Does Stainless Steel Turn Green?

Stainless steel is naturally more resistant to corrosion than other metals, so why does stainless steel turn green? Well, not all stainless steel is created equal. Depending on its chromium amount and environment, stainless steel may be more or less likely to experience a surface reaction leading to the unwanted green color. Understanding the composition of your stainless steel drums and IBC totes helps identify their needs, allowing you to implement proper maintenance and storage practices.

stainless steel ibc tote and drum accessories

Key Takeaways

Stainless steel contains chromium, which creates a protective layer on the metal’s surface. This layer will generally shield your stainless steel from turning green. The more chromium your stainless steel has, the stronger the protective layer will be. All stainless steel has at least 10.5% chromium.
If your stainless steel is made with copper, brass, or nickel, it is more likely to turn green or turn your skin green.
Stainless steel is also more likely to turn green when exposed to high temperature, moisture and oxygen levels, or when its surface is damaged by chemicals, salt, or water.
To protect your stainless steel, keep it away from excess amounts of the items listed above. Additionally, regularly clean and dry the stainless steel’s surface.

Understanding Stainless Steel’s Composition

Stainless steel is a ferrous metal composed of iron, carbon, and chromium. This chromium content is what sets stainless steel apart as a “stainless” metal. Chromium reacts with oxygen to create a thin, protective layer of chromium oxide, increasing the stainless steel’s corrosion resistance. Because of this, stainless steel is used in a wide range of industries. Common applications of stainless steel include kitchen appliances, medical equipment, winemaking, automotive industries, construction industries, chemical industries, air filtration and many more.

Will Stainless Steel Turn Green?

The chemical reaction that occurs when a substance comes into contact with oxygen is called oxidation. During oxidation, the chromium (Cr) in stainless steel reacts to oxygen (O2) by forming a chromium oxide layer (Cr2O3). This layer stays on the surface of the stainless steel in order to protect the metal underneath. In proper conditions, this layer is also self-healing.

Since chromium oxide itself is a green compound, some people may assume the chromium oxide layer will also be green. However, the protective layer that forms on stainless steel is a “passive layer”, meaning it is microscopic, transparent and thin, only 1-3 nm thick. The oxide layer only risks turning green when the layer is formed improperly or affected by the environment.

diagram of chromium and oxygen forming a chromium oxide layer

5 Factors That Cause Green on Stainless Steel

The formation of the chromium oxide layer depends on the stainless steel’s composition and external elements. If the protective chromium oxide layer is affected, it can develop a green color. Below are some of the factors that can determine if stainless steel turns green.

1. Chromium Content Based on Stainless Steel Types & Grades

There are around 150 grades of stainless steel classified under five types: austenitic, ferritic, duplex, martensitic, and precipitation hardening. Different types and grades of stainless steel have different levels of chromium and other elements. An increased amount of chromium content increases the strength of the chromium oxide film.

Stainless steel contains at least 10.5% chromium, but different stainless steel grades will vary. The most common grades of stainless steel are 304 grade which contains 18% chromium, and 316 grade, which contains 16% chromium. Surgical stainless steel contains higher amounts of chromium making it ideal for medical use. Some typical grades of surgical stainless steel are 316, 440, and 420.

2. Combined Metal Components

When stainless steel’s composition includes metals that are more likely to turn green, it is more likely to develop discoloration. These metals can form compounds with the chromium, destroying the protective oxide film. A few different metals that turn green include copper, brass, bronze, zinc, and other kinds of steel.

3. Moisture & Oxygen Levels

This is often observed when stainless steel is put in a furnace where the atmosphere is not optimized. When there is too much oxygen or moisture, the stainless steel will develop discoloration. If this does occur, the green-hued chromium oxide layer remains on the metal’s surface and does not discolor all of the metal.

4. High Temperature

Stainless steel’s resistance to oxidation is challenged when exposed to heat. Stainless steel can begin to change color at 500° F, exhibiting shades of yellow, brown, and blue. Some of these colors are only temporary and disappear once the steel is cooled down, while others cause more permanent discoloration. You may encounter such discoloration on stainless steel kitchenware.

5. Harsh Chemicals & Liquids

Repeated exposure to liquids and harsh chemicals can damage stainless steel’s protective oxide layer. Many stainless steel types offer chemical compatibility and stability, but can still endure damage from certain substances. Hydrochloric and sulphuric acids in particular are aggressive towards stainless steel. Similarly, prolonged contact with mineral or salt water can affect the passive layer.

How to Prevent Stainless Steel From Turning Green

Routine maintenance is critical in preventing stainless steel metal from turning green. Stainless steel may start to turn green due to improper storage, failure to properly maintain and clean, or a harmful environment. Below are tips to properly maintain your stainless steel products:

Keep the surface of your stainless steel clean and dry. If impurities gather at the surface for too long, they can affect the stainless steel’s oxidation reaction.
Make sure your stainless steel is stored in its proper, controlled environment. Limit exposing your stainless steel to excess moisture or oxygen.
Learn about your stainless steel’s composition. Understanding your stainless steel’s grade, chromium content, etc. will allow you to match stainless steel items to their ideal application. For example, 316 grade stainless steel is preferred for marine environments due to added resistance provided by its molybdenum content.

Will Stainless Steel Turn My Skin Green?

Stainless steel should not turn your skin green. However, if the stainless steel contains copper, brass, or nickel and reacts with oils or acids in your body, it can develop a green tint which can then transfer to your skin. Products made of medical grade steel are less likely to contain these cheaper metals that turn green.

Why Choose The Cary Company?

Stainless steel discoloration does not happen overnight. Its properties are made to last and is a reliable choice across industries. Understanding what stainless steel grade is right for you, and with proper maintenance, can ensure your stainless steel’s appearance for the long haul.

Apart from answering questions such as “Does stainless steel turn green?”, we take pride in our bulk distribution and excellent customer service. Enjoy the corrosion-resistance and versatility of stainless steel at great prices, shipped your way by our proactive logistics team. Whether you're looking for drums and IBC totes, filter vessels and air filters, pumps and mixers, or valves and parts washers, we have the stainless steel solutions for you. Just give us a call at 630.629.6600 or email us at sales@thecarycompany.com!