Stainless steel pipe fittings are the collective name of various stainless steel pipe connection workpieces, which can be divided into different categories according to shape, purpose, and connection method. It has the characteristics of easy installation, high performance and durability, and it is widely used in various pipeline construction and installation. Stainless steel pipe fittings can be divided into stainless steel tees, stainless steel flanges, stainless steel heads, stainless steel elbows, stainless steel pipe caps, stainless steel heads, etc.
Iron and steel are distinguished by their carbon content. Iron-carbon alloys with carbon content below 2% are steel, and those with carbon content above 2% are called iron. Steel is widely used because of its toughness, elasticity and rigidity. All you come into contact with in life are steel, but people call it differently. For stainless steel, no matter whether the magnet can be attracted or not, as long as it meets its quality standards, it is stainless steel.
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 abroad, the service life of stainless steel water pipes can reach 100 years, or at least 70 years, which is the same life as buildings. The most prominent advantage of stainless steel pipe fittings is corrosion resistance. If stainless steel pipes can be used and maintained correctly during use, the service life can be effectively extended.
(1) The influence of material on the service life of pipe fittings
Stainless steel material, the main difference between 304 and 304L is: 304 contains C (carbon) content ≤0.08%, while 304L contains C content ≤0.03%; 316 material relative to 304L contains NI (nickel) 1% higher than that of 304-2 %, mainly to reduce the content of Cr (chromium) and increase the content of Mo (molybdenum) by 2%-3%, so that their corrosion resistance and corrosion resistance environment are different. L represents low carbon, such as 304L has lower carbon content than 304, H and S represent high temperature resistance, such as 310S is stronger than 310, and 304H is more heat resistant than 304. 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 continues to increase during the processing of pipes, the precision 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 molding process is used to maintain stable quality and improve 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 fixed punch on the press to deform the stainless steel tube, and the size requirements of the tube are obtained. main feature:
(1) Smooth and clean surface. The general dimensional accuracy of extruded parts can reach 8 to 9, 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 processed again.
(2) The cold extrusion process is equipped with auxiliary means to meet product quality requirements. For example, the pipe fittings "U-shaped groove" and "three-way pull-out" are formed, and the wall thickness of the "U-shaped groove" and "three-way pull-out" is not reduced during the extrusion process to ensure the quality of the product .
(3) Cold extrusion will cause tensile stress on the pipe fittings. The cold extrusion process has the characteristics of cold deformation. The metal blank is in a three-way pressure state during the extrusion process, 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 tube to change plastically to meet the dimensions of the workpiece. main feature:
(1) During bulging, the deformation of the material is limited to the fixed mold, and the quality is stable. There is no wrinkling of the workpiece, and the surface of the formed workpiece is smooth and the rebound is small.
(2) During bulging, the material is in a two-way tensile stress state. Under the action of the mold, the pipe wall thickness is reduced and the surface area is increased to obtain the required geometric shape.
(3) During bulging, the deformation zone of the pipe is limited to the scope of the deformation zone, and the pipe does not transfer to the outside of the deformation zone. 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 pipe connection and life
The thickness of the thin-walled stainless steel water pipe is the key to the strength of the pipe connection. When the wall thickness is reduced below the safety factor, the reliability will inevitably 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 ability of the pipeline to withstand external impact, and the service life and corrosion resistance in concealed projects. This article focuses on the relationship between the wall thickness of stainless steel pipe fittings and the connection and service life.
(1) The impact of wall thickness changes on quality during production
In the production process, pipe fittings have to go through multiple processes such as cutting, bending, forming (cold extrusion, bulging) and so on. The first thing that affects the wall thickness is the bending and forming processes. The different molding processes used will have a greater impact on the wall thickness of the pipe fittings
(2) The influence of wall thickness on pipe connection
The principle of compression connection of pipe fittings: make full use of the effective rigidity of stainless steel and the principle of elastic compression ratio of the sealing material. Hexagonal shape), play a role in positioning and fixing, thereby improving the resistance to pull and rotation, and realize the effective connection of stainless steel pipes.
It can be seen that, according to the rigidity of stainless steel, it is connected by compression and shrinkage, so the wall thickness of the pipe and the pipe plays an important role. If the wall thickness of the pipe and the pipe fitting are inconsistent, the rigidity will be different, and the compression force will be uneven.