Manufacturing defect

　　The stainless steel drying cylinder is manufactured by using the GTAW single-sided welding and double-sided forming process to weld the longitudinal seam of the cylinder. There will be insufficient welders in the manufacturing process, which leads to the failure of the stability of the process, and the longitudinal welding seam is not formed ideally or even welded. Penetration and roots are not fused from time to time. After the welding of the longitudinal seam of the stainless steel drying cylinder is completed, rounding is required. The inner wall of the stainless steel drying cylinder is extruded by the extrusion device to achieve the purpose of rounding. This will form a compressive stress in the longitudinal seam of the cylinder and a tensile pressure in the circumferential direction. It is easy to cause new defects in the weld due to the applied stress. The plate of the stainless steel drying cylinder body is a coiled plate, and the material should be re-inspected during the first regular inspection.

　　Defects during use

　　There is tensile stress in the weld area of the stainless steel drying cylinder. The internal stress is caused by the alternating temperature and pressure. The cylinder body is not synchronized with the rotating central axis. It is easy to cause torque. The stainless steel is particularly sensitive to the medium containing chloride ions under the stress environment, and the chloride ion penetrates into the stainless steel. Passivation film pores, ionization and dissolution reactions occur, causing local corrosion of the drying cylinder. In the work of the ironing machine, the drying cylinder drives the traction belt to move in a circumferential direction. The belt and the drying cylinder move relative to each other. The friction surface of the relative movement is easy to wear and reduce the wall thickness.

　　Inspection

　　Non-destructive testing: the positioning of the longitudinal welding seam. After the stainless steel cylinder is rounded and polished during the manufacturing process, the outer surface is smooth. In addition to the lack of holes on the cylinder, it is difficult to locate the longitudinal weld of the cylinder. Endoscope to locate the longitudinal weld.

　　Penetration testing The stainless steel drying cylinder is subjected to alternating stress, and the surface is in frictional conditions for a long time. 100% penetration testing shall be carried out on the longitudinal welds, the circumferential welds connecting the head and the cylinder.

　　Radiographic inspection: The endoscope can conduct a macro inspection of the corrosion condition of the inner surface of the stainless steel drying cylinder and the quality of the weld in the lens coverage. However, the coverage area of the lens is limited, and the welding seam in the area not covered by the lens needs to be spot-checked by radiographic inspection.

　　Thickness measurement: The head and the cylinder adopt an overlapping structure, the straight side section must be closely attached to the inner wall of the cylinder, and the calculated thickness of the head with a length greater than or equal to 3 times. In order to ensure that the straight side section fits closely with the cylinder body, the straight side section of the head needs to be machined according to the size of the inner diameter of the cylinder. The processing will cause the thickness of the straight side section to be reduced. The straight side section of the stainless steel drying cylinder head should be regular The focus of thickness measurement during the inspection process. After the inner and outer surfaces of the stainless steel drying cylinder are polished, rounded, and polished, the thickness of the final weld is reduced, and the weld area is also a key area for thickness measurement.

　　Manufacturing aspect

　　After the inner and outer surfaces of the stainless steel drying cylinder are polished, rounded, and polished during the manufacturing process, the longitudinal welds are difficult to locate. It is recommended that the manufacturing unit permanently mark the position of the longitudinal weld on the head during the manufacturing process to facilitate later inspection and inspection.

　　Installation aspect

　　The installation of stainless steel drying cylinders involves two departments, one is the ironing machine manufacturing department, and the other is the department that installs the ironing machine for the user. Relevant departments should improve relevant regulations as soon as possible to delineate the boundaries of the responsibilities of the two departments in the installation process.

　　Using management

　　The lack of knowledge about the use of special equipment in the user unit often brings huge disasters. For the ironing machine, at the beginning of the start-up, a part of the steam will be condensed when the steam meets the low-temperature water in the drying cylinder, and an instantaneous pressure drop will occur in this area. The steam in the pipeline will increase the flow rate to fill. The driving force of the steam condensation process is steam The difference between the pressure and the saturation pressure of the water surface, the lower the water temperature, the greater the driving force of the condensation process, and the use of ironing machines in winter is most likely to cause explosions. The user unit should strengthen the training and management of the stainless steel drying cylinder operators, and frequently check and repair the piping system, safety accessories and instruments, and drainage equipment.

　　As a pressure-bearing equipment, the stainless steel drying cylinder has its own special structure and working environment, which will often produce stress corrosion, fatigue failure and wear and other defects during operation. Therefore, the inspector should formulate effective inspection measures to ensure the safe operation of the equipment.