Application of SA-533 Class 2 Vessels in Floating LNG Plants
Abstract ASME SA-533 Class 2 steel provides 30% higher tensile strength and 90% higher yield strength compared to ASME SA-516 Grade 70 steel, which is commonly used for onshore pressure vessels. Owing to the higher allowable stress, the use of the SA-533 Class 2 steel leads to significant reduction of the vessel weight by permitting thinner vessel walls, which in turn, leads to lighter supporting steel structures. This is quite beneficial for offshore applications, since the space and weight capacity are limited on an offshore platform or the structure modules on a ship. Further, when vessels are intended for use in gas processing plants, depending on the process design, not only higher tensile strength but also greater impact toughness at low temperatures [e.g., minus 29°C (minus 20°F) or lower] are required. This consequently imposes special considerations on the vessel fabrication. Especially, careful attention is needed in establishing welding and heat treatment procedures to achieve both properties in the weldment. This paper presents the use of ASME SA-533 Type C Class 2 steel for a pressure vessel intended for use in the gas inlet facility of a floating LNG plant.