In most cases, the passive film is self-healing if damaged, but because it is only a few microns thick, it can lead to permanent damage under certain environmental and stress-related conditions. In stainless-steel, the chromium reacts with oxygen to form a protective passive layer of chromium oxide, (Cr 2O 3) on the surface of the bulk matrix, as shown in Figure 1 4.įigure 1: The chromium forms an oxide layer of Cr 2 O 3 on the surface on the stainless steel. However, since stainless steels contains high levels of chromium (up to 20%), the characteristics of the oxidation process are different. The oxide formed on ordinary steel allows the oxidation to continue producing the typical brown rusty appearance. We know that all metals react with oxygen in the air to form a film or oxide layer on the surface. The term stainless steel is used to describe more than two hundred different grades of steel, containing alloying elements such iron, chromium, nickel, molybdenum, and niobium with each one tailored to give corrosion resistance in specific applications 3. So, before we focus on the different grades used in the pharmaceutical manufacturing process, let us first take a closer look at how stainless steel gets its corrosion resistance properties. The cannabis industry should look for guidance from pharmaceutical manufacturers on the real-world applicability of stainless steel and what types are most suitable, as they have a much better understanding and experience of the risks associated with sources of elemental impurities generated by manufacturing equipment, including the optimum grades of stainless-steel components to minimize the likelihood of product contamination 2. And as there are a multitude of types and grades of stainless steels available, with different physical and chemical properties, it is critically important that the optimum grades are used to ensure they do not contaminate any of the products they are in contact with. It is therefore worth exploring what types of stainless-steel are used in the cannabis industry, because it is such a common material found in many areas of the production process. However, states that include chromium and/or nickel in their panel of regulated heavy metals would immediately flag this as being a potential problem, especially if the cannabis material was intended for vaping applications, where the inhalation action limits are significantly lower than for orally delivered products. ![]() Normally this might escape the scrutiny of most state regulators, because the majority of states only require the big four heavy metals (lead, cadmium, arsenic, mercury) to meet compliance. This has been exemplified by recent reports of high chromium levels in cannabis flower and biomass samples, which have been attributed to cutting them with stainless steel shears and blades 1. However, because cannabis and hemp are hyper-accumulating plants, which naturally absorb metals from the soil and even surfaces and materials they are in contact with, there needs to be careful consideration to the purity and quality of the grades of stainless steel used. ![]() It is probably the most widely used material in the preparation, processing, and manufacturing of cannabis consumer products. Stainless steel is widely used in many areas of the cannabis industry, including in cutting and grinding equipment, extraction/processing vessels, mixing tanks, storage containers, screens, vaping delivery devices and much, much more.
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