Duplex Steel Piping

Duplex stainless steel is among various metals used in corrosion-resistant applications.

Duplex steels have a mixed microstructure with about equal proportions of ferrite and austenite. Duplex stainless steels are a family of grades, which range in corrosion performance depending on their alloy content.

The chemical composition based on high contents of Cr and Mo, improves intergranular and pitting corrosion resistance, respectively. Additions of nitrogen can promote structural hardening by interstitial solid solution mechanism, which raises the yield strength and ultimate strength values without impairing toughness.

When welding duplex alloys, the heat input and interpass temperature must be controlled to maintain the ferrite-austenite balance. Otherwise, the advantages of using the duplex material will be sacrificed. The time spent at 1,300 °F to 1,800 °F must be controlled. The heat-affected zone (HAZ) time-at-temperature is critical in controlling the intermetallic phases.

Following is a typical specification for class 150 Duplex stainless steel piping 275 psig @ 130° F.

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