Differences between ASTM A691 And ASTM A335 Alloy Steel Pipes

ASTM A691 and ASTM A335 are both used in high-pressure, high-temperature industrial applications, but they are fundamentally different. ASTM A691 covers electric-fusion-welded (EFW) pipes manufactured from pressure-vessel-quality plate, making it ideal for large-diameter piping. In contrast, ASTM A335 specifies seamless ferritic alloy-steel pipes, which are preferred when seamless construction is required.

They also utilize different grading systems, with A335 commonly featuring P-grades like P11, P22, and P91. Selecting the correct standard depends on operating conditions, dimensions, and applicable design codes rather than assuming they are interchangeable.

What Is ASTM A691 Steel Pipe?

ASTM A691 steel pipe is a type of carbon and alloy steel pipe designed for high-pressure service at high temperatures. It is manufactured from pressure-vessel-quality plate and is generally produced as welded pipe. The standard is commonly used for demanding piping systems in power generation, petroleum processing, petrochemical plants, and other industrial facilities.

Key Features

Common Applications

Grade and Class – Important Note

ASTM A691 vs. ASTM A335

Key Takeaway

ASTM A691 steel pipe is a practical option for high-pressure and high-temperature piping systems where:

• Welded construction is suitable

• Pressure-vessel-quality plate is appropriate for the application

Because A691 pipe contains a welded seam, weld quality and examination are particularly important. Selection should be based on the complete project specification—pressure, temperature, pipe size, grade, class, welding, testing, and applicable codes.

What Is ASTM A335 Alloy Steel Pipe?

ASTM A335 alloy steel pipe is a seamless ferritic alloy-steel pipe designed for high-temperature service. It is widely used in power plants, refineries, petrochemical facilities, and other industrial systems where piping must maintain reliable mechanical performance at elevated temperatures.

Key Features

Common A335 Grades

Common Applications

Manufacturing & Quality Requirements

ASTM A335 vs. ASTM A691

Key Takeaway

ASTM A335 alloy steel pipe is a reliable option for high-temperature and high-pressure applications, particularly in:

• Power generation

• Refining

• Petrochemical industries

Where elevated-temperature mechanical performance is critical. Select the correct P-grade for the specific application—each grade has different composition, properties, heat treatment, and hardness requirements.

ASTM A691 vs. ASTM A335: Key Differences

ASTM A691 and ASTM A335 are both used for demanding industrial piping, including applications involving high pressure and elevated temperatures. However, they are different standards covering different types of steel pipe. Understanding their differences is important when selecting materials for power plants, refineries, petrochemical facilities, and other process systems.

Comparison Table

Key Differences

Which One Should You Choose?

Key Takeaway

• A691 – welded carbon/alloy steel pipe made from pressure-vessel-quality plate

• A335 – seamless ferritic alloy-steel pipe for high-temperature service

They may serve similar industries, but they should not be treated as direct equivalents. Before selecting or substituting, review:

• Material grade

• Manufacturing method

• Operating pressure and temperature

• Dimensions

• Heat treatment

• Testing

• Welding requirements

• Applicable design code

ASTM A691 vs. A335: Which Pipe Should You Choose?

Choosing between ASTM A691 and ASTM A335 steel pipe depends on the project's operating conditions, required manufacturing method, material grade, and applicable design standards. Neither pipe is universally better. The correct choice is the one that meets the technical requirements of the specific piping system.

Quick Selection Guide

Choose ASTM A691 When Welded Pipe Is Suitable

Choose ASTM A335 When Seamless Pipe Is Required

Key Factors to Consider

Is A691 Better Than A335?

Key Takeaway

The safest approach is to provide the supplier with:

• Operating pressure and temperature

• Pipe size

• Grade

• Quantity

• Applicable standard

• Inspection requirements

The supplier can then recommend the appropriate pipe and confirm whether the selected material meets the project specification.

ASTM A691 and ASTM A335 Applications

ASTM A691 and ASTM A335 steel pipes are both used in demanding industrial environments, especially in the power generation, petroleum, refining, and petrochemical industries. However, their manufacturing methods and material specifications make them suitable for somewhat different applications.

ASTM A691 Steel Pipe Applications

ASTM A335 Steel Pipe Applications

Application Comparison

How to Select the Right Pipe

Key Takeaway

• ASTM A691 – when welded pipe made from pressure-vessel-quality plate is appropriate

• ASTM A335 – when seamless ferritic alloy-steel pipe for high-temperature service is required

Selecting the correct pipe at the design stage ensures reliable operation, easier inspection, and compliance with project technical specifications.

Our ASTM A691 & A335 Alloy Steel Pipe Products and Shipping Services

We supply premium ASTM A691 and ASTM A335 alloy steel pipes for demanding high-pressure and high-temperature industrial applications. We provide welded A691 pipes for large-diameter systems and seamless A335 pipes (including P11, P22, and P91) for critical boiler and steam systems.

Quality and compliance are paramount. We conduct rigorous inspections—including hydrostatic testing, NDT, and heat-treatment verification—and provide comprehensive Mill Test Certificates (MTCs) to guarantee full adherence to ASTM standards.

Beyond manufacturing, we provide end-to-end global shipping solutions. We understand that timely delivery is critical to maintaining project schedules. Our logistics team manages secure packaging and flexible transportation options (container and bulk freight) to prevent transit damage and ensure your pipes arrive safely and on time.

To receive a customized product and shipping quotation, please contact us today with your required standard, grade, dimensions, testing requirements, quantity, and delivery destination. Our expert team will recommend the optimal alloy steel pipe configuration tailored to your exact needs.

Conclusion

ASTM A691 and ASTM A335 are not interchangeable standards. The key difference lies in manufacturing: ASTM A691 covers welded pipes made from pressure-vessel-quality plate, ideal for large-diameter systems, while ASTM A335 specifies seamless ferritic alloy-steel pipes (e.g., P11, P22, P91) for high-temperature service.

Selecting the correct pipe requires evaluating operating pressure, temperature, wall thickness, and applicable design codes rather than assuming they are equivalent. Rigorous quality control, including nondestructive testing and comprehensive material certificates, is essential to guarantee compliance and safety.

FAQ：

1. What is the main difference between ASTM A691 and ASTM A335?

ASTM A691 covers welded carbon and alloy steel pipe made from pressure-vessel-quality plate, while ASTM A335 covers seamless ferritic alloy-steel pipe for high-temperature service.

2. Is ASTM A691 equivalent to ASTM A335?

No. They are different standards with different manufacturing methods, material requirements, grade systems, and applications. They should not be considered direct equivalents.

3. Is ASTM A335 seamless pipe?

Yes. ASTM A335 specifically covers seamless ferritic alloy-steel pipe for high-temperature service.

4. What are common ASTM A335 grades?

Common A335 grades include P5, P9, P11, P22, and P91. The appropriate grade depends on operating temperature, pressure, mechanical requirements, and the applicable design code.

5. What is ASTM A691 pipe used for?

ASTM A691 pipe is commonly used in power plants, refineries, petrochemical facilities, and high-pressure process piping systems, particularly where welded pipe made from pressure-vessel-quality plate is suitable.

6. Which is better, ASTM A691 or A335?

Neither is universally better. A691 is suitable for certain welded high-pressure applications, while A335 is commonly selected when seamless alloy-steel pipe is required for high-temperature service. The project specification should determine the final choice.