Compatibility  – You Can’t Rely on Eye Charts

“The surgery was a success but the patient died.” 

As a manufacturer, you are the surgeon. Think of the product as your “patient.” The goal of cleaning is to remove soil, or matter out of place.  If as a result of the washing, rinsing, and/or drying step the product is deformed, if the surface becomes modified, if for any reason the product fails to function, cleaning has not been successful.

How do you know you have materials compatibility problems? Sometimes you know them when you see them.  On a gross level, the part may dissolve in the process fluid. Process fluids may change color.  There may be a change in the surface texture, finish, or quality.  There can be weight change or loss.  The change may be more subtle, but there can be immediate product failure.  While aggravating, at least the problem is detected immediately.  The worst compatibility problems are the ones that result in failure in the field. 

Understanding materials compatibility issues can help you to avoid manufacturing problems. For additional information, please see our article “Compatibility” in the July/August 2013 issue of “Controlled Environments Magazine.” (

Eye charts – a starting point
A quick web search can yield hundreds of materials compatibility tables; many of them run on for pages and pages.  However, while such eye charts can provide a starting point, they don’t tell the whole story.  Such tables are not standardized.  They may use phrases like “recommended,” “marginal,” or “not recommended.” Or, there may be gradation levels from 1 to 4, where a grade of 4 could mean very good or very bad.  The conditions under which studies were performed may not be apparent. The criteria of the grading system can be a mystery – you get much more information from the judges on “Dancing with the Stars.”

Cleaning and compatibility
It’s important to consider cleaning and materials compatibility hand in hand; and compatibility studies must be customized for your particular process conditions.  Why? Well, let’s think about a typical cleaning process. Most cleaning processes involve one or more chemicals (cleaning and rinsing agents), elevated temperature, one or more physical forces, and time. What factors contribute to materials compatibility problems? You guessed it: chemistry, temperature, physical forces, and time.

Of course, some materials are more prone to damage than others. Acrylics can become crazed or cloudy after exposure to cleaning agents such as chlorinated solvents and isopropyl alcohol.  Corrosion and erosion of metals are examples of materials compatibility.  Even the configuration of parts can increase the likelihood of compatibility problems.  The reason is that both entrapped cleaning agents and entrapped residual soils have more time to react unfavorably with the part.

Dynamic compatibility
A typical compatibility table involves one chemical and one material of construction. This information may not be adequate to predict the behavior of a chemical under actual process conditions. Most products are composed of multiple materials of construction, so we suggest the “minestrone” approach. Test the various materials of construction together, not just separately. If you are using a blend of chemistries, be aware that there can be synergistic effects. A blend that cleans more effectively than do any of the ingredients may also be more likely to interact with the substrate.

A static compatibility test, the type typically used in materials compatibility tables, determines if a surface will be damaged by exposure to one particular chemical. However, your critical cleaning process is unlikely to consist of soaking the component in a beaker of the chemistry in question. Instead, we suggest a dynamic approach. Invoke all the factors that can impact compatibility, including the materials of construction of the part, chemistries, temperature, forces, and time. In addition, stress the system by using a reasonable multiple of the process time and a reasonable increase in process temperature and applied forces. Please keep in mind that some engineers have been known to use unreasonable process conditions (eg. 24 hours of a cleaning process that typically takes 10 minutes). 

Art and Manufacturing
Many art conservators are expert formulators; and they are experts in materials compatibility.  The carefully test formulations to determine the balance that will most effectively remove accumulated grime without detectably altering the beauty of the underlying art. In manufacturing, part of achieving cleaning genius involves removing the soil from the part without altering the part itself.  That is, we have to achieve materials compatibility.

Critical cleaning has to be value added. Consider the potential down side of cleaning, or of any other manufacturing process.  Every cleaning and manufacturing activity has the potential to damage materials of construction.  You’re the doctor –  first, do no harm.

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