Longitudinal welded steel pipe anti-rust maintenance and inspection methods

The longitudinal welded steel pipe has a simple production process, high production efficiency, low cost, and rapid development. The strength of spiral welded pipes is generally higher than that of straight seam welded pipes. A narrower blank can be used to produce welded pipes with larger pipe diameters, and a billet with the same width can be used to produce welded pipes with different pipe diameters. However, compared with the straight seam pipe of the same length, the weld length is increased by 30-100%, and the production speed is lower. Therefore, most of the smaller diameter welded pipes adopt straight seam welding, and the large diameter welded pipes mostly adopt spiral welding.

Longitudinally welded steel pipe derusting and maintenance method:
But the maintenance of longitudinally welded pipe equipment has become a headache. Longitudinally welded pipe equipment plays an important role in life and work. Generally, the surface of longitudinally welded pipe fittings is required to reach the nearly white level (Sa2.5). The practice has proved that the commonly used epoxy, vinyl, phenolic, and other anticorrosive coatings for longitudinally welded pipe fittings can be almost removed by using this grade of rust removal. All the oxide scale, rust, and other dirt are removed, and the depth of the anchor pattern reaches 40~100μm, which fully meets the requirements of the adhesion of the anticorrosive layer and the steel pipe. The spray (projection) rust removal process can be achieved with lower operating costs and stable and reliable performance. Near the white level (Sa2.5 technical conditions. When the rust of the longitudinally welded pipe occurs, it should be treated by the rust removal method and method to ensure the performance and performance of the longitudinally welded pipe. It can be used in different industries and fields and is suitable for the construction industry. Make important contributions and roles.

Spray (throw) abrasive for longitudinal welded steel pipe:
To achieve the ideal rust removal effect, the abrasive should be selected according to the surface hardness of the longitudinally welded pipe equipment, the original rust level, the required surface roughness, and the coating type. For single-layer epoxy, two-layer, or three-layer polyethylene coating Layer, using a mixed abrasive of steel grit and steel shot can easily achieve the ideal rust removal effect. Steel shot has the effect of strengthening the steel surface, while steel grit has the effect of etching the steel surface. A mixed abrasive of steel grit and steel shot (usually the hardness of steel shot is 4050HRC, and the hardness of steel grit is 5060HRC. It can be used on various steel surfaces. Even if it is used on the surface of grade C and D corrosion, the rust removal effect is also very good.

Derusting speed of longitudinal welded pipe:
That is, the total kinetic energy E of the abrasive applied to the steel pipe per unit time and the kinetic energy of the single-grain abrasive E1 The rust removal speed of the steel pipe depends on the type of abrasive and the displacement of the abrasive. Where: m abrasive spray (throwing) amount; V abrasive running speed; m1 single-grain abrasive. The size of m is related to the crushing rate of abrasives, and the crushing rate directly affects the interest of surface disposal operations and the cost of derusting equipment. When the equipment is fixed, m is a constant, y is a constant, so E is also a constant, but because the abrasive is broken, m1 changes. Therefore, the abrasive with a lower loss rate should generally be selected, which will help improve the cleaning speed and length. The life of the blade.

Abrasive particle size and the ratio of the longitudinal welded pipe:
To obtain better uniform cleanliness and roughness distribution, the design of abrasive particle size and ratio is very important. Too much roughness will easily cause the anti-corrosion layer to become thinner at the peak of the anchor pattern; at the same time, because the anchor pattern is too deep, the anti-corrosion layer will easily form bubbles during the anti-corrosion process, which will seriously affect the performance of the anti-corrosion layer.

The high-strength impact of large-grain abrasives cannot be used alone. Too small roughness will cause the adhesion and impact resistance of the anti-corrosion layer to decrease. For severe internal pitting. It is also necessary to use small particles to polish away the corrosion products to achieve the cleaning effect. At the same time, a reasonable ratio design can not only slow down the abrasive wear on the pipe and nozzle (vane) but also greatly improve the utilization rate of the abrasive. Generally, the grain size of the steel shot is 0.81.3mm, and the grain size of steel grit is 0.41.0mm, of which 0.51.0mm is the main component. The sand shot ratio is generally 58. It should be noted that in actual operation, the ideal ratio of steel sand to steel shot in the abrasive is difficult to achieve. The reason is that hard and fragile steel sand has a higher crushing rate than steel shot. For this reason, the mixed abrasive should be sampled and tested from time to time during the operation. According to the particle size distribution, new abrasives should be added to the rust remover, and the amount of steel grit should be the main one.

Various inspection methods of longitudinal welded steel pipe:
 
At present, it is widely used to detect longitudinally welded pipes with magnetic powder. Generally, a magnetic inspection can only detect defects on the surface of welded pipes. Many problems cannot be well reflected, and they are usually judged based on experience. So the purpose is to use waves and rays together. Such inspection can sensitively detect the defects of the welded pipe, but there are also defects in this inspection method, and it is impossible to judge the material, shape, and size of the welded pipe.

The current inspection methods are all physical inspection methods, which can not only reduce the damage to the material but also accurately reflect the material defect problem and obtain good information. However, there are two sides to everything, and such a detection method is not reliable. It is still necessary to use your own experience to tell yourself the answer based on the customer's long-term use and purchase process. Also remind everyone to choose long-term welded pipes with a good reputation and a good reputation in the procurement process, which can also reduce losses.