1.1 This specification covers steel plates produced by the thermo-mechanical control process (TMCP). The plates are intended primarily for use in welded pressure vessels.

1.2 The TMCP method consists of rolling-reduction and cooling rate controls that result in mechanical properties in the finished plate that are equivalent to those attained using conventional rolling and heat treating processes, which entail reheating after rolling. A description of the TMCP method is given in Appendix X1.

1.3 Due to the inherent characteristics of the TMCP method, the plates cannot be formed at elevated temperatures without sustaining significant losses in strength and toughness. The plates may be formed and post-weld heat-treated at temperatures not exceeding 1200°F [650°C], providing the requirements of are met.

1.4 The maximum permitted nominal thickness of plates furnished to this specification is 4 in. [100 mm] for Grades A, B, and C; and 1.5 in. [40 mm] for Grades D, E, and F.

1.5 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents. Therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with this specification.