Einführung
Steel pipes are a necessity in almost every industry. They are integral to accelerating industrial work and making processes more efficient.
Among the many steel pipes, seamless pipes are one of the most sought after. Due to their mechanical properties, they offer better durability than welded pipes. Since they come from a solid metal billet, they are more resistant to stress and breaking. They are often required in high-precision and high-pressure applications.
Continue reading this blog to learn more about seamless pipes and how they are made.
What is a seamless pipe?
Seamless pipes are a steel pipe variant manufactured without any welded joints, hence its name. Their lack of seams reduces the risks of breakage under intense pressure and stress. Unlike welded pipes, they offer smoother surfaces and uniform diameters.
These properties allow them to have superior durability and corrosion resistance. All these remarkable characteristics make them ideal for the oil and gas industry and construction.
Development history of seamless pipe
The history of seamless pipes can be traced back to the end of the 19th century. With the advancement of industrialization, various manufacturing processes have gradually developed. In 1885, the Mannesmann brothers invented a machine. It drilled holes through rollers. This allowed steel to be made into pipes without welding. This invention led to better rolling processes in 1891. It marked a new stage in making seamless pipes.
In 1903, Ritteriefel of Switzerland invented the automatic pipe-rolling machine, which further improved production efficiency. With the advent of extension equipment, the modern seamless steel pipe industry took shape. This was due to continuous pipe rolling mills and pipe jacking machines.
In 1930, the introduction of three-roll mills, extruders and cold rolling mills promoted the advancement of seamless pipe manufacturing technology. By the mid-20th century, stress relief machines and continuous casting blanks improved efficiency. This made seamless pipes more competitive than welded ones.
By the 1970s, the sales of seamless and welded pipes were basically the same. Seamless pipes have no welds and resist high pressure. They are widely used in high-strength fields. Their demand grows over 5% a year. They are becoming a core product in the global steel pipe market.
How is a seamless steel pipe made?
Seamless pipe manufacturing commences with a solid steel billet. This chunk of metal goes through a heating process to reach an ideal malleability and temperature. Then, workers pierce and stretch it, transforming it into a hollow tube.
This tube continues to run through an elongation and rolling process to reduce its diameter. During this process, workers insert a mandrel to maage the pipe’s internal diameter. A series of heat treatments is in place to achieve the pipe’s mechanical properties.
After reaching the desired diameter and length, the pipe is cooled. The final touches include post-treatment, such as surface polishing and coating. Finally, the machine cuts the seamless pipe into its desired length.
Raw material selection
Seamless pipes are a durable option for various applications. However, to maximize their versatility, different materials must be available for processing. The selection of raw materials is key to achieving the ideal properties of the pipe, including tensile strength, yield strength, and hardness.
Here are the most common materials for seamless pipe manufacturing:
Kohlenstoffstahl: Common for general-purpose pipes, offering good strength and weldability. Suitable for lower-pressure applications like water, gas, and low-temperature systems.
Alloy Steel: Composed of alloying elements like chromium, nickel, and molybdenum. This composition provides higher strength, toughness, and resistance to heat and corrosion.
Stainless Steel: Guarantees exceptional corrosion resistance and toughness. It’s often for utility in corrosive environments, like marine and chemical processing.
Manufacturing steps in detail
Here’s a more detailed guide to seamless pipe manufacturing.
Heating
The whole manufacturing process begins with the first heating process. Before you can dent the massive steel billet, you’ll have to run it through a furnace at around 1,200°Celsius. This extreme temperature softens the steel without melting it. What comes out of the furnace is a glowing hot steel that’s malleable enough for the next steps.
Extrusion
Industrial rotary tools pierce through the blazing billet to create a hollow shell. The elongation process passes the shell through a series of heavy-duty rollers. This then forms the pipe’s initial shape and size to work on.
Hole Expansion
While expanding the hollow tube, the workers will continue forcing a mandrel into it. This step is crucial to secure a smooth internal diameter and uniform wall thickness. Mandrel milling involves continuous rolling and stretching to the desired dimensions.
Cooling
After realizing the ideal size and dimensions, the pipe is gradually cooled. This cooling process happens in a controlled environment to avoid thermal stress. It also helps maintain the pipe’s integral mechanical properties. The complete cooling of the tube marks the solidification of the pipe in its final diameter.
Straightening
The prior steps do not guarantee complete success in crafting a perfect pipe. Even after cooling, there will be distortions and bends. Hence, the pipes still need to run through a straightening machine. Rollers or a straightening machine will apply controlled pressure to align the pipe. This ensures the final product is geometrically accurate and usable.
Post-Processing
Post-processing may include surface polishing, threading, or heat treatment for enhanced properties. Workers can also add a surface coating to guard against abrasion and corrosion. This step ensures the pipe meets specific application standards.
Qualitätskontrolle
Quality control checks the pipe for dimensional accuracy, strength, and surface defects. Safe testing mechanisms, including X-ray and ultrasonic inspections, ensure flaw-free pipes. The pipe undergoes final inspection before shipment.
Process comparison
| Property | Warmgewalzte nahtlose Rohre | Cold-Rolled Seamless Pipe |
| Manufacturing Temperature | Produced at high temperatures (>1,000°C) | Produced at room temperature or slightly elevated |
| Surface Finish | Rough, may have scale | Smooth, clean surface, minimal oxidation |
| Stärke | Lower tensile strength and hardness | Higher tensile strength, more precise dimensions |
| Kosten | Less expensive | More expensive due to additional processing |
| Anwendungen | Heavy-duty, low-precision uses | Precision engineering, automotive, aerospace, pressure vessels |
Besides hot-rolled seamless pipe, there’s also this type called cold-drawn seamless pipe. Both offer distinct properties necessary for different applications. Here’s a closer look at how these two vary in process.
Hot-rolled seamless pipe
The key point in hot-rolled pipe is that the billet is heated to around or a little over a thousand degrees Celsius. The whole process centers on shaping the pipe while it’s glowing hot.
This process creates a pipe that is better than a welded pipe in most aspects. But, the hot-rolled seamless pipe remains inferior to the cold-drawn seamless type. It has a rougher surface finish due to oxidation while also offering lower tensile strength.
Although it is more affordable and can withstand general application for seamless pipes.
Cold-drawn seamless pipe
Cold-drawn seamless pipes are your go-to choice if you’re looking for a better choice than hot-rolled pipes. The process involves working on a hot-rolled pipe at room temperature. From here, the pipe goes through a series of pilfering or cold-drawing processes. Working on the pipe while gradually cooling ensures higher tensile strength. It also has a more refined and smoother surface.
But, cold-drawn seamless pipes are more expensive than hot-rolled. They are also more exclusive to high-precision applications. This include hydraulic systems, automotive manufacturing, and pressure vessels.