Surface treatment technology for hot-dip steel pipes

manufacturer introduced the surface treatment method of large-diameter hot-dip tube.
1. Cleaning: Clean the surface of the steel with solvents and emulsions to remove organics such as oil, grease, dust, and cleaners, but not the rust and scale of the steel surface. It can only play a complementary role in the production of corrosion protection.
2. Rust removal: First, the surface of the steel is ground with a wire brush or the like to remove loose or raised scale, rust, welding slag, and the like. Hand tools can reach Sa2 level, power tools can reach Sa3 level, if the steel surface is attached with solid oxide scale, the tool rust removal effect is good. OD. The construction anchoring depth is not ideal and cannot meet the anti-corrosion requirements of the construction anchoring depth.
three. Pickling: Chemical and electrolytic methods are often used for pickling. Chemical pickling is only used for pipeline corrosion protection. It removes oxide scale, rust and old paint. Sometimes it can be used for reworking after sand blasting. Although chemical cleaning can achieve the necessary cleanliness and smoothness of the appearance, the anchoring line is shallow and prone to contamination.
4. Cast iron rust removal: Cast iron rust removal is driven by high-power motor blades to make high-speed torsion, so that steel sand, steel balls, wires, minerals and other abrasives are thrown into the surface under the action of centrifugal force, which can not only pierce rust, oxide and dust. Strongly removed, but the steel tube is also affected by abrasive impact and friction. It also achieves the required smoothness.
Hot-dip tube: Low-carbon structural steel or low-alloy structural steel strip is rolled into a billet at a certain hot-rolling angle (called forming angle) and then welded to produce a large-diameter narrow-belt steel pipe. Hot-dip pipes are mainly used to transport oil and gas pipelines, and their specifications are expressed by the outer diameter * wall thickness. If the hot-dip tube is welded on one or both sides, the welded pipe shall ensure that the hydrostatic test, the tensile strength of the weld and the cold bending performance of the welded joint meet the requirements.
GB50236-98 (field equipment and industrial pipeline welding engineering construction and acceptance specifications) and GB50242-2002 (construction water supply, drainage, heating engineering construction quality acceptance specifications). The end of the pipe must be machined prior to hand soldering to a thickness greater than 3 mm.
The groove cutting of the plasma arc slot machine can also be cut with oxygen. The groove size and shape of steel pipes and pipe joints shall be in accordance with the relevant provisions of the national standard GB50236-98.
For machined grooves, use a manual grinding wheel to clean the surface of the groove and use 150mm edges on both sides of the groove to remove burrs, oil, paint, rust and other dirt. Through inspection, it was found that there were no defects such as cracks or interlayers. Qualified welded pipes shall be welded in time.
4.2. Welding repair and root cleaning:
Welded pipe joints should be repaired and planted prior to welding. The groove angle, blunt edge and gap at the end of the pipeline shall comply with the relevant provisions of GB50236-98 "Code for Construction and Acceptance of Welding of Field Equipment and Industrial Pipelines". It is not permissible to clamp the solder strip in the opposite gap or to shorten the gap by heating.
4.3, corresponding:
First, the site is trimmed and leveled. Two steel pipes are hung on the board.
The calibration procedure is as follows: Check the pipe calibration joint for clean size, ensure longitudinal weld misalignment, first pipe calibration, first pipe calibration, gap calibration, second pipe calibration, spot welding.
When using pipes, the difference in wall thickness between the two pipes should not exceed 3 mm. Excess shall be handled in accordance with the relevant provisions of the national standard GB5023-98.
The two longitudinal welds should be staggered with a staggered distance of less than 100 mm.
The circle should be completed in front of the opponent. For non-circular holes, the tube ends should be cut.
Straight tube ends are shorter, DN<100mm, short tube length <150mm, DN> 150mm, short tube length When the pipes are reversed, the deviation is allowed to not exceed 15% of the wall thickness. During the reaction, the rotating tube is repeated a plurality of times to reduce the interlacing value and the gap is uniform. 4.4. welding:
The spot weld thickness should not exceed 70% of the wall thickness and the root of the weld must be completely welded. Due to the different diameters, the length and spacing of the spot welds are different. DN500 mm steel pipe.