ASTM A335 P11 vs P22 Pipes: Key Differences, Properties and Applications

When selecting alloy steel pipes for high-temperature industrial applications, choosing the correct material grade is an important decision. Two grades commonly considered for boilers, power plants, refineries and process piping systems are ASTM A335 P11 and ASTM A335 P22.

At first glance, these grades may appear similar because both are chromium-molybdenum alloy steels designed for elevated-temperature service. However, their chemical composition, high-temperature performance and suitability for particular operating conditions are different.

So, what is the difference between ASTM A335 P11 and P22 pipes? Is P22 always a better option than P11, or can P11 be the right choice for your project?

The answer depends on the operating temperature, pressure, design requirements and service conditions of the piping system. Understanding these differences can help engineers, procurement teams and industrial buyers make a more informed decision.

What Are ASTM A335 P11 and P22 Pipes?

ASTM A335 is a material specification covering seamless ferritic alloy steel pipes intended for high-temperature service. These pipes are used in applications where ordinary carbon steel may not provide the required performance under the specified operating conditions.

P11 and P22 belong to the chromium-molybdenum, or chrome-moly, family of alloy steels. Chromium and molybdenum are added to the steel to improve its performance at elevated temperatures and its resistance to oxidation and creep, subject to the material condition and operating environment.

ASTM A335 P11 pipe is commonly identified as 1.25Cr-0.5Mo alloy steel. It is used in a range of elevated-temperature piping applications.

ASTM A335 P22 pipe is commonly identified as 2.25Cr-1Mo alloy steel. Its higher chromium and molybdenum content makes it a suitable candidate for many demanding high-temperature applications, subject to the applicable design code.

Both grades require appropriate material certification, inspection and processing. The correct selection should always follow the engineering specification for the project.

For product details, visit ASTM A335 P11 Alloy Steel Pipes and ASTM A335 P22 Alloy Steel Pipes.

ASTM A335 P11 vs P22 Pipes: Quick Comparison

The following table highlights the main differences between these two alloy steel pipe grades.

Property	ASTM A335 P11	ASTM A335 P22
Material family	Chromium-molybdenum alloy steel	Chromium-molybdenum alloy steel
Common designation	1.25Cr-0.5Mo	2.25Cr-1Mo
Chromium content	1.00–1.50%	1.90–2.60%
Molybdenum content	0.44–0.65%	0.87–1.13%
Carbon content	0.05–0.15%	0.05–0.15%
Minimum tensile strength	415 MPa	415 MPa
Minimum yield strength	205 MPa	205 MPa
Typical application areas	High-temperature process piping, boilers and industrial plants	Boiler systems, steam piping and demanding high-temperature services
Main consideration	Suitable when its design-code allowable stresses meet project requirements	Often considered when the service conditions justify the higher alloy content

Note: Chemical composition and mechanical property values are typical ASTM A335 grade requirements. Always verify the applicable standard edition, product specification, test requirements and material certificate before procurement. The table does not establish a universal maximum operating temperature for either grade.

1. Chemical Composition: The Biggest Difference

The first major difference between ASTM A335 P11 and P22 pipes is their chemical composition.

Both grades contain chromium and molybdenum, but P22 contains higher amounts of these two alloying elements.

Chromium Content

P11 generally contains 1.00% to 1.50% chromium, while P22 contains 1.90% to 2.60%.

Chromium helps improve oxidation resistance at elevated temperatures. The higher chromium content in P22 can make it more suitable for certain services involving demanding temperature and oxidation conditions.

However, higher chromium content does not mean that a pipe can automatically withstand every aggressive chemical environment. Material compatibility still depends on the process fluid, operating conditions and relevant corrosion mechanisms.

Molybdenum Content

P11 contains approximately 0.44% to 0.65% molybdenum, whereas P22 contains approximately 0.87% to 1.13%.

Molybdenum contributes to high-temperature strength and resistance to creep deformation. Creep is the gradual deformation of a material when it remains under stress for an extended period, particularly at elevated temperatures.

This is an important consideration for power plants, boilers and other industrial systems that operate continuously under heat and pressure.

Because P22 contains more chromium and molybdenum, it may provide advantages in specific high-temperature applications. Whether those advantages are necessary depends on the engineering design.

2. Mechanical Properties of P11 and P22 Pipes

When comparing two pipe grades, buyers often assume that the grade with a higher alloy content will always have greater tensile and yield strength.

That is not necessarily true.

Under the commonly listed ASTM A335 requirements, P11 and P22 have the same minimum tensile strength of 415 MPa and minimum yield strength of 205 MPa.

However, these minimum values do not tell the complete story.

High-temperature piping design also considers allowable stress at the operating temperature, resistance to creep, material condition, wall thickness and expected service life.

A pipe that performs adequately in one application may not be appropriate for another application with higher temperature, different pressure or a longer design life.

For this reason, engineers should evaluate the applicable material properties at the intended operating conditions rather than comparing the grades using room-temperature strength alone.

3. Temperature Performance and High-Temperature Service

Temperature is one of the main factors when selecting ASTM A335 P11 or P22 pipes.

P11 is used in many elevated-temperature applications where the grade satisfies the project’s pressure, temperature and design-code requirements.

P22 is frequently considered for applications such as boiler piping, superheater systems, steam lines and other services where its chromium-molybdenum composition offers the required high-temperature performance.

However, there is no single maximum operating temperature that can safely be applied to every P11 or P22 installation.

The permitted operating conditions depend on the design code, design pressure, pipe dimensions, wall thickness, allowable stress, material condition and service requirements.

For example, a pipe used at a particular temperature under relatively low stress cannot automatically be considered suitable for the same temperature at a much higher pressure.

Before selecting either grade, consult the applicable ASME pressure design rules and project specifications. The final decision should be based on the calculated design requirements, not just the material’s grade name.

4. Applications of ASTM A335 P11 Pipes

P11 pipes are used in industrial applications where chromium-molybdenum alloy steel is suitable for the specified operating conditions.

Common application areas include:

• Power generation: Selected piping systems operating at elevated temperatures.
• Boiler installations: Applications where the P11 grade satisfies the relevant design requirements.
• Petrochemical plants: Process lines carrying fluids under controlled high-temperature conditions.
• Oil refineries: Industrial piping specified for suitable pressure and temperature ranges.
• General process engineering: Systems requiring certified alloy steel pipe for elevated-temperature service.

P11 can be a practical option when its approved design properties meet the project’s requirements.

Choosing a lower-alloy grade simply to reduce initial material cost is not appropriate unless the engineer has verified that it meets the necessary service conditions.

5. Applications of ASTM A335 P22 Pipes

P22 is commonly used in more demanding elevated-temperature applications where its alloy composition is appropriate for the design.

Typical applications include:

• Power plants: Steam and other high-temperature piping systems.
• Boiler systems: Selected superheater, reheater and associated piping applications.
• Petrochemical facilities: High-temperature process services requiring a specified chromium-molybdenum grade.
• Refineries: Process piping where temperature, pressure and material compatibility requirements support P22.
• Heavy engineering: Industrial installations designed around the properties of P22 alloy steel.

The use of P22 should not be based only on the assumption that it is a higher grade. Its suitability must be established through the applicable design calculations and material specifications.

Where the project requires P22, substituting P11 without formal engineering approval can create serious compliance and performance risks.

6. Is P22 Always Better Than P11?

Not necessarily.

P22 has a higher chromium and molybdenum content, which can provide useful advantages in certain high-temperature services. However, that does not mean it is the correct choice for every application.

Suppose a piping system has been designed and approved for P11. If the material meets all applicable pressure, temperature and service requirements, changing to P22 may offer no necessary benefit.

On the other hand, if a project specification calls for P22 because of its required high-temperature properties, selecting P11 simply because it costs less would be inappropriate.

There are several factors to consider:

Operating conditions: Review the design temperature, pressure and expected service life.

Engineering requirements: Follow the specified grade, applicable code and approved material selection.

Material availability: Confirm the required pipe dimensions, schedule, length and certification.

Total project cost: Consider material price alongside fabrication, inspection, welding procedures and long-term service requirements.

The better grade is the one that meets the engineering requirements safely and reliably, not necessarily the one with more alloying elements.

7. Welding and Fabrication Considerations

Welding is another important consideration when purchasing P11 and P22 pipes.

Although both grades belong to the chromium-molybdenum steel family, their welding procedures should not be assumed to be interchangeable in every situation.

Factors such as wall thickness, material condition, joint design, restraint and service requirements can affect the welding procedure.

Depending on the applicable specification and approved welding procedure, preheating, control of interpass temperature and post-weld heat treatment may be required.

Incorrect welding practices can affect joint integrity and the properties needed for long-term high-temperature operation.

For critical piping systems, welding should be performed using a qualified welding procedure and by appropriately qualified personnel. The procedure must specify the applicable consumables, temperature controls, inspection requirements and heat treatment where required.

Material traceability should also be maintained throughout fabrication so that the installed pipe can be linked to its relevant inspection and material records.

8. How to Select the Right ASTM A335 Pipe Grade

Before ordering P11 or P22 pipes, confirm the complete technical requirement with the project’s engineering or procurement team.

Start with the material grade specified in the approved piping material specification. Then verify the operating pressure, design temperature and required pipe dimensions.

Pipe size and schedule are important because wall thickness affects pressure capacity, weight and the suitability of the piping system for its design conditions.

Also confirm the following information before finalising a purchase:

• Required standard: ASTM A335 or the applicable ASME SA335 specification.
• Material grade: P11 or P22, as approved for the application.
• Nominal pipe size and required wall thickness or schedule.
• Required length, end preparation and quantity.
• Applicable heat treatment, inspection and testing requirements.
• Mill Test Certificate and material traceability requirements.
• Any additional project-specific documentation.

For certified industrial piping, the material certificate and traceability documents should be checked against the purchase order and applicable specification.

These checks help prevent grade mismatches, documentation issues and delays during material approval.

9. Buying P11 and P22 Alloy Steel Pipes from Leoscor Alloy Pipes

Finding a suitable supplier is an important part of the procurement process, especially when alloy steel pipes are required for a power plant, refinery, petrochemical facility or other industrial project.

Leoscor Alloy Pipes supplies a range of alloy steel pipes for industrial requirements, including ASTM A335 P11 and P22 grades.

Buyers can review the available product information and submit their requirements for quotation and availability confirmation.

Explore the following product pages:

• ASTM A335 P11 Pipes for product specifications and enquiry details.
• ASTM A335 P22 Pipes for grade-specific product information.
• Alloy Steel Pipes to explore Leoscor’s broader alloy steel pipe range.

Before placing an order, share the required grade, size, schedule, quantity and certification details. The supplier can then confirm availability and provide a quotation based on the stated requirements.

Request a Quote for ASTM A335 P11 or P22 Pipes

Looking for ASTM A335 P11 or P22 alloy steel pipes for your next industrial project?

Contact Leoscor Alloy Pipes to discuss your pipe specifications, material requirements and quotation needs.

Visit the Leoscor Alloy Pipes Contact Page to submit your enquiry.

Providing the complete technical specification at the enquiry stage helps the procurement team confirm the correct grade and available supply options.

Frequently Asked Questions

What is the main difference between ASTM A335 P11 and P22 pipes?

The main difference is their chemical composition. P22 contains more chromium and molybdenum than P11, which can make it suitable for particular demanding high-temperature applications. Both grades have the same commonly specified minimum tensile and yield strengths under ASTM A335.

Can P11 pipes be replaced with P22 pipes?

Not automatically. Any material substitution must be reviewed and approved by the responsible engineer. The selected grade must comply with the project’s design code, material specification and operating requirements.

Are ASTM A335 P11 and P22 pipes seamless?

ASTM A335 is a specification for seamless ferritic alloy steel pipes intended for high-temperature service. Always verify the specified product form and applicable standard before ordering.

Which industries use P11 and P22 pipes?

Both grades are used in suitable applications across power generation, boiler systems, oil refineries, petrochemical plants and other industrial facilities. The exact grade depends on the service conditions and engineering requirements.

What documents should buyers request when purchasing these pipes?

Buyers should confirm the applicable Mill Test Certificate, material grade, heat number and traceability records, along with any inspection, testing and heat treatment documentation required by the purchase order.

ASTM A335 P11 and P22 are both important chromium-molybdenum alloy steel pipe grades used in elevated-temperature industrial applications.

P11 offers a suitable option for projects where its specified properties satisfy the design requirements. P22 contains higher chromium and molybdenum levels and is commonly selected for applications that require its particular high-temperature characteristics.

The right choice depends on the actual operating conditions, design calculations, applicable standards and approved project specification.

For engineers, contractors and procurement professionals, confirming the grade and documentation before purchasing is the best way to avoid material selection problems.

Explore the P11 pipe range and P22 pipe range from Leoscor Alloy Pipes, or contact the team to discuss your industrial piping requirements.

Technical reference: ASTM A335/A335M – Standard Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service.