Many people confuse seamless steel pipes with welded steel pipes, even believing they can be used interchangeably. This is incorrect. Seamless steel pipes and welded steel pipes have very different uses. Let’s distinguish between them today!
Welded steel pipes, also known as welded tubes, are steel pipes made by rolling and welding steel plates or strips. They are typically 6 meters long. Welded steel pipe production is simple, efficient, and offers a wide variety of specifications with low equipment investment. However, their strength is generally lower than that of seamless steel pipes. Most people distinguish them by the presence or absence of weld seams, which is too simplistic. Seamless steel pipes do not have weld seams because their construction process differs from that of welded steel pipes. Seamless steel pipes are manufactured at a high temperature of 2200°F, a hot-rolled process. Seamless steel pipes are made from continuously cast or pre-rolled slabs, with a hole punched into the billet. This results in uneven wall thickness and high eccentricity. Therefore, the wall thickness difference of seamless steel pipes is greater than that of welded pipes, and they lack the internal weld lines found in welded steel pipes.
In short, seamless steel pipes are drawn directly from steel ingots, while welded steel pipes are made by rolling and welding steel plates. Regarding whether they are interchangeable, if used for trusses, they can be substituted as long as the material and wall thickness are the same. Essentially, the properties of seamless and welded steel pipes are similar. However, compared to welded pipes, seamless steel pipes can be produced in more specifications, require more advanced manufacturing processes, and are relatively more expensive.
First, feasible areas for welded steel pipes to replace seamless steel pipes:
1. Currently, welded steel pipes can replace seamless steel pipes in an increasing number of fields. Firstly, because welded steel pipes have more uniform thickness, they can be used in decorative pipes and can compensate for the difficulty in manufacturing large-diameter seamless steel pipes (sizes above 219*6). Secondly, they can replace some structural pipes. Furthermore, with the development of high-strength welded steel pipe technology, some high-strength welded steel pipes can already replace high-end seamless steel pipes.
2. Compared with foreign countries, my country lags significantly behind in the replacement of high-end seamless steel pipes with welded steel pipes. For oil well pipes, my country mainly relies on long-process steel mills for production, and the characteristics of limited specifications and large output are not suitable for oil well supply and sales. Other high-end pipe varieties lack relevant core technologies.
3. The future development of new energy vehicles and the hydrogen energy industry brings more possibilities for welded steel pipes to replace seamless steel pipes. The replacement of high-end seamless steel pipes not only requires leading companies to research relevant technologies but may also require policy intervention.
1) In terms of decoration: Since welded steel pipes are usually welded from strip steel, they generally have more uniform wall thickness and can replace steel pipes used in lightweight building structures such as doors and windows, furniture, scaffolding, electrical conduits, and high-rise shelves.
2) In terms of size: Depending on the welding process, welded pipes are divided into straight seam welded pipes and spiral welded pipes. Spiral welded pipes generally have higher strength than straight seam welded pipes and can be produced with narrower blanks to create larger diameter pipes. Seamless steel pipes are usually difficult to manufacture in large diameters, and spiral welded pipes can overcome this limitation.
3) In terms of structure, Spiral welded pipes can also be used for piling, bridges, docks, roads, and building structures.
4) High-strength welded pipes: Unlike ordinary welded pipes, high-strength welded pipes can meet the requirements of some high-precision fields, such as automotive structural pipes, oil pipes, and boiler tubes.
Second, the substitution of seamless steel pipes by welded pipes in China lags significantly behind that of foreign countries.
The Princeton Steel Report in the US compared the proportions of welded and seamless steel pipes in seven categories: oilfield pipes, line pipes, standard pipes, machinery pipes, structural pipes, pressure pipes, and stainless steel pipes. The proportion of welded steel pipes used far exceeded that of seamless steel pipes, even in high-pressure boiler tubes. Unlike the situation abroad, where welded pipes replaced high-end seamless steel pipes, in my country, only high-strength welded pipes for oilfield applications can replace seamless steel pipes. However, it’s worth noting that while they can be substituted in strength, the substitution rate is not large. The main reason for this low substitution rate is related to the steel production process. Many European and American countries primarily use short-process production, and the consumption characteristics of oil well pipes vary depending on the conditions of oil wells in different regions, featuring small batches and multiple varieties. This is similar to the electric arc furnace steel production method. In contrast, my country’s production is mainly based on long-process production, with the advantage of fewer specifications and larger batches, making it unsuitable for the supply and sales model of oil well pipes. The ability of welded steel pipes in the petroleum industry to replace seamless steel pipes and reach world-class levels is closely related to the supporting industry-academia-research collaboration. My country’s petroleum system has its own welded pipe enterprises, along with supporting petroleum universities, research institutes, and testing facilities. This collaborative effort is the result of various aspects working together. However, welded pipes in other sectors of my country, such as mechanical pipes, boiler pipes, petrochemical pipes, and structural pipes, still fall far short of the strength required to replace high-end seamless steel pipes.
Third, potential future directions for welded steel pipes to replace seamless steel pipes.
1. The development of new energy vehicles provides more possibilities for welded pipes to replace seamless steel pipes: New energy vehicles have significantly increased requirements for high strength and lightweight design. Even a weight reduction of one kilogram is crucial for improving the driving range of new energy vehicles. Currently, leading domestic companies can use special alloy steel materials combined with unique ERW (straight seam resistance) technology, enabling welded pipes to replace seamless steel pipes in automotive stabilizer bars. This not only meets the strength requirements but also achieves lightweighting and a price advantage. However, it is worth noting that the aforementioned special alloy materials are not widespread, and only a few companies can achieve this level of replacement for seamless steel pipes.
2. With the rapid development of the hydrogen energy industry, welded pipe products may see further development: Previously, domestic pipes were mainly used in low-pressure, high-proportion hydrogen blending or high-pressure, low-proportion hydrogen blending transportation. High-pressure, high-proportion welded pipe transportation for petroleum applications offers the possibility of further reducing costs and improving efficiency. This is also one of the future directions for welded pipes to replace seamless steel pipes in my country.
3. Policy may play a role in the replacement of high-end seamless steel pipes by welded pipes: Referring to the development model of welded steel pipes in the petroleum industry, core technologies may become key. If welded pipes in other downstream fields are to replace related high-end seamless steel pipes, it requires the combined efforts of industry, academia, and research. Besides leading companies taking the lead, policy also needs to play an important role.
In conclusion, from the perspective of cost savings and carbon emission reduction, the replacement of seamless steel pipes by welded pipes is an inevitable trend. Based on international development experience, domestically, welded pipes can only replace some seamless steel pipes in oil well pipes, while seamless steel pipes still dominate exports. The strength of welded pipes for other high-end pipes is far from being achieved. Future development will still be driven by technology.
Fourth, can straight seam steel pipes be used to impersonate seamless steel pipes?
How to distinguish them? Competition is fierce in all industries, including the steel pipe industry. Many manufacturers, to increase profits, use straight seam steel pipes to impersonate seamless steel pipes. This practice is completely unacceptable. Let’s explain in detail below. Straight seam steel pipes are made using submerged arc welding or resistance welding. These pipes are connected at the weld seam. These companies use polishing machines to grind and polish the weld seam. After polishing, the weld seam will be worn down, the surface will be smooth, and overall, it will look like a seamless steel pipe. No expert can detect this deception. This type of fraud cannot be detected by equipment, whether it’s a straight seam steel pipe or a seamless steel pipe. Only experts can tell the difference. Some projects even apply anti-rust paint to the outside, making it even more difficult to distinguish, which makes many buyers very uneasy. So, how do you distinguish between straight seam steel pipes and seamless steel pipes? When purchasing seamless steel pipes, a two-centimeter-long mark in the entire pipe can be used to verify if there is a problem. A simple, albeit crude, method to check for issues with the anti-rust paint on seamless steel pipes is to examine the pipe during the cutting process. Seamless steel pipes have no butt joints, while straight-seam steel pipes are made by folding a steel plate in half, creating a joint. Due to different manufacturing processes, seamless and welded steel pipes are produced. Seamless steel pipes include hot-rolled, cold-rolled, cold-drawn, and rarely cold-extruded pipes. Welded steel pipes consist of pressed and welded steel plates. Smaller ones are usually straight-seam welded, while larger ones are usually spiral welded. Due to the presence of the weld seam, welded joints have poorer mechanical properties and limited applications, but are inexpensive. The difference lies in the weld seam: welded steel pipes have a weld seam, while seamless steel pipes do not. If welded steel pipes are not treated, obvious weld seams and protrusions, such as marks, will appear. A better approach is to wipe off the weld seam, but the difference is still noticeable to the naked eye. A small amount of cold-rolled, welded steel pipes, with high surface roughness and precision, can also be sold as counterfeit seamless steel pipes. Careful observation reveals a continuous metallic spiral on the pipe wall, indicating that the metallographic structure of the original weld differs from that of other components.
Fifth, Seamless Steel Pipe Geometric Dimensions and Shape Inspection.
① Seamless steel pipe wall thickness inspection: Micrometer, ultrasonic thickness gauge, at least 8 points at both ends, and record the readings.
② Seamless steel pipe outer diameter and ovality inspection: Caliper gauge, vernier caliper, ring gauge, measure the large and small points.
③ Seamless steel pipe length inspection: Steel tape measure, manual, or automatic length measurement.
④ Seamless steel pipe curvature inspection: Ruler, spirit level (1m), feeler gauge, fine string to measure curvature per meter, and total length.
⑤ Seamless steel pipe end face bevel angle and blunt edge inspection: Square, caliper.
Post time: May-25-2026