Production and Application of Sanitary (Food Grade) Stainless Steel Pipe
1. Surface analysis of stainless steel pipe fittings
Both the Auger Electron Spectroscopy (AES) and X-ray Spectroscopy (SPS) methods can be used to analyze the surface of stainless steel to determine the corrosion resistance of the inner and outer surfaces of stainless steel pipe fittings. The analysis diameter of the AES method is very small, which can be less than 20nm, and its initial role is to distinguish between elements. The analysis of XPS method is about 10μm, which is suitable for clarifying the organic chemistry of adjacent surface elements.
AES and XPS detectors are used to carry out the scanner on the surface of the ground and polished 316 stainless steel plate that has been exposed to the air. It is concluded that the most typical total depth of the surface analysis of the stainless steel pipe is 15nm, and the relevant passivation treatment layer is shown. Composition, thickness and its anti-corrosion ability, etc.
According to the definition, low-alloy steel has high chromium and nickel, and some contain molybdenum (such as 316L00Cr17Ni14Mo2), titanium, etc., usually with 10.5% chromium, which has good corrosion resistance. Corrosion resistance As a result of the maintenance characteristics of the chromium-rich passivation layer, the passivation layer is generally 3-5nm thick, or as thick as 15 layers of molecules. The passivation layer is produced during the entire process of air oxidation-reduction reaction, in which chromium and iron are oxidized by air. If the passivation layer is damaged, a new passivation layer will be produced quickly or the principle of a galvanic cell will be produced immediately. Stainless steel plates will experience deep crevice corrosion and stress corrosion. The corrosion resistance of the passivation layer is related to the water content of the components contained in the stainless steel plate. For example, high chromium, nickel, and molybdenum can increase the potential difference of the binding energy of the passivation layer and the corrosion resistance of the passivation layer. It also relates to the treatment of metal surfaces in stainless steel pipes and the application of hydrodynamic substances.
2. Surface erosion status of stainless steel pipe fittings
1. The passivation treatment layer of the stainless steel surface in the Ci-containing material is very easy to be destroyed, due to the high oxidation potential of Ci-air. The printed layer of the passivation layer is only continuously corroded by the metal. In many cases, the passivation layer is only destroyed in the part of the passivation area of ??the stainless steel. The effect of the etching depends on the generation of fine holes or dents. The small pit-like etching that is not regularly spread on the surface of the raw material is called Crevice corrosion. The rate of crevice corrosion increases with increasing temperature and increases with increasing concentration. The solution is to use ultra-low carbon or low-carbon stainless steel (such as 316 liters 304 liters)
2. During the manufacturing and welding of austenitic stainless steel, the blunt warping layer on the surface of the stainless steel is easily damaged. When the heating temperature and heating speed during manufacturing and welding are in the stainless steel sensitization temperature range (about 425-815°C), the supersaturated carbon in the material first precipitates to the crystal grain boundary and combines with chromium to form chromium CRC r2-3c 6 . In this case, the diffusion rate of carbon in the austenite is greater than that of chromium, and chromium cannot compensate for the chromium lost due to the formation of chromium carbide at the crystal grain boundary. As a result, the chromium content of the crystal grain boundary increases with the chromium carbide Analyze and reduce when it comes into contact with etch materials such as Ci- in the material, it will cause the corrosion of the micro rechargeable battery. Corrosion is only the surface of the crystal grains, which quickly enters the interior to form intergranular corrosion. Very stainless steel pipes are more prominent in electric welding.
3. Stress corrosion cracks: It is the comprehensive effect of static data ground stress and erosion that causes cracks and metal material blooming. The natural environment that causes stress corrosion cracking and destruction is usually very complex. It is not only the tensile ground stress, but also the ground stress and internal stress caused by manufacturing, electric welding or quenching and tempering in metal materials.
3. Correlation between internal and external metal surface treatment and corrosion resistance of stainless steel pipe fittings
The inner and outer surface layers of stainless steel pipe fittings (much like chemical polishing, grinding and polishing) have excellent passivation treatment layers, which have strong corrosion resistance. The inner and outer surface layers have high smoothness, and there is very little material adhesion, which is beneficial to corrosion resistance. The less the liquid medium with high surface roughness is retained in the tube, the better it is for cleaning, especially in the pharmaceutical industry.
1. Electrolytic grinding (electrochemical grinding) of the inner surface of the tube: The electrolytic grinding fluid is phosphoric acid, sulfuric acid, anhydrous chromic acid, gelatin, potassium dichromate, etc. The inner surface of the stainless steel pipe is anodized, and the fluidity of the polishing liquid is passed through the low pressure and large current to carry out chemical polishing to solve the problem. At this time, the outer surface of the tube is carrying out two divergent whole processes, that is, the conversion and melting of the stainless steel passivation passivation layer (including the thick mucosa). This is because the standard for the demulsification and passivation of the economical protrusions and recesses on the outside of the surface layer is different, and the anodic oxidation melts. Due to the different conditions for film formation and passivation of the surface microscopic convex and concave parts, and the dissolution of the anode, the concentration of metal salt in the anode area continues to increase, forming a high-resistance viscous mucosa on the surface. The difference in thickness of the film at the convex and concave parts results in high current intensity of the anodized surface layer, faster electrostatic induction melting, and in a short period of time surpasses the goal of flattening the prominent part of the external economy, and can exceed a high smoothness Ra≤0.2-0.4μm. And under this kind of effect, the chromium water content of the pipe surface is increased, and the anti-corrosion ability of the stainless steel passivation passivation treatment layer is improved.
How to grasp the quality of polishing should be related to the secret recipe of lithium battery electrolyte, concentration value, temperature, plug-in time, current intensity, electrical level, and tube metal surface treatment level. Failure to master this technology will actually destroy the smoothness of the pipe surface. If the electrolysis method is too level, there will be a lot of convex and concave surfaces, and even each tube will have to charge a lot of fees. The real quality must be technical and the cost is relatively high.
2. Grinding and polishing of the outer surface of the tube: grinding and polishing with rotation and parallel lines. Here, taking rotary mechanical grinding as an example, mechanical grinding equipment is relatively simple, power and grinding discs and advanced grinding equipment are relatively simple, power and grinding discs, and advanced grinding wax. The cloth disc and cloth disc made of graded fine sand particles are polished back and forth on the inner and outer surfaces of the pipe many times, and the finish can reach Ra ≤ 0.2-0.4μ m
Compared with electrolytic grinding, mechanical grinding is widely used because of its simple equipment, low technical content, easy grasp, low consumption cost, and no damage to the tube. However, the corrosion resistance of the surface printing layer is much better than electropolishing.
The larger defect of the cold-rolled tube is the hard state, that is, the yield index is very large, and it is not suitable for flaring and bending. Strictly speaking, it does not meet the national industry standard, so thermosolidification (quenching) must be carried out.
3. Gas-protected bright annealing furnace: consists of two parts: bright annealing furnace body and a full set of ammonia decomposition equipment.
Bright annealing furnace: The key structure consists of a ring-shaped cross-section muffle tank, and a heating method with high temperature heating wires arranged on both sides and bottom ends. Ammonia dissolved gas is used as the maintenance steam and circulating system water cooling gas. The pipes subjected to this heat treatment method do not need to be pickled and passivated, which ensures the smoothness of the inner and outer surface layers and avoids the slight unevenness of the pipe surface caused by pickling. Because these slight irregularities will make the pipe fall short of the surface smoothness specifications of environmental sanitation pipes. Therefore, choose a protective atmosphere bright annealing furnace. Hangao Tech's intelligent protective gas bright solution furnace fully meets your needs, not only has superior airtight performance, but also high efficiency and energy saving. Compared with the same type of equipment, it can save about 20%-30% of energy consumption.
