Seamless steel pipes are important piping materials widely used in various applications. The welding technology of seamless steel pipes is a crucial aspect of ensuring the quality and performance of pipelines. This article will introduce the key points of seamless steel pipe welding technology from four aspects: welding process, welding materials, welding environment, and quality control, for reference.
I. Welding Process
The welding process of seamless steel pipes should comply with relevant standards, including welding current, voltage, welding speed, welding gas, etc. Before welding, an inspection of welding equipment should be conducted to ensure its normal operation. During welding, strict control of welding conditions should be maintained to ensure the quality of weld seams. After welding, an inspection should be performed to ensure that the welding quality meets the standard requirements.
The main welding methods for seamless steel pipes include manual arc welding, gas-shielded welding, brazing, etc. Suitable welding methods and parameters should be selected according to different pipe materials, diameters, wall thicknesses, groove forms, welding positions, etc. The characteristics and essentials of these three welding methods are described below.
1）Manual Arc Welding
Manual arc welding is a commonly used welding method suitable for seamless steel pipes and welded steel pipes. Its features include simple operation, low equipment cost, and strong adaptability. However, it also has disadvantages such as unstable welding quality, large spatter, significant deformation, and the possibility of defects like pores and cracks.
Essentials of manual arc welding:
Choose suitable welding electrodes based on the material, thickness, and position of the pipe, selecting appropriate electrode models, diameters, and welding currents. Generally, low hydrogen electrodes such as J507, J507Fe, E7018, etc., with diameters between 2.5mm to 5mm and welding currents ranging from 80A to 300A are commonly used.
Groove processing: When preparing for welding, proper beveling or chamfering should be performed according to the wall thickness of the steel pipe, using "V" or "I" type grooves. The groove surface should be neat and clean. Unqualified grooves should not be welded. The forms and dimensions of the "I" and "V" shape grooves are as follows:
| Wall thickness | Groove shape | Groove angle | Groove gap |
| ≤6mm | V | 60°~70° | 1~2mm |
| >6mm | I | 30°~40° | 2~4mm |
Pipe alignment: Pipe alignment involves adjusting the center using brackets or hangers to ensure the alignment of pipes. Space should be maintained at the open end without causing displacement of the pipe centers. Pipes must be aligned flush on the outer wall. A steel ruler should be tightly placed against one side of the pipe's outer surface, and at a distance of 200mm from the weld, measure the outer surface of the other side of the pipe. The alignment between pipes and fittings should also ensure flush outer walls.
Tack Welding: After aligning the steel pipes, tack welding should be carried out. The thickness of tack welding should be consistent with the first layer of welding but should not exceed 70% of the pipe wall thickness. The root of the tack weld must be fully penetrated, and the tack welding positions should be evenly symmetrical.
Sequential welding: Based on the wall thickness and electrode diameter, determine the number of welding layers and the welding sequence. Generally, a bottom-up approach is adopted, welding the root first, followed by filling and capping layers. Proper welding speed and electrode angle should be maintained to ensure uniform and defect-free welds. Before each layer of welding, remove slag and spatter from the previous layer and allow the pipe to cool naturally. Arc starting and stopping points for each layer should be staggered by 20mm or at a 30° angle.
2）Gas Shielded Welding
Gas-shielded welding uses inert gases or active gases to protect the arc and weld pool, preventing impurities such as oxygen and nitrogen in the air from entering the weld. It is suitable for welding seamless steel pipes and welded steel pipes. Its features include high welding quality, minimal deformation, low spatter, and high efficiency. However, it also has disadvantages such as high equipment costs, high operating requirements, and sensitivity to environmental conditions.
Essentials of gas-shielded welding:
Choose suitable welding gas with the appropriate gas type, flow, and pressure according to the material, thickness, position, and form of the weld. Generally, a mixture of carbon dioxide gas or argon gas and carbon dioxide is used. The gas flow rate is between 10L/min to 25L/min, and the gas pressure is between 0.2MPa to 0.4MPa.
Choose the appropriate welding wire with the correct wire type, diameters, and polarity according to the material, thickness, position, and form of the weld. Generally, low carbon steel welding wires such as H08MnA, H08Mn2SiA, etc., with diameters between 0.8mm to 1.6mm are used. Direct current reverse polarity is commonly used, with the workpiece connected to "-" and the welding gun connected to "+".
Proper opening or chamfering treatment must be carried out during grove processing, with "V" or "I" type bevels used according to the wall thickness of the steel pipe. The bevel surface should be neat and smooth, and unacceptable pipe mouths should not be butt welded. See the table above for the forms and dimensions of I and V-type bevels.
Pipe Alignment: Pipe alignment involves adjusting the center using brackets or hangers to ensure the alignment of pipes without causing displacement of the pipe centers. Space should be maintained at the open end without causing displacement of the pipe centers. Pipes must be aligned flush on the outer wall. A steel ruler should be tightly placed against one side of the pipe's outer surface, and at a distance of 200mm from the weld, measure the outer surface of the other side of the pipe. The alignment between pipes and fittings should also ensure flush outer walls.
Tack Welding: After aligning the steel pipes, tack welding should be performed with a thickness consistent with the first layer of welding but not exceeding 70% of the pipe wall thickness. The root of the weld must be fully penetrated, and tack welding positions should be uniformly symmetrical.
Sequential Welding: Determine the number of welding layers and welding sequence based on the wall thickness of the pipe and the diameter of the welding wire. Generally, welding should proceed from bottom to top, welding the root first followed by the filling layer and cover layer. Maintain appropriate welding speed and welding wire angle to ensure uniform and defect-free welds. Before each layer of welding, remove slag and spatter from the previous layer and allow the pipe to cool naturally. Arc starting and ending points for each layer should be staggered by 20mm or 30°.
3）Brazing
Brazing is a welding method that uses high-temperature melted metals or alloys as filler materials to join two or more metal components together. It is suitable for welding seamless steel pipes and welded steel pipes. Its features include high welding quality, minimal deformation, low spatter, and high efficiency. However, it also has disadvantages such as high equipment costs, high operating requirements, and sensitivity to environmental conditions.
Essentials of brazing:
Choose suitable brazing materials with the correct type, diameters, and fusion point according to the material, thickness, position, and form of the weld. Generally, copper-based or silver-based brazing materials such as BCuP-2, BCuP-3, BAg-1, etc., with diameters between 1mm to 3mm and melting points between 600°C to 900°C are used.
Choose the appropriate flux with the correct kind, volume, and methods according to the material, thickness, position, and form of the weld. Generally, inorganic acids such as phosphoric acid or boric acid or their salts are used as flux. The flux quantity is between 5% to 10%, and it is uniformly applied to both sides of the weld or the surface of the brazing material.
During groove processing, proper opening or chamfering treatment must be performed. Bevels should be "V" or "I" type according to the wall thickness of the steel pipe. The surface of the bevel should be neat and smooth. Unqualified pipe mouths should not be butt welded. See the table above for the forms and dimensions of I and V-type bevels.
Pipe Alignment: Pipe alignment is achieved using brackets or hangers to adjust the center, retaining space at the open end without causing displacement of the pipe centers. Pipes must align flush on the outer wall. Use a steel ruler tightly against one side of the pipe's outer surface and measure the outer surface of the other side of the pipe at a distance of 200mm from the weld. Alignment between pipes and fittings should also ensure flush outer walls.
Tack Welding: After aligning the steel pipes, tack welding should be performed with a thickness consistent with the first layer of welding but not exceeding 70% of the pipe wall thickness. The root of the weld must be fully penetrated, and tack welding positions should be uniformly symmetrical.
Sequential Welding: Determine the number of welding layers and welding sequence based on the wall thickness of the pipe and the diameter of the brazing material. Generally, welding should proceed from bottom to top, welding the root first followed by the filling layer and cover layer. Maintain appropriate welding speed and brazing angle to ensure uniform, defect-free welds. Before each layer of welding, remove slag and spatter from the previous layer and allow the pipe to cool naturally. Arc starting and ending points for each layer should be staggered by 20mm or 30°.
II. Welding Materials
Welding materials for seamless steel pipes are essential factors affecting welding quality and performance. Welding materials should match the material of the pipe and have good welding and mechanical properties. Welding materials should comply with relevant standards, including chemical composition, mechanical properties, welding performance, etc. Welding materials should be stored in a dry, ventilated, and cool place to avoid moisture, rust, pollution, etc.
Welding materials for seamless steel pipes mainly include welding electrodes, welding wires, brazing materials, etc. The characteristics and selection principles of these three welding materials are described below.
1）Welding Electrodes
Welding electrodes are welding materials used for manual arc welding, consisting of a core wire and a flux coating. The core wire conducts current and provides filler metal, while the flux coating protects the arc and weld pool, stabilizes the arc, and improves the quality of the weld seam.
Characteristics of welding electrodes: simple operation, low equipment cost, strong adaptability, but unstable welding quality, large spatter, significant deformation, and possible defects like pores and cracks.
Selection principles of welding electrodes:
Choose welding electrodes that match the material of the pipe, generally low carbon steel or low alloy steel welding electrodes such as J421, J422, J507, J507Fe, E6013, E7018, etc.
Choose welding electrodes that match the thickness of the pipe material. The larger the electrode diameter, the higher the welding current and efficiency, but it also increases the likelihood of spattering and deformation.
Select the appropriate electrode type based on the position and form of the weld seam. Generally, low hydrogen electrodes such as J507, J507Fe, E7018, etc. are used. Low hydrogen electrodes have good welding and mechanical properties, reducing the occurrence of pores and cracks, and improving the impact toughness and crack resistance of the weld seam.
2）Welding Wires
Welding wire is a welding material used for gas-shielded welding, composed of a core wire and a flux. The core wire, which is the main body of the welding wire, conducts electricity and provides filler metal. The flux, located inside the wire, protects the arc and the weld pool, stabilizes the arc, and improves weld seam quality.
The characteristics of welding wire include high welding quality, minimal deformation, low spattering, and high efficiency. However, it also has disadvantages such as high equipment costs, high operational requirements, and sensitivity to environmental conditions.
Selection principles of welding wires:
Choose welding wires that match the material of the pipe, generally low carbon steel or low alloy steel welding wires such as H08MnA, H08Mn2SiA, ER50-6, ER70S-6, etc.
Select the appropriate wire diameter based on the thickness of the pipe, usually between 0.8mm to 1.6mm. A larger wire diameter results in higher welding current and efficiency, but it may also increase spattering and deformation.
Depending on the position and form of the weld seam, choose the appropriate wire type, typically solid wire or flux-cored wire. Solid wire has good welding and mechanical properties, while flux-cored wire provides good protection and helps reduce porosity.
3）Brazing Metal
Brazing metal is a welding material used for brazing, consisting of brazing filler metal and flux. The brazing filler metal, or brazing alloy, serves as the main component of the brazing metal and is used to join metals together. The flux, either applied externally or internally to the brazing alloy, is used to remove oxides, promote wetting and spreading of the brazing alloy, and enhance the quality of the brazing joint.
Characteristics of brazing materials: high welding quality, minimal deformation, less spatter, and high efficiency, but high equipment costs, high operating requirements, and sensitivity to environmental conditions.
Selection principles of brazing materials:
Choose brazing alloys that match the material of the pipe, generally copper-based or silver-based brazing metals such as BCuP-2, BCuP-3, BAg-1, BAg-2, etc.
Select the appropriate brazing metal diameter based on the thickness of the pipe, usually between 1mm to 3mm. A larger brazing alloy diameter results in higher welding efficiency, but it may also increase spattering and deformation.
Depending on the position and form of the brazed joint, choose the appropriate type of flux. Typically, inorganic acids such as phosphoric acid or boric acid, or their salts, are used as flux. The flux is applied in a uniform manner on both sides of the brazed joint or on the surface of the brazing metal, with a flux dosage ranging from 5% to 10%.
III. Welding Environment
The welding environment of seamless steel pipes is an important factor affecting welding quality and performance. The welding environment should comply with relevant standards, including temperature, humidity, wind speed, light, noise, etc. The welding environment should be kept dry, ventilated, well-lit, and quiet, avoiding interference from high temperatures, high humidity, strong winds, intense light, strong noise, etc.
The requirements for the welding environment of seamless steel pipes are as follows:
Temperature: The temperature of the welding environment should be between 5°C and 40°C. Both excessively high and low temperatures can affect welding quality and performance. Excessively high temperatures can cause overheating of the weld seam, leading to defects such as porosity, cracks, burn-through, etc. Excessively low temperatures can cause the weld seam to be too cold, resulting in defects such as cold cracks, lack of fusion, lack of penetration, etc.
Humidity: The humidity of the welding environment should be between 40% and 80%. Both excessively high and low humidity can affect welding quality and performance. Excessively high humidity can cause welding materials to absorb moisture, leading to defects such as porosity, cracks, oxidation, etc. Excessively low humidity can cause welding materials to become too dry, resulting in defects such as spattering, deformation, detachment, etc.
Wind speed: The wind speed of the welding environment should be between 0.5m/s and 1.5m/s. Both excessively high and low wind speeds can affect welding quality and performance. Excessively high wind speeds can disperse the welding gas, leading to defects such as porosity, cracks, oxidation, etc. Excessively low wind speeds can cause welding gas to accumulate, resulting in defects such as spattering, deformation, detachment, etc.
Lighting: The lighting of the welding environment should be between 300lx and 500lx. Both excessively high and low lighting can affect welding quality and performance. Excessively high lighting can damage the vision of welding personnel, leading to welding errors, operational mistakes, etc. Excessively low lighting can result in insufficient visibility for welding personnel, leading to welding defects, operational hazards, etc.
Noise: The noise level of the welding environment should be between 60dB and 80dB. Both excessively high and low noise levels can affect welding quality and performance. Excessively high noise levels can damage the hearing of welding personnel, leading to welding errors, operational mistakes, etc. Excessively low noise levels can result in a lack of concentration for welding personnel, leading to welding defects, operational hazards, etc.
IV. Quality Control
Quality control of seamless steel pipe welding is essential to ensure the quality and performance of pipelines. Quality control should be implemented throughout the entire welding process, including pre-welding, in-welding, and post-welding stages. Quality control measures should comply with relevant standards, including inspection, testing, evaluation, certification, etc.
The quality control for seamless steel pipes is as follows:
Quality Plan: The quality plan refers to the specifications and measures developed based on the characteristics and requirements of the welding project, including reasonable welding processes, welding materials, welding equipment, welding personnel, welding environment, welding inspection, welding evaluation, etc., to ensure welding quality and performance standards are met. The quality plan should be developed before welding, implemented during welding, and reviewed after welding.
Quality Inspection: Quality inspection refers to the process of inspecting, analyzing, and evaluating the welds before, during, and after welding to ensure welding quality and performance standards are met. Quality inspection should be conducted by professional quality inspectors or third-party organizations. Methods of quality inspection include non-destructive testing, destructive testing, metallographic testing, etc. The content of quality inspection includes the conformity, effectiveness, and continuity of aspects such as the appearance, dimensions, shape, defects, structure, and mechanical properties of the welds. The results of quality inspection should be promptly fed back to welding personnel and management for necessary corrective actions and improvements.
Quality Evaluation: Quality evaluation refers to the process of classifying and certifying the quality grades of welding projects based on the inspection results of welding quality and performance to ensure welding quality and performance standards are met. Quality evaluation should be conducted by professional quality evaluators or third-party organizations. Standards for quality evaluation include national standards, industry standards, enterprise standards, etc. The content of quality evaluation includes the conformity, effectiveness, and continuity of aspects such as the quality grades of welds, the quality grades of welding projects, and the acceptance conditions of welding projects. The results of the quality evaluation should be promptly fed back to welding personnel and management for necessary corrective actions and improvements.
V. Conclusion
Seamless steel pipe welding technology is a comprehensive discipline involving various aspects such as welding processes, welding materials, welding environments, and quality control. Mastering the key points of seamless steel pipe welding technology is of great significance for improving welding quality and performance, ensuring the safety and reliability of pipelines. This article introduces the key points of seamless steel pipe welding technology from the above four aspects, hoping to be helpful to you.
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