Preventive Measures for Defects of Stainless Steel Pressure Vessel Heads

In the process of pressing the stainless steel pressure vessel head, the force is complex, and various defects are prone to occur. According to the reasons for the formation of different defects, taking corresponding preventive measures is an important link to ensure the quality of the head.
1. Preventive measures for crack defects Different measures are taken according to different situations of stainless steel pressure vessel head cracks. The cracks in the straight edge section are mainly controlled by the speed of the hemming, the pressure, and the punching speed; the cutting process is strictly controlled, and the edges of the blank are polished and smoothed to prevent Port cracks; welds and heat-affected zone cracks, it is necessary to strictly control the welding process parameters, slow down the cooling rate, appropriately increase the shape factor of the weld, and use low-current multi-layer multi-pass welding as much as possible to avoid cracks in the center of the weld. Prevent undercut, control welding height, and conduct reasonable heat treatment on the weld area, etc.
2. Preventive measures for bulging defects Measures to prevent bulging include: adopting a secondary stretching process to reduce residual stress; adopting a tapered edge blanking ring; improving the heating quality of the blank to make the blank heated evenly. Measures taken to prevent overburning include: using electric furnaces, gas furnaces and oil furnaces with a uniform temperature field, placing the furnace head in the center as much as possible, uniformly distributing the thermocouples of the electric furnace and the nozzles of the oil and gas furnace, and checking the temperature field in the furnace. Check regularly. To prevent the occurrence of wrinkles, the following measures should be taken: adding pressure rings, especially the pressure vessel factories with self-made heads, lack of professional equipment; control the gap between the upper and lower molds; control the processing technology, and the materials that are not easy to form can be stretched multiple times take shape.
3. Preventive measures for thinning and exceeding defects The control of thinning is mainly in the manufacturing process. For the overall thinning, it is necessary to consider whether the thickness of the ingredients is sufficient, and whether the size of the billet can ensure sufficient blank holder width; the control of local thinning should ensure that the pressing The correctness of drum technology and the proficiency of workers.
4. Preventive measures for scratch defects In order to reduce scratch defects, before pressing the head, the surface of the blank should be cleaned to avoid attaching hard objects to scratch the surface during the stamping process; the upper and lower molds should be cleaned regularly to reduce oxide scale adhesion. ; Regularly check the mold for damage.
5. Preventive measures for cracking and pit defects The measures for cracking control are: strictly control the quality of the material, the mechanical properties, chemical composition, metallographic structure and process performance indicators of the material comply with the technical standards; workers are proficient in the processing technology and control well For stamping speed and pressure, lubricating oil is often applied to the contact surfaces of the upper and lower pressure rings to prevent the head from cracking. To prevent the generation of pits, the main purpose is to ensure that the upper die is in the center of the blank holder to prevent eccentricity. There must be measuring tools on site, and do not rely on eye estimation.

Analysis of Repair Measures for Defects of Stainless Steel Pressure Vessel Heads
During the processing of stainless steel pressure vessel heads, the occurrence of defects is inevitable. Although some defects exceed the standard, their safety performance will not be affected much after repair. In line with the principle of energy saving and consumption reduction, on the premise of ensuring the quality of the head, it should be repaired as much as possible. Some defects cannot be repaired, or the mechanical properties of the head cannot be guaranteed after repair, and they must be scrapped. Crack defects can be eliminated by grinding. Use ultrasonic non-destructive testing to determine the position and length of the defect, and then use a grinding wheel to grind it. First, start grinding from both ends of the crack, grind the defect position into a U-shaped groove, and then carry out surface inspection to check whether the defect is completely removed, until it is confirmed that it is completely removed. When the depth exceeds 5% or 2mm of the steel thickness, repair welding should be carried out. The bulge defect can be repaired by hydraulic topping, but serious bulge deformation will cause uneven stress level in each area of the head, and uneven mechanical properties of each part of the head, which is not suitable for repair. Over-burning defects may lead to changes in the metallographic structure, deterioration of the mechanical properties of materials, and difficulty in defining overheating, over-burning, and burning. It is recommended that the head be scrapped. Slight wrinkles can be removed by grinding; scratches and local pits can be ground and welded according to the situation; the pits can not be repaired and should be scrapped.

in conclusion
Defects such as cracks, bulging, over-burning, wrinkles, thinning and exceeding the standard, scratches, cracks, and pits will occur during the manufacture and use of stainless steel pressure vessel heads. From the main causes of defects, it can be summarized as follows: material control is not strict; process execution is not in place, stamping speed and pressure are improperly controlled, mold eccentricity, and incorrect welding parameters are all in this category; equipment does not meet the requirements for processing heads, including The temperature field of the heating furnace is uneven, and the mold is damaged. In order to reduce the occurrence of these defects as much as possible, the following points should be done in the manufacture of the head: strictly control the material and personnel; formulate a reasonable process; strengthen the training of operators; strictly implement the process discipline; carry out regular inspection of the processing equipment ; Reduce the influence of external factors.