Duplex Stainless Steel and Duplex Steel Valves Introduction

Duplex Stainless Steel Summary:

Duplex stainless steels are a family of stainless steels. These are called duplex (or austenitic-ferritic) grades because their metallurgical structure consists of two phases, austenite (face-centered cubic lattice) and ferrite (body centered cubic lattice) in roughly equal proportions. They are designed to provide better corrosion resistance, particularly chloride stress corrosion and chloride pitting corrosion, and higher strength than standard austenitic stainless steels such as Type 304 or 316. The main differences in composition, when compared with an austenitic stainless steel is that the duplex steels have a higher chromium content, 20–28%; higher molybdenum, up to 5%; lower nickel, up to 9% and 0.05–0.50% nitrogen. Both the low nickel content and the high strength (enabling thinner sections to be used) give significant cost benefits. They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc.

Duplex Stainless Steel Futures:

• Improved Strength

Many duplex grades are as much as two-times stronger than austenitic and ferritic stainless steel grades.

• High Toughness and Ductility

Duplex stainless steel is often more formable under pressure than ferritic grades and provides greater toughness. Though they often offer lower values than austenitic steels, the unique structure and characteristics of duplex steel often outweigh any concerns.

• High Corrosion Resistance

Depending on the grade in question, duplex stainless steels offer comparable (or better) corrosion resistance as common austenitic grades. For alloys with increased nitrogen, molybdenum, and chromium, steels exhibit high resistance to both crevice corrosion and chloride pitting.

• Cost Effectiveness

Duplex stainless steel offers all of the above benefits while requiring lower levels of molybdenum and nickel. This means that it is a lower-cost option than many traditional austenitic grades of stainless steel.The price of duplex alloys is often less volatile than other steel grades making it easier to estimate costs — both at an upfront and lifetime level. The higher strength and corrosion resistance also means that many parts made using duplex stainless can be thinner than their austenitic counterparts providing lower costs.

Duplex Stainless Steel Valve Applications:

Due to their excellent corrosion resistance, increased strength, and affordable pricing, duplex stainless steels are popular in a variety of industries and markets, including:

• Offshore and near-shore operations such as oil drilling, desalination, water treatment, and other industrial operations
• Chemical and liquid processing
• Naval parts and components
• Pollution control equipment
• Pulp and paper production
• Construction
• Hot water and brewing tanks

Duplex Stainless Steel Material Grades: