1.1 This specification covers chromium-molybdenum alloy steel plates intended primarily for welded boilers and pressure vessels designed for elevated temperature service.
1.2 Plates are available under this specification in several grades having different alloy contents as follows:
| Nominal | Nominal | |
| Chromium | Molybdenum | |
| Grade | Content, % | Content, % |
| 2 | 0.50 | 0.50 |
| 12 | 1.00 | 0.50 |
| 11 | 1.25 | 0.50 |
| 22, 22L | 2.25 | 1.00 |
| 21, 21L | 3.00 | 1.00 |
| 5 | 5.00 | 0.50 |
| 9 | 9.00 | 1.00 |
| 91 | 9.00 | 1.00 |
| 911 | 9.00 | 1.00 |
1.3 Each grade except Grades 21L, 22L, 91 and 911 is available in two classes of tensile strength levels as defined in the Tensile Requirements tables, depending on heat treatment. In the annealed condition all grades are available only as Class 1. Grades 21L and 22L are available only as Class 1. Grade 91 and 911 are available only as Class 2.
1.4 The maximum thickness of plates is limited only by the capacity of the composition to meet the specified mechanical property requirements.
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.
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