What is the production process of ASTM A333 Gr.6 low-temperature seamless steel pipe

What is the production process of ASTM A333 Gr.6 low-temperature seamless steel pipe?

1. Smelting and Continuous Casting:

Smelting is carried out in an electric furnace or converter. Refining processes (such as LF refining and VD vacuum degassing) are used to control the purity of the molten steel, reducing the content of impurities such as sulfur and phosphorus, and avoiding the formation of inclusions. During continuous casting, the cooling rate is strictly controlled to prevent internal cracks or segregation in the billet, ensuring uniform microstructure.

2. Billet Heating and Piercing:

The continuously cast billet is heated to the plastic deformation temperature range of 1100-1250℃, softening it and making it easier to shape. A piercing mill (such as tapered roll skew piercing) is used to process the heated round steel into a thick-walled hollow A333 seamless steel pipe. During piercing, the rotation speed and forward speed must be controlled to ensure a smooth inner wall.

3. Hot Rolling and Extending:

A333 seamless steel pipe is rolled multiple times on a hot rolling mill to gradually reduce the wall thickness and extend the length, forming a rough tube close to the finished size. Strict control of heating temperature, rolling speed, and deformation is required during rolling to prevent material performance degradation or cracking.

4. Cold Working of A333 Seamless Steel Pipe (Optional):

For A333 seamless steel pipes with high dimensional accuracy requirements, cold rolling or cold drawing processes are used for further processing:

- Cold Rolling: Using a two-roll mill with a tapered mandrel, multiple rolling passes improve dimensional accuracy and surface quality.

- Cold Drawing: Drawing at room temperature using a drawing die reduces the outer diameter and wall thickness, while controlling the reduction rate to prevent internal cracks.

- After cold working, intermediate annealing is required to eliminate work hardening and restore material toughness.

5. Heat Treatment

- Normalizing: The A333 seamless steel pipe is heated above the critical temperature, held at that temperature, and then air-cooled to refine the grain size and improve strength and toughness.

- Normalizing and Tempering: Tempering is performed after normalizing to further adjust the microstructure, reduce residual stress, improve overall mechanical properties, and ensure low-temperature toughness (e.g., impact energy at -45℃ meets standards).

6. Finishing and Inspection

Finishing processes include cutting, deburring, straightening, pickling (to prevent over-acid corrosion), and surface polishing to ensure the appearance quality of the steel pipe.

7. Quality Inspection of A333 Seamless Steel Pipes:

- Dimensional Inspection: Using laser diameter gauges, ultrasonic thickness gauges, and other equipment, strict control is exercised over outer diameter, wall thickness, and ellipticity deviations (e.g., outer diameter tolerance ±0.5%, wall thickness tolerance ±12.5%).

- Non-destructive Testing: Internal defects (e.g., cracks, inclusions) are inspected using ultrasonic testing, eddy current testing, and other methods.

- Mechanical Property Testing: Sampling is used for tensile testing (tensile strength ≥415MPa, yield strength ≥240MPa), impact testing (impact energy at -45℃ ≥ specified value), and hardness testing.

- Hydrostatic Test: Apply 2.5 times the working pressure to the steel pipe and hold the pressure for 10 seconds to verify its sealing performance and pressure resistance.

8. Packaging and Warehousing

Qualified A333 seamless steel pipes must undergo rust prevention treatment (such as oiling or painting), be bundled and packaged according to specifications, labeled, and then stored in the warehouse.