Material Selection for Chemical Valves
Release date:
2019-02-19
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Abstract
Corrosion has long been one of the most challenging threats to chemical equipment—carelessness can lead to minor damage to equipment at best, or even more serious accidents and disasters in extreme cases. According to statistics, approximately 60% of chemical equipment failures are caused by corrosion. That’s why, when selecting chemical valves, it’s crucial to prioritize the scientific choice of materials. Unfortunately, there’s a common misconception that stainless steel is a "universal material," leading some to automatically opt for stainless steel valves regardless of the medium or environmental conditions—a practice that can be highly risky.
Here are the key considerations for material selection when dealing with some commonly used chemical media:
Sulfuric acid
As one of the most strongly corrosive media, sulfuric acid is a crucial industrial raw material with an extremely wide range of applications. The degree of corrosion caused by sulfuric acid varies significantly depending on its concentration and temperature. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80°C, carbon steel and cast iron exhibit relatively good corrosion resistance. However, these materials are not suitable for high-velocity sulfuric acid flows and thus cannot be used as materials for pumps or valves. Similarly, common stainless steels like 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) also have limited applicability in sulfuric acid environments. As a result, pumps and valves designed to handle sulfuric acid are typically made from high-silicon cast iron (which is challenging to both cast and machine) or high-alloy stainless steel (such as Alloy 20). Additionally, fluoroplastics offer excellent resistance to sulfuric acid, making lined-fluoroplastic valves a more cost-effective option.
Hydrochloric acid
Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel grades), and even high-molybdenum, high-silicon iron can only be used in hydrochloric acid solutions below 50°C and 30% concentration. In contrast to metals, the vast majority of non-metallic materials exhibit excellent resistance to hydrochloric acid. Therefore, rubber-lined valves and plastic valves—such as those made from polypropylene or fluoroplastics—are the best choices for handling hydrochloric acid.
Nitric acid
Most common metals are rapidly corroded and damaged in nitric acid, but stainless steel is the most widely used material resistant to nitric acid, exhibiting excellent corrosion resistance even at room temperature across all concentrations. Notably, molybdenum-containing stainless steels (such as 316 and 316L) not only fail to outperform standard stainless steels (like 304 and 321) in nitric acid resistance—they sometimes perform worse. Meanwhile, for high-temperature nitric acid applications, titanium and titanium alloys are typically employed.
Acetic acid
It is one of the most corrosive substances among organic acids—ordinary steel suffers severe corrosion in acetic acid at all concentrations and temperatures. Stainless steel, however, is an excellent material for resisting acetic acid, and 316 stainless steel containing molybdenum is particularly well-suited even for high-temperature applications and dilute acetic acid vapors. For more demanding conditions, such as high temperatures combined with highly concentrated acetic acid or environments containing additional corrosive media, high-alloy stainless steel valves or fluoroplastic valves are recommended.
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