Factors affecting the performance and life of stainless steel pipe fittings

Stainless steel water pipes have a long service life. Judging from the use of stainless steel pipes in foreign stainless steel water pipe factories, the service life of stainless steel water pipes can reach 100 years, or at least 70 years, which is the same as that of buildings. The most prominent advantage of stainless steel pipe fittings is corrosion resistance. If the stainless steel pipe can be properly used and maintained during use, it can effectively prolong the service life.
Factors affecting the performance and life of stainless steel pipe fittings
(1) Influence of material on the service life of pipe fittings
For stainless steel, the main difference between 304 and 304L is that the C (carbon) content of 304 is ≤ 0.08%, while the C content of 304L is ≤ 0.03%; the NI (nickel) content of 316 is 1% higher than that of 304 compared to 304-2 %, mainly to reduce the Cr (chromium) content and increase the Mo (molybdenum) 2% - 3%, so the corrosion resistance and corrosion resistance of the respective environments are different. L stands for low carbon. For example, 304L has lower carbon content than 304. H and S stand for high temperature resistance. For example, 310S has stronger high temperature resistance than 310, 304H is more heat-resistant than 304, and 316 and 316L are marine materials with strong corrosion resistance.
(2) The influence of forming process on the performance and life of pipe fittings "Pipe fitting forming" is the most important step in the production process of pipe fittings. As the stress of the pipe material continues to increase during the processing process, the accuracy is prone to change under the action of force. At present, most pipe fitting manufacturers mainly adopt "cold extrusion" and "bulging" processes in the forming process. Depending on the production process, the size, wall thickness and function of the pipe fittings will be different. Therefore, what kind of forming process is used to maintain the stable quality and improve the production efficiency is a very important issue. The characteristics of the two processes are described below.
1. "Cold extrusion" process: put the blank stainless steel tube into the mold cavity, and apply pressure to the blank through the punch fixed on the press, so that the stainless steel blank tube is deformed, and the size requirements of the pipe fittings are obtained. Main features: (1) The surface is smooth and clean. The general dimensional accuracy of extrusion parts can reach 8 to 9 grades, and if lubrication is used, it is second only to the polished surface. The surface of parts manufactured by extrusion method generally does not need to be reworked. (2) The cold extrusion process is equipped with auxiliary means, which can meet the product quality requirements. (3) Cold extrusion will generate tensile stress on the pipe fittings. The cold extrusion process has the characteristics of cold deformation. During the extrusion process, the metal blank is in a state of three-way pressure, and the metal structure is modified after deformation.
2. "Bulging" process: The bulging process is to pass a high-pressure liquid, gas or solid soft mold inside the tube blank to force the plastic change of the tube to meet the size requirements of the workpiece. Main features: (1) During bulging, the deformation of the material is limited to a fixed mold, and the quality is stable. The workpiece will not be wrinkled, the surface of the formed workpiece is smooth and the rebound is small. (2) During bulging, the material is in a state of bidirectional tensile stress. Under the action of the mold, the wall thickness of the pipe is forced to be thinned and the surface area is increased to obtain the required geometric shape. (3) During bulging, the deformation area of the pipe is limited to the deformation area, and the pipe does not transfer to the outside of the deformation area. For example, the formation of the U-shaped groove of the pipe is realized by the local thinning of the pipe.
(3) The influence of wall thickness on the connection and life of pipe fittings The wall thickness of thin-walled stainless steel water pipes is the key to the strength of pipe connections. The wall thickness is reduced below the safety factor, and the reliability is bound to drop by several levels. In fact, the wall thickness of the pipeline is to ensure the strength of the pipeline connection. At the same time, the wall thickness also has the function of anti-vibration in various environments, the performance of the pipeline's resistance to external force impact, and the service life and corrosion resistance in concealed engineering. .
(4) Influence of anti-corrosion function and service life of solid solution process
The processing of pipe fittings will affect the fatigue properties of metal parts. The processes that affect the fatigue properties of metals include welding, grinding, forming, etc., which will generate tensile stress on the pipe fittings, thereby accelerating the occurrence of metal fatigue failure and reducing the service life of stainless steel. Therefore, it is necessary to A solution (heat treatment) step is performed.