Selecting Stainless Steel Types for Valves

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The timeline in valve design shows that the choice of material is extremely significant alongside the use of technology. However, right now if stainless steel is the material of choice, there are over 400 commercially viable types of stainless steel for valves and new alloys are being introduced periodically. Which one should be used?

Some of the factors that have to be considered are: use, life cycle costs, product design, level of corrosion-resistance, and even the cost of downtime when the machine cannot be used. There are some industries where no compromise is possible like in the pharmaceuticals and semi-conductors. The stainless steel valves are precisely designed to avoid contamination and product rejects. Those that can be compromised have these factors to consider:

Corrosion Resistance – This refers to eliminating the need for over-alloying while being able to resist rust and corrosion. One has to know and understand what types of elements in the environment can cause corrosion and work that as a basis. The general rule for selecting based on anti-corrosion elements is to start with type 304 or 304L. If higher anti-corrosion is needed, shift to Type 316 or 316L

Physical Properties – This refers to the density needed and the presence or demand for magnetic properties. For non-magnetic valves, the Type 304 should be avoided since it has some amount of ferro-magnetic properties.

Mechanical Properties – This refers mainly to the strength needed. It could also include a study on the alloy that can be used as far as hardness, resistance to impact, ductility, and stress resistance.

Fabrication – A decision must be made on whether to use cold form, welding, or machines to manufacture the valve. There is also the level of difficulty in manufacturing probably because of design or specifications

Cost – Cost should not just be design and manufacturing but also the cost installing and the life expectancy of the valve. The longer the valve will last, the higher you can charge because it won’t need to be replaced any time soon after being installed

Even before one finalizes the selection of stainless steel material, a complete and thorough analysis must be made either by an experienced design engineer or with the help of the stainless steel company’s in-house engineers.