PREVENT CORROSION! BASIC GUIDE TO AVOID GALVANIC CORROSION

It is not just rust, nor is it merely an aesthetic issue. Corrosion can manifest itself in anything from barely visible surface marks to serious damage over time. With good decisions in materials and design, many of these problems can be avoided... as well as the extra costs they generate.

If you work in an industrial environment where metal parts are assembled, you know that choosing the right materials is not just a question of price or mechanical strength. It also involves understanding how different metals interact with each other, especially in the presence of moisture or salinity. 

That's why we've prepared a basic guide to help you. Because yes, at MRF we understand your concerns: 

•    Can I combine stainless steel with carbon steel?

•    Is there corrosion between steel and aluminium?

•    Does oxidation occur between zinc-plated steel and stainless steel? 

•    What happens if I use fasteners made of a different metal than the rest of the assembly? 

These issues are more common than you might think, and resolving them can save you from claims, emergency replacements... and losses.

Read on to learn how to prevent galvanic corrosion, see a table of corrosion between metals, examples, and direct recommendations for making better decisions in your Purchasing, Engineering, or Quality department.

What is galvanic corrosion?  that can ruin your project

Be very careful! It is not enough for a metal component to be resistant on its own. It must also be compatible with the other materials it will come into contact with.

When two different metals touch directly and moisture is present—or worse, salinity—an electric current can be generated between them. This is known as galvanic corrosion.

The consequence? One of the metals will degrade prematurely. It will gradually lose material, weakening the joint, affecting the aesthetics, contaminating the other metal and compromising the integrity of the whole.

Galvanic corrosion

Physical-chemical explanation of corrosion

• Water, humidity, and even environmental salinity act as conductors.
• The less noble metal will act as the anode (-): it gives up electrons and corrodes faster.
•  The more noble metal acts as the cathode (+): it receives electrons and, although initially protected, exposure to the corrosion of its neighbour can contaminate it, causing it to lose its protective layer and also suffer damage.

The nobility of metals. The galvanic series.

The galvanic corrosion process shows that differences in nobility between metals affect their durability: the greater the difference in the ‘nobility’ of metals - that is, their natural resistance to corrosion-, the more intense the reaction will be. That is why it is essential to know which metals are more noble and which corrode more easily.

Knowing the nobility scale of the main metals used in industrial sectors can help you prevent the galvanic corrosion.

Galvanic series

• The greater the distance between metals on the scale, the greater the risk of galvanic corrosion if they are combined without protection.
• In other words: the closer the metals are on the nobility scale, the lower the risk of galvanic corrosion between them.

Now you know the most important thing: it is not a problem with the hardware, but rather how it has been combined with other materials.

Example: zinc-plated steel fasteners mounted on a 304 stainless steel component. In humid conditions, the zinc-plated steel screws will rust and weaken rapidly due to the galvanic effect.  At the points of contact between the stainless steel and the zinc-plated steel, the galvanic corrosion of the screws can also affect the protective passive layer of the stainless steel part, eventually destroying it and leading to the appearance of stains, pitting or localised corrosion.

Practical table of metal compatibility

One of the most common mistakes in the design and assembly of metal components is assuming that any combination of materials will work well. This is not the case! Therefore, when selecting components, fittings or fasteners, it is essential to understand how metals behave when they come into contact with each other, how they interact.

To help you, we provide a practical table with some common combinations in the industry, their compatibility, the consequences of a poor choice, and some key recommendations to avoid corrosion problems in the future.

Metal compatibility

Common errors that promote corrosion

• Throughout our experience, we have detected some recurring faults that often cause corrosion problems:
• Combining zinc-coated steel with stainless steel in humid environments: the zinc coating degrades quickly and leaves the part exposed.
• Using standard fasteners without checking their compatibility: the screw, being less noble, becomes the first point of corrosion.
• Designs that accumulate water or dirt: grooves, cavities or joints without drainage that accelerate deterioration.
• Thinking that the coating solves everything: without maintenance or periodic checks, the protection loses its effectiveness.

Galvanic corrosion in fasteners due to poor material selection.	Damaged protective coating. Exposed metal rusts.

Best practices for preventing corrosion. Recommendations.

The correct selection of materials is one of the most effective strategies for reducing the risk of corrosion in industrial projects. The smaller the difference in nobility in the galvanic series, the lower the probability of corrosion between the elements.

Screws and bolts deserve special attention: as they are smaller and have a larger exposed surface area, they can corrode sooner and become the critical point of the joint. To minimise risks, it is best to use screws and fittings made of the same material as the main part or, failing that, to choose the most noble metal within the assembly. This prevents the fasteners from accelerating the degradation of the assembly.

In addition, there are additional measures that can be taken to reduce risk and extend the service life of the assembly, with minimal corrosion.

Surface protection

Coating metals with paints, varnishes or other finishes, such as galvanising or cataphoresis, depending on the environment, acts as a physical barrier, preventing direct contact between the metal and corrosive agents. It is an affordable and very common solution in industrial environments. The effectiveness of this method over time will depend on its maintenance: a damaged coating leaves the material exposed and can accelerate the corrosion process, so periodic inspections are necessary.

Insulation between metals

A physical separation in the design, insulating the metals from each other using other non-conductive materials, such as plastics or rubbers, prevents the flow of electrons between them, breaking the cycle that leads to corrosion. It is a simple and effective technique that can have a major impact on durability.

Stainless steel fittings in steel generator set	Stainless steel fittings in stainless steel industrial machinery

Design focused on drainage and ventilation

The design of parts and joints must prevent the accumulation of water or moisture between metal surfaces. Incorporating drainage holes, ensuring adequate ventilation and avoiding geometries that retain liquids are key measures to reduce the risk of corrosion and extend the service life of the assembly.

Use of anti-seize greases

In threaded joints, friction can cause metal to stick to itself and block the threads, making it impossible to disassemble. This is known as seizing, which occurs more frequently in humid or high-temperature environments.

To prevent this, it is recommended to apply anti-seize greases, which form a protective film that reduces friction, facilitates assembly, allows the joint to be opened later without damaging the thread, and maintains its strength.

Choice of material in aggressive environments

In areas with high humidity or close to the sea, materials are subject to particularly corrosive conditions and it is advisable to choose 316 stainless steel, which is more resistant in these environments. Zinc-plated steel should be avoided in these cases, as it deteriorates quickly and does not offer any guarantees of durability.

Inspection and ongoing maintenance

Early detection is key. A routine of periodic checks allows action to be taken before corrosion critically affects the structure or component.

At MRF, we have a salt spray chamber where we carry out corrosion tests on our products. This allows us to anticipate how they will behave in real environments and provides practical data for establishing more accurate and effective maintenance plans.

Before concluding

In this article, we have compiled basic questions and practical advice on galvanic corrosion as a starting point to help you understand the problem. Corrosion cannot always be prevented with a single measure, but rather with the right combination of design, materials, and maintenance. Small steps taken in the early stages of a project can prevent major problems in the future, resulting in greater safety, durability, and efficiency.

We hope we have clarified some of the most common questions, although we know that each project has its own particularities and that sometimes the solutions that work in one environment are not valid in another. What is your case?

AISI304 stainless steel MRF hinge installed on a truck door

Do you need help preventing corrosion?

At MRF, we have been manufacturing stainless steel fasteners, hinges, and solutions for nearly 60 years for sectors where durability and safety are non-negotiable. Experience has shown us that many corrosion problems can be prevented through design and the correct choice of materials. We are familiar with the most common corrosion issues and work with our customers to design the best solution for each environment. 

Would you like us to help? The MRF team is available to design and manufacture a customised technical solution for your project. Let's talk.