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Steel pipes: How to distinguish inferior steel pipes

Views: 0     Author: Site Editor     Publish Time: 2020-10-28      Origin: Site

Nowadays, the demand for spiral steel pipes is increasing. In order to win the initiative in the competition, many manufacturers produce and sell unqualified spiral steel pipes in quality. Here is how to distinguish spiral steel pipes,Prevent you from being deceived in the purchase.

1. The actual size is about one specification smaller than the nominal size. The dealer purchases goods by actual weight, and the theoretical weight is delivered to earn metal and obtain huge profits.

2. The intensity is low.

3. High rate of unqualified chemical composition. The main reason is that the raw materials purchased by the small spiral steel pipe factory are unqualified, and the poor chemical composition is unqualified.

 When purchasing spiral steel pipes, first look at the appearance size. You can use a vernier card to simply measure whether the actual size is smaller than the indicated size (generally spiral steel pipes are rolled with specification marks) by about one specification or more. At the same time, some fake and inferior spiral steel pipes deceive people's vision by smashing the mouth. Therefore, the end face of the steel pipe is oblong, while the end face of the regular steel should be basically round. Second, from the perspective of surface quality, the fake spiral steel pipe is due to Rolled with unqualified raw materials, its surface quality is poor, often with defects such as scars, and overall roughness. At the same time, some small steel mills have a reddish surface due to insufficient heating temperature and rolling speed; third, the regular spiral steel pipes are mostly packaged in large bundles when they leave the factory, and the bundles of steel are hung with metal signs corresponding to the physical objects. Manufacturer, steel grade, batch number, specification and inspection code, etc. Because of the crude production conditions and no large-scale hoisting equipment, the fake and inferior steel bars are mostly packaged in small bundles (about ten bundles) or in bulk, without metal signs and quality guarantees.

Many friends will ask why spiral steel pipes develop rapidly? Let me introduce to you.

When the spiral steel pipe is blasted, because the normal stress and the composite stress on the weld are relatively small, the blasting opening generally does not originate from the spiral weld, and its performance is higher than that of the straight seam welded pipe. But whether it is the yield pressure or the burst pressure, the spiral steel pipe is lower than the longitudinally welded pipe. According to the test indications of relevant research institutions, spiral welded pipe and longitudinal welded pipe are of the same level, but spiral welded pipe has higher impact toughness.

Moreover, according to the submerged arc welding process, each weld should have an arc ignition point and an arc extinction point, but each longitudinal welded pipe cannot meet this premise when welding the circumferential seam, so there may be an arc extinction point. More welding defects. When the pipe receives internal pressure, two main stresses are usually generated on the pipe wall, namely radial stress δ and axial stress δ. As the diameter of the steel pipe increases and the grade of steel used increases, the tendency of ductile fracture to steadily expand will increase.

Because the radial stress is a large stress on the large diameter spiral steel pipe, the weld is subjected to a large load when it is in the direction of the vertical stress. According to the measurement results, the fatigue strength of spiral welded pipes is the same as that of seamless pipes and resistance welded pipes. The test data is distributed in a unified area with seamless pipes and resistance pipes, and is higher than that of ordinary submerged arc longitudinal welded pipes. In the actual control process, the steel pipe is subjected to random alternating loads. Solving the low cycle fatigue strength of steel pipes is of great significance for determining the service life of pipelines. Under the same working pressure, the wall thickness of spiral welded pipe with uniform pipe diameter can be smaller than that of straight seam welded pipe. The trend of pipeline development is large diameter and high strength.

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