Complete knowledge of welded pipe

We can also call the welded pipe a welded steel pipe. Its manufacturing process is to weld some steel plate profiles or some materials containing steel components into the shape of a steel pipe after crimping and forming. The production method of welded steel pipe is very simple, the production efficiency is high, and there are many types and specifications of it, and the cost of production is very small, but the only disadvantage is that compared with seamless steel pipe, its strength is higher lower than seamless steel pipe.

2. welded pipe Standards
Commonly used standards for spiral welded pipes
● Spiral seam submerged arc welded steel pipe (SY5036-83), used for pipelines for transporting oil and natural gas; spiral seam high frequency welded steel pipe for pressurized fluid transport (SY5038-83), welded by high frequency lap welding , Spiral seam high-frequency welded steel pipe for pressurized fluid transportation. The steel pipe has strong pressure bearing capacity, good plasticity, and is convenient for welding and processing;

● Spiral submerged arc welded steel pipes for low-pressure fluid transportation (SY5037-83), which are made by double-sided automatic submerged arc welding or single-sided welding and are used for general low-pressure fluid transportation such as water, gas, air and steam. Steel Pipe.

Welded pipe hardness index
The ability of metal materials to resist the indentation of the surface by hard objects is called hardness. According to different test methods and scope of application, hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, microhardness and high temperature hardness. For pipes, there are three types of hardness commonly used: Brinell, Rockwell, and Vickers.

● Brinell hardness (HB), use a steel ball or hard alloy ball of a certain diameter to press into the surface of the sample with the specified test force (F), remove the test force after the specified holding time, and measure the pressure on the surface of the sample Scar diameter (L). The Brinell hardness value is the quotient obtained by dividing the test force by the spherical surface area of the indentation. Expressed in HBS (steel ball), the unit is N/mm2 (MPa).
● Rockwell hardness (HK), the Rockwell hardness test is the same as the Brinell hardness test, which is an indentation test method. The difference is that it measures the depth of the indentation. That is, under the sequential action of the initial test force (Fo) and the total test force (F), press the indenter (Jingang factory cone or steel ball) into the surface of the sample, and after the specified holding time, remove the main test force. Force, the hardness value is calculated using the measured residual indentation depth increment (e). Its value is an unnamed number, represented by the symbol HR, and the scales used are A, B, C, D, E, F, G, H, K, etc. 9 scales, among which the scales commonly used in steel hardness tests are generally A, B, C, namely HRA, HRB, HRC.
● Vickers hardness (VH), the diamond indenter with a regular square pyramid with an angle of 1361 is pressed into the surface of the sample with a certain load and kept for a certain period of time before removing the test force. The load used is the same as that formed on the surface of the sample. The ratio of the area of the indentation.

3. Identification skills of welded pipes
● Inferior welded pipes are prone to folds. Folds are various fold lines formed on the surface of the spiral steel pipe. This defect often runs through the longitudinal direction of the entire product. The reason for the folding is that the defective manufacturers pursue high efficiency, and the reduction is too large, resulting in ears. Folding occurs during the next rolling process. The folded product will crack after bending, and the strength of the steel will drop greatly.

● The surface of defective spiral steel pipes often has pockmarks. The pockmarks are due to the serious wear and tear of the rolling groove, which causes the surface of the steel to be irregular and uneven. Because manufacturers of inferior spiral steel pipes want to pursue profits, there are often overruns in grooving and rolling.

● The appearance of defective welded pipes is prone to scarring, the reason is because ． The raw materials of defective welded pipes are uneven and have many impurities.

● The surface of the residual material is prone to cracks, the reason is that its blank is adobe, and the adobe has many pores, and the adobe is subjected to thermal stress during the cooling process, causing cracks, and there are cracks after rolling.

● Inferior welded pipes are easy to scratch. The reason is that the manufacturers of inferior spiral steel pipes have poor equipment, which is prone to burrs and scratches on the surface of the steel. Deeply scratches the strength of falling steel.

● Inferior welded pipes have no metallic luster and are light red or similar to pig iron. The reason is that the rolling temperature of the defective materials is not standard. Their steel temperature is measured visually, so they cannot be rolled according to the regular austenite area. , the performance of steel is naturally unqualified.

● The transverse ribs of defective welded pipes are thin and low, and often appear to be insufficient. The reason is that in order to achieve a large negative tolerance, the reduction in the first few passes of the finished product is too large, the iron shape is too small, and the hole shape is not full. the

● The cross-section of the defective welded pipe is elliptical. The reason is that in order to save materials, the reduction amount of the first two passes of the finished roll is too large. standard.