First, what are the raw material preparations for Q390D straight seam welded steel pipes?
Material selection requirements: The processing of Q390D straight seam welded steel pipes begins with strictly selecting steel plates or strips that meet the Q390D standard. Q390D steel is a low-alloy high-strength structural steel. Its chemical composition includes a carbon content generally not exceeding 0.18%, a silicon content of around 0.50%, a manganese content of approximately 1.0-1.60%, and alloying elements such as niobium, vanadium, and titanium. The presence of these elements can refine the grains and enhance the strength and toughness of the steel. At the same time, there are strict limits on the content of harmful elements such as sulfur and phosphorus to ensure the quality of the steel.
Inspection process: Before the materials enter the production line, a comprehensive quality inspection is required. This includes a visual inspection of the steel plates or strips to check for surface defects such as cracks, folds, and rust; chemical composition analysis and mechanical property testing are also required to ensure that the yield strength, tensile strength, elongation, and other indicators of the material meet the standard requirements of Q390D steel.
Second, what is the processing technology of Q390D straight seam welded steel pipe?
1) Pre-forming treatment of Q390D straight seam welded steel pipe:
Cutting and blanking: According to the design length and size requirements of the Q390D straight seam welded steel pipe, use cutting equipment to cut the steel plate or strip into suitable blanks. During the cutting process, ensure the flatness and perpendicularity of the cut to provide a good foundation for subsequent forming processing.
Edge processing: Process the edges of the blank, such as milling and planing. This is to ensure the flatness, smoothness, and suitable bevel shape of the edges, facilitating subsequent welding processes and improving welding quality.
2) Forming process of Q390D straight seam welded steel pipe:
Bending and forming: Use cold bending or hot bending to gradually bend the blank into a tubular shape. Cold bending involves applying pressure to the blank at room temperature using a mold to bend and deform it; hot bending involves heating the blank to a certain temperature before bending. This method is suitable for thicker materials or Q390D straight seam welded steel pipes with complex shapes. During the bending process, the bending radius and angle must be carefully controlled to avoid defects such as excessive bending and wrinkling.
Forming Equipment: Common forming equipment includes JCO forming machines. This equipment gradually bends the steel plate into a near-circular tube blank through multiple stampings, resulting in a tube blank with high dimensional and shape accuracy.
3) Welding Process of Q390D Straight Seam Welded Steel Pipe.
Pre-welding: The edges of the formed tube blank are pre-welded, typically using gas shielded welding (such as CO2 gas shielded welding). The purpose of pre-welding is to initially fix the shape of the tube blank and prevent problems such as excessive gaps or deformation during subsequent welding.
Internal and External Welding: After pre-welding, internal and external welding is performed. Internal welding generally uses automatic submerged arc welding, while external welding can use multi-wire submerged arc welding or other high-efficiency welding methods. During welding, welding parameters such as welding current, voltage, and welding speed must be strictly controlled to ensure weld quality. After welding, the weld should be full, uniform, and free from defects such as porosity, slag inclusions, and cracks.
4) Post-processing of Q390D straight seam welded steel pipes.
Weld inspection: Non-destructive testing is performed on the weld, including ultrasonic testing and X-ray testing. Ultrasonic testing can detect internal defects in the weld, such as porosity and slag inclusions; X-ray testing allows for a more direct observation of the internal structure of the weld, detecting defects such as micro-cracks. Simultaneously, a visual inspection of the weld surface is required to check if the weld shape and dimensions meet requirements, and to identify surface defects such as undercut and lack of fusion.
Straightening and sizing: After welding, Q390D straight seam welded steel pipes may exhibit deformations such as bending or elliptic distortion. A straightening machine is used to straighten the Q390D straight seam welded steel pipes to ensure their straightness meets standard requirements. Simultaneously, sizing equipment is used to precisely control the outer diameter of the Q390D straight seam welded steel pipes, ensuring dimensional accuracy.
Cutting off the ends: Based on the actual usage requirements of Q390D straight seam welded steel pipes, the parts at both ends of the Q390D straight seam welded steel pipes that do not meet dimensional accuracy or have poor welding quality are cut off, making the overall quality of the Q390D straight seam welded steel pipes more uniform.
Third, what are the processing techniques for Q390D straight seam welded steel pipes?
(1) Steel strip uncoiling and pretreatment
Uncoiling: Unwind the coiled steel strip on an uncoiling machine. During the uncoiling process, pay attention to the tension control of the steel strip to avoid stretching deformation or wrinkling.
Cleaning and rust removal: Clean and remove rust from the uncoiled steel strip. Chemical pickling or mechanical rust removal methods can be used to remove oil stains, rust, and other impurities from the surface of the steel strip to improve the surface quality of the steel strip and provide good conditions for subsequent welding.
(2) Integrated forming and welding
Continuous forming and welding: Q390D straight seam welded steel pipes are usually processed using continuous forming and welding processes. On a forming machine, a steel strip is gradually bent into a tubular shape by a series of rollers, while welding is performed at the edges of the tube blank. Welding methods can include high-frequency resistance welding and submerged arc welding. High-frequency resistance welding utilizes the resistance heat generated by high-frequency current at the edge of the steel strip for welding, resulting in fast welding speeds; submerged arc welding is suitable for welding thick-walled welded steel pipes, producing high-quality welds.
Fourth, what are the post-weld treatments for Q390D straight seam welded steel pipes?
Weld cleaning: After welding, slag, spatter, and other debris on the inner and outer surfaces of the weld must be cleaned. Mechanical grinding and blowing methods can be used to ensure a clean and tidy weld surface.
Heat treatment: Depending on the needs, Q390D straight seam welded steel pipes undergo heat treatment, such as normalizing or tempering. Heat treatment can improve the microstructure of Q390D straight seam welded steel pipes, eliminate internal stresses generated during welding, and improve their mechanical properties and corrosion resistance.
Quality Inspection and Finishing: Similar to straight seam steel pipes, welded steel pipes also require comprehensive quality inspection, including visual inspection, dimensional measurement, and non-destructive testing. After passing inspection, welded steel pipes also need to undergo finishing processes such as pipe cutting and chamfering to ensure they meet the final product specifications and usage requirements.
Post time: Jan-19-2026