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Why ASTM A335 Seamless Steel Pipe is Popular in High Temperature Application?


ASTM A335 Seamless Steel Pipe is generally named chrome moly pipe for the chemical elements- Molybdenum and Chromium. Molybdenum improves steel performances as steel strength, elastic limit, wear resistance, impact and hardenability. While Element Moly increases steel pipe resistance to softening, restrains grain growth and slows down the steel structure embrittlement speed. Through experiment and production test, moly is by now the most effective additive which can increase high temperature creep strength. Seamless Steel pipe with moly added also shows enhanced corrosion resistance and inhibits pitting.


Chromium (or chrome) is one essential element in stainless steel production. Steel product is defined as stainless steel for 12% or more Chrome added. For its outstanding heat resistant feature, chrome is widely used and is irreplaceable in resisting oxidation at elevated temperatures applications. In addition, chrome element raises the steel tensile, yield, and hardness at room temperatures. This is why ASTM A335-chrome moly alloy seamless steel pipe is mostly used for in power plants, refineries, chemical plants, and oil field platforms where fluids and gases are at extremely high temperatures and pressures while transportation.

 ASTM A335 Seamless Alloy-Steel Pipe

 ASTM A335 Seamless Steel Pipe Specifications:

Scope: This specification covers nominal wall and minimum wall seamless chrome moly seamless pipes for the power generation and petrochemical industries. ASTM A335 Seamless Steel Pipe ordered to this specification shall be suitable for fusion welding, bending, flanging (vanstoning), and similar forming operations. With chrome and moly element added, ASTM A335 offers good tensile strength, fine resistance to high temperature and corrosion.

Grades and Application:

It covers steel grades from P1 to P5, P9, P11, P12, P91. Grades P11/P22 and P91/92 are commonly used in power stations, while A335 grade P5 and P9 are mostly used for application in the petrochemical industry.

  • Name: ASTM A335 alloy steel pipe

  • Diameter:16-1016mm

  • Thickness: 2---120mm

  • Steel grade: P1 P2 P5 P9 P11 P12 P22

  • Surface: oiled, black painted to prevent rust

  • APPLICATION Fileds:Industrial Boilers, Power Plants, Nuclear Plants

 ASTM A335 Steel Pipe Chemical Composition:


A335 Grade P10.10---0.200.10---0.500.30---0.800.0250.0250.440.65
A335 Grade P5Max 0.15Max 0.500.30---0.600.0250.0250.450.654.006.00
A335 Grade P110.05---0.150.5---1.00.30---0.600.0250.0250.450.651.001.50
A335 Grade P120.05---0.15Max 0.500.30---0.610.0250.0250.450.650.801.25
A335 Grade P220.05---0.15Max 0.500.30---0.600.0250.0250.871.131.902.60

 ASTM A335 Steel Pipe Mechanical Properties:

MaterialTensile N/mm2Strength min N/mm2Yield %min
A335 Grade P1Min38020530
A335 Grade P5Min41520530
A335 Grade P11Min41520530
A335 Grade P12Min41520530
A335 Grade P22Min41520530

 ASTM A335 Steel Pipe Heat Treatment Requirements

ASTM A335 steel pipe may be either hot finished or cold drawn with the finishing heat treatment noted below.

ASTM A335 GradeHeat Treatment TypeNormalizing Temperature Range F [C]Subcritical Annealing or Tempering 
Temperature Range F [C]
P5 (b,c)Full or Isothermal Anneal

Normalize and Temper-1250 [675]

Subcritical Anneal (P5c only)-1325 - 1375 [715 - 745]
P9Full or Isothermal Anneal

Normalize and Temper-1250 [675]
P11Full or Isothermal Anneal

Normalize and Temper-1200 [650]
P22Full or Isothermal Anneal

Normalize and Temper-1250 [675]
P91Normalize and Temper1900-1975 [1040 - 1080]1350-1470 [730 - 800]

Quench and Temper1900-1975 [1040 - 1080]1350-1470 [730 - 800]

 ASTM A335 steel pipe Permissible Variation in Wall Thickness

NPS [DN] DesignatorTolerance, % from Specified

1/8 to 2 1/2 [6 to 65] incl., all t/D ratios20.0%12.5%
Above 2 1/2 [65], t/D < or = 5%22.5%12.5%
Above 2 1/2 [65], t/D > 5%15.0%12.5%
(t = Specified Wall Thickness; D = Specified Outside Diameter)

 ASTM A335 Steel Pipe Elongation Requirements:

Calculated Minimum Elongation Values
Elongation in 2 in. or 50 mm, min %
Wall ThicknessP5, P9, P11, P22P91
5/16 (0.312)8302020
9/32 (0.281)7.2281919
1/4 (0.250)6.4271818
7/32 (0.219)5.626
3/16 (0.188)4.824
5/32 (0.156)422
7/8 (0.125)3.221
3/32 (0.094)2.420
1/18 (0.062)1.618

 ASTM A335 Steel Pipe Permissible Variations in Outside Diameter:

Outside Diameter at any point shall not vary from standard specified more than:

NPS [DN] DesignatorOverUnder
1/8 to 1 1/2 [6 to 40], incl.1/64 (0.015)0.401/64 (0.015)0.40
Over 1 1/2 to 4 [40 to 100], incl.1/32 (0.031)0.791/32 (0.031)0.79
Over 4 to 8 [100 to 200], incl.1/16 (0.062)1.591/32 (0.031)0.79
Over 8 to 12 [200 to 300], incl.3/32 (0.093)2.381/32 (0.031)0.79
Over 12 [300]+/- 1% of the specified outside diameter

 ASTM A335 Steel Pipe Mechanical Tests Specified:

The steel material shall conform to chemical composition, tensile property, and hardness requirements. Each length of pipe shall be subjected to the hydrostatic test.

Transverse or Longitudinal Tension Test and Flattening Test, Hardness Test, or Bend Test
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].
Hydrostatic TestEach length of pipe shall be Hydro tested, at option of manufacture nondestructive electric testing can be used.
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