Exclusive Insights: Comprehensive Analysis of Welded Steel Pipes and Seamless Steel Pipes

With the continuous development of the industrial field, pipeline products and systems also need to be continuously innovated to meet the needs of development. Among numerous pipeline manufacturing methods, the comparison between Electric Resistance Welded (ERW) steel pipes and Seamless (SMLS) steel pipes has become a topic of great concern within the industry. The manufacturing processes of both ERW steel pipes and seamless steel pipes have withstood the test of time. However, which manufacturing process results in steel pipes with more advantages? Next, we will conduct an in-depth analysis.

welded pipes 

The manufacturing of welded pipes starts with a long strip of steel coiled into a roll, which is commonly referred to as a steel strip coil in the industry. First, the steel strip is cut into corresponding lengths according to specific requirements, thus obtaining flat rectangular plates. The width of the short side of the plate will determine the outer circumference of the final pipe, and through this value, the outer diameter of the pipe can be accurately calculated. Subsequently, the rectangular plate is fed into a plate rolling machine. Through specific mechanical operations, the plate rolling machine gradually rolls up the long sides of the plate, making it gradually take on the shape of a cylinder. During the Electric Resistance Welding (ERW) process, high-frequency current passes rapidly between the edges of the plate. The powerful current instantly generates extremely high heat, causing the edges of the plate to quickly melt and fuse tightly together. ERW steel pipes have unique advantages. Since no additional fusing metal is added during the welding process, the weld seam of the final product is very fine. It is almost invisible from the appearance, and there are no obvious weld seam marks when touched by hand, which is significantly different from the Double Submerged Arc Welding (DSAW) process. The DSAW process will leave a more obvious weld seam after welding, and in many actual application scenarios, additional treatment is required to eliminate the impact of the weld seam. After years of technological innovation, the manufacturing technology of welded pipes has made great progress, and one of the most crucial breakthroughs is the shift of the welding current from low frequency to high frequency. Before the 1970s, low-frequency current dominated the welding process. However, the low-frequency ERW process has obvious disadvantages. The weld seam it produces performs poorly in terms of corrosion resistance and weld seam strength. During long-term use, problems such as corrosion and weld seam fracture are more likely to occur. It is worth noting that most types of welded pipes need to go through a heat treatment process after being manufactured. This process plays a crucial role in improving the comprehensive performance of the welded pipes, such as improving the internal structure of the material and enhancing the strength and toughness of the pipeline.

seamless pipes

The production process of seamless pipes is quite different from that of welded pipes. It starts with a cylindrical solid steel block, which is called a billet in the industry. When the billet is in a high-temperature state, a special mandrel is used to pierce its center, thus initially forming a hollow structure in the billet. The next crucial step is to carry out rolling and stretching operations on the hollow billet. By precisely controlling the process parameters of rolling and stretching, the billet gradually meets the requirements of length, diameter, and wall thickness specified in the customer’s order.

In the field of seamless pipe manufacturing, different types of products have different post-manufacturing treatment requirements. For some types of seamless pipes, due to the characteristics of the manufacturing process, their own structure already has high strength and stability, and no heat treatment is required after manufacturing. However, there are also some types of seamless pipes that require additional heat treatment in order to further optimize their performance and meet the needs of specific application scenarios. Therefore, when selecting seamless pipes, it is necessary to carefully check the relevant product specifications to clarify whether heat treatment is required, so as to ensure the reliability of subsequent use.

A Review of the History and Use Cases of Welded Steel Pipes and Seamless Steel Pipes

Currently, on the market, ERW steel pipes and seamless steel pipes are substitutes for each other, and this situation is largely due to historical perceptions. In traditional understanding, welded pipes are considered to have relatively low strength due to the existence of weld seams, while seamless pipes are considered to have higher safety because they have no such obvious structural connection parts. Although theoretically, the weld seam of a welded pipe may indeed be its relatively weak point, with the rapid development of modern manufacturing technology and the continuous improvement of the quality assurance system, as long as various parameters are strictly controlled within the specified tolerance range during the production process, welded pipes can fully achieve the expected performance in practical applications. However, seamless pipes are not without defects. Different from the high-precision control of the steel plate thickness in the manufacturing process of welded pipes, during the rolling and stretching processes of seamless pipes, due to the complexity of the process, there may be a certain degree of wall thickness inconsistency. Currently, various industry standards for the manufacturing and specifications of ERW steel pipes and seamless steel pipes still reflect the above traditional concepts to a certain extent. For example, in industries with extremely high requirements for safety and stability, such as oil and gas, power generation, and pharmaceuticals, in many application scenarios involving high pressure and high temperature, it is often clearly specified that seamless pipes must be used. In other industries, as long as the relevant service variables such as temperature and pressure in actual work do not exceed the parameter range specified in the applicable standards, welded pipes will usually be the first choice due to their relatively low production costs and wider market availability. In the field of structural applications, there is no significant difference in the performance of ERW steel pipes and seamless steel pipes. Although the two can be substituted for each other in actual use, from the perspective of economic cost, when the cheaper welded pipes can meet the engineering requirements, it is obviously not a wise choice to select seamless pipes.

Good Purchasing Specifications for Welded and Seamless Steel Pipes

When specifying pipeline products for engineering projects, engineers need to pay special attention to an important detail: in various specification documents for writing standards (such as ASTM, ASME, ANSI, and API provided by authoritative organizations), usually only the pipeline grade standards are listed, without elaborating whether the pipeline is manufactured using the ERW process or the seamless process. It should be noted that not all pipeline grades can be produced by these two manufacturing methods. In addition, a deep understanding and proficient grasp of industry standards are of great significance for effectively controlling procurement costs. Taking the A106 and A53 carbon steel pipe standards as examples, pipes compliant with the A106 standard must be manufactured using the seamless process, while pipes compliant with the A53 standard can be either seamless or welded. Therefore, in a given project, if engineers must follow the A53 standard, they can flexibly choose a more suitable pipeline type according to the actual needs of the specific application scenario, thus achieving optimized cost control.
 
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