Metal corrosion and protection and related technical standards

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Metal corrosion is the destructive effect caused by chemical and electrochemical reactions when metal comes into contact with the surrounding medium. From a thermodynamic point of view, except for a few precious metals (such as gold and platinum), all metals have a tendency to transform into ions, which means that metal corrosion is a spontaneous and ubiquitous phenomenon. After metal is corroded, its appearance, color, and mechanical properties will change. It can lead to equipment damage, pipeline leakage, product contamination, combustion or explosion and other vicious accidents, as well as serious waste of resources and energy, causing huge economic losses. It is estimated that all developed countries in the world * * The annual economic losses caused by metal corrosion account for approximately 3.5%-4.2% of its gross national product. Therefore, it is of great significance to study the corrosion mechanism of metals and take protective measures. Yierzhai [Basic types of metal corrosion] 1. Uniform corrosion Metals will dissolve to varying degrees in most acidic solutions, forming uniform corrosion, and the dissolution rate is basically uniform. Generally, the increase in solution temperature and increase in solute concentration may accelerate the corrosion of metals. Not only that, metals will also undergo uniform corrosion to varying degrees in the atmosphere, ocean, soil and high temperature conditions. 2. Pitting Corrosion Pitting corrosion, also known as pitting corrosion (tiny hole corrosion), is a local corrosion form that produces needle-like, dot-like, and hole-like shapes on metal. Pitting corrosion is a unique form of anodic reaction and is an autocatalytic process, that is, the corrosion process within pitting corrosion holes creates conditions that both promote and are sufficient to sustain the continuation of corrosion. 3. Crevice Corrosion Crevice corrosion is a kind of localized corrosion. When metal parts are in the electrolyte solution, due to the formation of gaps between metals and metals or metals and non-metals, the width is large enough to immerse the medium while keeping the medium in a stagnant state (generally 0.025 ~ 0.1mm), which intensifies the corrosion inside the gaps and is called crevice corrosion. Crevice corrosion mostly occurs at metal connections (seams) and surface dirt. 4. Galvanic corrosion: Due to different corrosion potentials, localized corrosion at the contact parts of dissimilar metals in the same medium is galvanic corrosion, also known as contact corrosion or bimetal corrosion. At this time, the two metals form a macroscopic corrosion battery and generate a galvanic current, which increases the dissolution rate of the metal with a lower potential (anode) and decreases the dissolution rate of the metal with a higher potential (cathode). The area ratio of cathode and anode increases and the conductivity of the medium decreases, which aggravates the anode corrosion. 5. Intergranular corrosion (intergranular corrosion; intercrystalline corrosion) is a localized corrosion that extends inward along the interface between metal grains. It is mainly caused by the difference in chemical composition between the surface and interior of the grain ("poor" in passive elements) and the presence of grain boundary impurities or internal stress. Intergranular corrosion destroys the bond between grains, and after corrosion occurs, the surfaces of metals and alloys still maintain a certain metallic luster. Generally, there are no signs of damage to the naked eye, but the bonding force between grains is significantly weakened, and the mechanical properties * * Deterioration cannot withstand knocks or internal pressure (such as containers), so it is a very dangerous form of corrosion. Usually found in brass, duralumin alloys and some stainless steels and nickel-based alloys. 6. Welded corrosion is an intergranular corrosion phenomenon that easily occurs outside the stainless steel weld area. The main mechanism is that when these steels are heated between 425-815°C, or slowly cooled through this temperature range, carbides will precipitate at the grain boundaries (sensitization), which will cause chromium depletion in the nearest areas and make these areas sensitive to corrosion. 7. Selective Corrosion In the process of metal corrosion, certain specific parts on the surface are selectively dissolved. One of the components of a metal solid solution is preferentially transferred into the solution due to corrosion, while the metal surface is gradually enriched with another component, which is called selective corrosion of the component. Such as brass dezincification. In multi-phase alloys, any phase is preferentially dissolved, which is called selective corrosion of the structure. The dissolution of ferrite and the accumulation of carbides and graphite on the surface of cast iron due to corrosion are examples of this type of corrosion. Since a microstructure with certain alloy components removed after corrosion remains, it is often called dealloying. The overall size of the material does not change much after dealloying, but the metal has lost its strength and is prone to dangerous accidents. 8. Stress Corrosion Cracking (SCC) A type of damage that occurs in metal under the combined action of stress (tensile stress or internal stress) and corrosive media is called SCC. SCC is characterized by the formation of corrosion-mechanical cracks that can develop along grain boundaries or propagate through grains. Since the crack propagates inside the metal, it will weaken the metal structure. * * decline, and sudden destruction may occur in severe cases. SCC will only occur under certain conditions. They are: Specific metal materials encounter special working media and are affected by external tensile stress or internal residual stress. 9. Hydrogen Attack mainly occurs in steel equipment such as petroleum hydrogenation and cracking. It is a high-temperature corrosion phenomenon. Under high temperature and high pressure, hydrogen in the gas phase penetrates into the steel in the form of hydrogen atoms, and combines with the carbon in the steel to generate methane, causing decarburization of the steel surface, reducing strength and plasticity, and in severe cases, causing surface bubbling or cracking. The hydrogen corrosion resistance of carbon steel decreases as the carbon content in the steel increases ； Low alloy steel containing a small amount of titanium, niobium, vanadium, molybdenum and other elements that have strong binding ability with carbon has good resistance to hydrogen corrosion. 10. Hydrogen embrittlement Hydrogen embrittlement is hydrogen dissolved in steel that aggregates into hydrogen molecules or forms brittle hydrides, causing stress concentration inside the steel to exceed its strength limit and form small internal cracks or bubbling. Also known as white spots, hydrogen bubbling, etc. Once hydrogen embrittlement occurs, it cannot be eliminated (it can only be prevented, not cured). Workpieces with hydrogen embrittlement can partially eliminate hydrogen embrittlement through hydrogen removal treatment (such as heating, etc.). Hydrogen embrittlement can be avoided by heating in a vacuum, low hydrogen atmosphere or inert atmosphere. For example, electroplated parts are dehydrogenated at a temperature of 200 to 240 degrees, and most of the hydrogen can be removed by heating for 2 to 4 hours. 11. Wear corrosion refers to the phenomenon in which the surface material of a metal friction pair reacts chemically or electrochemically with the surrounding medium during the relative sliding process, and causes losses accompanied by mechanical action. It is also called corrosion wear. Corrosive wear is usually mild wear, but may turn into severe wear under certain conditions. 12. Corrosion fatigue: Under the action of alternating loads, when the metal is corroded by the medium, the internal stress is constantly redistributed, which will accelerate the formation of cracks. This is the phenomenon of corrosion fatigue. This corrosion fatigue can be observed in almost any medium, and its fracture surface is less branched, dull, and has multiple sources (so it is different from mechanical fatigue and stress corrosion cracking phenomena). 13. High temperature corrosion refers to the deterioration or destruction of metal materials caused by chemical or electrochemical reactions with oxygen, sulfur, carbon, nitrogen and other elements in the ambient atmosphere at high temperatures. There is no strict temperature limit for high-temperature corrosion. It is generally believed that when the working temperature of the metal reaches more than 0.3 to 0.4 of its melting point (absolute temperature scale), it can be considered a high-temperature corrosion environment. High-temperature corrosion problems are common in petrochemical, energy, power, metallurgy, aerospace and other fields. Different types of materials can be used for different high-temperature corrosion environments, or high-temperature corrosion-resistant coatings can be used for protection. Yirzhai [Metal Anti-Corrosion Technology] There are many methods for metal anti-corrosion, which mainly include improving the nature of the metal, isolating the protected metal from the corrosive medium, or surface treatment of the metal, improving the corrosion environment, and electrochemical protection. 1. Improve the nature of metals. Select different materials to form corrosion-resistant alloys according to different uses, or add alloy elements to metals to improve their corrosion resistance, which can prevent or slow down the corrosion of metals. For example, adding nickel to steel to create stainless steel can enhance corrosion resistance. 2. Forming a protective layer to cover various protective layers on the metal surface to isolate the corrosive medium from the protected metal gas is an effective method to prevent metal corrosion. There are two types of protective layers commonly used in industry: non-metallic protective layers and metal protective layers. The following methods are usually used to form protective layers.: ① Phosphating treatment of metals: After removing oil and rust from steel products, they are soaked in a phosphate solution of a specific composition to form a water-insoluble phosphate film on the metal surface. This process is called phosphating. The phosphating film is dark gray to black gray, generally 5 to 20 microns thick, and has good corrosion resistance in the atmosphere. The membrane has a microporous structure and has strong adsorption capacity for paint, etc. If used as a base layer for paint, the corrosion resistance can be further improved. ② Oxidation treatment of metals: Add steel products to a mixed solution of NaOH and NaNO2 and heat them to form a blue oxide film (main component Fe3O4) with a thickness of about 0.5 to 1.5 microns on the surface to achieve the purpose of anti-corrosion of steel. This process is called bluing treatment, or bluing for short. This oxide film has greater elasticity and lubricity and does not affect the accuracy of the parts. Therefore, components of precision instruments and optical instruments, such as spring steel, thin steel sheets, thin steel wires, etc., are commonly treated with blue. ③ non-metallic coating : Spraying metal surfaces with plastic (such as polyethylene, polyvinyl chloride, polyurethane, etc.) is more effective than spray painting. The plastic covering is dense and smooth. The color is bright and has the dual functions of anti-corrosion and decoration. Enamel is a glass enamel with a high SiO2 content and has excellent corrosion resistance. Therefore, as a corrosion-resistant non-metallic coating, it is widely used in industrial sectors such as petrochemicals, medicine, and instruments, as well as in daily necessities. ④ metal protective layer: This is a protective coating formed by plating one metal on the surface of another metal product to be protected. The former metal is called a plated metal. In addition to electroplating and chemical plating, there are also methods for forming metal plating, such as hot dip plating, thermal spray plating, penetration plating, and vacuum plating. Among them, hot dip plating is a method of immersing metal parts in molten metal to obtain a metal coating. As the metal of the dip coating, low melting point metals are usually used, such as zinc, tin, lead and aluminum. Hot-dip galvanizing is mainly used for steel pipes, steel plates, steel strips and steel wires, and is the most widely used ； Hot-dip tin is used for thin steel sheets and storage containers for food processing, etc. ； Hot-dip lead is mainly used for chemical corrosion protection and coating of cables ； Hot-dip aluminum is mainly used to resist high-temperature oxidation of steel parts. 3. Improve the environment Improving the environment plays an important role in reducing and preventing metal corrosion. For example, reducing the concentration of corrosive media, removing oxygen from the media, and controlling ambient temperature and humidity can all reduce and prevent metal corrosion. Substances (corrosion inhibitors) that can reduce the corrosion rate can also be added to the corrosive medium to reduce and prevent metal corrosion. 4. Electrochemical protection method Electrochemical protection method is to take measures on metal equipment based on electrochemical principles to make it the cathode in the corrosion battery, thereby preventing or reducing metal corrosion. There are two main methods:: ① sacrificial anode protection method: This method uses a metal or alloy with an electrode potential lower than that of the protected metal as the anode, which is fixed on the protected metal to form a corrosion electrode, and the protected metal is protected as the cathode. Commonly used materials for sacrificial anodes include aluminum, zinc and their alloys. This method is often used to protect the shell of seagoing ships, various metal equipment and components in seawater, and to prevent corrosion of giant equipment (such as oil storage tanks) and oil pipelines. ② Impressed current method (cathodic protection method): The protected metal and another additional electrode are used as the two poles of the battery, and the protected metal is used as the cathode. The cathode is protected under the action of external direct current. This method is mainly used to prevent corrosion of metal equipment in soil, seawater and river water. Although metal corrosion brings great harm, the principle of corrosion can also be used to serve mankind, and it has now been developed into corrosion processing technology. For example, in the electronics industry, printed circuits are widely used. Its production method and principle is to use photocopying to print circuits on copper foil, and then corrode the copper that is not protected by photosensitive adhesive except the graphics with ferric chloride solution to obtain a printed circuit board with clear lines. In addition, there are new technologies of electrochemical etching and plasma etching, which are better and have higher resolution than the wet chemical etching method of using ferric chloride to corrode copper. Yierzhai [The following is the description from Wikipedia] Corrosion means the breaking down of essential properties in a material due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to o * dation of the iron atoms is a well-known example of electrochemical corrosion. This is commonly known as rust. This type of damage usually affects metallic materials, and typically produces o * de(s) and/or salt(s) of the original metal. Corrosion also includes the dissolution of ceramic materials and can refer to discoloration and weakening of polymers by the sun's ultraviolet light. Most structural alloys corrode merely from exposure to moisture in the air, but the process can be strongly affected by exposure to certain substances (see below). Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area to produce general deterioration. While some efforts to reduce corrosion merely redirect the damage into less visible, less predictable forms, controlled corrosion treatments such as passivation and chromate-conversion will increase a material's corrosion resistance. 1 Electrochemical theory 2 Galvanic corrosion 2.1 Galvanic series 3 Resistance to corrosion 3.1 Intrinsic chemistry 3.2 Passivation 4 Corrosion in passivated materials 4.1 Pitting corrosion 4.2 Weld decay and knifeline attack 4.3 Crevice corrosion 5 Microbial corrosion 6 High temperature corrosion 6.1 Surface treatments 6.1.1 Applied coatings 6.1.2 Reactive coatings 6.1.3 Anodization 6.2 Controlled Permeability Formwork 6.3 Cathodic protection 7 Economic impact 8 Corrosion in nonmetals 9 Corrosion of glasses 9.1 Glass corrosion tests 10 References 11 See also 12 External links Yi Er Zhai attached: Relevant technical standards 1. * * Standard GB/T 4334. (1～5)-2000 "Standard for test method of intergranular corrosion susceptibility of stainless steel" (choose the corresponding standard according to the sensitivity of different materials) GB/T 15260-1994 "Standard of test method for intergranular corrosion susceptibility of nickel alloy" GB/T 21433-2008 "Test of intergranular corrosion susceptibility of stainless steel pressure vessels" GB/T 4948-2002 Aluminum-zinc-steel alloy sacrificial anode GB/TT4949-1985 Aluminum-zinc-steel alloy sacrificial anode chemical analysis method GB/T 4950-2002 Zinc-aluminum-chromium alloy sacrificial anode GB/T 4951-1985 Zinc-aluminum-chromium alloy sacrificial anode chemical analysis method GB/T 9792-2003 Determination of film mass per unit area of conversion coating on metal materials GB/T 9800-1988 Chromate conversion coating for electroplated zinc and electroplated tin layers GB/T10123-2001 Basic terms and definitions of corrosion of metals and alloys GB/Tl0l25-1997 Artificial atmosphere corrosion test Salt spray test GB/T11185-1989 Paint film bending test (tapered shaft) GB/TI 720-1979 Paint film adhesion determination method GB/T1722-1992 Varnish, varnish and thinner color determination method GB/T1723-U93 Paint viscosity determination method GB/T1724-U79 Paint fineness determination method GB/T1725-1979 Paint solid content determination method GB/T1726-1979 Paint hiding power determination method GB/T1727-U92 General preparation method of paint film GB/T 1728-1979 Method for determination of drying time of paint film and putty film GB/T1730-1993 Method for determination of paint film hardness pendulum damping test GB/T1731-1993 Method for determination of flexibility of paint film GB/T1732-U93 Method for determination of impact resistance of paint film GB/T1733-1993 Determination method for water resistance of paint film GB/T1734-1993 Determination method for gasoline resistance of paint film GB/T1735-1979 Determination method for heat resistance of paint film GB/T1740-l 979 Determination method for moisture and heat resistance of paint film GB/T l 743-1979 According to gloss determination method GB/T l 758-1979 Determination method for coating usage amount GB/T1763-1979 Determination of paint film resistance to chemical reagents GB/T1764-1979 Determination of paint film thickness GB/T1031-1995 Surface roughness parameters and their values GB/T11372-l 989 Rust removal terminology GB/T11373-198g General rules for surface pretreatment of thermal spray metal parts GB/T11374-1989 Non-destructive measurement method of thermal spray coating thickness GB/T l1376-1997 Phosphate conversion coating for metals GB/T12612-1990 General technical conditions for multifunctional steel surface treatment fluids GB/T13222-1991 Determination of shear strength of metal thermal spray coatings GB/T13288-1991 Evaluation of surface roughness grade of steel before coating (comparative sample method) GBl5599-1995 Lightning Safety Specifications for Petroleum and Petroleum Facilities GB/T15957-1995 Corrosive Classification of Atmospheric Environments GB/T16906-1997 Determination of Resistivity of Electrostatically Conductive Paints on Petroleum Tanks II. Industry Standards SY/T 0003-2003 Petroleum and Natural Gas Engineering Drawing Standards SY0007-1999 Design Specifications for Corrosion Control Engineering of Steel Pipelines and Storage Tanks SY/T 0009-2004 Petroleum surface engineering design document preparation procedures SY/T0017-96 Buried steel pipeline DC drainage protection technology standard recommendation SY/T0019-97 Buried steel pipeline sacrificial anode cathodic protection design specification SY/T 0023-1997 Buried steel pipeline cathodic protection parameter test method SY/T0026-1999 Water corrosivity test method SY/T0029-98 Corrosion rate test method for buried steel inspection pieces SYJ30-87 Basic terminology for buried steel pipelines and storage anti-corrosion projects SY/T 0032-2000 Technical standard for AC drainage protection of buried steel pipelines SY/T0036-2000 Design specification for forced current cathodic protection of buried steel pipelines SY/T 0037-97 Cathodic stripping test method for pipeline anti-corrosion layer SY/T0038-97 Test method for specific bendability of pipeline anti-corrosion layer SY/T0039-97 Test method for chemical stability of pipeline anti-corrosion layer SY/T 0040-97 Test method for impact resistance of pipeline anti-corrosion layer (falling weight test method) SY/T0041-97 Test method for shear strength of pipe anti-corrosion layer and metal bond SY/T0042-2002 Economic calculation method for anti-corrosion engineering SY/T0043-96 Oil and gas field surface pipelines and equipment coloring standards SY/T 0047-I 999 Technical specifications for internal cathodic protection systems of crude oil processing vessels SY/T0059-1999 Technical specifications for controlling the hardness of steel equipment welds to prevent sulfide stress cracking SY/T0060-92 Oilfield anti-static grounding design regulations SY/T0061-2004 Technical specifications for organic anti-corrosion layers on the outer walls of buried steel pipelines SY/T 0062-2000 Test method for penetration of pipeline anti-corrosion layer (blunt rod method) SY/T 0053-1999 Test method for leak detection of pipeline anti-corrosion layer SY/T 0064-00 Test method for water permeability of pipeline anti-corrosion layer SY/T 0065-2000 Test method for wear resistance of pipeline anti-corrosion layer (drum method) SY/T0066-1999 Non-destructive measurement method of steel pipe anti-corrosion layer thickness (magnetic method) SY/T0067-1999 Pipe anti-corrosion layer impact resistance test method (limestone falling method) SY/T0072-93 Pipe anti-corrosion layer high temperature cathodic peeling test method standard SY/T0073-93 Pipe anti-corrosion layer patch material test method standard SY/T0074-93 Standard for test method of insulation sealing of pipeline anti-corrosion layer SY/T 0078-93 Standard for internal corrosion control of steel pipelines SY/T 0082-93 Specification for preliminary design content of crude oil and natural gas surface engineering SY/T 0084-94 Test method for circular bending performance of pipeline anti-corrosion layer SY/T 0085-1994 Test method for natural climate exposure chart of pipeline anti-corrosion layer SY/T0086-2003 Electrical insulation standard for cathodically protected pipelines SY/T0087-95 Standard for investigation methods of corrosion and protection of steel pipelines and storage flaring SY/T 0088-95 Technical standard for cathodic protection of steel storage bottom outer walls SY/T0315-2005 Technical specification for single-layer fused ring hydrogen powder outer coating of steel pipelines SY/T 0379-98 Technical standard for coal tar porcelain thickened external anti-corrosion layer of buried steel pipelines SY/T0407-97 Specification for surface pretreatment of steel before painting SY/T 0413-2002 Technical standard for polyethylene anti-corrosion layer of buried steel pipelines SY/T 0414-98 Technical standard for polyethylene adhesive tape anti-corrosion layer of steel pipelines SY/T 0415-96 Technical Standard for Rigid Polyurethane Foam Anticorrosive Insulation Layer of Buried Steel Pipelines SY/T 0420-97 Technical Standard for Petroleum Asphalt Anticorrosive Layer of Buried Steel Pipelines SY/T 0429-2000 Quality Inspection and Assessment Standard for Petroleum Construction Projects Oil and Gas Pipeline Lines: SY/T0442-97 Technical standard for sintered epoxy powder internal coating of steel pipelines SY/T0447-96 Technical standard for epoxy coal pitch anti-corrosion layer of buried steel pipelines SY/T 0453-98 Quality inspection and assessment standard for petroleum construction projects Oilfield gathering and transportation pipeline engineering SY/T 0457-2000 Technical standard for internal anti-corrosion layer of liquid ring hydrogen coating for steel pipes SY/T0468-2000 Petroleum construction project quality inspection and assessment standards (anti-corrosion and insulated steel pipe production) SY/T 0526.1-0 526.2-93 Coal tar enamel coating SY/T 0530-93 Determination of oil content in oil field sewage spectrophotometry SY/T 0531-94 Resistance induction method for determination of suspended particles in oil field injection water SY/T 0532-93 Bacterial analysis method for oilfield injection water Insulation dilution method SYJ 4006-90 Specifications for the construction and acceptance of cathodic protection projects for long-distance pipelines SYJ 4039-89 Basic terminology for petroleum engineering construction SY/T 4054-2003 Radiation cross-linked polyethylene heat shrinkable tape (set) SY/T 4075-95 Centrifugal molding construction technology for steel pipeline fly ash cement mortar lining SY/D 4076-95 Air-fed extrusion coating process for steel pipeline liquid paint inner coating SY/T 4077-95 Air-fed extrusion coating process for steel pipeline cement mortar lining SY/D 4078-95 Steel pipeline inner coating liquid paint patching machine patching process SY/T 40 79 1% Oil and gas pipeline crossing engineering construction and acceptance specifications SY/T 4080-95 Pipeline and storage leakage detection method SY/T 4091-95 Technical Specification for Anti-Corrosion in Offshore Petroleum Engineering SY/T 5273-2000 Performance Evaluation Method of Corrosion Inhibitors for Oilfield Produced Water SY/T 5329-94 Recommended Indicators and Analysis Methods for Clastic Reservoir Water Injection Water Quality SY/T 5510-92 Common Terms in Oilfield Chemistry SY/D 5533-2003 Analysis Methods for Oil and Gas Field Water SY/T 5548.5-92 Acceptance of commonly used chemical products in the petroleum industry - General regulations SY/T 5673-93 Performance evaluation method of antiscalants for oil fields SY/T 5756-1995 SL-2 series corrosion and scale inhibitors SY/T 5757-1995 General technical conditions for fungicides in oilfield injection water SY/T 5796-93 Flocculant evaluation method SY/T 5889-l 993 Oxygen scavenger performance evaluation method SY/T 58go-1993 Bactericide performance evaluation method SY/T 5918-2004 Technical specifications for repair of external anti-corrosion layer of buried steel pipelines SY/T 5919-1994 Technical management regulations for electrical protection of buried steel pipeline main lines SY/T 5951-94 Technical conditions for epoxy phenolic anti-corrosion oil pipes SY/T 6007-94 Procurement regulations for fungicides for oilfield injection water quality treatment SY/T 6064-94 Technical regulations for the setting of pipeline trunk markers SY/T 6l 05-94 Technical requirements for conceptual design preparation of oilfield development SY/T 6421-1999 Determination of heat loss in equipment and pipelines SY/T 7506-1996 Determination of carbon dioxide content in natural gas using barium hydroxide method SY/D 7507-1997 Determination of water content in natural gas by electrolysis method SY/T10037-2002 Specification for submarine pipeline systems