Analysis of common quality problems of stainless steel pipe fittings

Now stainless steel pipe fittings are widely used in all kinds of pipeline projects, especially for the three way, elbow and size head. The main reason is that the stainless steel pipe has good forming, strong pressure resistance and easy welding, which can effectively guarantee the pressure bearing capacity of the pipeline. Therefore, in pipeline engineering, especially petrochemical and other high temperature, high pressure and flammable and explosive pipelines, the rational use of stainless steel pipe fittings and the quality of pipe fittings are very important.

Because of this, in the design and installation of pipelines, especially in petrochemical industry and high temperature and high pressure inflammable and explosive pipeline project, whether from design or manufacturing, even to each link of construction installation and inspection of the design, manufacture and installation personnel are in need of strict quality control, to ensure the selection, pipeline timber, manufacture, installation and quality inspection, otherwise it will cause huge losses in installation construction and production process. In the course of construction, there are several problems in the quality of the general stainless steel pipe. The following is the following.

First, the wall thickness of the stainless steel pipe fittings is not uniform. The uneven wall thickness of the pipe usually occurs in the parts of the maximum deformation of the pipe. For example, the wall thickness of the back of the elbow is thinner than the other, and the wall thickness of the pipe and pipe body is not equal. In the relevant national standards, the thickness reduction of stainless steel pipe can not exceed 12.5 of nominal thickness of pipe fittings. However, field measurement shows that some wall thickness thinning amounts to 20-30. However, it is difficult to find the measurement tools such as ordinary caliper and so on. Only by using the ultrasonic thickness gauge can be detected.

The second is the problem of excessive hardness. The reason is the heat treatment process after forming. The solution is to use the right heat treatment process and do a heat treatment again.

The third is the defects formed in the material and processing. The safety of this problem is the most dangerous, and it is not easy to check out. The factors that cause defects are many and complex. They not only have their own defects of stainless steel, but also have problems in manufacturing process. In addition, they may also be caused by incorrect heat treatment process.

Inspection of stainless steel welded pipe fittings before and after delivery is a key process to ensure the quality of pipe fittings, especially for pipes that are subjected to high temperature, high pressure and flammable and toxic media. Now the stainless steel pipes are usually inspected for appearance size, hardness, thickness and magnetic particle inspection (MT) and ultrasonic flaw detection (uT) before they leave the factory. From the aspect of inspection and arrival fittings, it is easier to detect magnetic particle defects and ultrasonic flaw detection. Because of the magnetic particle inspection, the commonly used yoke method (carbon steel pipe) is used in the factory. But restricted by the equipment, the method is limited in the outer surface of stainless steel pipe fittings, but the problem appears most is on the pipe wall, the crack usually appears such stainless steel pipe especially the crack of small diameter tube wall, to use the magnetic method or eddy current method to do inspection ultrasonic examination, and this is a the equipment and technology requirements are very high test items.

Source: China Pipe Fittings Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)