First, what are the raw material preparations for Q390D straight seam steel pipe processing?
(a) Material selection requirements: The processing of Q390D straight seam steel pipes begins with strictly selecting steel plates or strips that meet Q390D standards. 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 approximately 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.
(b) Inspection process: Before the materials enter the production line, a comprehensive quality inspection is required. This includes visual inspection of the steel plate or strip 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 are the processing techniques for Q390D straight seam steel pipes?
(1) Pre-forming treatment of Q390D straight seam steel pipes
(a) Cutting and blanking: According to the design length and size requirements of the 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.
(b) Edge processing: Process the edges of the blanks, 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 Steel Pipe
(a) Bending Forming: The billet is gradually bent into a tubular shape using cold bending or hot bending. Cold bending involves applying pressure to the billet at room temperature using a mold to deform it; hot bending involves heating the billet to a certain temperature before bending. This method is suitable for thicker materials or steel pipes with complex shapes. During the bending process, the bending radius and bending angle must be controlled to avoid defects such as excessive bending and wrinkles.
(b) Forming Equipment: Common forming equipment includes the JCO forming machine. This equipment gradually bends the steel plate into a near-circular tube blank through multiple stampings. The formed tube blank has high dimensional and shape accuracy.

Third, What are the Welding Processes for Q390D Straight Seam Steel Pipe?
(a) Pre-welding: The edges of the formed tube blank are pre-welded, usually using gas shielded welding (such as carbon dioxide 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.
(b) 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 the welding process, welding parameters, such as welding current, voltage, and welding speed, must be strictly controlled to ensure the quality of the weld. After welding, the weld should be full, uniform, and free from defects such as porosity, slag inclusions, and cracks.

Fourth, what are the subsequent treatments for Q390D straight seam steel pipes?
(a) Weld Inspection: Non-destructive testing of the weld is performed, 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 can provide a more direct view of the internal structure of the weld and detect defects such as tiny cracks. Simultaneously, a visual inspection of the weld surface is required to check whether the shape and size of the weld meet the requirements and whether there are surface defects such as undercut and lack of fusion.
(b) Straightening and Sizing: After welding, the steel pipe may exhibit deformations such as bending and elliptic distortion. The steel pipe is straightened using a straightening machine to ensure its straightness meets standard requirements. Simultaneously, a sizing device is used to precisely control the outer diameter of the steel pipe, ensuring dimensional accuracy.
(c) End trimming: Based on the actual usage requirements of the steel pipe, the ends that do not meet dimensional accuracy or have poor welding quality are cut off, making the overall quality of the steel pipe more uniform.

Fifth, what are the processing techniques for Q390D straight seam steel pipes?
(1) Steel strip uncoiling and pretreatment
(a) Uncoiling: The coiled steel strip is uncoiled on an uncoiling machine. During the uncoiling process, attention should be paid to tension control of the steel strip to avoid stretching deformation or wrinkling.
(b) Cleaning and rust removal: The uncoiled steel strip is cleaned and rust removed. Chemical pickling or mechanical rust removal methods can be used to remove oil, rust, and other impurities from the surface of the steel strip, improving the surface quality and providing good conditions for subsequent welding.
(2) Integrated Forming and Welding
Continuous Forming and Welding: Q390D straight seam steel pipes are typically processed using a continuous forming and welding process. On a forming machine, the steel strip is gradually bent into a tubular shape through a series of rollers, while welding is performed simultaneously at the edge of the pipe 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 a fast welding speed; submerged arc welding is suitable for welding thick-walled Q390D straight seam steel pipes, producing high-quality welds.
(3) Post-Weld Treatment
(a) Weld Cleaning: After welding, the weld slag, spatter, etc., on the inner and outer surfaces of the weld must be cleaned. Mechanical grinding, blowing, and other methods can be used to ensure a clean and tidy weld surface.
(b) Heat Treatment: Depending on the requirements, Q390D straight seam steel pipes may undergo heat treatment, such as normalizing or tempering. Heat treatment can improve the microstructure of Q390D straight seam steel pipes, eliminate internal stress generated during welding, and improve the mechanical properties and corrosion resistance of Q390D straight seam steel pipes.
(c) Quality Inspection and Finishing: Similar to straight seam steel pipes, Q390D straight seam steel pipes also require comprehensive quality inspection, including visual inspection, dimensional measurement, and non-destructive testing. After passing inspection, Q390D straight seam 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.