1.1 This specification covers grades of minimum-wall-thickness, seamless, hot-finished and cold-finished, austenitic chromium-nickel steel still tubes as designated in Table 1 for use in carrying fluids at elevated temperatures and pressures in various types of heaters, in which the tubes may be subjected to a furnace temperature higher than that of the contained fluid.

1.2 The specification covers tubes 2 to 9 in., (50.8 to 228.6 mm) inclusive, in outside diameter and over 0.220 in. (5.59 mm) in minimum wall thickness.

1.3 Grades TP304H, TP321H, TP347H, and TP316H are modifications of Grades TP304, TP321, TP347 and TP316, and are intended for high-temperature service.

1.4 Optional supplementary requirements are provided, and when desired, shall be so stated in the order.

1.5 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.