Instrument corrosion of common materials and main measures
1, what is the metal corrosion? What are the major measure instrument corrosion?
A: the corrosion is caused by the environment under the action of damage and deterioration. Corrosion of metals or alloys, mainly chemical or electrochemical effects caused by damage, sometimes at the same time also contain physical or mechanical erosion damage.
Anti-corrosion instrument has the following four main steps:
(1) direct contact with the medium part adopts the corresponding corrosion materials, such as throttle device, temperature measuring to protect casing, pressure, differential pressure tables (variable
Send measuring mechanism), the regulator can flow of parts;
(2) on the surface of contact corrosion medium instrument parts, internal coating (including spraying, electroplating, welding, lining) corrosion materials, such as regulating valve body, valve core, the temperature measuring to protect casing, analyzer sampler room, orifice, nozzle, etc.;
(3) with corrosion resistant spacer in isolation anticorrosion, requirements of continuous use not metamorphism as well, more than half of it is mainly used for pressure transmitter, differential pressure
Transmitter and pressure gauge anti-corrosion;
(4) with a neutral liquid or gas purging isolation, it is mainly used for guide tube long distance pressure, differential pressure, liquid level transmitter isolation anticorrosion.
2, instrument, what are the main types of corrosion resistant metal and alloy material? Their corrosion resistance? Each what instrument used for?
Answer: the current commonly used anticorrosion performance and metal and alloy material of roughly as follows:
1 Cr18Ni9Ti stainless steel, or nickel chromium stainless steel, the atmosphere, water, strong oxidizing acid, organic acid, less than 30% of alkali and chlorine oxide, not resistant to non oxidizing acid (sulfuric acid, hydrochloric acid), a large number of used for instrument as a general antiseptic material;
(2) Cr18Ni12Mo2Ti stainless steel (or 2 titanium molybdenum stainless steel), sulphuric acid and chloride corrosion resistance, it is better than Cr18Ni9Ti stainless steel, but not resistance to hydrochloric acid, as a substitute for nickel, can resist the corrosion of high concentration of alkali and chlorine oxide, can be used as a control valve seats, valve core, turbine flow transmitter, differential pressure and pressure transmitter measuring mechanism and diaphragm material;
(3) Ni70Cu30 alloy (or monel alloy), because of the nickel content is high, in addition to good alkali resistance, resistance to non oxidizing acid, especially for chlorine fluorhydric acid have good corrosion resistance, but not resistant to strong oxidizing acid and solution, can be used as a regulator and transducer measuring mechanism, diaphragm and other corrosion materials;
(4) nickel ferro chrome molybdenum alloy (hartz alloy), hartz molybdenum containing 26% - 26% B R, hartz C chromium containing 14%, 16%, hydrochloric acid, sulfuric acid, nitric acid and other acids, alkali resistant and corrosion of hydroxide, also can be used as a regulator and instrument measuring mechanism and diaphragm material;
5 Ni76Cr16Fe7 alloy (due to resistance alloy), because of the nickel content is high, it is mainly used for high temperature and alkali resistant and sulfide material, can be used as a regulator of anticorrosion materials;
6 titanium, titanium and titanium alloy, chloride and hypochlorite, chlorine, temperature oxidizing acid, organic acid and alkali corrosion, but because of the price
More expensive, general as instrument anticorrosive coating and thin layer lining;
All landowners tantalum, tantalum (Ta)), its corrosion resistance performance and similar work, except hydrofluoric acid, fluoride, fuming sulfuric acid, alkali, almost all the chemical can medium (including the boiling point of hydrochloric acid, nitric acid and sulfuric acid under 175 ℃) of the corrosion, due to the expensive, used as instrument anticorrosive diaphragm.
3, the corrosion resistance of stainless steel? In what situations can be used as instrument anticorrosive material?
Answer: stainless steel is more than 11% chromium, nickel steel appellative and at the same time, it is in the normal temperature oxidation environment, such as atmosphere, water, strong oxidizing acid, etc.) easy purification, the surface layer is given priority to with chrome oxide (Cr2O3), protective film, the corrosion rate is extremely low, so the name of "stainless steel". But when the temperature increased or environment oxidation ability reduce, will be changed from passive to live condition, significant increase in corrosion. All kinds of stainless steel to organic acid, organic compound, alkali, neutral solution and a variety of gas has good corrosion resistance. In non oxidizing acid (sulfuric acid, hydrochloric acid, etc.) in severe corrosion.
Often for local corrosion, when on the verge of pure state, living state and in salt solution containing halogen ions can produce corrosion hole.
Used in instruments, mainly Cr18Ni9Ti stainless steel, a lot of measuring mechanism for gauges, valve seats, valve core, the throttle device of orifice, nozzle, temperature measuring to protect casing and sampler of analytical instruments, etc.
4, what kind of instruments commonly used anti-corrosion of nonmetal materials are there? Their corrosion resistance? Each what instrument used for?
A: non-metallic corrosion material is a lot of more phyletic, applicable to the instrument of general has the following three kinds of anticorrosion.
1) plastic categories: phenolic resin, epoxy resin, polyester plastic, polyethylene, polypropylene, polyvinyl chloride (PVC), purchasing glass, chlorinated polyether, PPS, ABS plastic, polytrifluorochloroethylene, ptfe and so on. Instrument and control valve shell material, of which three fluoride vinyl chloride and ptfe on the instrument corrosion, the most widely used is suitable for below 200 ℃, corrosion of acid, alkali, sulfide, because the price is expensive, usually as a coating and lining.
(2) rubber categories: divide into two kinds of natural rubber and synthetic rubber, which is a wide variety of synthetic rubber, resistant to corrosion and heat resistance performance is optimal with fluorine rubber,
Because the price is expensive, commonly used for sealing washer, the rest of the rubber is used as transmitter and regulator of the lining.
(3) glass and ceramic: are the melting or burning of silica as the main products, has the very good resistance to corrosion. Many varieties and used in strong corrosive environment variety with high aluminum, boron glass (the latter are better acid resistance and heat resistance), acid-resistant ceramics except hydrofluoric acid and some other substances containing fluorine and thick hot alkali liquor, can almost all corrosive medium, including strong hot nitric acid, hydrochloric acid and aqua regia, salt solution, organic solution, etc. But its main drawback is: low strength, low thermal conductivity, thermal expansion coefficient is bigger, easy to fracture, is suitable for below 300 ℃, measure for adjusting the lining in the transmitter, or spraying in the instrument internal coating, the sampler as analytical instruments, can also be made under the condition of low pressure below 0.6 Mpa temperature protection sleeve (tube wall is less than 3 mm).
5, please describe teflon corrosion resistant performance.
A: take tetrafluoroethylene PTFE plastic English abbreviations, sometimes called the Teflon (du pont marks). It is one of the most stable chemical milk in plastic material, the ability of boiling hydrochloric acid, sulfuric acid (98% and fuming sulfuric acid concentration is a bit poor), nitric acid and aqua regia, strong alkali and a variety of organic solvents, so a plastic king said. Suitable temperature - 200 ~ 260 ℃ and decomposition temperature is 415 ℃.
6, the protection of the thermometer table casing which anticorrosion measures can be adopted? Need to pay attention to what issues?
Answer: the thermometer table of the measuring are generally in a protective sleeve tube, insert the process piping, its anticorrosion measures mainly choose corresponding corrosion materials, according to the medium corrosion properties of the following options:
1) select well corrosion of metal or alloy material to protect casing, such as titanium, tantalum, 2 titanium acid aluminum, steel, nickel base alloy, etc.;
(2) if the temperature measuring is the thermocouple or heat resistance, using precious metals embalming material, can be made into armoured type, in order to save materials;
(3) when the metal or alloy is not high temperature resistant corrosion medium, can choose quartz glass as a protective casing, can heat resistance above 1000 ℃.
(4) can also be used in ordinary metal protective casing outside plating, coating, rubber lining, etc., the temperature is below 200 ℃ can be used with three fluoride vinyl chloride or ptfe, when filling besmear non-metallic materials, coating shoulds not be too thick, lest affect heat transfer.
Should be paid attention to when using the anti-corrosion measures, the following points:
(1) temperature protection tube and pipeline to use flange connection, easy to corrosion and tear open outfit;
(2) as far as possible need not heat transfer difference of nonmetal materials to protect casing, lest increase temperature measuring inertia time;
(3) measurement in the line with medium, the particle impurities in order to prevent the protective casing damage by scouring for a long time, but in front of the thermometer with a baffle, the anti-corrosion protection casing by spraying method makes more sense
7,What are the anticorrosion measures pressure gauge?
Answer: (1) the general corrosion medium, if stainless steel spring tube corrosion ability of 1 ~ 2 years, can be chosen for ammonia pressure gauges, when installation, guide tube shorter, buffer coil switch buffer tank, to prevent impurities clogging.
(2) if the medium is aimed for stainless steel and copper corrosion, buffer tank can be switch to isolation tank and corrosion resistant spacer. Every kinds of liquid can be according to the nature of the measured medium, but requires the use of more than six months is not bad as well. If ordinary spacer can apply, available fluorine chlorine oil as a spacer, but the price is very expensive, so the isolation tank to do small, should recycle when disassembling fluorine oil reuse.
(3) the diaphragm type pressure gauge can be used, there are 2 titanium molybdenum and tantalum sheet, diaphragm and ballistic tube with methyl silicone oil transfer between pressure and range can be 0 ~ 100 kpa, if diaphragm material is not be able to bear or endure corrupt, can add a layer of F46 (fep) diaphragm, but the bottom of the instrument is sensitive. May also directly with F46 isolation diaphragm, but should pay attention to the permeability of medium, the transmission fluid can choose fluorine oil, can double isolation effect.
8, corrosion medium?
A: not corrosive medium, but it has the penetration ability, because molecules is very small, it will enter the metal lattice, make metal bubbling (called "embrittlement"). This phenomenon for thicker metal, maybe problem is not big, but for only 0.1 mm thick transmitter isolation of bellows diaphragm, penetration is very important. Because of some molecules even through pot metal diaphragm, enter the filling liquid inside, so that the filling liquid containing gas, affects its performance. A solution to permeation is in the metal diaphragm surface finishes. Xx company's new transmitter, it is in the bellows of SUS316L isolation diaphragm on the two layers of plating coating, plating a layer of ceramic first, and then gold plating on ceramic, purpose is to suppress penetration.