The rapid assessment of online weld quality is based on the rapid detection of the above-mentioned processes. 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 factors affecting 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.
1. Rapid assessment and diagnosis in the initial machine adjustment stage:
The main assessment indicators in the initial machine adjustment stage include dimensional variables (such as plate, tube, gap, extrusion amount, component position, height, and angle, etc.), instrument variables (forming liquid condition, power, current voltage, and speed, etc.) and visual variables (plate connection method and welding form, 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 quick assessment and diagnosis based on the operator’s experience.
1.1. Quick assessment and diagnosis of welding sparks:
Usually, the welding state without a large amount of sparks and no darkening is normal. When it is dark, it 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 the distance between the welding point and the extrusion point or the welding angle is too small.
1.2. Quick assessment and diagnosis of welding burrs:
The weld just out of the extrusion roller is orange-red. The red and white color can be judged that the temperature (power) is too high, and the dark red color can be judged that the temperature (power) is too low. The weld is straight and uniform, the burr width is large, the height is small, the top is shiny and round, and the convex points with slightly discontinuous distribution on the line can be judged as moderate temperature and extrusion. According to whether the size of the burrs on the inner and outer sides of the weld is similar, it can be judged whether the heating of the material edge 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 molten material extruded by the outer burr is not in the middle or the inner burr is intermittently forked or cracked, and the tool position is normal, it can be judged that the plate is misaligned.
1.3. Quick evaluation and diagnosis of HAZ color:
After removing the outer burr, there is a clear and continuous blue straight thin line on both sides of the heat-affected zone. The evaluation standard is that the color in the area between the two lines gradually fades and the axial uniformity is consistent. 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 outer weld after the burr is removed changes, which can be inferred as a misalignment of the plate.
2. Quick evaluation and diagnosis of small sample detection:
2.1. Quick evaluation and diagnosis of fusion line:
At present, there is no unified regulation on the control of fusion line width in various countries. The existing standards are generally the internal control standards of each enterprise. my country’s welded pipe industry once believed that it was most appropriate to control the fusion line width to 0.02-0.11 mm. The evaluation standard for fusion line deflection or distortion was S≤t/10. Generally, a single inclusion length of ≥0.05t in the fusion line area and inclusions in the 15% area close to the inner and outer surfaces were not allowed. The specific acceptance standards can be formulated by each enterprise after discussion and analysis based on its production practice. The fusion line shape is closely related to the welding input energy, welding extrusion force, welding speed, and other parameters, and is an important indicator of weld quality.
Adverse consequences Thick fusion line Welding temperature is too high, metal surface decarburization increases, in most cases due to insufficient extrusion pressure Obvious gray spots or oxide inclusions are often produced in the center of the fusion line Causes of bad shape diagnosis Thin fusion line Extrusion pressure is too large, molten metal is squeezed out excessively Welds are prone to cold welding and flattening test failures Irregular fusion line Highly unbalanced extrusion pressure There are fusion lines or S-shaped fusion lines tilted in different directions, thermal deformation is complex, and internal stress is high 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. Rapid assessment and diagnosis of welding flow line: The welding flow line is the most important metallographic feature in weld quality assessment. It is a special shape of the crystalline structure formed by the extrusion of locally molten or semi-molten metal under welding conditions. It is a comprehensive reflection of factors such as extrusion force size, extrusion direction, input heat, and welding speed during welding. There is no unified standard for the rise angle of streamlines in various countries. At present, each country uses its internal control standard. There should be no hook-shaped segregation in the welding streamline area, and the distance between the streamline centerline and the wall thickness centerline should be less than t/5. Each welded pipe enterprise can determine the evaluation standard suitable for its product characteristics according to its production practice.
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 it is easy to produce cold welding. Cause the diagnosis of bad shape, The streamline angle is too small. The extrusion pressure is too small, and the streamline display is not clear, or even invisible. The fusion line in the middle of the weld is often accompanied by more oxide inclusions, which becomes the crack source of the 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 not clear.
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. Streamline angle asymmetry. If the plate edges are not parallel, 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 will be uneven, the local temperature difference will be significant, and the plate edges cannot be synchronously contacted to achieve tight welding.
When the plate edge appears in a positive “V” shape, the inner edge of the weld should be in contact with 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 rise angle of the inner wall metal streamline that contacts first is larger, while the rise angle of the outer wall metal streamline is smaller, and in severe cases, no streamline is even displayed.
On the contrary, when the plate edge appears in an inverted “V” shape, 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 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 extend to the weld point, which will cause the solidifying weld metal to deviate or crack.
2.3. Rapid assessment and diagnosis of waist drum and other items:
The waist drum width is related to 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. Some articles have proposed that the ideal waist drum shape is the center width hn= (1/4~1/3) t, and the inner and outer wall widths h0≈hi≈(1.5~2.2)hn. Similarly, each welded pipe enterprise can determine whether to include it in the assessment content or specify the assessment scope based on its production reality.
2.4. Rapid assessment and diagnosis of large sample and full line inspection stage:
The 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 the 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 during these two stages, the design, process, quality, and other related departments must be asked to conduct a comprehensive analysis of the causes of the defects. If necessary, the possible problems in the design links such as raw materials, molding, and welding should be fully considered and the root cause analysis should be conducted based on the actual production. Various measures including design optimization and process optimization should be taken to eliminate quality defects that may occur at this stage.
Post time: Jun-12-2024