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不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel)

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不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel)不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel) 不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel) This paper is contributed by yysshh0 DOC documents may experience poor browsing on the WAP side. It is...

不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel)
不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel) 不锈钢酸洗钝化的方法与工艺(Method and process of pickling passivation of stainless steel) This paper is contributed by yysshh0 DOC documents may experience poor browsing on the WAP side. It is recommended that you select TXT first or download the source file to the local machine. Stainless steel pickling passivation method and process 1 pickling passivation treatment method, stainless steel equipment and parts pickling passivation treatment according to different methods of operation, its scope of application and characteristics are shown in table 1. Table 1 Comparison of pickling passivation methods for stainless steel Method of impregnation brush paste method system circulation circulation system of electrochemical method can be used for parts, and can be used to brush field equipment surface treatment technology is complex, for DC power supply or potentiostat scope but not suitable for large equipment for large equipment inside and outside surface and local treatment for the installation or maintenance of the scene, especially for welding department of manual operation and poor working conditions, high production cost spraying method for large equipment, such as heat exchanger, shell and tube processing has the advantages of convenient construction, acid solution can be reused, but the piping and the pump is connected with the advantages and disadvantages of low; a large volume of equipment with acid impregnation liquid consumption of too much manual operation, poor working conditions, acid the liquid can not be recycled for on-site installation, large container with liquid quantity is low, low cost, fast speed, but the need to configure a spray gun and a ring can be used in cutting Pickling bath or passivation tank parts, pickling liquid can be used for a long time, high production efficiency, cost 2 acid passivation formula examples of 2.1 general treatment (1) acid reagent HNO3 6% ~ 25%+HF 0.5% ~ 8% (volume fraction); temperature 21 to 60 DEG C; the time according to the need; or agent ammonium citrate 5% ~ 10% (mass fraction); temperature 49 to 71 DEG C; 10 min ~ 60min. (2) 20% ~ 50% passivation reagent HNO3 (volume fraction); temperature 49 to 71 DEG C; 10 min ~ 30min; or the temperature of 2l to 38 DEG C; 30 min ~ 60min; or HNO3 agent 20% ~ 50%+Na2Cr207H2O 22% ~ 6% (mass fraction); temperature 49 to 54 DEG C; 15 ~ Min 30min; or the temperature of 21 DEG to 38 DEG C; 30 min ~ 60min. (3) a acid descaling agent H2SO4 8% ~ 11% (volume fraction); The temperature ranged from 66 to 82; the temperature ranged from 6 min to 45min; the dosage of HNO3 ranged from 6% to 25%+HF 0.5% to 8% (volume fraction); the temperature ranged from 21 to 60, or HNO3 15% to 25%+HF l% to 8% (volume fraction). 2.2 paste method (1) in Guangzhou petrochemical equipment in urea stainless steel weld and base material surface passivation and repair of surface grinding the weld local passivation for pickling paste: 25%HNO3~+4%HF+7l% condensed water (volume fraction) and BaSO4, transferred to a paste. Passivation paste: 30%HNO3 or 25%HNO3+1% (mass fraction) K2Cr2O7 and BaSO4 adjust to paste. Coating surface 5 ~ 30min, rinse with condensed water to pH=7, a single device can also be used to spray hydrogen peroxide chemical passivation method. (2) taking the patent m of Daming iron factory in Shanghai as an example. Pickling passivation cream: HNO38% ~ 14% (HF l0%; passivation agent) to 15% (as corrosive); hard S acid magnesium 2.2% ~ 2.7% (thickening agent) 60% ~ 70% (magnesium nitrate as filler to improve adhesion and permeability); sodium polyphosphate (2.3% ~ 2.8% as corrosion inhibitor agent); water (adjust viscosity). Electrochemical treatment of 2.3 stainless steel workpieces to be treated as anode, control of potentiostatic anodic treatment, or the first stainless steel as cathode, control of constant potential polarization, then the stainless steel workpiece as anode, control of potentiostatic anodization, and continue to change its potential for passivation, electrolyte solution using HNO3. After this treatment, the passive film of stainless steel has been improved and its corrosion resistance has been greatly improved. The pitting critical potential (Eb) increases by about 1000mV (in 3%NaCl), and the corrosion resistance increases by three orders of magnitude (at 45 to 20% 30%H2SO4). Application scope of pickling passivation for 3. stainless steel 3. Pickling passivation treatment of 1 Stainless Steel during the manufacturing process 3.1.1 cleaning and pickling passivation after cutting Stainless steel workpiece by machining on the surface of iron and steel usually residue and at the end of the coolant and dirt, will appear on the surface of stainless steel and rust stains, so should degreasing and cleaning, can remove nitrate, iron and steel, passivation. 3.1.2 before and after welding cleaning and pickling passivation because oil is the source of hydrogen in the weld formation, no pores will remove grease in the low melting point metal pollution (such as zinc rich paint) will cause cracking after welding, so the welding must be stainless steel surface and groove 20mm on both sides of the clean up oil, scrub with acetone, paint rust should first use sand cloth or steel wire brush to clean, wipe with acetone. Stainless steel equipment manufacturing, regardless of what kind of welding technology, welding should be cleaned, all welding slag, spatter, stain and oxidation color should be removed, cleaning methods include mechanical cleaning and chemical cleaning. Mechanical cleaning has sanding, polishing and sandblasting, shot peening, etc., should avoid using carbon steel brush, in order to prevent surface rust. In order to obtain the best corrosion resistance, it can be soaked in the mixture of HNO3 and HF, or using pickling passivation paste. In fact, common mechanical cleaning combined with chemical cleaning is applied. 3.1.3 forging and casting cleaning by heat malleable stainless steel workpiece after machining, there is often a layer of oxide or oxide surface and lubricant pollution, pollutants including graphite and MoS2 and carbon dioxide etc.. Shot peening, salt bath treatment and multi-channel pickling treatment should be adopted. Such as the United States stainless steel turbine blade treatment process for salt bath (10min), water quenching (2.5min), sulfate (2min), wash water wash (2min), alkaline permanganate bath (10min), cold water wash, wash sulfuric acid (2min) (1rain), cold water (1min), nitrate (1.5min), cold water wash wash (1min), hot water washing and air drying (1min). 3.2 the pickling and passivation process before the new plant put into operation, the stainless steel equipment and pipes of many large chemical, chemical fiber, chemical fertilizer and other devices are required to be washed and passivated before operation. Although the equipment in the factory has been removed pickling, welding slag and scale, but in the storage, transportation and installation process will inevitably cause grease, mud and sand, rust and other pollution, to ensure that the installation and equipment commissioning products (especially chemical intermediates and products) quality can meet the requirements, to ensure a the test must be carried out successfully, pickling and passivation. H2O2 production equipment stainless steel equipment and piping, such as cleaning before production, otherwise, if there is dirt, heavy metal ions will cause poisoning of the catalyst. In addition, such as metal surface grease and free iron ions will cause H2O2 decomposition, a large amount of heat released, causing fire, and even explosion. Also for oxygen pipeline, there is a trace of oil and metal particles may also produce sparks and serious consequences. 3.3 pickling and passivation treatment in the field of overhaul, equipment and materials for refining terephthalic acid (PTA), polyvinyl alcohol (PVA), acrylic fiber, acetic acid and other production equipment The material, use a lot of austenitic stainless steel 316L, 317, 304L, because materials containing Cl-, SCN-, Br -, formic acid and other harmful ions, or due to dirt and material base, will produce pitting, crevice corrosion and corrosion of welding equipment. In the parking overhaul, the equipment or components can be completely or locally pickled passivation treatment, repair its passivation film, in order to prevent local corrosion expansion. For example, Shanghai petrochemical PTA plant dryer stainless steel pipe renovation and maintenance of acrylic device stainless steel heat exchanger, such as pickling passivation. 4.4 in-service equipment cleaning in petrochemical plant of stainless steel equipment, especially heat exchanger, after a certain period of time after the operation, the inner wall will be deposited dirt, such as carbonate, sulfate, silicate, iron oxide scale scale, organic fouling and scaling effect of catalyst, the effect of heat transfer, and will cause underdeposit corrosion. It is necessary to choose suitable cleaning agent to remove dirt, Nitric acid, nitric acid + hydrofluoric acid, sulfuric acid, citric acid [page], EDTA, water-based cleaning agent, etc., and adding appropriate amount of corrosion inhibitor. After descaling and cleaning, if need to be further blunt. Chemical treatment. For example, Shanghai petrochemical PTA, acetic acid, acrylic and other devices of stainless steel heat exchangers have been descaling cleaning. 4. stainless steel pickling passivation 4.1. Pretreatment of pickling passivation, stainless steel workpiece before pickling passivation, such as surface dirt, etc., should be through mechanical cleaning, and then degreasing degreasing. If the acid wash and passivation solution can remove grease, the grease surface will affect the quality of pickling and passivation, the oil removal can not be omitted, the lye, emulsifier, organic solvent and steam etc.. 4.2 acid solution and rinse water control some of the Cl- stainless steel pickling or pickling paste by adding hydrochloric acid and perchloric acid, corrosive medium ferric chloride and sodium chloride, chlorine ion as the main agent or agents to remove the surface oxide layer, removing grease by trichloroethylene and other chlorinated organic solvents, prevent from stress corrosion cracking is not suitable. In addition, industrial water can be used for preliminary washing water, but strict control of halide content is required for final cleaning water. Deionized water is usually used. Such as petrochemical austenitic stainless steel pressure vessel pressure test water, controlling the content of C1- is less than 25mg / L, if cannot meet this requirement, adding sodium nitrate in water treatment, so as to meet the requirements, the C1- content exceed the standard, will destroy the passive film of stainless steel, is the root of pitting corrosion, crevice corrosion and stress corrosion cracking etc. the. 4.3 pickling passivation process in operation to control nitrate solution alone for the removal of free iron and other metal contaminants are effective, but to remove iron oxide, corrosion product film thickness, tempering is invalid, should generally be used HNO3+HF solution, in order to convenient and safe operation, available fluoride instead of HF. Single HNO3 solution does not add corrosion inhibitor, but HNO3+HF needs Lan-826 addition when pickling. Use HNO3+HF pickling, in order to prevent corrosion, the concentration should maintain the proportion of 5:1. The temperature should be lower than 49 degrees, if too high, HF will volatilize. The passivation solution, HNO3 should be controlled at 20% ~ 50%, according to the electrochemical test, the concentration of HNO3 is easy to produce pitting, HNO3 concentration is greater than 50%, but less than 20% passivation film quality is not stable, to prevent the passivation. One step treatment of oleic acid wash passivation, although easy to operate, save time, but the pickling passivation liquid (paste) will be corrosive HF, so the final protection film quality is better than multi-step method. Acid concentration, temperature and contact time are allowed to be adjusted in a certain range. With the increase of acid washing time, attention should be paid to the change of acid concentration and metal ion concentration. Attention should be paid to avoid over pickling, and the concentration of titanium ion should be less than 2%, otherwise it will lead to serious pitting corrosion. Generally speaking, increasing the pickling temperature will accelerate and improve the cleaning effect, but it may also increase the risk of surface contamination or damage. 4.4 stainless steel pickling control sensitized condition some stainless steel due to poor heat treatment or welding caused by HNO&HF sensitization, pickling may produce intergranular corrosion caused by intergranular corrosion cracks in the operation, or cleaning, or subsequent processing, can concentrate halides, caused by stress corrosion. These sensitizing stainless steels are generally not suitable for descaling or pickling with HNO3+HF solution. The ultra low carbon or stabilized stainless steel should be used if the pickling process must be carried out after welding. 4.5 stainless steel and carbon steel assembly pickling of stainless steel and carbon steel components (such as heat exchanger tube, stainless steel tube plate and steel shell), pickling and passivation if we use HNO3 or HNO3+HF serious corrosion of carbon steel, you should add the appropriate inhibitor such as Lan-826. When stainless steel and carbon steel combination in a sensitized state, HNO3+HF acid can be used when no hydroxy acetic acid formic acid (2%) + (2%) + inhibitor, temperature 93, time 6h or EDTA neutral ammonium solution + inhibitor, temperature: 121 C, time: 6h, Then rinse with hot water immersion and 10mg / L +100mg / L ammonium hydroxide in hydrazine. After pickling and water washing after 4.6 stainless steel pickling and passivation of the postprocessing, available with 10% (mass fraction) NaOH+4% (mass fraction) and alkaline permanganate solution in 71 ~ KMnO4 for 82 DEG C and 5 ~ 60min, to remove the acid residue, then rinse thoroughly with water, and dry. The stainless steel surface by pickling passivation spotted or stains, use fresh passivation solution or higher concentration of nitrate and eliminate scrub. Finally, the stainless steel equipment or parts should be protected and covered or wrapped with polythene film to avoid the contact between dissimilar metal and nonmetal. The treatment of acid and passivation waste liquid should comply with the national environmental protection emission regulations. For example, fluoride wastewater can be treated with lime milk or calcium chloride. Passivation solution as much as possible without dichromate, such as chromium containing wastewater, ferrous sulfate can be reduced treatment. Acid washing may cause hydrogen embrittlement in martensitic stainless steels, such as by heat treatment (heating to 200 c) A period of time. 5. stainless steel pickling passivation quality inspection, because chemical test will destroy the passivation film of the product, usually on the template for inspection. Methods are as follows: (1) copper sulfate titration test with 8gCuSO4+500mLH2O+2 ~ 3mLH2SO4 solution drops into the sample surface, keep wet, 6min if there is no copper precipitation qualified. (2) the 2mLHCl+1mLH2SO4+1gK3Fe (CN) 6+97mLH2O solution was dripped on the surface of the sample in the potassium ferricyanide titration test. The quality of the passivation film was determined by the number of blue spots and the length of the occurrence time. Multifunctional stainless steel acid lotion, a and B two components, the first component containing 60 sulfuric acid and nitric acid 20 ~ 80% ~ 40%, group B contains hydrochloric acid 70 ~ 90% and LK inhibitor from 10 to 30%, and the second component in the weight ratio: a 90 ~ 98%, 2 ~ B 10% general water solution of sulfuric acid and other parts immersed, with metal oxide on the surface of the film is removed. It is the pretreatment or intermediate treatment of electroplating, enamel, rolling and other processes. (1) the method of removing the oxide scale and corrosion substance on the steel surface by acid solution is called pickling. Iron oxides such as oxide, rust and so on (Fe3O4, Fe2O3, FeO, etc.) react with acid solutions to form salts which are dissolved in acid solutions and removed. The acid used in pickling is sulfuric acid, hydrochloric acid, phosphoric acid, nitric acid, chromic acid, hydrofluoric acid and mixed acid. Sulfuric acid and hydrochloric acid are the most commonly used. Pickling method, spray pickling and acid cream derusting method. General use of dipping acid pickling method, injection method can be adopted in mass production. Iron and steel parts are usually pickled in 10% ~ 20% volume sulfuric acid solution, the temperature is 40 degrees centigrade. When the iron content exceeds 80g/L in the solution and the ferrous sulfate exceeds 215g/L, the acid pickling solution should be replaced. Under normal temperature, 20% to 80% (volume) hydrochloric acid solution is used to pickling steel, and corrosion and hydrogen embrittlement are not easy to occur. Because of the great corrosion of acid on metals, corrosion inhibitors need to be added. After cleaning, the surface of the metal becomes silvery white, and the surface is passivated at the same time to improve the corrosion resistance of stainless steel. (two) in order to eliminate the adsorption of diatomite carrier surface and reduce the tailing peak of chromatographic peak, the carrier should be washed or washed before being used. Acid washing is the carrier with 6mol/L hydrochloric acid immersion boiling 2H or concentrated hydrochloric acid heating leaching 30min, filter, washed to neutral, drying. Acid removing table One
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