TECH TALK
Stainless Steel Valves in the Chemical Industry
Valves are essential to many industries and are used under all sorts of circumstances . While their application usually determines the optimal materials for the specific valve , stainless steel offers properties that can be very beneficial .
By Srikumar Chakraborty , ex ASP / SAIL , Freelance Consultant
Valves play a vital role in any piping system in the chemical , oil , and gas industries . Stainless steel , with its properties of strength , ductility , corrosion and heat resistance , low maintenance , and unlimited lifecycle , has become an obvious choice due to its low cost . By adding alloys like chromium ( Cr ), nickel ( Ni ), molybdenum ( Mo ), manganese ( Mn ), and silicon ( Si ), stainless steel can attain higher degrees of corrosion resistance , durability , high temperature and pressure tolerance , and versatility .
Stainless steel is ideally suited for aggressive environments , which in industrial applications include pharmaceutical and food and drink manufacturing processes that take their toll on processing equipment . In such demanding applications , stainless steel is a good material for valves because of its favorable lifecycle cost .
Valve Selection for the Chemical Industry
Valves are critical components with a wide range of applications , from power plants to water systems . The fundamentals of valve selection should be considered to ensure optimal performance , and safety .
When selecting chemical valves , the most important elements to consider are the chemical properties of the working medium , the product being handled , temperature , and pressure .
The valve body , plug , and operating components should be able to withstand the highest temperatures under continuous normal and transient operating conditions , as well as the highest transient pressures expected . Finally , the field requirements for leakage should be considered .
Materials
Common materials for the valve body and area of applications are :
• Grey cast iron / carbon steel : unsuitable for use in seawater without cathodic protection or coating .
• Austenitic ( Ni Resistant ): for seawater , brackish water , and wastewater .
• Stainless steel : generally good corrosion resistance to water , alkalis , minerals , and dry solvents .
• Type austenitic 304 : unsuitable for use in seawater , unlike 316 . 316 will likely be subjected to crevice corrosion without galvanic coating or use of 316L / 316 ELC .
• Duplex : more corrosion resistant , especially regarding stress corrosion cracking .
• Super austenitic : excellent corrosion resistance to a wide range of fluids , seawater , brine solution , caustic , and any mineral acid .
• Super duplex : for caustic and mineral acids .
Valve Manufacturing Process
Based on the relevant requirements , industrial valve manufacturers consider the advantages and disadvantages of casting and forging methods . Choosing which method to employ depends on factors such as desired strength , design complexity , production volume , and budget constraints .
By understanding the pros and cons of each method , manufacturers can optimize their valve manufacturing process for various applications . At first glance , valves may seem to consist of a few parts , but sealing is complex , particularly when demanding zero leakage during fluid / gas-tight testing . This complicates the manufacturing process . Due to the wide variety of valve specifications and the presence of the valves in all types of environments , the material requirements for stainless steel are very strict . However , valve manufacturers perform a bubble seal test before the valve leaves the factory . Here , the seat is tested for significant leakage . Other key parameters include flow speed , valve function ( on / off or modulating ), whether fire safety is required , and other additional functional requirements .
Casting Process
The correct and effective control of casting solidification is the first important condition for obtaining quality products . This process program includes the pouring system , riser , and complementary process amount . Due to their uneven wall thickness , valve parts cast in steel should undergo sequential cooling and sequential solidification to reduce the internal stress of the casting , shrinkage , and other defects .
28 Valve World Americas | April 2024 • www . valve-world-americas . net