ASTM A335 P9 / ASME SA335 P9 Seamless Alloy Steel Pipe

ASTM A335 P9, also designated ASME SA335 P9, is a seamless ferritic alloy steel pipe containing approximately 9% chromium and 1% molybdenum. Its 9Cr-1Mo composition provides improved elevated-temperature strength, oxidation resistance and resistance to certain high-temperature process environments compared with lower-chromium Cr-Mo steels.

P9 seamless pipe is commonly used in refinery piping, petrochemical processing units, process heaters, boiler systems and other high-temperature pressure-piping applications.

We manufacture and supply ASTM A335 P9 / ASME SA335 P9 seamless alloy steel pipes with complete material traceability, EN 10204 certification and project-specific inspection when required.

ASTM A335 P9 Pipe Specification

Download astm-a335-p9-pipe-specification

Item	Specification
Standard	ASTM A335/A335M
ASME Designation	ASME SA-335/SA-335M
Grade	P9
UNS Number	S50400
Material Type	Ferritic chromium-molybdenum alloy steel
Nominal Alloy Content	9Cr-1Mo
Manufacturing Process	Seamless, hot-finished or cold-finished
Heat Treatment	In accordance with ASTM A335/A335M
Dimensions	ASME B36.10M or project-specific dimensions
Ends	Plain, beveled or threaded
Certification	EN 10204 Type 3.1; Type 3.2 when specified
Primary Service	High-temperature pressure piping

What Is ASTM A335 P9 Pipe?

ASTM A335 /A335M covers seamless ferritic alloy steel pipes intended for high-temperature service.

The standard includes several chromium-molybdenum grades, such as:

Grade P9 is distinguished by its approximately 8.00–10.00% chromium and 0.90–1.10% molybdenum content.

The higher chromium content provides better oxidation resistance than lower-alloy grades such as P11 and P22. Molybdenum contributes to elevated-temperature strength and microstructural stability.

P9 is not a stainless steel grade. Its suitability for corrosion service must be evaluated against the actual fluid composition, temperature, pressure and expected corrosion mechanism.

Chemical Composition of ASTM A335 P9

Element	Requirement
Carbon, C	0.15% max
Manganese, Mn	0.30–0.60%
Phosphorus, P	0.025% max
Sulfur, S	0.025% max
Silicon, Si	0.25–1.00%
Chromium, Cr	8.00–10.00%
Molybdenum, Mo	0.90–1.10%

The actual chemical composition of each supplied heat must be confirmed by the corresponding material test certificate.

Mechanical Properties

Property	Minimum Requirement
Tensile Strength	415 MPa
Yield Strength	205 MPa
Longitudinal Elongation	30%

Elongation requirements may vary according to specimen orientation and wall thickness under the applicable ASTM provisions.

These room-temperature mechanical values should not be used directly as allowable design stresses. High-temperature piping design must refer to the applicable ASME code and material stress tables.

Manufacturing Process

ASTM A335 P9 pipe must be manufactured by a seamless process.

Hot-Finished P9 Pipe

Hot-finished pipe is commonly selected for:

Larger outside diameters
Heavy wall thicknesses
Standard pressure-piping dimensions
High-volume industrial applications

Cold-Finished P9 Pipe

Cold finishing may be specified where the project requires:

Closer dimensional tolerances
Improved surface condition
More precise outside diameter
Specific mechanical-property control

The required finishing method should be stated in the purchase order when it is important to fabrication or final installation.

Heat Treatment

ASTM A335 P9 seamless pipe must be supplied in a heat-treated condition complying with the ordered edition of ASTM A335/A335M.

Common P9 heat-treatment conditions include:

Full annealing
Isothermal annealing
Normalizing and tempering

Heat treatment is used to achieve:

Uniform microstructure
Required tensile properties
Controlled hardness
Stable elevated-temperature performance
Suitable welding and forming characteristics

The final heat-treatment condition should be stated on the material test certificate.

Typical Supply Range

Parameter	Typical Availability
Size	NPS 1/2 to NPS 36
Wall Thickness	Standard and heavy-wall dimensions
Schedule	SCH 40, SCH 80, SCH 120, SCH 160, STD, XS and XXS
Length	6 m, 9–12 m, random or fixed length
Ends	Plain end, beveled end or threaded end
Surface	Black, descaled, shot-blasted or temporarily protected
Packing	Steel-banded bundles, wooden crates or project-specific packing

These figures describe a typical commercial supply range and are not the dimensional limits of ASTM A335. Actual availability depends on outside diameter, wall thickness, quantity and production route.

Dimensions and End Preparation

ASTM A335 P9 pipe is commonly ordered according to ASME B36.10M dimensions.

The purchase order should specify:

NPS or outside diameter
Schedule or wall thickness
Nominal-wall or minimum-wall requirement
Random or fixed length
Outside-diameter tolerance
Wall-thickness tolerance
End preparation
Required dimensional standard

Beveled ends may be supplied in accordance with ASME B16.25 or the purchaser’s specified bevel drawing.

Inspection and Testing

ASTM A335 P9 pipe is subject to chemical, mechanical, dimensional and nondestructive examination requirements.

Standard Tests

Standard inspection generally includes:

Heat chemical analysis
Product analysis where required
Tensile testing
Flattening or bend testing, as applicable
Hardness testing
Visual inspection
Dimensional inspection
Hydrostatic testing
Nondestructive examination

Each length of pipe must undergo the required hydrostatic test and an applicable nondestructive examination method.

Additional Project-Specific Tests

The following tests can be specified when required by the purchaser:

Ultrasonic testing
Eddy-current testing
Magnetic-flux-leakage testing
Positive material identification
Magnetic particle examination of pipe ends
Hardness mapping
Metallographic examination
Additional product analysis
Third-party inspection
Supplementary requirements under ASTM A335

PMI, additional UT, third-party inspection and EN 10204 Type 3.2 certification should be clearly identified in the enquiry because they are not automatically required for every order.

Hydrostatic and Nondestructive Examination

Each ASTM A335 P9 pipe length must be hydrostatically tested in accordance with the applicable specification requirements.

Each pipe must also be examined using an accepted nondestructive examination method, subject to the dimensional limitations of that method.

The inspection basis normally includes:

ASTM A335/A335M
ASTM A999/A999M
Purchase-order requirements
Project inspection and test plan
Applicable ASME construction code

Marking and Traceability

Pipe marking should include, as applicable:

Manufacturer’s name or trademark
ASTM A335/A335M
Grade P9
ASME designation when ordered
NPS or outside diameter
Wall thickness or schedule
Heat number
Manufacturing identification
Length where required
Additional project markings

The heat number must maintain traceability between the finished pipe and its material test certificate.

Applications of ASTM A335 P9 Pipe

Refinery Piping

P9 seamless pipe is commonly used in:

High-temperature process lines
Furnace and heater piping
Crude and vacuum units
Hot hydrocarbon transfer lines
Process headers
High-temperature sulfur-containing environments, subject to corrosion assessment

Petrochemical Plants

Typical applications include:

Reactor piping
Process-heater lines
High-temperature transfer piping
Hot-gas systems
Chemical-processing units
Compressor and pump connections

Power and Boiler Systems

P9 pipe may be used in:

Boiler piping
Steam-piping systems
High-temperature headers
Waste-heat recovery units
Thermal-processing systems
Auxiliary pressure piping

Industrial High-Temperature Systems

Other uses include:

High-temperature pressure lines
Heat-treatment plants
Thermal-processing equipment
Process-equipment connections
High-temperature gas piping

Final suitability must be confirmed against the design temperature, design pressure, ASME allowable stress, process medium and expected service life.

ASTM A335 P9 vs P5, P22 and P91

Property	P5	P9	P22	P91
Nominal Alloy Type	5Cr-0.5Mo	9Cr-1Mo	2.25Cr-1Mo	Modified 9Cr-1Mo-V-Nb
Chromium Range	4.00–6.00%	8.00–10.00%	1.90–2.60%	8.00–9.50%
Molybdenum Range	0.45–0.65%	0.90–1.10%	0.87–1.13%	0.85–1.05%
Microalloying	None specified	None specified	None specified	V, Nb and N controlled
Relative Oxidation Resistance	Higher than low-Cr grades	Higher than P5 and P22	Lower than P5 and P9	High
Relative Creep Strength	Conventional Cr-Mo	Conventional 9Cr-1Mo	Conventional Cr-Mo	Significantly higher
Typical Selection Basis	Refinery process conditions	Higher-chromium refinery and process service	Steam and elevated-temperature piping	Advanced high-temperature power service

These grades are not automatically interchangeable. Substitution requires engineering approval because their allowable stresses, heat treatments, welding procedures and service behavior differ.

Related P9 Material Grades by Product Form

Component	Related Material Specification
Seamless Pipe	ASTM A335 P9 / ASME SA335 P9
Boiler or Heat-Exchanger Tube	ASTM A213 T9 / ASME SA213 T9
Butt-Welding Fittings	ASTM A234 WP9
Forged Flanges and Fittings	ASTM A182 F9
Forged Pressure Components	ASTM A336 F9

These specifications cover different product forms. They share a related alloy family but must not be treated as identical or substituted without technical review.

Welding and Fabrication

ASTM A335 P9 is suitable for fusion welding, but fabrication must follow a qualified welding procedure.

Important considerations include:

Correct filler-metal selection
Qualified WPS and PQR
Preheat control
Interpass-temperature control
Low-hydrogen welding consumables
Post-weld heat treatment where required
Hardness control
Controlled heating and cooling
Required nondestructive examination

Welding requirements depend on wall thickness, joint design, service conditions and the applicable construction code.

P9 should not be welded using procedures developed for P91 without engineering review. Although both grades contain approximately 9% chromium, P91 has a different microalloyed metallurgy and requires different heat-treatment and welding controls.

ASTM A335 P9 vs ASME SA335 P9

Item	ASTM A335 P9	ASME SA335 P9
Issuing Organization	ASTM International	ASME
Designation	A335/A335M P9	SA-335/SA-335M P9
Product Form	Seamless ferritic alloy steel pipe	Seamless ferritic alloy steel pipe
Alloy Type	9Cr-1Mo	9Cr-1Mo
Primary Application	High-temperature industrial piping	ASME code pressure piping and equipment

ASME SA335 is the ASME-adopted material specification used within the ASME Boiler and Pressure Vessel Code framework.

The required standard designation and edition should be identified in the purchase order, especially for ASME-certified construction.

Ordering Information

A complete ASTM A335 P9 enquiry should include:

Required standard and edition
ASTM A335 P9 or ASME SA335 P9
Quantity or total length
NPS or outside diameter
Schedule or wall thickness
Nominal-wall or minimum-wall basis
Hot-finished or cold-finished condition
Random or fixed length
End preparation
Heat-treatment condition
Inspection and testing requirements
Supplementary requirements
Material certificate type
Third-party inspection requirements
Packing and marking instructions

Ordering Example

Product: Seamless ferritic alloy steel pipe
Standard: ASTM A335/A335M
Grade: P9
Size: NPS 6
Wall Thickness: SCH 80
Length: 6 m
Ends: Beveled ends
Quantity: As specified
Testing: Hydrostatic test and nondestructive examination
Certification: EN 10204 Type 3.1

Frequently Asked Questions

What is ASTM A335 P9 pipe?

ASTM A335 P9 is a seamless ferritic alloy steel pipe containing approximately 9% chromium and 1% molybdenum. It is intended for high-temperature pressure-piping applications.

Is ASTM A335 P9 seamless or welded?

ASTM A335 covers seamless pipe only. Welded pipe cannot be certified as ASTM A335 P9.

What is the chemical composition of P9?

The principal alloy limits are 8.00–10.00% chromium and 0.90–1.10% molybdenum, with carbon limited to a maximum of 0.15%.

What is the operating temperature of P9 pipe?

ASTM A335 does not establish one universal operating-temperature range for every P9 installation.

The allowable temperature depends on:

Design pressure
ASME allowable stress
Wall thickness
Process medium
Corrosion mechanism
Design life
Applicable piping code

A fixed 550–650°C range should not be used without engineering verification.

What is the difference between P9 and P91?

P9 is a conventional 9Cr-1Mo steel. P91 is a modified 9Cr-1Mo steel containing controlled vanadium, niobium and nitrogen additions.

P91 generally provides much higher creep strength, but it also requires stricter heat-treatment, welding and fabrication controls.

Is ASTM A213 P9 a correct designation?

No. The corresponding tube designation is ASTM A213 T9. P9 is the pipe grade designation under ASTM A335.

Can P9 pipe be welded?

Yes. P9 is suitable for fusion welding when an approved welding procedure, suitable filler metal, preheating, interpass-temperature control and required post-weld heat treatment are applied.

What documents can be supplied?

Available documents may include:

EN 10204 Type 3.1 certificate
EN 10204 Type 3.2 certificate
Heat-treatment records
Hydrostatic-test reports
Nondestructive-examination reports
PMI reports
Third-party inspection release notes

We also supply a wide range of alloy steel pipes and fittings for high-temperature and high-pressure applications:

ASTM A335 P9 Alloy Seamless Steel Pipe

ASTM A 335 P9 Seamless Pipes Chrome Moly Pipe ASME B36.10

Published by ADMIN on December 22, 2019December 22, 2019