For more than 50 years, 9% Ni steel with excellent mechanical properties at a cryogenic temperature of less than –162°C has been used as inner-tank material for liquefied-natural-gas (LNG) storage tanks. However, a reduction of the nickel content in steel can save construction costs of LNG storage tanks. A new steel plate for LNG storage tanks has been developed by optimizing chemical composition and applying recent thermomechanical-control-process (TMCP) technology.

Introduction

With demand for LNG rising, construction of above-ground LNG storage tanks is expected to increase. 9% Ni steel plate has excellent strength and cryogenic toughness. For LNG storage tanks, a double-integrity structure has been proposed to prevent peremptory destruction (Fig. 1).

Although a high safety standard is demanded for such steel plates, in terms of saving construction costs of LNG tanks, a reduction in the amount of nickel used was desired. The new steel plate, equivalent to conventional 9% Ni steel, has been developed by adopting a TMCP to obtain the refined microstructure and a large amount of retained austenite.