Views: 2 Author: Site Editor Publish Time: 2024-10-16 Origin: Site
To efficiently and stably control the weld quality of high-frequency straight seam welded steel pipes, a set of convenient online weld quality rapid evaluation and diagnosis schemes is proposed. The scheme optimizes the design of each link of online weld quality rapid detection, and analyzes and diagnoses the causes of different weld forms from four aspects: preliminary machine adjustment evaluation and diagnosis, small sample evaluation and diagnosis, large sample evaluation and diagnosis, and full-line evaluation and diagnosis. It is pointed out that the scheme can be continuously improved in combination with the actual production of each enterprise, and can efficiently and conveniently complete the adjustment of relevant product parameters to ensure the quality of online welds; at the same time, with the help of relevant data statistics or software application tools, it can further improve the data processing efficiency and scientifically guide the machine adjustment operation.
1. Online weld quality rapid detection
1.1 Feeding detection: The steel strip entering the welded steel pipe forming unit is focused on detecting 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 plate width wall thickness and other dimensions, and comparison charts or special tools are used to quickly detect plate edge quality. Generally, the inspection frequency is determined according to the furnace number or the roll number, and the head and tail of the sheet 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 edge. 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 steel pipe production line.
1.2 Forming inspection: 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 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.
1.3 Pre-welding inspection: After adjusting and recording the parameters of the forming unit, the pre-welding inspection mainly determines the specifications and positions of the internal and external burr cutters, resistors, 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 a tape measure or special equipment, and quickly measured and recorded.
1.4 In-welding inspection: During welding, focus on the values of the main parameters such as welding power, welding current voltage, and welding speed. Generally, the corresponding sensors or auxiliary instruments in the unit directly read and record. According to the relevant operating procedures, ensure that the main welding parameters meet the requirements of the process specifications.
1.5 Post-welding inspection: Post-welding inspection needs to pay attention to welding phenomena such as welding spark state and post-welding burr morphology. Generally, the weld color, spark state, internal and external burr morphology, hot zone color after deburring, and wall thickness variables at the extrusion roller during welding are all key inspection items. It is mainly based on the operator's actual production experience, and the naked eye monitors and supplements the relevant comparison charts to quickly measure records, and ensure that the relevant parameters meet the requirements of the process specifications.
1.6 Metallographic testing: Compared with other testing links, metallographic testing 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 achieve rapid evaluation.
1.7 Large sample inspection: According to the small sample inspection data, the pipeline is further refined, the relevant parameters are adjusted, and the requirements of the process specifications are met. After that, a steel pipe sample of a specified size needs to be taken for a small sample processability test. The process performance test includes flattening test, bending test, flaring test, curling test, torsion test, longitudinal pressure test, unfolding 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.
1.8 Full-line inspection: All the above-mentioned inspections are carried out according to the relevant specifications or standards, so it is inevitable that missed inspections will occur. To ensure the quality of finished welded steel pipes, special attention should be paid to the application of online non-destructive testing technology. In the production of welded steel pipes, the commonly used non-destructive testing methods include 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 the 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 the welding quality, ensure that there is no missed inspection, and isolate the welded steel pipes with excessive defects in time.
2. Online rapid assessment and diagnosis of weld quality
The rapid assessment of online weld quality is based on the rapid detection of the above-mentioned processes, and it can be quickly determined by comparing the process specifications of the relevant processes. Due to the differences in pipe specifications, forming processes, welding methods, technical requirements, and differences in equipment processes, production processes, and technologies of various enterprises, the specific acceptance scope of the process specifications of each relevant process needs to be determined in combination with the actual situation of each pipeline. In general, the main influencing factors of weld quality are the consistency of the temperature of the inner and outer edges of the plate and the matching of the extrusion amount and the heating temperature.
2.1 Rapid assessment and diagnosis in the initial adjustment stage: The main assessment indicators in the initial adjustment stage include dimensional variables (such as plates, tubes, gaps, extrusion volume, component positions, heights, and angles, etc.), instrument variables (molding liquid conditions, power, current voltage, and speed, etc.) and visual variables (plate connection methods and welding forms, etc.). Dimensional variables and instrument variables can be directly judged by comparing the measured values according to the numerical range required by the actual process specifications. Visual variables generally require the operator to compare the relevant descriptions or reference drawings during processing and make a rapid assessment and diagnosis based on the operator's experience.
2.1.1 Rapid assessment and diagnosis of welding sparks: Generally, a welding state without a large number of sparks and no darkening is a normal state. Darkening can be diagnosed as too small welding power or too fast welding speed; a large amount of splashing can be diagnosed as too large welding power or too small distance between the welding point and the extrusion point or welding angle.
2.1.2 Rapid assessment and diagnosis of welding burrs: The weld just out of the extrusion roller is orange-red. Red and white can be judged as too high temperature (power), and dark red can be judged as too low temperature (power). The weld is straight and uniform, the burr width is large, the height is small, the top is shiny and smooth, and the convex points with slight discontinuities on the line can be judged as moderate temperature and extrusion. According to whether the size of the burrs protruding inside and outside the weld is similar, it can be judged whether the heating of the edge of the material is consistent. If the outer protrusion of the weld is thicker, the heating temperature of the outer edge is higher than that of the inner edge; conversely, the temperature of the inner edge is higher. When the melt-extruded by the outer burr is not in the middle or the inner burr is intermittently split or cracked, and the tool position is normal, it can be judged that the plate joint has a wrong edge.
2.1.3 Rapid assessment and diagnosis of HAZ color: After removing the external burrs, there is a clear and continuous blue straight thin line on each side of the heat-affected zone. The color in the area between the two lines gradually fades and the axial uniformity is used as the assessment standard. The uniform blue color of the HAZ indicates that the welding temperature is too high; the lighter color indicates that the welding temperature is too low. The width or shape of the external weld after the burrs are removed changes, which can be inferred as the wrong edge of the plate.
2.2 Rapid assessment and diagnosis of small sample testing
2.2.1 Rapid assessment and diagnosis of fusion line:
Adverse consequences Thick fusion line The welding temperature is too high, and the decarburization of the metal surface increases. In most cases, it is caused by insufficient extrusion pressure. Obvious gray spots or oxide inclusions are often produced in the center of the fusion line. Causes of poor shape diagnosis Thin fusion line Extrusion pressure is too large, and the molten metal is squeezed out excessively. The weld is prone to cold welding and flattening test failure Irregular fusion line High unbalanced extrusion pressure There are fusion lines tilted in different directions or S-shaped fusion lines, complex thermal deformation, and high internal stress The fusion line has oxide inclusions or gray spots. The parallelism of the plate edge is not good or the extrusion pressure is too small so that the oxidized metal surface layer of the plate edge cannot be effectively squeezed out. Gray spots or oxide inclusions often become the crack source of weld cracking.
2.2.2 Rapid evaluation and diagnosis of welding flow line: The welding flow line is the most important metallographic feature in weld quality evaluation. It is a special shape of the crystalline structure formed by the extrusion of partially molten or semi-molten metal under welding conditions. It is a comprehensive reflection of factors such as extrusion force, extrusion direction, input heat, and welding speed during welding. There is no unified standard for the rise angle of streamlines in various countries.
Adverse consequences: The streamline angle is too large. The extrusion pressure is too large during welding. The larger extrusion pressure can squeeze out more molten metal, making the metal welding of the plate edge poor and prone to cold welding. Causes of bad shape diagnosis: The streamline angle is too small. The extrusion pressure is too small, the streamline display is unclear, and even the fusion line in the middle of the weld cannot be seen. It is often accompanied by more oxide inclusions, which become the crack source of weld cracking. The unbalanced extrusion pressure can easily cause the streamlined shape to change. Some rise angles are too large and the streamlines are very thick; some rise angles are too small, the streamlines are thin and the display is unclear.
If the plate edges are not parallel, it is easy to produce misalignment on the weld, resulting in unidirectional loss of weld metal and stress concentration, and the probability of defects in the weld will also increase. The streamline angle is asymmetric. The plate edge parallelism is not good and it is easy to have a positive "V" shape and an inverted "V" shape. If the plate edges are not parallel, the high-frequency voltage distribution is uneven, the local temperature difference is significant, and the plate edges cannot be synchronously contacted to achieve tight welding.
When a positive "V" shape appears on the edge of the plate, the inner edge of the weld should contact the outer edge, so the current density of the inner edge should be larger, and the heating temperature should also be higher than the outer edge. Under the same extrusion pressure conditions, the metal streamlines rise angle of the inner wall that contacts first is larger, while the metal streamline rise angle of the outer wall is smaller, and in severe cases, no streamline is even displayed.
On the contrary, when an inverted "V" shape appears on the edge of the plate, the outer burr is larger than the inner burr, and its metal streamline rise angle is significantly larger than that of the inner wall of the welded steel pipe. The unreasonable parallelism of the plate edge may cause the edge of the rolled plate to bend, which makes it easy to make the edge wavy and increases the tendency to form gray spots. At the same time, the weld may be dislocated during forming and continue to the welding point, which will cause the solidifying weld metal to be welded or cracked.
2.2.3 Rapid assessment and diagnosis of waist drum and other items: The width of the waist drum is related to the welding temperature, extrusion pressure, steel strip thickness, steel strip trimming, welding cycle, etc., and can be used as a reference indicator for weld quality assessment.
2.3 Rapid assessment and diagnosis of large sample and full-line inspection stages: Large sample and full-line inspection are generally carried out according to the inspection standards specified in the product's technical requirements. The operator can quickly complete the corresponding assessment and diagnosis by visual inspection or recording relevant inspection data. The focus of non-destructive testing assessment and diagnosis in full-line inspection is the defect calibration and standardized operation of the equipment. If quality problems are found in these two stages, the relevant departments such as design, process, and quality should be asked to comprehensively analyze the causes of the defects. If necessary, the possible problems in the design links such as raw materials, forming and welding should be considered comprehensively, and the root cause analysis should be made based on the actual production. Various measures including design optimization and process optimization should be taken to eliminate the quality defects that may occur at this stage.
3. Integration, optimization, and prospect of system structure
The online weld quality rapid assessment and diagnosis system of high-frequency straight seam welded steel pipe can be divided into 4 stages: preliminary machine adjustment assessment and diagnosis, small sample assessment and diagnosis, large sample assessment and diagnosis, and full-line assessment and diagnosis. Among them, the preliminary adjustment stage ensures that the values of each process control point meet the requirements of the corresponding process specifications; the small sample evaluation stage is to further optimizes the adjustment data according to the metallographic test data. If the small sample test data after the preliminary adjustment meets the process specification requirements, mass production can be started directly. Otherwise, further fine-tuning is performed within the specification range of the preliminary adjustment until the requirements are met; the large sample evaluation stage focuses on the verification of process performance such as weld strength and toughness. If it does not meet the relevant requirements, after excluding accidental factors, it is necessary to conduct a full-link cause analysis of design, production, and testing, and supplement or improve relevant design equipment or process parameters to ensure that all subsequent production stages meet the requirements; the full-line inspection stage is more focused on monitoring the quality of the weld, preventing welding defects caused by uncertain factors and marking and isolating them to ensure that the quality of the welded steel pipes shipped is all qualified.
In actual production, generally only when a certain specification of welded steel pipe is produced for the first time, the initial adjustment, fine adjustment, and repeated adjustment are carried out in the whole stage until the requirements are met, and then the large sample inspection is confirmed, and the full-line inspection and monitoring measures are taken to ensure the quality of the weld. With the continuous accumulation of actual production experience, when subsequently mass-producing the same or similar pipes that have been produced before, the previously recorded control data is repeated or imitated, and the machine adjustment can often be completed in one stage. The subsequent small samples, large samples, and full-line evaluation stages are more of a repeated confirmation or real-time monitoring role, and the actual machine adjustment and production efficiency advantages are more obvious.