How to Prevent Rust on Metal Parts, Especially While Shipping

Rust on metal parts can turn a successful shipment into a costly headache. For many small machine shop owners and shop foremen, questions like "Why are our parts fine when they
leave the shop but rusty when they arrive to my customer?" or "What factors lead to rust in my machine shop?" are all too familiar.

Almost weekly, we field calls from small machine shops (and some larger ones) wondering how to improve product quality and prevent rust when shipping parts. And while every situation is
the answer usually lies in a combination of environmental factors and water quality.

Because we hear this frequently, we’ve created this article to help you mitigate rust in your shop.

It’s not always about shipping — sometimes it’s about the air near your shop and how it differsfrom the air at the final destination (as well as key points in transit). However, the process of shipping can also expose parts to conditions that accelerate corrosion on metal. The key culprits include:

High humidity levels or direct contact with water create an ideal environment for rust. Even trace amounts of moisture in packaging can lead to metal corrosion over time.

When oxygen comes into contact with metal in the presence of water, it initiates an electrochemical reaction, forming rust. In machine shops, when parts are exposed to moist air for extended periods, they can rust more quickly, especially if protective coatings or treatments are not applied.

Because salt is an electrolyte, it speeds up the chemical reactions caused by water/moisture and oxygen, leading to rust developing more quickly.

When parts are shipped over the ocean, near an ocean, or are created in or shipped to a coastal area, the added salt in the air can contribute to the formation of rust.

Additionally, when you live in a winter climate where municipalities salt the roads to prevent ice, that salt ultimately seeps into the groundwater and watershed and may mean you start with
Higher chloride levels in your shop are again causing corrosion.

While you’re prepping products for shipping, minuscule water molecules can get trapped in the packaging — especially when the products are still warm. If you’re shipping from a cool climate
to a warm one, temperature fluctuations during transit can also cause condensation, hastening corrosion.

While summer heat and humidity absolutely play a role in condensation and corrosion, the challenge is exacerbated further in winter with dramatic temperature differences between climate zones. Additionally, changes in temperature from warehouse to truck to loading dock contribute to the rust dilemma.

Water isn’t just H₂O—its chemical makeup can significantly impact corrosion rates. These are
the water quality parameters to watch:

• pH Levels: Water that’s too acidic or too alkaline can destabilize metal surfaces, leading to rust.
• Chlorides & Sulfates: High concentrations of these ions are especially corrosive.
• Alkalinity: Insufficient alkalinity offers less buffering capacity against pH changes, promoting corrosion.
• Organic Matter: Impurities like organic residues can accelerate rust formation.

Chlorine & Chloramines are often added to water supplies and can cause localized corrosion, especially in metals like steel and copper.

Excess manganese or nitrate ions increase water acidity, making parts more prone to corrosion.

Understanding the types of corrosion can help tailor your prevention strategy:

Occurs in low-temperature metals exposed to water with high pH, chloride, and sulfate levels. Pinhole corrosion is particularly dangerous because it’s harder to detect and predict.

Typically affects high-temperature water pipes with high copper content, low pH, and high alkalinity. This type of corrosion is easier to spot but can spread rapidly.

To minimize corrosion risks, we recommend keeping your water in the following parameters:

• Water hardness: Maintain levels between 75-175 ppm.
• Chloride: Below 100 ppm.
• Chloride & sulfate combined: Below 125 ppm.

While it’s not always as simple as saying “Today I’m going to bring my water hardness down,”
testing your water against these guidelines can help you understand when it’s time to do a
dump, clean, and recharge.

Since salt — and specifically chloride — can lead to corrosive water, it might seem like the
answer is to filter minerals from your water. However, desalinated water, though highly purified,
can also contribute to corrosion issues due to its lack of minerals.

Water with high alkalinity and hardness generally has lower corrosion aggressiveness compared to low alkalinity water. Desalinated water often lacks these stabilizing minerals, increasing its corrosive potential.

The electrochemical process of corrosion accelerates when dissolved oxygen in desalinated water interacts with metal surfaces. Oxygen readily accepts electrons, creating anodic sites on the metal and promoting rust formation or other corrosion products.

Preventing rust on metal requires a proactive approach. Here are practical steps to
protect your metal parts:

Use moisture-resistant materials and desiccants to shield metal surfaces from humidity and oxygen exposure. Moisture-resistant materials, such as specialized coatings or wraps, create a barrier that prevents water from reaching the metal surface, effectively reducing the risk of corrosion during transit. Desiccants are materials designed to absorb excess moisture, helping to maintain a dry environment and reduce the risk of rust during shipping.

While you can’t control the weather, you can take steps to minimize temperature fluctuations by choosing climate-controlled shipping options where possible, especially for long-distance or international shipments.

Improperly treated water used in machining processes can introduce corrosive
elements. Regularly test and treat your shop’s water supply to meet recommended
parameters.

Want to Read More: Set It And Forget It – Does It Work For Your Shop’s Water Quality?

Cleaning fluids aid in removing dirt, debris, and contaminants that can lead to rust. Incorporating cleaning into your shop’s fluid monitoring and maintenance schedule helps preserve tools and consistently produce quality end products. The type of cleaner you use depends on your product and application:

• Water-Based Cleaners: Ideal for removing salts, oxides, and chips. These cleaners emit fewer volatile organic compounds (VOCs) and are generally easier to dispose of than solvents, but they may contribute to rust if not properly dried.
• Solvent-Based Cleaners: Highly effective at removing oils, greases, and waxes. These cleaners dry quickly but can emit VOCs and require careful handling due to their flammability and disposal complexity.

Additionally, we recommend applying rust preventives to every product you ship. Rust preventives create a protective layer on metal surfaces, ensuring that your products arrive in the same condition as they left your shop. This reduces rejects, saves time, and improves your bottom line.

Want to Read More: Optimise Your Machining Process with the Right Combination of Metalworking Fluids

Now, when clients ask why their parts arrive rusty despite appearing fine when shipped, you’ll be able to better understand the factors that cause corrosion, especially during shipping. Better yet, you’ll be able to fine-tune your corrosion prevention strategy.

So what’s the bottom line?

Rust and corrosion don’t have to be unavoidable costs of doing business. By understanding the factors at play—from moisture and oxygen exposure to water quality—and taking proactive steps, you can protect your metal parts during shipping. Invest in quality industrial fluids and stay vigilant about environmental conditions to keep your parts rust-free.

With the right knowledge and tools, you can prevent rust—saving time, money, and your reputation with customers.

Learn how our line of rust preventives, cleaners, and other industrial process fluids can help you protect your parts and improve your operations. Contact us for personalized recommendations on reducing rust in your shop.