ASTM A335 chrome moly pipe

Dec 04, 2025

What is ASTM A335 material?

‌ASTM A335 steel pipe is a seamless ferritic alloy steel employing a chromium-molybdenum (Cr-Mo) alloy system. Its material characteristics feature core alloying elements of chromium (Cr: 0.44-0.65%) and molybdenum (Mo: 0.44-0.65%), formed through hot-rolling or cold-drawing processes. With a tensile strength ≥415 MPa and hardness ≤197 HB, it is designed for long-term service in high-temperature, high-pressure environments (≤550°C). Primary applications include power boiler piping, petrochemical cracking units, and chemical reactor pipelines.

ASTM A335 Pipe Chemical Composition

Grade	UNS	C	Mn	P	S	Si	Cr	Mo
P5	K41545	0.15 max	0.30 – 0.60	0.025 max	0.025 max	0.25 – 1.00	8.00 – 10.00	0.90 – 1.10
P9	S50400	0.05 – 0.15	0.30 – 0.60	0.025 max	0.025 max	0.50 – 1.00	1.00 – 1.50	0.44 – 0.65
P11	K11597	0.05 – 0.15	0.30 – 0.60	0.025 max	0.025 max	0.50	1.90 – 2.60	0.87 – 1.13
P22	K21590	0.08 – 0.12	0.30 – 0.60	0.020 max	0.010 max	0.20 -0.50	8.00 – 9.50	0.85 – 1.05
P91	K91560	0.08 - 0.12	0.30 – 0.60	0.020 max	0.010 max	0.20 -0.50	8.00 – 9.50	0.85 – 1.05

ASTM A335 Pipe Mechanical Properties

A335 Grade	Tensile Strength, min., psi		Yield Strength, min., psi
	ksi	MPa	ksi	MPa
P5	60	415	30	205
P9	60	415	30	205
P11	60	415	30	205
P22	60	415	30	205
P91	85	585	60	415

Outside Diameter Tolerance

Outside Diameter (mm)	Tolerance (mm)
10.3 – 48.3	±0.40
>48.3 – 114.3	±0.79
>114.3 – 219.1	-0.79 ~ +1.59
>219.1 – 323.8	-0.79 ~ +2.38
>323.8	‌±1% of Nominal OD

‌Delivery Conditions:‌

‌Grades P5, P5b, P9, P21, P22, P1, P2, P12, P11, and P15‌ shall be delivered in one of the following conditions:

Fully annealed,

Isothermally annealed, or

Normalized and tempered.

When normalized and tempered:

‌P5, P5b, P9, P21, P22‌: Minimum tempering temperature ≥675°C.

‌P1, P2, P12, P11, P15‌: Minimum tempering temperature ≥650°C.

‌For Grades P1, P2, and P12‌ manufactured by hot rolling or cold drawing:

The manufacturer may perform final heat treatment at ‌650–705°C‌ as an alternative to the treatments specified in Item 1.

‌Grade P5c‌ shall undergo final heat treatment at ‌approximately 715–745°C‌.

‌Grades P23 and P91‌:

Must be normalized at ‌≥1040°C‌,

Followed by tempering at ‌≥730°C‌.

Surface Quality and Appearance

‌Straightness‌: Finished pipes shall exhibit ‌reasonable straightness‌.

‌Major Defects‌: Defects with depth ‌≥12.5% of wall thickness (S)‌ must be ‌ground, repair-welded, or removed‌. Repaired areas shall not cover large surfaces.

‌Minor Surface Imperfections‌:

Mechanical scratches, abrasions, or dents ‌≤10.6 mm deep‌ are acceptable if they ‌preserve minimum wall thickness‌.

Otherwise, grinding or removal is required.

‌Shallow Flaws‌:

Scars, cracks, folds, tears, or laminations ‌≤5% S deep‌ are permissible.

Defects exceeding this limit must be ground.

‌Grinding Allowance‌:

All ground areas must maintain ‌minimum wall thickness‌, but the ‌outer diameter may be reduced by the grinding depth‌.

inspection

Hydrostatic Testing

‌Requirement‌: Hydrostatic testing shall be performed ‌on each pipe‌.

‌Alternatives‌:

With the purchaser's agreement, ‌non-destructive testing (NDT)‌ may replace hydrostatic testing.

Pipes may be delivered ‌without hydrostatic testing or NDT‌.

Non-Destructive Testing (NDT)

‌Requirement‌: When specified by the purchaser, ‌each pipe shall undergo NDT‌.

‌Acceptance Standards‌:

‌Test Method‌	‌Defect Criteria‌
‌Ultrasonic Testing‌	Notch depth ≤ ‌12.5% of nominal wall thickness or 0.1 mm (whichever is greater)‌; notch width ≤ depth.
‌Magnetic Flux Leakage‌	Notch depth ≤ ‌12.5% of nominal wall thickness or 0.1 mm (whichever is greater)‌; notch width ≤ depth; length ≤ ‌25.4 mm‌.
‌Eddy Current Testing‌	Calibration hole diameter:
‌Outside Diameter (D)‌	‌Hole Diameter‌
≤21.3 mm	1.0 mm
>21.3–42.2 mm	1.4 mm
>42.2–60.3 mm	1.8 mm
>60.3–141.3 mm	2.2 mm
>141.3 mm	2.7 mm