1. Feeding detection:
The steel strip entering the welded pipe forming unit is focused on its size and plate edge quality to ensure that the plate width, wall thickness, and feeding direction meet the process requirements. Generally, digital calipers, digital wall thickness micrometers, and tape measures are used to quickly measure the plate width wall thickness and other dimensions, and comparison charts or special tools are used to quickly detect the plate edge quality. Generally, the inspection frequency is determined according to the furnace number or the volume number, and the head and tail of the plate are measured and recorded. If conditions permit, the edge of the steel strip must also be inspected to ensure that there are no defects such as delamination or cracks on the steel strip and its processed edges. At the same time, the raw materials with processed edges must also be prevented from mechanical damage to the edge of the steel strip when they are transported to the welded pipe production line.
2. Forming detection:
The key to plate and strip forming is to prevent excessive tensile stress on the edge of the strip to avoid the formation of wave bends. The relevant inspection items in the installation and commissioning of the forming unit include the rapid inspection and recording of the dimensions and gaps of the forming, finishing and sizing rollers, the circumference variables of the strip, the curling of the strip edge, the welding angle, the plate edge docking method, the extrusion amount, etc. Digital calipers, angle gauges, feeler gauges, tape measures, tape measures, and corresponding special tools are often used for rapid measurement to ensure that each control variable is within the range required by the production process specifications.
3. Pre-welding inspection:
After adjusting and recording the various parameters of the forming unit, the pre-welding inspection mainly determines the specifications and positions of the internal and external burr cutters, impedance devices, and sensors, the state of the forming liquid and the air pressure value and other environmental factors to meet the startup requirements determined by the process specifications. The relevant measurements are mainly based on the operator’s experience, supplemented by tape measures or special instruments, and quickly measured and recorded.
4. In-welding inspection:
During welding, the values of the main parameters such as welding power, welding current voltage, and welding speed are focused on. Generally, they are directly read and recorded by the corresponding sensors or auxiliary instruments in the unit. According to the relevant operating procedures, it is sufficient to ensure that the main welding parameters meet the requirements of the process specifications.
5. Post-weld inspection:
Post-weld inspection needs to pay attention to welding phenomena such as welding spark state and post-weld burr morphology. Generally, the weld color, spark state, internal and external burr morphology, hot zone color, and wall thickness variables at the extrusion roller during welding are key inspection items. It is mainly based on the actual production experience of the operator, and the naked eye is monitored and supplemented by relevant comparison maps to quickly measure and record, and ensure that the relevant parameters meet the requirements of the process specifications.
6. Metallographic inspection:
Compared with other inspection links, metallographic inspection is difficult to carry out on-site, generally takes a long time, and directly affects production efficiency. Therefore, it is of great practical significance to optimize the metallographic inspection process, improve inspection efficiency, and realize rapid evaluation.
6.1 Optimization of sampling link:
In the selection of sampling points, there are generally finished pipe sampling, flying saw point sampling, and pre-sizing sampling. Considering that cooling and sizing have little effect on weld quality, it is recommended to sample before sizing. In terms of sampling methods, gas cutting, metal saws, or manual grinding wheels are generally used. Due to the small sampling space before sizing, it is recommended to use electric grinding wheels to cut samples. For thick-walled pipes, gas-cutting sampling efficiency is higher, and each company can also design relevant special tools to improve sampling efficiency. In terms of sampling size, to reduce the inspection area to improve the efficiency of sample preparation, on the premise of ensuring the integrity of the weld, the sample is generally 20 mm × 20 mm and above. For upright microscopes, when sampling, the inspection surface should be parallel to its opposite side as much as possible to facilitate focusing measurement.
6.2 Optimization of sample preparation:
The sample preparation process generally uses manual grinding and polishing of metallographic samples. Because the hardness of most welded pipes is low, 60 mesh, 200 mesh, 400 mesh, and 600 mesh sandpaper can be used for water grinding, and then 3.5 μm diamond spray particle canvas is used for rough polishing to remove visible scratches, and then water or alcohol-moistened woolen polishing cloth is used for fine polishing. After obtaining a clean and bright inspection surface, it is directly dried with hot air from a hair dryer. If the relevant equipment is in good condition, sandpaper, and other equipment are properly prepared, and the processes are connected conveniently, the sample preparation can be completed within 5 minutes.
6.3 Optimization of corrosion process:
The metallographic inspection of welds mainly detects the center width and streamline angle of the fusion line in the weld area. In practice, a supersaturated picric acid aqueous solution is heated to about 70°C and corroded until the light disappears before removal. After the stains on the corrosion surface are wiped off with absorbent cotton in the water flow, it is rinsed with alcohol and blown dry with hot air from a hair dryer. To improve the preparation efficiency, picric acid can be poured into a large beaker, added with water and a little detergent or hand soap (to act as a surface active agent), and stirred evenly to make a supersaturated aqueous solution at room temperature (with obvious crystal precipitation at the bottom) and placed for use. When used, after stirring and the bottom precipitation rises, the suspension is poured into a small beaker for heating and can be used. To improve the corrosion efficiency, the corrosion solution can be heated to the specified temperature in advance according to the production sample delivery time point before the test and kept warm for use. If corrosion needs to be further accelerated, the heating temperature can be increased to about 85°C. A skilled tester can complete the corrosion process within 1 minute. If the measurement of organization and grain size is required, a 4% nitric acid alcohol solution can also be used for rapid corrosion.
6.4 Optimization of inspection links:
The metallographic inspection links include fusion line inspection, streamline inspection, waist drum morphology inspection, metallographic organization and banded organization evaluation of parent material and heat affected zone, grain size rating, etc. Among them, fusion line inspection includes fusion line inclusion, inner, middle, and outer width, fusion line skew, etc.; streamline inspection includes upper, lower, left, and right streamline angles, streamline angle extreme value, streamline center deviation, hook pattern, streamline double peak, etc.; waist drum morphology inspection includes inner, middle and outer width, burr tolerance, misalignment, etc.
7. Large sample inspection:
According to the small sample inspection data, the pipeline is further refined, the relevant parameters are adjusted the requirements of the process specifications are met, and a steel pipe sample of the specified size needs to be taken for a small sample process test. Process performance tests include flattening test, bending test, flaring test, curling test, torsion test, longitudinal pressure test, expansion test, water pressure test, internal pass test, etc. Generally, according to the standards or user requirements, samples are taken and tested near the production line according to the operating procedures, and visual judgment is sufficient.
8. Full-line inspection:
All the above-mentioned tests are sampled according to the relevant specifications or standards, so missed inspections will inevitably occur. To ensure the quality of finished welded pipes, special attention should be paid to the application of online non-destructive testing technology. In the production of welded pipes, the commonly used non-destructive testing methods are ultrasonic testing, eddy current testing, magnetic testing, and radioactive testing. Various flaw detection equipment has a complete detection system, and the application of digital control technology and electronic computers also ensures the reliability of test results. The inspection personnel only need to ensure that the inspection equipment works normally according to the relevant operating procedures, monitor the stability of welding quality, ensure that there is no missed inspection, and isolate the defective welded pipes exceeding the standard in time.
Post time: Jun-12-2024