ASTM A691 chrome moly welded pipe

ASTM A691 is a specification for chromium-molybdenum alloy steel pipes that are fabricated by welding and designed to operate in high-pressure and high-temperature environments. These pipes are commonly referred to as "chrome-moly welded pipes" due to their composition, which includes chromium (Cr) and molybdenum (Mo).

This combination provides excellent strength, oxidation resistance, and corrosion resistance under elevated temperature and pressure conditions, making them ideal for critical applications like power plants, refineries, and chemical plants.

Key Features of ASTM A691 Chrome Moly Welded Pipe

- Material Composition:

Chromium (Cr): Enhances oxidation resistance and strength at high temperatures.

Molybdenum (Mo): Improves resistance to creep, corrosion, and pitting.

Additional alloying elements such as manganese, silicon, and carbon may vary by grade.

- High-Pressure and High-Temperature Capability:

Designed to perform in systems where high pressures and temperatures are encountered, such as steam pipelines and heat exchangers.

- Welded Construction:

Made using electric-fusion welding (EFW), ensuring consistent strength and reliability.

Heat-treated post-welding to restore mechanical properties.

- Variety of Grades:

Common grades include Grade 1.25Cr, 2.25Cr, 5Cr, 9Cr, where the numbers represent the percentage of chromium in the alloy.

Higher chromium and molybdenum content offer increased corrosion and temperature resistance.

- Mechanical Properties:

Tensile Strength: Varies by grade but typically exceeds 60 ksi (415 MPa).

Yield Strength: Typically exceeds 30 ksi (205 MPa).

Applications of ASTM A691 Chrome Moly Welded Pipe

- Power Generation:

Used in boilers, heat exchangers, and superheater tubes for thermal power plants due to excellent heat resistance.

- Petrochemical and Refinery Applications:

Piping for reactors, catalytic reformers, and hydrocrackers operating at high temperatures and pressures.

- Oil and Gas Industry:

Suitable for sour gas environments and pipelines carrying high-temperature fluids.

- Chemical Processing:

Pipes for processing corrosive chemicals at elevated temperatures.

- Industrial Steam Systems:

Steam transportation lines in industrial plants, especially where creep resistance is crucial.

Manufacturing Process

- Welding Method:

Electric Fusion Welding (EFW) is used to join the steel plates, ensuring a robust weld joint.

Followed by heat treatment to homogenize the weld zone.

- Heat Treatment:

Pipes undergo normalizing, tempering, or post-weld heat treatment (PWHT) to improve toughness and remove residual stresses.

- Inspection and Testing:

Non-destructive testing (NDT) such as radiographic or ultrasonic inspection is performed to ensure weld quality.

Hydrostatic tests verify pressure handling capability.

Advantages of ASTM A691 Chrome Moly Welded Pipe

- High-Temperature Performance:

Outstanding resistance to creep and oxidation under extreme conditions.

- Corrosion Resistance:

Excellent in environments exposed to acidic, oxidizing, or high-saline conditions.

- Strength and Durability:

The addition of chromium and molybdenum significantly enhances mechanical strength.

- Versatility:

Available in a wide range of sizes, wall thicknesses, and grades to suit different operational needs.

Common Grades and Applications

Standards and Compliance

ASTM A691: Standard for chrome-moly alloy steel pipes for high-pressure service.

ASME SA691: Equivalent standard for use in pressure vessels and piping systems.

NACE MR0175/ISO 15156: Compatibility with sour gas applications.