosion tests help to minimize rust before it occurs?
Corrosion tests have been standard practice in the telecommunications and automotive industries for many years. The corrosion test is also becoming an important quality feature for applications within the processing industries, in road construction and in wind power applications.
Reliable manufacturers execute corrosion tests to prove that corrosive effects do not occur or only occur below agreed limits. If the design of a power supply is done properly, the device will provide a reliable service for a long period of time. There is no need for early replacement after only a few years.
A realistic assessment of the corrosive behavior, requires that the corrosion tests are performed very closely to the actual operating conditions of the equipment. In addition to setting the corrosive gas concentration, it is important for the simulation to operate the test sample, as it would be used in practice. In continuous operation mode, the tendency towards corrosion is less pronounced. The constant heating reduces the moisture in the immediate vicinity of the corrosion-sensitive materials. Sulphur dioxide, however, requires moisture to react, and this is not typically present during continuous operation.
More meaningful results are therefore provided by a cyclical operation mode in which the test sample is switched on and off at regular intervals. The air flow arising from these cold/hot temperature fluctuations creates moisture, promotes reaction with sulphur dioxide and increases the tendency for corrosion. This cold/hot effect is particularly important in the case of power supplies, as they usually cause a hot spot in the control cabinet.
The test time is shortened by increasing the concentration of the corrosive gases. This means that the operating time of over 10 years is simulated within a test duration of just 21 days.
In one of our next BLOG posts you will learn more about the IEC standards which are used for environmental simulation testing as well as the preventative measures PULS implements in its product design.