How to Choose Valve Material for Acid Medium?
Anticorrosion has always been the main problem of chemical equipments. According to some statistics, about 60% damage to chemical equipments is caused by corrosion, so paying attention first to the applicability of the valve material is very important. As following we can see some commonly used valve
materials for corrosive medium.
1. Sulfuric acid is one of the strong corrosive medium, which is widely used as industrial chemical raw material. Carbon steel and cast iron have good corrosion resistance for concentrated sulphuric acid which is over 80% concentration and lower than 80℃ temperature, but these materials are not good enough for highly active sulphuric acid.
2. Acetic acid is one of the strongest corrosive medium in organic acids. General steel and iron materials would be seriously corroded in acetic acid with any concentration and temperature. Stainless steel can be the excellent option against acetic acid. 316 stainless steel valves with molybdenum can also be used for high temperature dilute acetic acid steam.
3. Most metal materials (including all kinds of stainless steel) intolerance the corrosion by hydrochloric acid, even ferrosilicon with high-Mo can only be used for only 50℃, 30% below hydrochloride. On the contrary to metal materials, most non-metal materials have excellent corrosion resistance for hydrochloric acid, e.g. rubber valves and plastic valves (C3H6).
4. Nitric acid has a corrosive effect on most metals. Stainless steel is the most widely used resistant material for all concentration nitric acid at normal temperature. And it's worth mentioning that corrosion resistance of stainless steel with molybdenum like 316 and 316L is not only not better than general stainless steel like 304 and 321, but sometimes even worse.