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Carbon Steel Tools on Process Equipment Introduce an Unnecessary Risk of Particulate Generation
|Though an extreme example, even tiny traces of iron oxide on maintenance tools introduce an unnecessary risk
The risk of particulate generation with carbon steel tools is twofold. In the first instance, contamination is introduced when a ferrous tool is used on a stainless steel fastener or surface of the equipment being serviced. The contact of the two different materials during the course of normal contact transfers iron particles from the tool to the surface of the stainless. The reaction between the exposed iron particles and oxygen in an environment with even low levels of humidity results in the formation of iron oxide, or rust. This poses an obvious threat to maintaining acceptable levels of airborne particulate. The second instance of contamination risk results from the deterioration of the chrome plating commonly used on ordinary industrial hand tools. The application of an electroplated surface coating is intended to provide carbon steel tools with some level of corrosion resistance by acting as a barrier between the free iron on the tool surface and the environment, and thus reduce the level of oxidation. However, it is this same plating that contributes an increased risk of contamination. Although it is possible to effectively sterilize a chrome-plated carbon steel tool before use in a Cleanroom, each successive autoclave cycle acts to deteriorate the plating, causing it to chip, flake, and peel. Once the chrome plating is degraded, contamination can result not only from particles of the plating itself, but also from the transfer of the now exposed iron of the tool to a stainless surface.
In contrast, stainless steel is an homogenous material, without plating or coating of any kind. Using stainless steel tools eliminates the risk of particulate generation. The chromium content of the stainless, an integral component of the alloy, eliminates the need for additional plating. The protective chromium oxide layer that forms on the surface of stainless steel is a spontaneous result of the inherent properties of the material. This invisible layer is non-reactive, and therefore non-corrosive, and unlike plating, has self-repairing properties if it is scratched or damaged. As long as there is oxygen in the environment, the chromium in the stainless will "heal" itself by forming a new chromium oxide layer. If "rouging" of the surface does occur over the course of extended use, the passivation of the tools can be enhanced with the use of a mild oxidant such as citric acid to remove the free iron and promote a fresh chromium oxide layer.
For these reasons stainless steel tools are ideally suited for use in sterile and critical environments. They can be sterilized repeatedly without deterioration. Eliminating the possible risk of particulate generation in critical environments results in a measurable effect on sterility as it provides validation personnel with a verifiable standard. With the integration of stainless steel tools into sterile processing facilities as a standard practice, facilities can more easily meet GMP requirements.
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