What are the steps involved in rapid online weld quality inspection of high-frequency straight seam welded pipes

To achieve efficient and stable control of weld quality in high-frequency straight seam welded pipes, a convenient online rapid weld quality assessment and diagnosis scheme is proposed. This scheme optimizes each step of the rapid online weld quality inspection process, analyzing and diagnosing the causes of different weld morphologies from four aspects: preliminary machine adjustment assessment and diagnosis, small sample assessment and diagnosis, large sample assessment and diagnosis, and full-line assessment and diagnosis. It is pointed out that this scheme can be continuously improved based on the actual production of each enterprise, enabling efficient and convenient adjustment of relevant product parameters to ensure online weld quality. Furthermore, supplemented by relevant data statistics or software application tools, data processing efficiency can be further improved, scientifically guiding machine adjustment operations. High-frequency straight seam welded pipes have advantages such as excellent dimensional accuracy, good surface quality, high production efficiency, low investment, short construction period, low production cost, and quick results, and are widely used in various fields of production and daily life. In the actual production of high-frequency straight seam welded pipes, apart from the design factors of related equipment and processes such as raw materials, forming, and welding, the technical level of the welded pipe unit's commissioning directly determines the weld quality and production efficiency.

Regarding Online Rapid Inspection of Weld Quality in High-Frequency Straight Seam Welded Pipes

1. Feeding Inspection of High-Frequency Straight Seam Welded Pipes: The dimensions and edge quality of the steel strip entering the welded pipe forming unit are the focus of inspection, ensuring that the width, wall thickness, and feeding direction meet process requirements. Digital calipers, digital micrometers, and measuring tapes are generally used to quickly measure dimensions such as width and wall thickness. Comparison charts or specialized tools are used to quickly inspect the edge quality. The inspection frequency is generally determined based on the furnace number or roll number, and measurements are taken and recorded at the beginning and end of the strip. If conditions permit, flaw detection of the steel strip edges is also necessary to ensure that the steel strip and its processed edges are free from defects such as delamination or cracks. Simultaneously, mechanical damage to the edges of the processed raw materials must be prevented when transporting them to the welded pipe production line.

2. Forming Inspection of High-Frequency Straight Seam Welded Pipes: The key to strip forming is to prevent excessive tensile stress on the strip edges to avoid wavy bends. Relevant inspection items during the installation and commissioning of the forming unit include rapid inspection and recording of the dimensions and gaps of each roller type in forming, finishing, and sizing; strip circumference variations; strip edge curling; welding angles; edge butt joint methods; and extrusion amounts. Digital calipers, angle gauges, feeler gauges, tape measures, and other specialized tools are commonly used for rapid measurement to ensure that all control variables are within the range required by the production process specifications.

3. Pre-Welding Inspection of High-Frequency Straight Seam Welded Pipes: After adjusting and recording the various parameters of the forming unit, pre-welding inspection mainly determines the specifications and positions of internal and external burr cutters, impedance devices, and sensors, as well as environmental factors such as the forming fluid state and air pressure values, to meet the start-up requirements specified in the process specifications. Related measurements are mainly based on experience, supplemented by tape measures or specialized tools, for rapid measurement and recording.

4. In-weld inspection of high-frequency straight seam welded pipes: During welding, the focus is on the values of key parameters such as welding power, welding current, voltage, and welding speed. These are generally read and recorded directly by corresponding sensors or auxiliary instruments in the unit. Following relevant operating procedures ensures that the main welding parameters meet the process specifications.

5. Post-weld inspection of high-frequency straight seam welded pipes: Post-weld inspection focuses on the welding spark state and post-weld burr morphology. Key inspection items include weld color at the extrusion roller, spark state, internal and external burr morphology, hot zone color after deburring, and wall thickness variation. This is mainly based on the operator's actual production experience, using visual monitoring supplemented by relevant comparative charts for rapid measurement and recording, ensuring that relevant parameters meet process specifications.

6. Metallographic inspection of high-frequency straight seam welded pipes: Compared to other inspection stages, metallographic inspection is difficult to perform on-site and generally time-consuming, directly impacting production efficiency. Therefore, optimizing the metallographic inspection process, improving inspection efficiency, and achieving rapid evaluation are of significant practical importance.

(1) Sampling Process Optimization: Sampling points can be selected from finished pipe samples, flying saw samples, and samples taken before sizing. Considering that cooling sizing has little impact on weld quality, sampling before sizing is recommended. Sampling methods generally include gas cutting, metal sawing, or manual grinding wheels. Due to the limited space before sizing, electric grinding wheels are preferred for sample cutting. For thick-walled steel pipes, gas cutting is more efficient, and companies can design specialized tools to improve sampling efficiency. Regarding sample size, to reduce the inspection area and improve sample preparation efficiency, samples should generally be 20 mm × 20 mm or larger, provided the weld integrity is ensured. For upright microscopes, the inspection surface should be kept as parallel as possible to the opposite surface during sampling to facilitate focused measurement.

(2) Sample Preparation Optimization: The sample preparation process generally involves manual grinding and polishing of metallographic specimens. Since most welded pipes have low hardness, 60-grit, 200-grit, 400-grit, and 600-grit sandpaper can be used for wet grinding. Then, a 3.5 μm diamond atomized abrasive cloth is used for rough polishing to remove visible scratches. Finally, a water- or alcohol-moistened felt polishing cloth is used for fine polishing to obtain a clean and bright inspection surface. The specimen is then dried directly with a hairdryer. With proper equipment, adequate sandpaper, and convenient connections between processes, sample preparation can be completed within 5 minutes.

(3) Corrosion Optimization: Metallographic inspection of welds mainly examines the center width of the fusion line and the streamline angle in the weld area. In practice, a supersaturated picric acid aqueous solution is heated to approximately 70°C to corrode the surface until the shine disappears. The specimen is then removed, and the surface is wiped clean with degreased cotton in running water. Finally, it is rinsed with alcohol and dried with a hairdryer. To improve preparation efficiency, picric acid can be poured into a large beaker, water and a small amount of detergent or hand soap (for surface activity) can be added, and stirred evenly to prepare a supersaturated aqueous solution at room temperature (with obvious crystal precipitate at the bottom). This solution can then be set aside for later use. In actual use, after stirring until the precipitate forms at the bottom, the suspension can be poured into a small heating beaker for use. To improve corrosion efficiency, the corrosion solution can be heated to the specified temperature and kept warm before the production sample delivery time. If further acceleration of corrosion is required, the heating temperature can be increased to approximately 85°C. A skilled operator can complete the corrosion process within 1 minute. If the measurement of microstructure and grain size is required, a 4% nitric acid alcohol solution can be used for rapid corrosion.

(4) Optimization of the testing process: Metallographic testing includes fusion line detection, flow line detection, waist drum morphology detection, evaluation of the microstructure and banded structure of the base material and heat-affected zone, and grain size rating. The inspection of fusion lines includes fusion line inclusions, inner, center, and outer widths, and fusion line skewness. Streamline inspection includes streamline angles (up, down, left, and right), extreme streamline angles, streamline center deviation, hook-like patterns, and streamline double peaks. Drum shape inspection includes inner, center, and outer widths, burr tolerances, and misalignment. Both drum shape and fusion line can characterize welding energy and extrusion pressure. However, drum shape is also related to steel strip thickness, edge condition, and welding periodicity. Furthermore, the measurement boundary is difficult to accurately identify after corrosion, leading to measurement errors. Therefore, it is generally only used as a reference indicator. The metallographic structure and banded structure rating of the base material, as well as the grain size rating, have already been inspected during incoming raw material acceptance and can also be used as reference items during online weld inspection. To improve inspection efficiency, relevant inspection items should be optimized according to product requirements. It is recommended to prioritize the inspection of fusion lines and streamline shapes, especially focusing on the two core indicators: fusion line center width and streamline angle.

7. Large-scale inspection of high-frequency straight seam welded pipe: Based on the small-scale inspection data, the pipeline is further refined, relevant parameters are adjusted to meet process specifications, and steel pipe samples of specified dimensions are taken for small-scale process performance tests. Process performance tests include flattening tests, bending tests, flaring tests, edge rolling tests, torsion tests, longitudinal pressure tests, unfolding tests, hydrostatic tests, and internal flow tests. Generally, samples are taken and tested near the production line according to standards or user requirements and operating procedures; visual inspection is sufficient for judgment.

8. Full-line inspection of high-frequency straight seam welded pipe: Since all the above tests are conducted according to relevant specifications or standards, omissions are inevitable. To ensure the quality of finished welded pipes, special attention should be paid to the application of online non-destructive testing (NDT) technology. Commonly used NDT methods in welded pipe production include ultrasonic testing, eddy current testing, magnetic particle testing, and radiographic testing. Various NDT equipment has sophisticated detection systems, and the application of digital control technology and computers ensures the reliability of test results. Inspection personnel only need to ensure that the inspection equipment is working properly according to the relevant operating procedures, monitor the stability of welding quality, ensure that no defects are missed, and promptly isolate welded pipes with defects exceeding the standard.