Magnetic particle testing of main bolts of urea synthesis tower Liu Minhua, Daqing Petrochemical Company, Daqing 163714, Heilongjiang, China) The urea tower is subjected to high pressure of 24MP* and high temperature of about 200+. The top cover is fastened to the tower body with 12 bolts. These bolts are called main bolts. If one of the main bolts breaks due to defects, the force it bears must be distributed to the other main bolts, so that these main bolts are super The load operation, and therefore the quality inspection of the main bolt is of great significance to ensure the safe operation of the synthesis tower. 1Technical conditions and stress conditions 1.1 Technical conditions The heat treatment state of the plug is quenched and tempered - the metallographic structure is sorbite. 1.2 Stress conditions and defects The main bolts that are in service are mainly subjected to the tensile force along the axial direction. This force changes with the pressure inside the tower. The result of its action is the defect at the weakest point of the thread - the root of the tooth. And this defect is generally a transverse crack perpendicular to the axis of the bolt. 2 Determination of the detection process 21 Selection of magnetic powder and preparation of magnetic suspension Since the main bolt is phosphatized before use, after the production operation, the background color of the thread part is deep, and the light at the root of the tooth is dim, such as black and white. The red magnetic powder has a low contrast ratio and low detection sensitivity, and the result is not satisfactory. Therefore, the use of fluorescent magnetic powder to prepare magnetic suspension can better solve this problem. Fluorescent magnetic suspension with the formulation of the fluorescent magnetic suspension of the formula 1 name emulsifier 6FC) / g triethanolamine / g nitrite / g defoamer / g fluorescent magnetic powder / g preparation, first emulsifier and Stir well evenly, dilute with a little water, then add magnetic powder, triethanolamine, then add the balance of water, and finally add nitrite and stir evenly to dissolve completely. The longitudinal magnetic field is magnetized to it. 2.3 Calculation of magnetizing current In order to detect small fatigue crack defects, sufficient sensitivity must be ensured; however, if the sensitivity is too high, it will cause false display, hinder the judgment of real defects, and the probability of misjudgment will increase, so it must be accurately Calculate the magnetizing current. The main bolt (hereinafter referred to as the workpiece) is made of 34CrMA steel. This material is a kind of special steel. If the empirical formula is used to calculate the magnetized ampoule number, the error is large, so the standard test piece is used to determine its magnetization field. When working the magnetization field HP>H! m, the magnetization work point is selected! When the m value is on the right side, the magnetic permeability of the material of the lower part of the workpiece defect decreases as the magnetization field increases. Because of B;/! And d-), so the reluctance Bm of the material under the defect becomes larger, so that the leakage magnetic field at the defect is strengthened, which is advantageous for the detection of defects. The standard specification is used to make the magnetization field close to the saturation region, taking =600e. This is the effective magnetic field strength of the workpiece surface. Since the workpiece is longitudinally magnetized, there is a demagnetizing field inside, so the actual magnetic field strength must be greater than the magnetic proximity of the A2 type test piece after the bolt is quenched and tempered, so the magnetization current value corresponding to the A2 display is 11. For the groove depth of the test piece, t is the thickness of the test piece. 2.4 Actual inspection of the workpiece In the actual work, the DZ-2000 magnetic flaw detector is used to longitudinally magnetize the pre-treated main bolt, the magnetizing current I=6A, and the number of ampere-turns is IK=9360. The continuous method is used. The magnetized side was burned with a fluorescent magnetic suspension and observed with a black light. In order to ensure the effective observation of the workpiece, the ambient light is specially treated so that it does not affect the observation and does not hinder the operation. During the test, it was found that a threaded portion of a bolt had a distinct fluorescent deposit, the magnetic trace was wiped off, the workpiece was demagnetized, re-magnetized, and the magnetic suspension was observed, and there was still a fluorescent display, thus judging that it was a true display of the defect. Then, using the ultrasonic straight probe for re-examination, it is a crack, thus preventing the accident. 3 Conclusions For longitudinal magnetization, the magnetization specification is generally selected according to the empirical formula method. However, due to the special material of the main bolt, the empirical formula will be biased. The magnetic characteristic curve is combined with the standard test piece to formulate the process, which basically meets the testing requirements. . 2.2 Selection of magnetization method In order to effectively detect the transverse crack on the surface of the bolt, a longitudinal magnetic field parallel to the axial direction must be generated in the interior, and thus the coil is generated by the energized coil. Fiberglas Mesh also names Fiberglass Cloth, Fiberglass Fabric, Fiberglass Wall Mesh, is made by C-glass or E-glass Fibers woven roll. by C-glass or E-glass fibers woven roving as its basis material, and then treated with Acrylic Acid Copolymer liquid. An ideal construction engineering material, Strength retention rate. Colorful Fiberglass Wire Mesh,Mosaic Tile Fiberglass Mesh,Fiberglass Scrim Mesh,Fiberglass Mesh Cloth HEBEI TUOHUA METAL PRODUCTS CO.,LTD , https://www.penetting.com
Magnetic particle testing of main bolts of urea synthesis tower Liu Minhua, Daqing Petrochemical Company, Daqing 163714, Heilongjiang, China) The urea tower is subjected to high pressure of 24MP* and high temperature of about 200+. The top cover is fastened to the tower body with 12 bolts. These bolts are called main bolts, if one of the main screws