ASTM A335 P91 Alloy Steel Pipe

Astm A335 standard specication for seamless ferritic alloy-steel pipe for high-temperature service

ASTM A335 standard is issued under the fixed designation A 335/A 335M; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon ( ュ) indicates an editorial change since the last revision or reapproval.

1.1This specification covers nominal (average) wall seamless alloy-steel pipe intended for high-temperature service (Mote 1). Pipe ordered to this specification shall be suitable for bending, flanging (vanstoning), and similar forming operations, and for fusion welding. Selection will depend upon design, service conditions, mechanical properties, and high-temperature characteristics.

NOTE 1 Α Appendix X1 lists the sizes and wall thicknesses of pipe which may be obtained under current commercial practice.

1.2 Several grades of ferritic steels (Note 2) are covered. 

ΑFerritic steels in this specification are defined as low and intermediate-alloy steels containing up to and including 10％ chromium.
1.3 Supplementary requirements (S1 to S7) of an optional nature are provided. These supplementary requirements call for additional tests to be made, and when desired, shall be so stated in the order together with the number of such tests required.
1.4 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 specification. The inch-pound units shall apply unless the "M" designation of this specification is specified in the order.

Note 3ΑThe dimensionless designator NPS (nominal pipe size) has been substituted in this standard for such traditional terms as "nominal diameter," "size," and "nominal size."

Pipe may be either hot finished or cold drawn with the finishing heat treatment noted below.

For material heat treated in a batch-type furnace, tests shall be made on 5% of the pipe from each treated lot. For small lots, at least one pipe shall be tested.
For material heat treated by the continuous process, tests shall be made on a sufficient number of pipe to constitute 5% of the lot, but in no case less than 2 pipe.

Notes for Hardness Test:
P91 shall not have a hardness not exceeding 250 HB/265 HV [25HRC].

Notes for Bend Test:
For pipe whose diameter exceeds NPS 25 and whose diameter to wall thickness ratio is 7.0 or less shall be subjected to the bend test instead of the flattening test.
Other pipe whose diameter equals or exceeds NPS 10 may be given the bend test in place of the flattening test subject to the approval of the purchaser.
The bend test specimens shall be bent at room temperature through 180 without cracking on the outside of the bent portion.

The inside diameter of the bend shall be 1 inch [25 mm].
Each length of pipe shall be Hydro tested, at option of manufacture nondestructive electric testing can be used.