Manufacturing Process of Heat Expanded Seamless Pipe

The manufacturing process of heat expanded seamless pipe involves several key steps that focus on transforming a solid steel billet into a high-performance pipe through heating, expansion, and finishing. Below is a detailed breakdown of the process:

1. Billet Preparation

Steel Selection: The process begins with the selection of a suitable steel billet. The material can be carbon steel, alloy steel, or stainless steel, depending on the intended application and required properties.

Cutting: The steel is cut into appropriate lengths to produce billets that will be heated and formed into pipes.

2. Heating

Heating the Billet: The cut billets are heated to a temperature typically ranging from 1,100°C to 1,200°C (2,012°F to 2,192°F), using either an electric induction furnace or a gas-fired furnace. This high temperature makes the steel malleable, allowing it to be shaped without cracking.

Temperature Control: Precise temperature control is crucial to ensure that the steel reaches the desired malleability for the expansion process.

3. Piercing

Piercing the Billet: After heating, the billet is pierced to create a hollow tube. This can be done using a piercer or a rotary piercing mill. The piercing process involves pushing a mandrel through the heated billet to create the initial hollow shape.

Initial Tube Formation: At this stage, a rough seamless tube is formed, which still requires further processing to reach the final dimensions.

4. Elongation

Stretching the Tube: The pierced tube is then elongated to reach the desired length and diameter. This is typically done using a combination of rotary and axial forces to stretch the tube while maintaining its seamless nature.

5. Heat Expansion

Heat Expansion: The elongation process is followed by the heat expansion phase. The tube is reheated to a high temperature and then mechanically expanded using a mandrel or an expansion die.

Mandrel Use: The mandrel is inserted into the tube, and hydraulic or mechanical forces are applied to expand the diameter of the pipe while reducing the wall thickness. This process enhances the pipe’s mechanical properties and uniformity.

6. Cooling

Controlled Cooling: After expansion, the pipe is allowed to cool down, often in a controlled manner to avoid the introduction of stresses. Controlled cooling can also improve the microstructure of the steel, enhancing its strength.

7. Finishing Operations

Straightening: The expanded pipe may undergo a straightening process to ensure that it has the proper geometry.

Surface Treatment: The outer surface of the pipe is often treated to remove any scale or oxidation formed during the heating process. This can include processes such as shot blasting, pickling, or coating.

Sizing: The pipe is then sized to ensure it meets the specified dimensions and tolerances.

8. Quality Control

Non-Destructive Testing (NDT): Various NDT methods, such as ultrasonic testing, radiographic testing, and magnetic particle testing, are employed to detect any internal or external flaws.

Mechanical Testing: Mechanical properties such as tensile strength, yield strength, and elongation are tested to ensure that the pipe meets the required specifications.

Certification: Finally, the products are certified according to industry standards and customer requirements, ensuring compliance with quality assurance protocols.

9. Packaging and Shipping

Final Inspection: Each pipe undergoes a final inspection and is marked with relevant specifications.

Packaging: The pipes are then carefully packaged for shipment to customers, ensuring they are protected during transit.