1. What does "welded pipe" mean?
A welded pipe is a type of steel pipe manufactured by rolling a flat steel plate or sheet (known as a "skelp") into a cylindrical shape and then joining its edges together with a weld. The fundamental concept is creating a tube from a flat piece of metal by forming and fusing the seam. This method allows for the production of pipes with large diameters and long continuous lengths. Welded pipes are a fundamental component in modern infrastructure for transporting fluids, gases, and structural applications.
2.What is a weld pipe?
"Weld pipe" is essentially another term for "welded pipe." It refers to the same product: a pipe that has a longitudinal seam running along its length where the edges of the steel strip have been fused together. The term "weld pipe" often emphasizes the presence of this seam. The quality and integrity of this weld are critical to the pipe's performance and its suitability for various pressure and structural applications.
3.What is the difference between seamless and welded pipes?
The primary difference lies in their manufacturing process. A seamless pipe is made by piercing a solid, heated steel billet to create a hollow tube without any seams. This makes it inherently stronger and more uniform in its circumference, especially under high pressure. A welded pipe, as described, is made from a rolled and welded steel plate, resulting in a visible seam.
Key comparative points:
* **Strength:** Seamless pipes are generally stronger and more reliable for high-pressure applications because they have no weak spot like a weld seam.
* **Cost & Availability:** Welded pipes are less expensive to produce and are available in larger diameters and longer lengths.
* **Wall Thickness:** Seamless pipes can have more consistent and thicker walls, while welded pipes may have more variation near the weld and are typically limited to thinner walls.
* **Surface Quality:** The interior and exterior surfaces of seamless pipes are generally smoother than welded pipes, where the weld bead may need to be removed for certain applications.
4.What are some uses for welded pipe?
Welded pipes are incredibly versatile and are used in a wide range of industries. Common uses include:
* **Water and Gas Transmission:** Large-diameter welded pipes are the standard for municipal water supply lines and natural gas distribution networks over long distances.
* **Structural Applications:** They are widely used in construction for scaffolding, structural supports, and fencing due to their cost-effectiveness and availability.
* **Oil and Gas Pipelines:** For transporting oil and gas, especially where very high pressure is not a primary concern, welded pipes are extensively used.
* **Mechanical and Automotive Parts:** Used for various mechanical components, exhaust systems, and hydraulic cylinders.
* **Industrial Plumbing:** For low to medium-pressure fluid transport within industrial plants and buildings.
5. How is a pipe welded?
The welding process for making pipe involves several key steps and different welding techniques. The most common methods are:
1. **Forming:** A flat steel strip is uncoiled and fed through a series of rolls that gradually bend it into a cylindrical shape.
2. **Welding:** The open edges are brought together and welded. The two most prevalent methods are:
* **Electric Resistance Welding (ERW):** High-frequency electrical current is passed between the edges, heating them to a molten state. Pressure is then applied to forge them together without a filler metal.
* **Submerged Arc Welding (SAW):** Used for large-diameter pipes. The weld arc is struck under a blanket of granular flux, which protects the molten weld from contamination and allows for a very strong, high-quality weld, often with filler metal added.
3. **Sizing and Shaping:** The welded pipe passes through more rolls to achieve its final diameter and roundness.
4. **Testing and Inspection:** The weld seam is critically inspected using non-destructive methods like ultrasonic testing or X-rays to ensure it is free of defects.
5. **Cutting:** The continuous pipe is cut to the required commercial lengths.
