Double-layer fused epoxy powder coated steel pipeTechnology
1. Double-layer epoxy powder coating production line's coating process
The coating process flow for the double-layer bonded epoxy powder exterior anti-corrosion production line is as follows:
Brief Description of Main Processes:
(1) Pretreatment
Each elbow pipe must be visually inspected individually; pipes with外观 and size deviations not meeting steel pipe standards should be removed. Clean the oil-stained surface of the elbows using acetone or other organic solvents; for elbows transported by sea, if the chloride salt content exceeds 20mg/m2, they must be flushed with high-pressure freshwater.
(2) Shot Blasting for Rust Removal
Bent pipes traverse along the circular conveyor line into the cleaning room for surface shot blasting and rust removal.
(3) Rust removal and post-inspection treatment
Step one involves visual inspection, trimming, or removing defective steel pipes. Additionally, use a wire rope depth gauge according to the specified inspection frequency to measure the wire rope depth, and inspect the rust removal grade by comparing with photo or grade standard samples.
(4) Preheat
Heat the surface of the bent pipe using a medium-frequency coil until it reaches the temperature required for the coating. To accurately control the surface temperature of the bent pipe, continuous measurements should be taken with a thermometer.
(5) Spray Coating
During the spraying process, the bent pipe moves along the circular conveyor line into the spray booth for coating. It is coated in a sequential order of inner to outer layers, ensuring that the outer layer is applied before the inner layer has fully cured.
(6) Water Cooling
Ensure the coating is fully cured before undergoing water cooling.
(7) Online Inspection
When the surface temperature of the tube to be bent is below 100°C, use a spark leak detector to inspect all coatings for leaks, and also mark the leak locations. After disassembly, repair according to relevant standards.
2. Key structural features of the double-layer fused epoxy powder coating production line
Bendable tube conveying equipment, shot blasting rust removal devices, spraying systems, and heating units make up the double-layer fusion epoxy powder coating production line.
Key Structural Features of the Production Line:
Transmission Cable
Utilize circular bend conduit for transmission lines, adjust the transmission speed as required, and ensure stable operation of bends at various angles when both the transmission wheel and the inner support wheel are engaged.
(2) Shot Blasting Rust Removal Equipment
The unit employs a shot blasting method for rust removal similar to that of straight tube production lines. Due to the even distribution of multiple blast nozzles along the circumference of the bend tube, it effectively ensures the quality of surface treatment.
(3) Heating Equipment
Because the heater moves radially with the bending pipe, it is suitable for anticorrosive treatment of pipes with different bending angles.
(4) Spraying System
In this system, the powder coating stand moves in a radial swing as the bend pipe moves, and it is suitable for the anti-corrosion treatment of pipes with various bending angles. Due to the uniform distribution of the powder gun along the circumference of the bend pipe, it is driven by the motor to oscillate uniformly around the pipe body, thereby ensuring the continuity and uniformity of the coating thickness. Moreover, the coating thickness can be adjusted between 300μm and 1200μm according to different requirements.
3. Technical key points and specifications of the production line
1. In actual production, the key technical aspects of the production line include: 1) Ensuring uniform coating thickness, as the bending tube structure poses unique challenges that make it difficult to maintain uniform thickness. This increases the difficulty in applying double-layer powder coatings. Therefore, it's essential to conduct process tests in advance to adjust the thickness of both inner and outer coatings, and develop reasonable process parameters before proceeding with formal production. 2) Achieving optimal integration between the inner and outer coatings. The integration of these coatings determines the overall anti-corrosion performance. Additionally, it helps prevent delamination between the layers. Therefore, it's crucial to accurately control the timing difference between the spraying of inner and outer coatings to ensure their integration. 3) Managing the curing temperature and time.The performance indicators of the coating are greatly affected by curing temperature and time, which must be accurately controlled here.
(2) Key Technical Indices of Production Line Performance
Applicable pipe diameter for bending: Φ≤1,200 mm
Surface rust removal quality; Near white grade (Sa2.5)
Heating Temperature: 230-250℃
Coating Thickness: 300-1200μm (adjustable as required)
Production Speed: 250-350 mm/min
Applicable bending angles: 10° to 90°.
Double-layer bonded epoxy powder coating system, with its excellent performance and low cost, is highly valued in the long-distance pipeline engineering industry. It is used as a strong anti-corrosion measure in special sections of long-distance pipeline projects, becoming an advanced technical method in the external anti-corrosion field of long-distance pipelines. As costs continue to decrease, this system is sure to gain wider application and promotion both domestically and internationally.
