Welding process classification of lsaw steel pipe

The classification of LSAW steel pipe welding processes refers to the systematic division of different welding methods and technologies used in the production of LSAW steel pipes. Its purpose is to better understand the manufacturing principles, weld quality, and applicable scenarios of steel pipes.

Welding process classification of lsaw steel pipe

In terms of welding technology, straight seam steel pipes can be divided into resistance welded straight seam steel pipes and submerged arc welding straight seam steel pipes. Resistance welded straight seam steel pipes are further divided into high frequency welded straight seam steel pipes, medium frequency welded straight seam steel pipes, and low frequency welded straight seam steel pipes. The submerged arc welded straight seam steel pipe is also called double-sided submerged arc welded straight seam steel pipe or LSAW straight seam steel pipe. The LSAW is (the abbreviation of Longitudinally Submerged Arc Welding is LSAW). Electric resistance welded straight seam steel pipe is also called ERW straight seam steel pipe, where ERW is (electric resistance welded pipe, abbreviated as ERW pipe). The following are the production methods of each welding process:

High-frequency welded straight seam steel pipe, also called ERW pipe, is a type of resistance welded steel pipe. ERW pipes are classified into AC and DC welding types. AC welding includes low, medium, and high-frequency welding, with high-frequency mainly used for thin or standard wall pipes. DC welding is generally for small-diameter pipes. Simply put, high-frequency welded pipes are ERW pipes made using high-frequency welding, offering good performance and cost-effectiveness, especially in oil and gas storage and transport.

On the other hand, submerged arc welded straight seam pipes, or LSAW pipes, are made from medium-thick plates rolled into tubes and welded with double-sided submerged arc welding. LSAW pipes can have large diameters and thick walls, with excellent toughness, uniformity, pressure resistance, low-temperature performance, and corrosion resistance. They are the preferred choice for high-strength, long-distance oil and gas pipelines, and are the only type allowed by API standards in sensitive areas like alpine zones, seabeds, and densely populated regions.

High-frequency welding works by using electromagnetic induction to heat pipe edges until molten, then roller extrusion fuses the edges into a strong, continuous weld.

Introduction to the production process of LSAW steel pipe

High-frequency welding is a type of induction welding, which we can also call pressure-based welding. High-frequency welding does not require filler materials for the weld seam, and there is no welding spatter during welding. The area affected by the welding heat during the welding process is narrow, the shape after welding is very beautiful, and the mechanical properties of the welding are very good. Due to these advantages of high-frequency welding, high-frequency welding has been widely used in the production of steel pipes.

High-frequency welding of steel pipes utilizes the skin effect and proximity effect of alternating current. After the steel is rolled and formed, a circular tube blank with a broken section is formed. Rotate one or a group of resistors in the tube near the center of the induction coil, and the resistor and the opening of the tube form an electromagnetic induction loop. Under the action of skin effect and proximity effect, a strong and concentrated heat effect is generated at the edge of the opening of the tube blank, which quickly heats the edge of the weld to the required welding temperature. After being extruded by the pressure roller, the molten metal achieves inter-crystal bonding, and forms a strong butt weld after cooling.

Features of LSAW Steel Pipe Production:

1. High Heating Speed and Production Efficiency: Due to the high concentration of energy in the welding zone, the welding edge of the pipe is heated to the required welding temperature in a short time (a few hundredths to a few tenths of a second). Furthermore, no "skip welding" occurs during high-speed welding, resulting in very high welding speeds.

2. Wide Range of Applicable Materials: High-frequency resistance welding falls under the category of pressure welding. It eliminates the need for external filler metal, avoiding problems such as chemical and metallurgical reactions between the welding material and the base metal. Therefore, it is suitable for a wide range of materials, including carbon steel, alloy steel, stainless steel, and many other metals.

3. Small Heat-Affected Zone: Due to the high welding speed and strong self-cooling effect of the workpiece, the heat-affected zone is small and less prone to oxidation, resulting in better weld microstructure.

4. Uniform Wall Thickness and High Dimensional Accuracy: Straight seam high-frequency welded steel pipes are made by cold-deforming rolled steel strips and then welding them. The uniformity of wall thickness and surface quality are superior to seamless steel pipes, and the dimensional accuracy is significantly better than seamless pipes or submerged arc welded pipes. Meanwhile, due to the use of hot-rolled steel strip as raw material, the pipe body has very few internal defects (such as cracks, inclusions, and porosity), and is increasingly being used to replace seamless steel pipes in various applications. However, due to limitations in forming equipment and heating power, its pipe diameter and wall thickness are restricted; currently, the pipe diameter is below Φ600mm, and the wall thickness is below 13mm.

In the past decade or so, through improvements in the quality of hot-rolled steel strip, and the increased automation of welding and heat treatment parameters through computer control and online inspection, the reliability of straight seam high-frequency welded steel pipes has been greatly enhanced. Currently, in the oil and gas industry, straight seam high-frequency welded steel pipes are widely used in long-distance pipelines, oil well casings, and other fields.

Conclusion

The welding processes of LSAW steel pipes can be classified into several categories, including:
Single vs double-sided welding
Single-wire vs multi-wire welding
Pre-welding vs final welding
Internal vs external welding
Among these, double-sided submerged arc welding with multi-wire technology is the most widely adopted due to its superior performance and efficiency.Understanding these classifications helps ensure the correct selection of LSAW pipes for demanding applications, especially in the oil and gas industry.
Building on these advanced welding technologies, BAOWI STEEL is a professional manufacturer of high-quality ERW and LSAW steel pipes, equipped with modern production lines and strict quality control systems.