Maintenance of elbows
Maintenance method of elbows
1. Elbows and elbows stored for a long time shall be inspected on schedule. The exposed processing surface shall be kept clean, and dirt shall be removed. They shall be stored in a clean and dry place indoors. Stacking or outdoor storage is strictly prohibited. Always keep the elbow dry and ventilated, keep the device clean and tidy, and store it according to the accurate storage method.
2. During installation, the elbow can be directly installed on the pipeline according to the connection mode, and installed according to the position used. Generally, it can be installed at any position of the pipeline, but it is necessary to facilitate the inspection of the operation. Note that the flow direction of the medium of the cut-off elbow should be from the bottom of the longitudinal valve flap to the top, and the elbow elbow can only be installed horizontally. When installing the elbow, pay attention to the leakproofness to prevent spillage and affect the normal operation of the pipeline.
3. When the ball valve, stop valve and gate valve of elbow are used, they are only used for full opening or full closing, and they should not be used for regulating flow, so as to avoid erosion of sealing surface and accelerated wear. The gate valve and upper thread stop valve are provided with back sealing device, and the hand wheel is screwed to the top position to prevent the medium from leaking from the packing.
Analysis on the causes of cracks in the process of bending pipe
Analysis on the causes of cracks in the process of bending pipe: the defects and protection microcracks produced in the medium frequency bending pipe will produce microcracks on the outside of the bend when the deformation temperature and deformation level exceed a certain level. Both of these conditions are related to the material of the bend. Under the similar forming conditions of low deformation speed and high tension resistance, all bending construction of the pipe bender may produce such data damage. In May, the domestic pipe bending market continued to decline. By the end of the month, there were signs of acceleration due to the impact of pipe bending processing price break. The social inventory of pipe bending continued to go through the process of de stocking, and the Langer composite index closed below the 140 level.
According to the forming conditions, the crack length can reach the austenite grain boundary which is perpendicular to the stress direction (longitudinal axis of the sub), so it is also perpendicular to the slag inclusion of the tube. After bending, the microstructure of the welded pipe is recrystallized by heat treatment, and the microcracks are transformed into crystal drag.
At present, compression bending is the most commonly used bending method in China
At present, compression bending is the most commonly used bending method in China. Most of the equipment used are general mechanical press or hydraulic press, and also have special bending press. The commonly used rolling and bending equipment is the rolling machine. According to the principle that a circle is determined by three points, the three roller plate rolling machine continuously bends the slab. The three roll rolling machine has two driving rolls and one pressing roll.
Adjust the up and down position of the press roll to change the relative distance between it and the drive roll. Since this year, the social inventory of elbows has been rising rapidly, reaching a record high of 21.92 million tons at the end of March. Due to the slow de stocking, there is a great pressure on the pipe bending market. Although April is the traditional peak season of pipe bending consumption, due to the high level of steel production and relatively weak demand growth, the contradiction between market supply and demand is intensified, coupled with high inventory, the price of pipe bending continues to decline.
During stretch bending, the plate is placed between the driving roller and the pressing roller, and the driving roller exchanges and rotates in the positive and negative directions to make the plate move back and forth. The plate can be bent into cylindrical surface, conical surface and hyperbolic surface with smaller curvature by adjusting the pressing roller to press it down gradually. One end of the pressing roller can be raised for easy unloading of the workpiece. In addition, there are four roll and multi roll rolling machines. The four roll rolling machine is used for rolling thick plate cylinder. The multi roll rolling machine with more than four rolls gradually bends the welded pipe into a complex profile with multiple pairs of rollers.
For the bending parts with high precision, large length and curvature radius, and small transverse dimension, the bending can be carried out on a special bending machine. In the process of bending pipe, the whole thickness of the plate is affected by the tensile stress, so it only produces elongation deformation. After unloading, the deformation caused by elastic recovery is small, which is easy to ensure the accuracy.
