Duplex stainless steels 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 the 300 series (304, 316L etc.). They are therefore used extensively in the offshore oil and gas industry for pipework systems, manifolds, risers, etc. and in the petrochemical industry in the form of pipelines and pressure vessels. In addition to the improved corrosion resistance compared with the 300 series stainless steels duplex steels also have higher strength. For example, a Type 304 stainless steel has a 0.2% proof strength in the region of 280 N/mm², a 22%Cr duplex stainless steel a minimum 0.2% proof strength of some 450 N/mm² and a super duplex grade a minimum of 550 N/mm².