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This post was last edited by B0SS on 2016-4-21 at 12:46. Phenomena, causes, and prevention measures of crevice corrosion in stainless steel pipes: Due to gaps in the structure of equipment and components, or the presence of metallic or non-metallic deposits on the surface of stainless steel pipes, gaps are formed between these deposits and the pipe surface. Under the action of corrosive agents, point-like and ulcerative damages occur preferentially in these gaps, and this is what is known as crevice corrosion. In aqueous media containing Cl- and similar substances, the local destruction of the passivation film occurs due to the acidification of the solution in the gaps (increase in Cl- concentration, decrease in pH) and oxygen deficiency (oxygen concentration gradient cells, oxygen scarcity in the gaps). The most fundamental way to eliminate gaps is to avoid their existence from the outset in the structural design; appropriate measures must be taken to prevent gaps at the joints between tubes and tube sheets in heat exchange equipment, as well as in the gaps around flanges, gaskets, bolts, and rivets. Clean regularly and maintain a flow rate of ≥1.5 m/S in environments such as seawater to prevent the accumulation of dirt (including marine organisms) on the surface of the stainless steel pipes. Choosing stainless steel pipes with high chromium and molybdenum content, or those with high chromium and molybdenum as well as nitrogen, to resist crevice corrosion is the general approach for selecting stainless steel pipes that offer resistance to pitting and crevice corrosion. It can also be seen that, in order to address crevice corrosion, starting with material selection is more difficult than addressing pitting, and the economic cost is higher as well. Phenomena, causes, and preventive measures for fatigue corrosion of stainless steel seamless tubes: Local corrosion of stainless steel seamless tubes caused by the combined effect of alternating stress and the medium. There are many theories regarding the causes of destructive corrosion fatigue, which results from the combined effects of mechanics (dynamic stress) and electrochemistry (corrosive media), and no consensus has yet been reached. Regarding its generation mechanism, a pitting stress concentration model was proposed ； Preferred dissolution model for deformed metals ； Metal film rupture model and active material adsorption model, etc. However, under alternating stress, the repeated processes such as the breakdown of the passivation film, the dissolution of slip steps, and re-passivation, driven by both the medium and the alternating stress, are key factors that affect the corrosion fatigue behavior of stainless steel pipes. Prevent and reduce the alternating stresses experienced by stainless steel seamless tube equipment and components, including eliminating structural stress concentrations and surface defects in the stainless steel seamless tubes ； Stainless steel seamless tubes with high fatigue strength, excellent corrosion resistance, and fine grains should be selected; dual-phase stainless steel seamless tubes are a material that can be given priority. Based on the manufacturing method, they are divided into hot-rolled and cold-rolled types, including thin cold plates with thicknesses ranging from 0.5 to 885 millimeters, as well as medium-thick plates with thicknesses ranging from 4.5 to 100 millimeters. It is required to be resistant to corrosion by various acids such as oxalic acid, sulfuric acid-ferrous sulfate, *ao acid, *ao acid-hydrofluoric acid, sulfuric acid-copper sulfate, phosphoric acid, formic acid, and acetic acid. It is widely used in industries such as chemicals, food, pharmaceuticals, papermaking, petroleum, and nuclear energy, as well as in various components for construction, kitchenware, tableware, vehicles, and household appliances. The overall heat transfer coefficient of a metal depends not only on its thermal conductivity but also on other factors. In most cases, the heat dissipation coefficient of the film layer, as well as the surface condition of the rust layer and the metal. Stainless steel can maintain a clean surface, so its heat transfer properties are better than those of other metals with higher thermal conductivity. Liaocheng Suntory Stainless Steel provides technical standards for stainless steel sheets: high-strength stainless steel sheets with excellent corrosion resistance, bending properties, toughness at welded areas, and stamping properties at those same areas, along with the methods for manufacturing such sheets. Specifically, it involves heating stainless steel sheets with a carbon content of 0.02% or less, a nitrogen content of 0.02% or less, a chromium content of 11% to less than 17%, and appropriate amounts of silicon, manganese, phosphorus, sulfur, aluminum, and nickel, and which also satisfy the conditions 12 ≤ Cr + Mo + 1.5Si ≤ 17, 1 ≤ Ni + 30(C+N) + 0.5(Mn+Cu) ≤ 4, Cr + 0.5(Ni+Cu) + 3.3Mo ≥ 16.0, and 0.006 ≤ C+N ≤ 0.030, to 850–1250°C, and then subjecting them to heat treatment involving cooling at a rate of 1°C/s or faster. This results in a high-strength stainless steel sheet with a martensite content of over 12% by volume, a strength of over 730 MPa, excellent corrosion resistance and formability, as well as good toughness in the weld heat-affected zone. The use of elements such as Mo and B can significantly improve the stamping performance of the welded area. A flame made of oxygen and gas cannot cut stainless steel plates because stainless steel is not easily oxidized. 5CM thick stainless steel plates require special cutting tools to process, such as: (1) Laser cutting machines with high power, (2) Hydraulic saws, (3) Grinding discs, (4) Hand saws, (5) Wire cutting machines. (6) High-pressure water jet cutting (professional water jet cutting: Shanghai Xinwei) (7) Plasma arc cutting