ASTM A335 is a standard specification for seamless ferritic alloy-steel pipe for high-temperature service. The specification generally covers “chrome-moly” seamless pipes with remarkable resistance to corrosion and good tensile strength at high-temperature service. The testing requirements for these pipes include the following:
- Transverse/longitudinal: tension and flattening, hardness, bend tests- for material which has been heat-treated in batch furnaces, these tests shall be made on the 5% of the pipes from each heat lot number. For smaller lots, one pipe at a minimum has to be tested
- ASTM A335 Gr. P91 shall have a hardness of 250 HB / 265 HV (25 HRC)
- Hydro testing: Each length of pipe shall be subjected to the hydrostatic test. Also, each pipe shall be examined by a non-destructive examination method in accordance to the required practices.
- The non-destructive electric test is optional
Alloying Elements of Steel and Its Impact on Properties of Alloy Steel Pipes or Chrome Moly Pipes:
- Chromium – Adds hardness. Increased toughness and wear resistance.
- Cobalt – Used in making cutting tools; improved Hot Hardness (or Red Hardness).
- Manganese – Increases surface hardness. Improves resistance to strain, hammering & shocks.
- Molybdenum – Increases strength. Improves resistance to shock and heat.
- Nickel – Increases strength & toughness. Improves corrosion resistance.
- Tungsten – Adds hardness and improves grain structure. Provides improved heat resistance.
- Vanadium – Increases strength, toughness and shock resistance. Improved corrosion resistance.
- Chromium-Vanadium – Greatly improved tensile strength. It is hard but easy to bend and cut.
Equivalents of Alloy Steel Pipes Under DIN, ASTM and EN
||A335 Grade P1
||A335 Grade P11, P12
||A335 Grade P22
||A335 Grade P5
||A335 Grade P9
||A335 Grade P91
Chemical Composition of Alloy Steel Chrome Moly Pipes – ASTM A335 P5, P9, P11, P22, and P91
||Ni 0.40 max
||Al 0.02 max
||Ti 0.01 max
||Zr 0.01 max
Mechanical Properties of Alloy Steel Chrome Moly Pipes – ASTM A335 P5, P9, P11, P22, and P91
||Grade P11, P22, P5, P9
|Tensile strength, min, psi, (MPa)
|Yield strength, min, (MPa)