Differences Between Stainless Steel Seamless Pipes and Welded Pipes

Stainless steel has good comprehensive performance and good appearance surface characteristics, and is widely used in all walks of life. Similarly, stainless steel pipes are no exception. Stainless steel pipes are a type of steel with a hollow cross-section, generally divided into stainless steel seamless pipes and welded pipes.

When choosing stainless steel pipes, you will encounter two main types: stainless steel seamless pipes and stainless steel welded pipes. Although they ultimately serve fluid transportation or structural support, their manufacturing processes, performance characteristics, application ranges, and costs are significantly different.

Understanding these differences is essential to making the right material choices for specific applications. Next, we will delve into the essential differences between stainless steel seamless pipes and welded pipes to help you better understand their advantages and disadvantages. 

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Stainless Steel Seamless Pipe

Stainless steel seamless pipe refers to a stainless steel pipe without welded seams along the entire length of the pipe. It uses a specific production process to directly process solid stainless steel billets into a tube, thus avoiding the inherent weld weakness of traditional welded pipes. Stainless steel seamless pipes are usually called industrial pipes. They are cold-rolled or cold-drawn. The raw material is round steel. The round steel is perforated to become a tube billet, and then the tube billet is cold-rolled or cold-drawn again and again.

Stainless Steel Welded Pipe

Stainless Steel welded Pipe is a pipe made by rolling stainless steel sheets or strips and then connecting the edges through welding. Unlike seamless stainless steel pipes, welded pipes have one or more welds along the length of the pipe body, which makes them different from seamless pipes in manufacturing process, performance characteristics and application areas.

Manufacturing Process of Stainless Steel Seamless vs Welded Pipes

Seamless Stainless Steel Pipe

Hot Rolling: A solid round billet is heated and pierced, then rolled and elongated through a series of rolling mills until the desired dimensions and wall thickness are achieved.

Cold Drawing / Cold Rolling: Based on the hot-rolled pipe, cold drawing or cold rolling is used to further reduce the diameter and wall thickness while improving dimensional accuracy and surface finish.

Welded Stainless Steel Pipe

Welded pipes are typically made from stainless steel plates or strips that are cold-formed into a cylindrical shape and then welded. The main welding methods include:

TIG Welding: Uses a tungsten electrode and an inert gas shield to weld the edges of the plate. It produces high-quality welds and is often used for pipes with strict quality requirements.

Laser Welding: Uses a high-energy-density laser beam for welding. It offers fast welding speed and a small heat-affected zone.

Plasma Welding: Falls between TIG and laser welding in terms of energy density. It is suitable for thicker materials.

Resistance Welding (ERW - Electric Resistance Welding): Heats the edges using electrical current until they fuse together. It is highly efficient but may produce welds of lower quality compared to TIG welding.

Performance Differences of Stainless Steel Seamless vs Welded Pipes

The performance of welded stainless steel pipes is significantly affected by the heat-affected zone (HAZ) created during the welding process, where the weld zone tends to have higher hardness. In contrast, seamless pipes do not have a heat-affected zone, resulting in more uniform hardness and more stable overall performance.

Welded stainless steel pipes generally have lower tensile strength, although the strength of the weld can approach that of the base material. Seamless pipes typically exhibit higher tensile strength, as there is no weld involved. Therefore, seamless pipes are more suitable for applications where high strength is required.

The corrosion resistance of welded stainless steel pipes is often compromised by potential defects in the weld area, which is more prone to corrosion. On the other hand, seamless pipes, with no welded joints, offer better integrity and higher corrosion resistance.

Costs of Stainless Steel Seamless vs Welded Pipes

In the stainless steel pipe market, the cost of stainless steel seamless pipes is usually higher than that of stainless steel welded pipes.

This is mainly because the manufacturing process of seamless pipes is more complicated. It is processed by a series of processes such as perforating, rolling, and cold drawing of solid steel billets, without welding points, but this process means large equipment investment, high energy consumption, and relatively low production efficiency, so the cost is naturally higher.

In contrast, stainless steel welded pipes are made of stainless steel sheets or coils, and the production process is relatively simple and efficient, and large-scale continuous production can be achieved. Its lower manufacturing cost makes it more economical in occasions where the pressure and corrosion resistance requirements are not so extreme.

Advantages and Disadvantages of Stainless Steel Seamless vs Welded Pipes

Stainless steel seamless pipe

Advantages

          High safety: suitable for conveying high pressure, high temperature, flammable, explosive or highly toxic media.

          Longer service life: more stable performance in harsh environments.

          Higher surface finish: the surface of cold-drawn/cold-rolled seamless pipes is usually smoother.

Disadvantages

          High manufacturing cost: the production process is complex and the scrap rate is relatively high.

          Long production cycle: there are many steps in the manufacturing process.

          Limited size range: especially large diameter thin-walled pipes are difficult to produce.

Stainless Steel welded Pipe

Advantages

          Low manufacturing cost: The production process is relatively simple and efficient.

          Short production cycle and fast delivery: Suitable for mass production.

          Wide range of sizes: Especially for large-diameter and thin-walled pipes, there are more choices.

          Controllable surface quality: A high surface finish can be achieved through polishing, wire drawing and other treatments.

Disadvantages

         Risk of weld defects

         Corrosion resistance may be affected by the weld

          Relatively low pressure bearing capacity

Conclusion

In general, seamless pipes are the first choice for high pressure, high temperature and critical applications due to their excellent strength and pressure resistance; while welded pipes dominate in low pressure, non-critical or appearance-oriented applications due to their cost advantages, size flexibility and good surface quality. When choosing, you need to weigh the working conditions, budget and performance requirements of the specific project.