不锈钢-使用环境牌号选择 Stainless Steel application

1. Introduction 2. Corrosion 3. Maintenance 4. Physical Properties 5. Chemical Resistance Chart 1 1. Introduction Stainless steel is a ferrous alloy made of iron metal and small amounts of other elements such as chromium and nickel. The chromium content in the alloy contributes to the corrosion resistance of the material by form­ ing a thin passive film. This film is produced when chromium reacts with oxygen to form chromium oxide, which packs neatly as an invisible layer on the surface of stainless steel, protecting it from rusting. Self-re­ pairing of this passive film after a cut or scratch is possible as long as stainless steel is exposed to oxygen. As steel is less easily stained, corrode and rust than normal steel, it is commonly used in a large number of applications and industries. There are several types and grades of stainless steel, the most common being type 304 and 316. The chem­ ical compositions of the two materials are as follows: Type 304 Chemical Composition, % C Mn P S Si Cr Ni 0.08 2.00 0.045 0.030 1.00 18.00 8.00 Max Max Max Max Max 20.00 10.50 Type 316 Chemical Composition, % C Mn P S Si Cr Ni Mo 0.08 2.00 0.045 0.030 1.00 16.00 10.00 2.00 Max Max Max Max Max 18.00 14.00 3.00 2 2. Corrosion of stainless steel A high quality alloy can also corrode under certain conditions. As these forms of corrosion are less easily spotted than rust, they are often left unnoticed and cause problems among those who are not familiar with them. The following discuss these uncommon modes of corrosion. • Pitting corrosion A passive film on the stainless steel surface provides corrosion resistance for the material. This film is damaged in the absence of oxygen, causing corrosion to be amplified and forming pits of different forms at a few critical points. Pitting can lead to stress concentration that can shatter tough alloys. It is hardly detectable before a part or structure fails. Pitting corrosion can also occur when the material is exposed to an environment rich in chloride ions, which will attack the film faster than it can be repaired in low oxygen atmosphere. • Rouging For polished stainless steel of smooth surfaces in a pure water environment, water tends to pull the iron ions away from the material surface. Precipitation of iron ions occurs in a neutral pH environment, forming reddish iron hydroxide film on the surface of stainless steel. This effect is termed rouging. • Intergranular corrosion Intergranular corrosion is a form of corrosion where the boundaries of crystallites of the material are more susceptible to corrosion than their insides. When stainless steel is heated to around 700oC, chromium carbide is formed at the intergranular boundaries, depleting the region of chromium. This decreases the resistance of the material. Addition of titanium, niobium and/or tantalum can increase corrosion resistance, as their carbides are formed in preference to chromium carbides, protecting against chromium depletion. • Crevice corrosion The process is similar to pitting corrosion occurring at a lower temperature. It is due to the break down of the protection layer when exposed to reducing acids or a reducing atmosphere. • Stress corrosion cracking Subjection to tensile stress or exposures to a corrosive environment, especially high concentration of chlorides, are the cause of stress corrosion cracking. Chlorine catalyzes the formation of hydrogen, result­ ing in the hardening of metal. Stress concentration and forming a microscopic crack. The chlorine attacks further into the crack. • Sulfide stress cracking When exposed to liquids or gases with considerable hydrogen sulfide content, sulfide stress cracking oc­ curs. However, no corrosion takes place under high concentration of hydrogen sulfide. Chloride ions can worsen the corrosion effect. • Galvanic corrosion Galvanic corrosion happens between two dissimilar metals, where a galvanic cell is formed, resulting in an electrochemical potential. The electric current that is flowing through dissolves those metals of less re­ sistance. Electrical insulation and sacrificial corrosion are methods to prevent galvanic corrosion. • Contact corrosion Attachment of small foreign material particles to the stainless steel is termed contact corrosion. A com­ mon contaminant is carbon steel. As this is a combination of galvanic and crevice corrosion, the attached particles form a galvanic cell and quickly corrode away. After that, a pit may be left behind where pitting corrosion starts to take place. Contact corrosion can be prevented by keeping stainless steel away from carbon steel. 3 3. Maintenance of stainless steel To prevent the above modes of corrosion from occurring, it is necessary to maintain the stainless steel. Rust­ ing of stainless steel is generally caused by the deposit of elements of harmful gases or cleaning chemicals. Rust refers to the rusting of the attached material and not the corrosion of the stainless steel. Therefore, these stains can be removed by proper cleaning procedures to restore its appearance. A few causes of rust and staining, and their mode of cleaning is listed below: • Deposition of steel powder from environment When the rust is cleaned up not long after staining, neutral detergent or a soap-and-water solution can be used to wipe them away. Rinse and wipe the surface dry after cleaning. However, if the rust is left there for a period of time, it will be transformed into a heavy rust mixture such as iron oxide. In this case, clean­ ing chemicals or 15% nitric acid is needed to remove the rust. If the rust remains, the surface has to be polished by scouring off the rust using emery paper or a stainless brush till the material surface is slightly damaged. Finally, wipe the surface with water to wash off the cleaning chemicals. • Attachment of harmful components of sulfur dioxide or other corrosive gas The surface of stainless steel will become dirty after exposure to these corrosive gases and they appear as fine spotted rust. In the case of relatively light staining, neutral detergent or a soap-and-water solution can be used, followed by rinsing. • Attachment of cleaning chemicals The rust can be removed by using neutral detergent or a soap-and-water solution. If the rust is hard to re­ move, cleaning chemicals should be used, follow by rinsing. • Stains due to fingerprints or dirt from handling Neutral detergent or a soap-and-water solution is usually used. Organic solvent such as alcohol, benzene and acetone can be used to wipe the surface with a sponge or cloth if the stain remains. For extreme cas­ es, cleaning chemicals are recommended. In any case, rinse and wipe the surface after cleaning. Although cleaning and maintaining of the stainless steel is important, care must be taken when doing so. If not, satisfactory results may not be achieved. Following are the precautions to take note when cleaning: • Choose the appropriate method of cleaning depending on the actual condition of the state of staining and rust. • When using cleaning chemicals, test the cleaning effect on a part of the surface first. Continue with the process only when satisfactory result is obtained. Clean the surrounding of the rusted and stained parts as well so as to give a more regular surface gloss for a better appearance. • Always rinse the surface with water after cleaning with chemicals as residual chemicals can be the cause of new rust. To avoid causing skin problems, wear rubber gloves when handling cleaning chemicals. • Clean the stainless steel in the direction of the polishing finish. Moving the tools in a circular motion is hard to remove the rust and results in a shabby appearance of the surface after cleaning. • Use of coarse cleaner or emery paper is not recommended except to remove heavy fouling. Fouling causes rust by allowing the attachment of steel powder on the stainless steel surface. 4 4. Physical Properties As a guide, we have provided some properties of stainless steel type 304 and 316, including their chemical physical properties in the annealed condition and how they are thermally treated. 304 316 Physical Properties in the Annealed Condition Modulus of elasticity in tension (GPa) : 193 193 Modulus of elasticity in torsion (GPa) : 86.2 - Density (kg/m3) : 8060 8060 Specific electrical resistance at room temperature (µcm): 72 74 Specific heat capacity (J/kg.K) (0 to 100 oC) : 503 503 Thermal conductivity (W/m.K) (100 oC) : 0.113 0.113 (500 oC) : 0.149 0.149 Coefficient of thermal expansion per oC (0 to 100 oC) : 17.3 x 10-6 15.9 x 10-6 (0 to 315 oC) : 17.9 x 10-6 16.2 x 10-6 (0 to 538 oC) : 18.4 x 10-6 17.5 x 10-6 (0 to 648 oC) : 18.8 x 10-6 18.6 x 10-6 (0 to 815 oC) : - 20.0 x 10-6 Melting point range (oC) : 1398 to 1454 1371 to 1398 After cold worked, the modulus is lowered. By stress relief heat treatment, the lowered modulus may be in­ creased. Thermal Treatment Intial forging (oC) : 1149 to 1259 Annealing (oC), cool rapidly from : 1008 to 1120 Hardening : Hardenable by cold work only 5 5. Chemical resistance chart A list of chemical resistance chart for stainless steel type 304, 316 and 403 is also included for reference. CHEMICAL NAME STAINLESS STEEL 304 316 430 A ACETAMIDE B A N/A ACETALDEHYDE A A N/A ACETATE SOLVENT A A N/A ACETIC ACID D B D ACETIC ACID 5% A A A ACETIC ACID 10% A A A ACETIC ACID 20% B A A ACETIC ACID 80% D B A ACETIC ANHYDRIDE B A A ACETONE A A A ACETYL CHLORIDE (DRY) A A N/A ACETYLENE A A A ACRYLONITRILE A A N/A ADIPIC ACID A A N/A ALUMINIUM D D D ALUMINIUM ACETATE A A N/A ALUMINIUM CHLORIDE B B A ALUMINIUM CHLORIDE 20% D C D ALUMINIUM FLUORIDE D D D ALUMINIUM HYDROXIDE A C A ALUMINIUM NITRATE A A N/A ALUMINIUM POTASSIUM SULFATE 10% A A B ALUMINIUM POTASSIUM SULFATE 100% D B C ALUMINIUM SULFATE B B D AMMONIA A A A AMMONIA NITRATE A A N/A AMMONIUM ACETATE B A N/A AMMONIUM BICARBONATE A A A AMMONIUM BIFLUORIDE D B N/A AMMONIUM CARBONATE B B A AMMONIUM CASEINATE N/A A N/A AMMONIUM CHLORIDE Fume C B N/A AMMONIUM HYDROXIDE A A N/A AMMONIUM NITRATE A A A AMMONIUM OXALATE A A A AMMONIUM PERSULFATE A B A AMMONIUM PERCHLORATE 10% A A A CHEMICAL NAME STAINLESS STEEL 304 316 430 A 6 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available AMMONIUM PERCHLORATE 10% A A A AMMONIUM PHOSPHATE B C A AMMONIUM SULFATE B B B AMMONIUM SULFITE B B N/A AMMONIUM THIOSULFATE N/A A N/A AMYL ACETATE A A A AMYL ALCOHOL A A N/A AMYL CHLORIDE A A B ANILINE A B A ANILINE HYDROCHLORIDE D D D ANTIMONY D D D ANTIMONY TRICHLORIDE D D D AQUA REGIA (80%HCl, 20% HNO3) D D N/A ARSENIC ACID A A N/A ASPHALT Fume B A N/A B BARIUM CARBONATE B B A BARIUM CHLORIDE A A B BARIUM CYANIDE A A N/A BARIUM HYDROXIDE B B N/A BARIUM NITRATE B B N/A BARIUM SULFATE B B A BARIUM SULFIDE B B A BENZALDEHYDE B B N/A BENZENE B B A BENZENE SULFONIC ACID B B N/A BENZOIC ACID B B A BENZOL A A A BENZONITRILE D D N/A BENZYL CHLORIDE C B N/A BIPHENYL B B N/A BORIC ACID B A B BROMINE D D D BUTANE A A N/A BUTADIENE A A N/A BUTYL ACETATE B A N/A BUTYL ALCOHOL A A N/A BUTYL AMINE N/A A N/A BUTYL ETHER N/A A N/A BUTYL PHTHALATE B B N/A BUTYLENE A A N/A BUTYRIC ACID B B B CHEMICAL NAME STAINLESS STEEL 304 316 430 C CALCIUM BISULFATE N/A A N/A CALCIUM BISULFIDE B B N/A CALCIUM BISULFITE B A N/A CALCIUM CARBONATE A B A CALCIUM CHLORATE A A N/A CALCIUM CHLORIDE C B C CALCIUM HYDROXIDE B B N/A 7 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available CALCIUM HYPOCHLORITE C B C CALCIUM NITRATE C B N/A CALCIUM OXIDE A A N/A CALCIUM SULFATE B B A CARBON BISULFIDE A B A CARBON DIOXIDE A A N/A CARBON DISULFIDE A B N/A CARBON MONOXIDE A A A CARBON TETRACHLORIDE B B B CARBONIC ACID A A A CHLORBENZOL A A A CHLORIC ACID D C D CHLORINE (Dry) A B B CHLORINE (Anhydrous liq) C C N/A CHLORINE WATER C C D CHLORACETIC ACID B A D CHLOROBENZENE A B N/A CHLOROFORM A A A CHLOROSULFONIC ACID D B N/A CHROMIC ACID >30% B B B CHROMIC ACID 50% C B D CIDER A A A CITRIC ACID B A A COAL TAR A A A COPPER ACETATE A A A COPPER CARBONATE A A A COPPER CHLORIDE D D D COPPER CYANIDE B B A COPPER FLUOBORATE D D N/A COPPER NITRATE A A A COPPER SULFATE B B A CRESOL A A N/A CRESYLIC ACID A A N/A CUPRIC ACID D B N/A CYANIC ACID A A N/A CYANOGEN GAS A A N/A CYCLOHEXANE A A N/A CYCLOHEXANONE A A N/A CHEMICAL NAME STAINLESS STEEL 304 316 430 D DETERGENTS ANIONIC A A N/A DIACETONE ALCOHOL B B N/A DICHLOROBENZENE N/A B N/A DICHLOROETHANE B B N/A DIETHYLAMINE A A N/A DIETHYLENE GLYCOL A A N/A DIETHYL ETHER B B N/A DIMETHYLANILINE B B N/A DIMETHYLFORMAMIDE A B N/A DINITROCHLOROBENZENE A A A DIPHENYL OXIDE B A N/A DISTILLED WATER A A N/A 8 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available DYES A A N/A E ETHANE A A N/A ETHANOLAMINE A A N/A ETHER A A A ETHYL ACETATE B B N/A ETHYL ALCOHOL A A A ETHYL CHLORIDE A A A ETHYLENE BROMIDE A A N/A ETHYLENE CHLORIDE B B N/A ETHYLENE CHLOROHYDRIN B B N/A ETHYLENE DIAMINE B B N/A ETHYLENE DICHLORIDE B B N/A ETHYLENE GLYCOL (Aerosols) B B A ETHYLENE OXIDE B B N/A ETHYL ETHER B B N/A ETHYL SULFATE D D N/A F FERRIC CHLORIDE D D D FERRIC HYDROXIDE A A N/A FERRIC NITRATE B B A FERRIC SULFATE B A N/A FERROUS CHLORIDE D D N/A FERROUS SULFATE B B B FLUOBORIC ACID B B N/A FLUORINE C A D FLUOSILICIC ACID C B N/A FORMALDEHYDE 100% C A N/A FORMALDEHYDE 40% A A B FORMIC ACID B A A FURFURAL A B N/A CHEMICAL NAME STAINLESS STEEL 304 316 430 G GALLIC ACID A B A GASOLINE (50 – 100 octane) A A A GELATIN A A A GLYCERIN A A A GLYCOLIC ACID A A N/A GOLD MONOCYANIDE A A N/A H HEPTANE A A N/A HEXANE A A N/A HEXYL ALCOHOL A A N/A HYDRAZINE A A N/A HYDROBROMIC ACID 100% D D D HYDROCHLORIC ACID 35% D D D HYDROCHLORIC ACID 100% D D D 9 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available HYDROCYANIC ACID B A B HYDROFLUORIC ACID 100% B B D HYDROFLUORIC ACID 20% D D D HYDROFLUORIC ACID 50% D D D HYDROFLUORIC ACID 75% D D D HYDROGEN FLUOSILICIC ACID 100% D D N/A HYDROGEN FLUOSILICIC ACID 20% C B N/A HYDROGEN PEROXIDE 90% B B A HYDROGEN SULFIDE C A A HYDROQUINONE B B N/A I IODINE D D D IODOFORM A A N/A ISOBUTYL ALCOHOL A A N/A ISOOCTANE A A N/A ISOPROPYL ACETATE C A N/A ISOPROPYL ALCOHOL B B N/A ISOPROPYL ETHER A A N/A K KEROSENE A A A KETONES A A N/A CHEMICAL NAME STAINLESS STEEL 304 316 430 L LACQUER THINNERS A A N/A LACQUERS A A N/A LACTIC ACID B B B LEAD ACETATE B B N/A LEAD NITRATE B B N/A LEAD SULFAMATE C C N/A LINOLEIC ACID B A N/A LITHIUM CHLORIDE A A N/A LITHIUM HYDROIDE B B N/A LYSOL A A D M MAGNESIUM BISULFATE A A N/A MAGNESIUM CARBONATE B B A MAGNESIUM CHLORIDE D D C MAGNESIUM HYDROXIDE B A A MAGNESIUM NITRATE B B A MAGNESIUM Oxide Fume A A N/A MAGNESIUM SULFATE A B A MALEIC ACID A B N/A MALEIC ANHYDRIDE A A N/A MALIC ACID A A A MANGANESE SULFATE B B N/A 10 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available MELAMINE N/A D N/A MERCURIC CHLORIDE D D D MERCURIC CYANIDE C C N/A MERCUROUS NITRATE A A N/A MERCURY A A A METHANE A A N/A METHYL ACETATE A B N/A METHYL ACETONE A A N/A METHYL ACRYLATE A N/A N/A METHYL ALCOHOL A A A METHYLAMINE A A N/A METHYL BROMIDE A A N/A METHYL BUTYL KETONE A A N/A METHYL CELLOSOLVE B B N/A METHYL CHLORIDE A A N/A METHYLENE CHLORIDE B B N/A METHYL ETHYL KETONE A A N/A METHYL ISOBUTYL KETONE B B N/A METHYL ISOPROPYL KETONE A A N/A METHYL METHACRYLATE B B N/A MINERAL SPIRITS A A N/A MOLYBDIC ACID 5% A A N/A MURIATIC ACID D D D CHEMICAL NAME STAINLESS STEEL 304 316 430 N NAPHTHA A A A NAPHTHALENE A A N/A NICKEL CHLORIDE D C N/A NICKEL NITRATE B B N/A NICKEL SULFATE B B N/A NITRATING ACID (<15% HNO3) C D N/A NITRATING ACID (>15% H2SO4) C C N/A NITRATING ACID (S1% acid) C A N/A NITRATING ACID (S15% H2SO4) C C N/A NITRIC ACID 20% A A A NITRIC ACID 50% A A A NITRIC ACID (5-10%) A A B NITRIC ACID (Concentrated) A A B NITROBENZENE B B N/A NITROMETHANE A A N/A NITROUS ACID B B A NITROUS OXIDE B B N/A O OCTANOL A A N/A OLEIC ACID A A A OLEUM 100% A A N/A OLEUM 25% B B N/A OXALIC ACID B A A OZONE B A N/A 11 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available P PALMITIC ACID B A N/A PARAFFINE A A A PENTANE C C N/A PERCHLORIC ACID C C N/A PERCHLOROETHYLENE B A N/A PHENOL B B A PHOSPHORIC ACID 10% D D A PHOSPHORIC ACID D D A PHOSPHORUS TRICHLORIDE A A N/A PHOSPHORUS yellow A A N/A PHTHALIC ACID B A N/A PHTHALIC ANHYDRIDE A A N/A PICRIC ACID B B A POTASSIUM CARBONATE B B A POTASSIUM BICARBONATE B B N/A POTASSIUM BICHROMATE A A A CHEMICAL NAME STAINLESS STEEL 304 316 430 P POTASSIUM BROMIDE B B N/A POTASSIUM CHLORATE B B A POTASSIUM CHLORIDE B A B POTASSIUM CHROMATE B B N/A POTASSIUM CYANIDE B B N/A POTASSIUM DICHROMATE B B A POTASSIUM FERRICYANIDE B B A POTASSIUM FERROCYANIDE B B A POTASSIUM HYDROXIDE B A A POTASSIUM HYPOCHLORITE C B N/A POTASSIUM IODIDE A A N/A POTASSIUM NITRATE B B N/A POTASSIUM OXALATE B B A POTASSIUM PERMANGANATE B B A POTASSIUM SULFATE B A A POTASSIUM SULFIDE B B N/A PROPANE A A N/A PROPENE B A N/A PROPYL ALCOHOL A A N/A PROPYLENE GLYCOL B B N/A PYRIDINE A A N/A PYROGALLIC ACID B B A Q QUININE BISULFATE Dry A A A QUININE SULFATE Dry A A A R ROSINS A A A RUM A A N/A 12 A = Excellent B = Good – Minor effect, slight corrosion or discoloration. C = Fair – Moderate effect, not recommended for continuous use. Softening, loss of strength, swelling may occur. D = Severe damage Not recommended for any use. N/A = Information not available S SALICYLIC ACID B B N/A SEAWATER C C C SILICON A A N/A SLIVER BROMIDE D D D SILVER CHLORIDE D D D SILVER NITRATE B B A SODIUM ACETATE B B A SOD