A history of valves

THE TRIM

The materials for valve trim or “trimmings” as it was called a century ago were limited as well. Valve stems, seats and discs were made of bronze, brass or iron. The first improvement in trim materials was the introduction of ­copper-nickel alloys, essentially Monel. This “Monel metal,” as it was called, was very useful because it was harder than anything yet available and also highly corrosion resistant.

The next valve-trim material to gain popularity was Martensitic, 400 series stainless steel. These alloys were highly durable because of their ability to be heat-treated into an extremely hard condition. The 400 series stainless steels, by virtue of the 11-13% chrome content, also were corrosion resistant, and they would be the trim material of choice for 30-40 years until supplanted by cobalt-based “Stellite” materials after World War II.

As the temperatures and pressures increased in the power industry in the 1920s and 1930s, a need arose for higher performance cast steel. The carbon-moly steel alloy was a stopgap that raised the continuous operating temperature of steel valves to 850° F(454° C). Although the carbon-moly steel was useful at higher temperatures, it suffered from creep problems. The pre-WWII period also saw the introduction of the first austenitic stainless-steel alloys (304ss and 316ss), which were vastly superior to the 400 series in corrosion resistance.

Additional alloy steels made their debut as valve materials during the decade following WWII. The chrome/moly steels helped to raise the operating temperatures of cast steel valves above the 1000° F (538° C) range; 1-1/4 Cr. (WC6), 2-1/4 Cr. (WC9), 5 Cr. (C5) and 9 Cr. (C12) were all developed during this period. The first ASTM standard to address these materials was ASTM A157, Alloy Steel Castings for Valves, Flanges and Fittings for High Temperature Service, which was issued in 1950. This standard would later be superseded by ASTM A217. All these alloys also are produced as forgings, with most listed in the ASTM A182 material standard.

Making patterns for iron valvesDuring the 1950-1960 time period, new processes in the chemical industry were outstripping the ability of stainless steels to cope with corrosion issues. As a result, higher grades of stainless steels were developed and tried. Alloy 20, stabilized stainless steels (347 & 321) and low-carbon grades (316L and 304L) became popular. However, the ability of these metals to perform satisfactorily would soon be surpassed by the needs of industry yet again. New “super alloys” were developed to meet those needs, including the Hastelloys, Inconels and duplex stainless steels. These materials were very strong at high temperatures and also had impressive corrosion resistance.

Twenty-first century valve manufacturers are still using the popular metals of the past 150 years, but newer materials are always under development. The latest alloy steel to attain great popularity is the “super 9 chrome” C12A cast steel and F91 forged steel, which allow for valve working temperatures of 1200° F (649° C), while providing better creep resistance than C12 material.