What Makes Stainless Steel Corrosion Resistant?
When you think about the sanitary process equipment, you only assume that it will be constructed of stainless steel. Interestingly, if you ask most users why stainless steel has the various properties it has, most people do not know. We thought we would use this blog post to give a brief description of stainless steel and its properties.
Let’s start with a brief history of stainless steel. In the early 1900s, metallurgists observed that chromium had a better oxygen consumption than iron, so they added the chromium element to the steel. Studies show that when a minimum of 10% chromium is added, the chromium bound with oxygen would form a transparent and hermetic layer on the steel surface that would not allow oxidation by stopping further oxidation. The transparent layer self-closes when it is damaged by scratches, water, or dents.
Stainless steels are long-term beauty materials. These steels also tolerate the corrosive attack of various acids, retain strength and tenacity at both ends of the temperature scale but can be manufactured in complex shapes for numerous uses. It is because of this exceptional versatility, stainless steel guarantees careful consideration for any product in which one of these six key requirements is involved.
- Resistance to corrosion
- Resistance to high temperatures
- Resistance and Ductility at Cryogenic Temperatures
- Resistance to oxidation at high temperatures
- Appearance
- Abrasion resistance
The many remarkable values offered by stainless steel make it a strong competitor in the selection of materials. Engineers and designers often underestimate or overlook these values because of what is seen as the largest initial cost of stainless steel. However, during the entire life of a project, stainless steel is usually the best value option.
The resistance of stainless steel to corrosion, stains, low maintenance, low cost, and known brightness make it a perfect base material for a variety of applications.
The stainless steel is 100% recyclable. More than 50% of the new stainless steel is made of remelted scrap, characterizing it as fairly ecological material.
There are more than 60 grades of stainless steel. Most of the products that Holland sells are grade 304 or 316L. Sanitary fittings and pipes are offered in both grades, 304 mainly for dairy products and many food applications, 316L in biopharmaceutical applications, and in any other where the products are more aggressive (main products with high chlorine content, such as sports drinks, salsa barbecue, etc.) Most pumps and valves are offered in type 316L only. Sanitary heat exchangers, mixers, and instrumentation are usually offered in 316L as well.
There are some process fluids in the food, beverage, and biopharmaceutical industries that, due to a combination of high temperature and high chloride content, even 316L stainless steel. In those cases, AL6XN, titanium, or Hastelloy materials are required. Although the selection is more limited, there are sanitary pumps, valve tubes, and accessories available in these materials, although they are very expensive.
