The subcommittee on Pressure Vessel Steels of JPVRC summarized a study report, entitled "Application of Controlled Rolled Steel Plates for Tank and Pressure Vessel" in 1981. The data included in the report was primarily obtained from line pipe steel with high strength and high toughness whose alloy system was Nb or Nb-V. In contrast to its superior toughness in the base plate, the toughness in weldment was not always satisfactory for a low-temperature service pressure vessel. The toughness testing was required at a temperature not lower than -20°C. Moreover, steel plate itself was not as heavy as used for many pressure vessel applications.

During the past five years, steel plate for low-temperature service has encountered a new situation. The design and the subsequent fabrication of arctic offshore structures, icebreaking carriers and pressure vessels for liquefied gas have escalated the demands for steel plate having a tensile strength of 500 MPa. They required high toughness not only in the base plate but also in the weldment and the applicability of high heat input welding and preheating free welding. In this period, both Japanese steelmakers and fabricators have advanced their new processes. Steelmakers have developed the Thermo-Mechanical Control Process (TMCP) that includes an accelerated cooling process in the plate mill. They have developed new low-temperature steels that meet the above described demands. Fabricators have utilized various highly efficient welding technologies in their fabrication. Accordingly, a great deal of joint work among them has been carried out to put such steel and welding technology into practical use, that has resulted in the accumulation of an abundance of useful data.

Presently, TMCP has been approved for the production of structural steels by major ship classification societies, JIS and ASTM. JIS G 3115 and G 3126 are standard specifications for steel plates for pressure vessels for intermediate temperature service and carbon steel plates for pressure vessels for low-temperature service. ASTM A 841 is the standard for steel plates for pressure vessels produced by TMCP. It is now being discussed as API standard 2W. Specifications and requirements of the JIS and ASTM standards are summarized in Table 1.

The objective of a new activity of the S/C on Pressure Vessel Steels of JPVRC, is to review TMCP and give unified comments on TMCP steels for structural applications in low-temperature service. This report summarizes the most recent data of Japanese steelmakers and fabricators on TMCP steels.