more aggressive as they are diluted with water. Some organic materials that are not corrosive by themselves become so in the presence of water.
• Temperature is an important factor in choice of materials because high temperature increases corrosion. In addition,
at very elevated temperatures, the pressure rating of the valve can be severely lowered due to deterioration of either metallic or nonmetallic material properties.
• Materials used in valves in hydrocarbon service experience sulfide stress cracking.
NACE standard MR provides specific guidelines for their selection criteria.
• Cast carbon steel (ASTM A – Grade WCB) is the most popular steel for valve bodies in moderate service such as air,
superheat or saturated steam, noncorrosive fluids.
• Cast chrome-moly steel (ASTM A – Grade WCB-C9) has addition of chromium/Molybdenum that provide corrosion resistance and also suitable for temperature up to F.
• Cast type 304 SST (ASTM A – Grade CF) is for oxidizing and very corrosive fluids.
• Cast type 316 SST (ASTM A – Grade CF8M) is same as 304 SST but since it has addition of Molybdenum it has better resistance to corrosion.
• Cast Iron (ASTM A) is used for steam, water, gas and noncorrosive fluids and is inexpensive.
• Cast Bronze (ASTM
Band Bis used for steam, air, water, oil and noncorrosive fluids. Also ask this question Does the valve stay closed (or open) most of the time Many materials exhibit different corrosion characteristics in stagnant versus flowing conditions. A casein point is Monel - a nickel-copper alloy. Monel is extremely well-suited to handling brine in flowing conditions, but is a poor choice in stagnant conditions (Inconel would be abetter choice.
