ASTM A213 T5 Alloy Steel Seamless Tube For Industrial Boilers Superheater

1. Material Composition

2. Standard: ASTM A213

This standard specifically covers seamless ferritic and austenitic steel boiler, superheater, and heat-exchanger tubes intended for high-temperature service under pressure.

Grade: T5

This designates a specific chromium-molybdenum (Cr-Mo) alloy steel composition.

3. Material Type: Low-Alloy Steel

Distinguished from carbon steels and stainless steels (austenitic grades like 304, 316 are also covered under ASTM A213 but have different grade designations like TP304, TP316).

4. Seamless Manufacturing:

Tubes are produced without a welded seam, typically by processes like extrusion, rotary piercing (Mannesmann process), or pilgering. This provides:

Higher Strength & Integrity: No weak point from a weld.

Better Pressure Containment: Essential for boiler and pressure applications.

Uniformity: More consistent structure and properties around the circumference.

Better Resistance to Corrosion/Erosion: No weld seam susceptible to preferential attack.

5. Key Properties & Why T5 is Used:

Good High-Temperature Strength (Creep Strength): Retains strength well at temperatures commonly encountered in boilers and superheaters (typically up to ~650°C / 1200°F for long-term service, though exact limits depend on stress). Molybdenum is key here.

Good Oxidation Resistance: Chromium forms a protective oxide scale, resisting degradation from hot flue gases.

Good Resistance to Sulphidation: Performs better than lower alloy steels (like T11/T12) in environments containing sulphur compounds.

Moderate Corrosion Resistance: Better than carbon steel, but less than stainless steels.

Weldability: Generally considered weldable with appropriate preheat, post-weld heat treatment (PWHT - stress relieving), and procedures (common processes include GTAW, SMAW, SAW). PWHT is critical to restore properties and relieve stresses in the HAZ.

6. Common Applications:

Primarily used in high-temperature, high-pressure sections of:

Fossil Fuel Power Plants:

Boiler tubes (especially in higher temperature zones)

Superheater Tubes

Reheater Tubes

Heat Exchangers: In chemical/petrochemical plants where operating temperatures require better strength than carbon steel but full stainless isn't necessary.

Refinery Piping & Equipment: For specific high-temperature process streams.

Pressure Vessels: Components operating at elevated temperatures.

7. Heat Treatment (Per ASTM A213):

T5 tubes are supplied in the stress-relieved condition.

Stress relieving involves heating the tubes to a temperature below the lower critical transformation temperature (Ac1), holding, and slowly cooling. This relieves internal stresses from manufacturing without significantly altering the microstructure (ferrite + carbide).

Note: Other Cr-Mo grades like T91 require normalizing & tempering, but T5 specifically is stress-relieved.

8. Testing & Inspection (Per ASTM A213):

Hydrostatic Test: Each tube is pressure tested.

Nondestructive Electric Test (NDE): Each tube undergoes an electromagnetic test (like eddy current) to detect significant longitudinal imperfections.

Flattening Test, Hardness Test, Reverse Flattening Test: Performed on samples from lots.

Tension Test: Determines mechanical properties (Yield Strength, Tensile Strength, Elongation) on samples from heat-treated material.

Chemical Analysis: Per heat (batch of steel melt).

Dimensions & Visual Inspection: OD, wall thickness, straightness, surface quality.