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Five questions about steel pipes

1. How to classify the defects and quality of finished steel pipes?
Defects and quality problems of finished steel pipes are checked according to their inspection methods.
1) the chemical composition found in chemical analysis is not qualified.
2) the physical properties, mechanical properties, process properties and metallographic structure of the test found that the performance and organization failed;
3) size, shape and surface defects detected by size measurement and surface inspection. If the section size is too poor, the shape is not right, the length of the steel pipe is very poor, and other surface defects. The surface defects here refer to the surface defects caused by rolling process. This kind of defect has different characteristics in different products.
The surface defects can be divided into the reasons for their production.
1) the surface defects caused by smelting and ingots are left on the steel pipes because of the unclean surface of the billet.
2) surface defects caused by rolling process are mostly produced on the surface of steel pipes. Such as straightening crack, internal crack and so on.
2. What steel pipe defects can be found in fracture inspection?
Fracture inspection is one of the methods to determine the quality of steel pipe. The fracture specimen can check the defect of the steel pipe with the transverse macrostructure. The fracture can directly show the defects such as white spots, inclusions, bubbles, internal cracks and shrinkage holes in tapping. By identifying the size and characteristics of the grain on the fracture surface, the overheating or overheating of the steel pipe can be determined. The fracture characteristics of the steel pipe (ductile fracture and brittle fracture) can be determined and the fracture cause of the steel pipe (part) can be judged, such as fatigue fracture and stress fracture.
The fracture types are: ductile fracture, brittle fracture, porcelain fracture, lamellar fracture, (coating) fracture, stone fracture and graphite fracture.
In the course of use, broken zero, parts and broken pieces of pieces caused by some reason in the production and manufacturing process, as well as the fracture of test sample for tensile force and force, no longer need any preparation processing, can be directly observed and tested. Direct observation on these natural surfaces can obtain direct capital. Material.
According to the variety of steel pipe and the different inspection requirements, the fracture test specimen should be heat treated in different ways before breaking. According to the different heat treatment methods, the fracture can be divided into annealing fracture and quenching and tempering fracture.
3. What are the contents of the finished product size and shape inspection of the steel pipe?
The inspection contents of the size and shape of the steel pipe are as follows:
1 check whether the section size of the steel pipe exceeds the deviation specified in the corresponding standard (including the withdrawal of square steel and the roundness of round steel).
2 check whether the length of the steel pipe meets the delivery length stipulated by the corresponding standard.
3 check whether the shape of the steel pipe has obvious bending (sickle or wave bending).
4 measure the bending degree and total bending degree of the steel pipe.
5 what is the size super difference? What is the unequal thickness of the thick and thin? What is the wrong shape?
The tolerance of dimension is the allowable deviation of the size of the workpiece. These include the upper limit and the lower limit of the specified size.
The uneven thickness is the phenomenon that the thickness of the steel pipe is different from each other on the cross section and longitudinal section. The uneven thickness of the steel pipe is called the uneven thickness of the wall. In fact, the thickness of a piece can not be equal everywhere. In order to control this inhomogeneity, some standards specify the three point difference of the section, the same plate difference, and the standard of the steel pipe, which stipulate the allowable range of uneven wall thickness.
The geometric shape of the cross section of the rolled material is not positive. This kind of defect is varied according to the variety of the rolled material, such as square steel, flat steel, six angle steel and six sides. In a broad sense, bending, twisting, breaking waves and lacking meat are all wrong in shape.
4. What is the degree of roundness? What is the nominal size and the actual size? What is the tolerance?
Circular cross section rolling materials such as round steel and round steel pipe appear on the same section; two different diameters are called roundness. The degree of roundness is expressed by the difference between the maximum and minimum diameters on the same section.
Nominal size refers to the nominal size specified in the standard, which is the desired size desired in the production process. The actual size obtained in production is called actual size, and the actual size of the steel pipe is usually larger than or smaller than the nominal size.
Because the actual size of the steel pipe is hard to reach the nominal size, the standard stipulates that there is a allowable difference between the actual size and the nominal size, which is called tolerance. Negative difference is called negative bias, positive value is called positive deviation.
5. What is the delivery length?
The delivery length of steel pipes is as follows:
1. Usually the length is also called the indefinite length. Where the length of the steel pipe is within the standard limits and has no fixed length, it is called the normal length. For example, the usual length of high quality steel is 2-6mm.
2. The length of the length of the length of the fixed length is fixed to the fixed length according to the order. For example, the fixed length of rail is 12.5mm and 25mm. The length of the fixed length steel pipe also permits the positive deviation of the length.
3. The length of the length of the steel pipe is cut into the integral multiple equal to the order length. If the length is 1000mm, the double ruler is 2000mm, and the three cup ruler is 3000mm. The same standard or technical condition should also provide positive deviation and cutting allowance for double length.
4. The length of a short ruler is shorter than that of the standard, but not less than the minimum allowable length.
In addition, the length of the gauge is the development of the normal length, requiring the same length of the steel pipe in each bundle, allowing a certain deviation. China’s export steel pipes are mostly delivered on the same length.
Source: China Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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