Valve inspection sequence and precautions before and after installation valve material applicable medium description

Valve inspection sequence and precautions before and after installation valve material applicable medium description

The shell test pressure of the valve is 1.5 times of the larger allowable working pressure when the valve is at 20℃, and the sealing test is 1.1 times of the larger allowable working pressure when the valve is at 20℃. The test duration shall not be less than 5min. The test temperature is 5 ~ 40℃. (4) The verification of safety valve shall be in accordance with the provisions of the current national standards and design documents for setting pressure adjustment and sealing test. Safety valve should be well recorded, sealed, issued a check report.
(1) The valve should be inspected for appearance quality before installation, the valve body should be intact, the opening mechanism should be flexible, the valve stem should not be skewed, deformed, jammed, and the sign should be complete.
(2) Valve shell pressure test and sealing test should be carried out, the valve shell pressure test and sealing test should be clean water as the medium, stainless steel valve test, the content of chloride ion in water should not exceed 25ppm.
(3) the shell test pressure of the valve is 1.5 times of the larger allowable working pressure when the valve is at 20℃, and the sealing test is 1.1 times of the larger allowable working pressure when the valve is at 20℃. The test duration shall not be less than 5min. The test temperature is 5 ~ 40℃.
(4) The verification of safety valve shall be in accordance with the provisions of the current national standards and design documents for setting pressure adjustment and sealing test. Safety valve should be well recorded, sealed, issued a check report.
Valve material applicable medium description valve material applicable medium description:
1, valve commonly used material performance
(1) Iron
(1) Gray cast iron: such as HT200, HT250, etc., suitable for PN≤16, operating temperature between -10℃~100℃ oil, general liquid medium (water, steam, petroleum products, etc.); PN≤10, working temperature between -10℃~200℃ steam, general nature of gas, gas, ammonia and other media (ammonia, alcohol, aldehyde, ether, ketone, ester and other less corrosive media). It is not suitable for hydrochloric acid, nitric acid and other media. But it can be used in concentrated sulfuric acid, because concentrated sulfuric acid can produce a purified film on its metal surface to prevent corrosion of cast iron by concentrated sulfuric acid.
(2) malleable cast iron: such as KTH350-10, KTH450-06, etc., suitable for PN≤25, working temperature between -10℃~300℃ between steam, general properties of gas and liquid, oil and other media. Its corrosion resistance is similar to gray cast iron.
③ Nodular cast iron: such as QT400-15, QT450-10, etc., suitable for PN≤25 working temperature between -10℃~300℃ steam, gas and oil and other media. Its corrosion resistance is strong, can work in a certain concentration of sulfuric acid, nitric acid, acid salt. But not resistant to fluoric acid, strong alkali, hydrochloric acid and ferric chloride hot solution corrosion. Use to avoid sudden heat, sudden cold, otherwise it will break.
(4) nickel cast iron: alkali resistance than gray cast iron, nodular cast iron valve; Nickel cast iron is an ideal valve material for dilute sulfuric acid, dilute hydrochloric acid and caustic soda.
(2) carbon steel
Carbon steel has WCA, WCB and WCC, suitable for steam, non-corrosive gas, oil and related products and other media with working temperature between -29~425℃.
(3) stainless steel
The 304 series of stainless steel is generally applicable to the working temperature between -196℃~650℃ steam, non-corrosive gas, oil and related products and other media; Corrosive media with operating temperature between -30℃ and 200℃. It has excellent gas resistance, resistance to nitric acid and other oxidizing media, but also alkali, water, salt, organic acid and other organic compounds corrosion. But it is not resistant to sulfuric acid, hydrochloric acid and other non-oxidizing acid corrosion, also is not resistant to drying hydrogen chloride, oxidizing chloride and oxalic acid, lactic acid and other organic acids.
② On the basis of 304 with 2% ~ 3% molybdenum 316 series stainless steel, its corrosion resistance is better than 304 series stainless steel, it is better than chromium nickel stainless steel in non-oxidizing acid and hot organic acid, chloride corrosion resistance than chromium nickel stainless steel, corrosion resistance is good.
The 321, 347 series stainless steel containing titanium or niobium has strong resistance to intergranular corrosion.
④ Contain high chromium, high nickel 904L series stainless steel, its corrosion resistance is higher than ordinary stainless steel, can be used to deal with sulfuric acid, phosphoric acid, mixed acid, sulfite, organic acid, alkali, salt solution, hydrogen sulfide, etc., and even can be used in some concentration of high temperature occasions. But not resistant to concentrated or hot hydrochloric acid, wet fluorine, chlorine, bromine, iodine, aqua regia corrosion.
(4) Copper alloy
Copper alloy is mainly suitable for PN≤25, operating temperature between -40℃~180℃ oxygen, seawater pipe valves, it has good corrosion resistance to water, seawater, a variety of salt solutions, organic matter. It has good corrosion resistance to sulfuric acid, phosphoric acid, acetic acid and dilute hydrochloric acid without oxygen or oxidant, and has good resistance to alkali. But it is not resistant to the corrosion of nitric acid, concentrated sulfuric acid and other oxidizing acids, and it is not resistant to the corrosion of molten metal, sulfur and sulfide. Avoid contact with ammonia, which can cause stress corrosion fracture of copper and copper alloy. Attention should be paid to the selection of copper alloy, its corrosion resistance has a certain difference.
(5) Aluminum alloy
Aluminum alloy has good corrosion resistance to strong oxidizing concentrated nitric acid and can withstand organic acids and solvents. But in reducing medium, strong acid, strong base corrosion resistance. The more pure aluminum is, the better it is against corrosion, but its strength decreases and can only be used for very low pressure valves or valve linings.
(6) Titanium alloy
Titanium alloy is mainly suitable for PN≤25, operating temperature between -30℃~316℃ seawater, chloride, oxidizing acid, organic acid, alkali and other media. Titanium is an active metal and can form oxide film with good corrosion resistance at room temperature. It is capable of seawater, various chloride and hypochlorite, chlorine, oxidizing acid, organic acid, alkali and other corrosion. But it is not resistant to more pure reducing acid, such as sulfuric acid, hydrochloric acid corrosion, but resistance to oxidizing acid corrosion. Titanium valve has good resistance to hole erosion. But in red smoke nitric acid, chloride, methanol and other media will produce stress corrosion.
(7) Zirconium alloy
Zirconium also belongs to the active metal, it can generate close oxide film, it has good corrosion resistance to nitric acid, chromic acid, alkali, molten alkali, salt liquid, urea, seawater, but not hydrofluoric acid, concentrated sulfuric acid, aqua regia corrosion, also not resistant to wet chlorine and oxidizing metal chloride corrosion.
(8) Ceramics
Ceramic valve is given priority to with silicon dioxide fusion sintering, such as zirconia, alumina, silicon nitride, etc., in addition to have extremely high wear resistance, heat resistance, insulation performance, also has the very high corrosion resistant ability, in addition to no oxygen fluorine acid, fluosilicic acid and alkali resistant, can heat concentrated nitric acid, hydrochloric acid, aqua regia, salt solution and organic solvents such as medium, generally applies to PN in line 6 or less. This kind of valve such as the use of other materials, when choosing, should consider the corrosion resistance of other materials.
(9) Glass fiber reinforced plastic
The corrosion resistance of FRP varies with its adhesive. Epoxy resin FRP can be used in hydrochloric acid, phosphoric acid, dilute sulfuric acid and some organic acids; The corrosion resistance of phenolic fiber reinforced plastics is better. Furan FRP has good alkali resistance, acid resistance and comprehensive corrosion resistance, which is generally suitable for PN≤16 pipeline.
(10) Plastics
Plastic valves are relatively characterized by strong corrosion resistance, and even metal valves can not have the advantages. Generally applicable to PN≤6 pipeline, with different types of plastic, its corrosion resistance difference is great.
(1) Nylon, also known as polyamide, it is a thermoplastic, has good corrosion resistance. It can resist the corrosion of dilute acid, salt and alkali, and has good corrosion resistance to hydrocarbon, ketone, ether, ester and oil. But not resistant to strong acid, oxidizing acid, phenol and formic acid corrosion.
(2) POLYvinyl chloride: polyvinyl chloride is a thermoplastic plastic, has excellent corrosion resistance. Acid, alkali, salt, organic matter. Not resistant to concentrated nitric acid, fuming sulfuric acid, acetic anhydride, ketone, halogenated, aromatic and other corrosion.
(3) POLYETHYLENE: polyethylene has excellent corrosion resistance, it has good corrosion resistance to hydrochloric acid, dilute sulfuric acid, hydrofluoric acid and other non-oxidizing acids as well as dilute nitric acid, alkali, salt solution and organic solvent at room temperature. But not resistant to concentrated nitric acid, sulfuric acid and other strong oxidant corrosion.
(4) polypropylene: polypropylene is a thermoplastic, its corrosion resistance is similar to polyethylene, slightly better than polyethylene. It can withstand most organic acid, inorganic acid, alkali, salt, but to concentrated nitric acid, fuming sulfuric acid, chlorsulfonic acid and other strong oxidizing acid corrosion resistance is poor.
⑤ Phenolic plastics: phenolic plastics can withstand the corrosion of hydrochloric acid, dilute sulfuric acid, phosphoric acid and other non-oxidizing acid, salt solution. But not resistant to nitric acid, chromic acid and other strong oxidizing acid, alkali and some organic solvents corrosion.
⑥ Chlorinated polyether, also known as polychlorinated ether, is linear, high crystallinity of thermoplastics. It has excellent corrosion resistance, * inferior to fluorine plastics. It is capable of concentrated sulfuric acid, concentrated nitric acid outside all kinds of acid, alkali, salt and most organic solvents corrosion, but not resistant to liquid chlorine, fluorine, bromine corrosion.
⑦ Polytrifluorovinyl chloride: it and other fluorine plastics, has excellent corrosion resistance and other properties, corrosion resistance slightly lower than ptfe. It has good corrosion resistance to organic acid, inorganic acid, alkali, salt and a variety of organic solvents. Certain solvents containing halogens and oxygen that cause them to swell at high temperatures. It is not resistant to high temperature fluorine, fluoride, molten alkali, concentrated nitric acid, aromatic, fuming nitric acid, molten alkali metal, etc.
Polytetrafluoroethylene: polytetrafluoroethylene has very excellent corrosion resistance, it in addition to molten metal lithium, potassium, sodium, chlorine trifluoride, oxygen trifluoride at high temperature, high flow rate of liquid fluorine, almost all the corrosion of chemical media, the disadvantage is that it has cold flow.
(11) Lining
Because of the low strength of plastic, many valves use metal materials to do the shell, with plastic, rubber lining. Lined valves are generally suitable for PN≤16 pipelines, with different lining materials, its temperature resistance, corrosion resistance is not the same. Plastic lining: The corrosion resistance of the plastic lining is the same as that of the corresponding material in the above plastics. However, when choosing, the corrosion resistance of other materials used in plastic lined valves should be considered.
Rubber lining: rubber is soft, so many valves use rubber lining to improve the corrosion resistance and sealing performance of the valve. The corrosion resistance of rubber varies greatly with different types of rubber. After vulcanization of natural rubber can withstand non-oxidizing acid, alkali, salt corrosion, but not resistant to strong oxidants, such as nitric acid, chromic acid, concentrated sulfuric acid corrosion, also not resistant to petroleum products and some organic solvents corrosion: therefore, natural rubber was gradually replaced by synthetic rubber. NBR in synthetic rubber has good oil resistance, but it is not resistant to oxidation acid, aromatic hydrocarbon, ester, ketone, ether and other strong solvent corrosion; Fluorine rubber has excellent corrosion resistance, can withstand all kinds of acid, alkali, salt, petroleum products, hydrocarbons, etc., but the solvent resistance is not as good as fluorine plastics; Polyether rubber can be used in water, oil, ammonia, alkali and other media.
Lead lining: lead is an active metal, but because of its soft material, it is often used as the lining of special valves. The corrosion product film of lead is a strong protective layer. It is a famous material resistant to sulfuric acid. It has high corrosion resistance in phosphoric acid, chromic acid, carbonic acid and neutral solution, sea water and other media, but it is not resistant to alkali and hydrochloric acid corrosion, and is not suitable for working in their corrosion products.