1.1 This specification covers chromium-molybdenum alloy steel sheet and strip intended primarily for use in coil form in the construction of welded layered pressure vessels designed for elevated temperature service.

1.2 Sheet and strip are available under this specification in one grade, 21/4 Cr-1 Mo, and in five Classes, or strength levels, as in Table 1.

1.3 Material of Classes 1, 2, 3, and 4 is intended for use in the subcritical-annealed condition. Material of Class 5 is intended for use in the as-hot-rolled condition.

1.4 Material of Classes 1, 2, 3, and 4 may be furnished in the heat-treated condition. However, the material is usually furnished in the as-hot-rolled condition, being qualified on the basis of tensile test specimens which have been subjected to a simulated heat treatment as specified by the purchaser.

1.5 Material of Class 5 is supplied in the as-hot-rolled condition.

1.6 Material of Class 5 cannot be subjected to temperatures above 800°F [425°C] without sustaining significant loss in strength. Therefore, hot-forming and post-weld heat treatment are not applicable to Class 5 material.

1.7 Material is usually furnished in coil form within the following size limits:

1.8 The values stated in either inch-pound units or SI units are to be regarded 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 the specification.

1.9 This specification is expressed in both inch-pound units and SI units. However, unless the order specifies the applicable "M" specification designation [SI units], the material shall be furnished to inch-pound units.