Chemical resistance describes a material’s ability to withstand exposure to chemicals over time while largely maintaining its properties. It indicates how well a material resists media such as acids, alkalis, salts, and solvents without suffering structural damage or loss of functionality.
Chemical resistance depends on the type of material, the contact medium, and the operating conditions. A high level of chemical resistance helps prevent corrosion, material damage, and premature wear. For this reason, it is one of the most important criteria when selecting materials for industrial equipment, components, and products that regularly come into contact with chemical substances.
Chemical resistance of different materials
Chemical resistance can vary significantly from one material to another. While some materials retain their properties even under demanding conditions, others react sensitively to certain chemicals. The following examples illustrate typical differences:
- Plastics: Chemical resistance varies greatly depending on the type of plastic. Polyolefins such as PE and PP offer good resistance to many aqueous acids and alkalis. However, these and other standard plastics are often attacked by organic solvents or oils. Fluorinated plastics such as PTFE (Teflon) are considered nearly universally resistant and are widely used in chemical processing and industrial applications.
- Metals: Many metals are sensitive to acids, atmospheric oxygen combined with moisture, or saline environments. Stainless steel provides greater resistance due to its protective passive layer. Under specific conditions, such as high chloride concentrations, even stainless steel can experience localized corrosion, including pitting corrosion or stress corrosion cracking.
- Glass: Borosilicate glass offers excellent resistance to most acids and many chemical media. As a result, it is commonly used in laboratories and industrial applications. Concentrated or hot alkalis can attack the glass surface through hydrolytic processes and damage the material structure, particularly during prolonged exposure.
Selecting a chemically suitable material plays a key role in extending the service life of components and preventing damage caused by chemical exposure.
Classification of chemical resistance
The chemical resistance of a material is generally assessed based on its reaction to a specific medium. The focus is on how strongly the material’s mechanical, physical, or chemical properties change during exposure. In practice, three resistance levels are commonly distinguished:
- Chemically resistant: The material largely retains its essential properties even after long-term contact with a chemical substance. Minor changes may occur but do not significantly affect functionality.
- Conditionally chemically resistant: The material is resistant to a medium only under certain operating conditions. Factors such as concentration, temperature, or exposure time may influence its properties. In many applications, this level of resistance is still sufficient.
- Chemically unstable: The material is significantly attacked by the medium and loses important properties within a short period. This can lead to deformation, loss of strength, cracking, or premature material failure.
This classification serves as an important guide when selecting materials. Since chemical resistance always depends on the actual operating conditions, resistance charts and manufacturer data should be evaluated within the specific application context.
Which factors influence chemical resistance?
The chemical resistance of a material does not depend solely on the material itself. Environmental conditions also play a crucial role and can significantly affect how a material behaves when exposed to chemicals. The most important influencing factors include:
|
Factor |
Significance |
|
Type and concentration of the medium |
The effect of a chemical medium can vary considerably depending on its concentration. A material that is resistant to a diluted acid may be attacked at higher concentrations. |
|
Temperature |
As temperature increases, chemical reactions occur more rapidly. This can significantly reduce a material’s resistance and accelerate corrosion processes. |
|
Exposure time |
Short-term contact often places lower demands on a material than continuous exposure. The longer a medium acts on a material, the greater the risk of changes or damage. |
|
Material and alloy composition |
Chemical composition has a major influence on resistance. Alloying elements such as molybdenum, nickel, or titanium can improve resistance to specific media. |
|
Flow conditions and mechanical stress |
Moving media continuously bring fresh chemicals into contact with the surface. This can reduce the effectiveness of protective layers and contribute to erosion or cavitation-related corrosion. |
|
Contaminants |
Even small amounts of additional substances, such as chlorides or solvents, can significantly alter resistance behavior and promote corrosion. |
If these factors are not adequately considered during material selection, damage such as pitting corrosion, stress cracking, general corrosion, or even complete component and equipment failure may occur.
How is chemical resistance tested?
Chemical resistance is determined through standardized testing methods in which materials are exposed to specific media for a defined period under controlled conditions. The goal is to evaluate potential changes in material properties under realistic service conditions.
A typical testing procedure includes the following steps:
- Sample preparation: Test specimens are cleaned, measured, and weighed to establish comparable starting conditions.
- Selection of the test medium: Depending on the application, water, oils, acids, alkalis, solvents, or other chemical media are used.
- Exposure: Samples are exposed to the selected medium at specified temperatures for a defined period.
- Measurement of material properties: After testing, changes in mass, volume, hardness, strength, or elongation are recorded.
- Evaluation: Measured values are compared with the original condition to assess the material’s chemical resistance.
During exposure, various processes may occur, including swelling caused by liquid penetration, loss of additives through extraction, or chemical reactions within the material structure. These changes often affect properties such as strength, elasticity, or dimensional stability and provide valuable information about the long-term suitability of a material for its intended application.