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The Working Principle And Characteristics Of Commonly Used Valves
1.Gate valve
Gate valve refers to the vertical movement of the closing element (gate) along the axis of the medium channel of the valve. Its advantages are small flow resistance coefficient, small torque required for opening and closing, and unrestricted flow direction of the medium. The disadvantages are large structural size, long opening and closing time, easy damage to the sealing surface, and complex structure.
Divide gate valves into different types, the most common being parallel and wedge gate valves, stem structures, and can also be divided into rising stem gate valves.
(1) Parallel gate valve
Refers to a gate valve with two sealing surfaces parallel to each other. Suitable for low pressure, medium and small diameter (DN50-400mm) pipelines.
(2) Wedge gate valve
Refers to a wedge-shaped gate valve with two sealing surfaces. It is divided into double ram, single ram, and elastic ram.
(3) Rising stem gate valve
It can visually display its opening and closing degree, and has been widely used for many years for small and medium-sized diameters. Generally, rising stem gate valves are used for DN less than or equal to 80mm.
(4) Non rising stem gate valve
The valve stem nut body is in direct contact with the medium. Suitable for large-diameter valves and pipelines with limited installation space.
2. Butterfly valve
Its name comes from the wing shaped structure of butterfly plates. On pipelines, it is mainly used for cutting and throttling. When butterfly valves are used for cutting, elastic seals are often used, and materials such as rubber and plastic are chosen. When used for throttling, metal hard seals are often used. The advantages of butterfly valves are small size, light weight, simple structure, fast opening and closing, good regulation and sealing performance, and low fluid resistance and operating torque.
Butterfly valves can be divided into lever type (double rocker), center symmetric gate type, offset plate type, and inclined plate type according to their structure.
For butterfly valves with a nominal diameter DN<800mm, an offset plate type should be selected.
3. Globe valve
Refers to the movement of the closing body (disc) along the centerline of the valve seat. It is generally only used for cutting and not for throttling in pipelines, and the nominal diameter is usually limited to DN250mm or less. The disadvantage is that there is a large pressure loss.
There are many types of globe valves, and their structures are generally divided into straight through, precise, and direct flow. Angle stop valve is widely used in refrigeration systems. Its inlet channel is at a right angle of 90 degrees, which will produce pressure drop. The biggest advantage is that the corner of the Plumbing is installed, which saves 90 degrees of elbow and is easy to operate.
4.Ball valve
Ball valves evolved from plug valves and are mainly used on pipelines to cut off, distribute, and change the flow direction of the medium. It is characterized by the smallest fluid resistance, its Drag coefficient is equal to that of pipe sections of the same length, quick opening and closing, reliable sealing, compact structure, easy operation and maintenance, and is widely used in many occasions.
Ball valves can be divided into the following three types according to their spherical structure:
(1) Floating ball valve
Its structure is simple, with good sealing performance. All the working medium load borne by the ball is transmitted to the outlet valve seat sealing ring. This structure is only suitable for medium and low pressure situations, but its disadvantages are difficult assembly, high manufacturing accuracy requirements, and high operating torque.
(2) Fixed ball valve
The ball valve is fixed by two fixed shafts connected to the ball, and under the pressure of the medium, the ball will not produce displacement. It is suitable for high-pressure and large-diameter pipelines.
(3) Elastic ball valve
Suitable for high-temperature and high-pressure media. There are elastic grooves on the ball, which can reduce friction between the two sealing surfaces when opening and closing, and also reduce the operating torque.
5. Check valve
Also known as reverse flow valve, check valve, back pressure valve, and one-way valve. It is a valve used to prevent medium backflow in pipelines and equipment, which automatically opens and closes by generating force from the flow of the medium itself in the pipeline.
The swing check valve disc rotates around the outer pin axis of the valve seat, and is divided into single disc and multi disc. The former is generally used for nominal diameter DN 50-500mm, while the latter is generally used for nominal diameter DN greater than or equal to 600mm.
There is also an air discharge check valve, which is used at the outlet of the boiler feed pump to prevent medium backflow and discharge; The new slow closing check valve has a diaphragm check valve to eliminate Water hammer, which has good performance in preventing water hammer; A spherical check valve is an ideal product to prevent reverse flow of media.
Steel Classification
(1) carbon structural steel (carbon structural steels);
(2) low alloy high strength structural steel (high strength low alloy structural steels);
(3) High-quality carbon structural steels (quality carbon structural steels);
(4) alloy structure steel (alloy structure steels);
(5) spring steel (spring steel);
(6) Bearing steel (bearing steel);
(7) carbon tool steel (carbon tool steels);
(8) alloy tool steel (alloy tool steels);
(9) high speed tool steel (high speed tool steels);
(10) stainless steel (stainless steel);
(11) heat-resistant steel (heat-resisting steels);
(12) Cold sensitive steel and cold extruded steel (cold heading and cold extruding steels);
(13) Free-cutting steel (free-cutting steel);
(14) Atmospheric corrosion resisting steel (atmospheric corrosion resisting steel);
(15) electrode steel and alloy (electrod steel and alloy);
(16) Corrosion resisting alloys (corrosion resisting alloys);
(17) precision alloys (precisions alloys);
(18) high temperature alloy (alloys for high temperature use);
(19) Electrical steel (steel for electrical use), including grain-oriented and non-oriented silicon steels (grain-oriented and non-oriented silicon steels) and electromagnetic
pure iron (magnetic iron);
(20) special steel (steel for special use),
Including hull structure steel (hull structure steel),
Steel plates for boilers,
Steel plates for pressure vessels,
steel plates for welded gas cylinders,
Steels for automobiles,
Hot-rolled wide strips for line pipe of oil and natural gas,
Steel for plastic mold
And railway steel (steel products for railways use), etc.
The Basic Principle Of Valve Sealing Surface Grinding
Grinding is a commonly used finishing method for the sealing surface of valves in the manufacturing process. Grinding can make the valve sealing surface obtain high dimensional accuracy, geometric shape roughness and surface roughness, but it cannot improve the mutual position accuracy between the surfaces of the sealing surface. The dimensional accuracy of the ground valve sealing surface is usually 0.001~0.003mm; the geometric shape accuracy (such as unevenness) is 0.001mm; the surface roughness is 0.1~0.008.
The basic principle of sealing surface grinding includes five aspects: grinding process, grinding movement, grinding speed, grinding pressure and grinding allowance
1 Grinding process
The grinding tool and the surface of the sealing ring are well combined, and the grinding tool makes complex grinding movements along the joint surface. Abrasives are placed between the lapping tool and the surface of the sealing ring. When the lapping tool and the surface of the sealing ring move relative to each other, part of the abrasive grains in the abrasive will slide or roll between the lapping tool and the surface of the sealing ring. layer of metal. The peaks on the surface of the sealing ring are first ground away, and then the required geometry is gradually achieved.
Grinding is not only a mechanical process of abrasives on metals, but also a chemical action. The grease in the abrasive can form an oxide film on the surface to be processed, thus accelerating the grinding process.
2 grinding movement
When the grinding tool and the surface of the sealing ring move relative to each other, the sum of the relative sliding paths of each point on the surface of the sealing ring to the grinding tool should be the same. Also, the direction of relative motion should be constantly changing. The constant change of the direction of movement prevents each abrasive grain from repeating its own trajectory on the surface of the sealing ring, so as not to cause obvious wear marks and increase the roughness of the surface of the sealing ring. In addition, the continuous change of the direction of motion cannot make the abrasive more evenly distributed, so that the metal on the surface of the sealing ring can be cut more evenly.
Although the grinding movement is complicated and the direction of movement changes greatly, the grinding movement is always carried out along the bonding surface of the grinding tool and the surface of the sealing ring. Whether it is manual grinding or mechanical grinding, the geometric shape accuracy of the sealing ring surface is mainly affected by the geometric shape accuracy of the grinding tool and the grinding movement.
3 grinding speed
The faster the grinding movement, the more efficient the grinding. The grinding speed is fast, more abrasive particles pass through the surface of the workpiece per unit time, and more metal is cut off.
The grinding speed is usually 10~240m/min. For workpieces requiring high grinding precision, the grinding speed generally does not exceed 30m/min. The grinding speed of the valve sealing surface is related to the material of the sealing surface. The grinding speed of the copper and cast iron sealing surface is 10~45m/min; the hardened steel and hard alloy sealing surface is 25~80m/min; the austenitic stainless steel sealing surface 10~25m/min.
4 grinding pressure
The grinding efficiency increases with the increase of the grinding pressure, and the grinding pressure should not be too high, generally 0.01-0.4MPa.
When grinding the sealing surface of cast iron, copper and austenitic stainless steel, the grinding pressure is 0.1~0.3MPa; the sealing surface of hardened steel and hard alloy is 0.15~0.4MPa. Take a larger value for rough grinding and a smaller value for fine grinding.
5 Grinding allowance
Since grinding is a finishing process, the amount of cutting is very small. The size of the grinding allowance depends on the machining accuracy and surface roughness of the previous process. Under the premise of ensuring the removal of the processing traces of the previous process and correcting the geometric error of the sealing ring, the smaller the grinding allowance, the better.
The sealing surface should generally be finely ground before grinding. After fine grinding, the sealing surface can be directly lapped, and the minimum grinding allowance is: the diameter allowance is 0.008~0.020mm; the plane allowance is 0.006~0.015mm. Take a small value when manual grinding or material hardness is high, and take a large value when mechanical grinding or material hardness is low.
The sealing surface of the valve body is inconvenient to be ground and processed, so fine turning can be used. After finish turning, the sealing surface must be rough ground before finishing, and the plane allowance is 0.012~0.050mm.
Heat Treatment Of High Performance Austenitic Stainless Steel - Solution Annealing
Austenitic stainless steel cannot be hardened through heat treatment. The purpose of heat treatment on these alloys is to remove the cold work hardening effect, dissolve harmful secondary phases again, and reduce residual stress to an acceptable level. Heat treatment can also produce recrystallized structures with smaller grain sizes in cold-worked stainless steel.
Solution annealing can soften materials after cold working and dissolve secondary phases that may precipitate during hot working or welding processes. The term "complete annealing" usually refers to the material being in its optimal metallurgical state, with complete dissolution of the secondary phase and complete homogenization of the metallographic structure. Completely annealed stainless steel has the best corrosion resistance and ductility. Due to the fact that solid solution annealing is carried out at high temperatures, annealing in an air environment can generate oxide scales on the surface, which must be removed by descaling or pickling to restore the surface's corrosion resistance.
prepare
Before annealing, it is necessary to remove surface grease, oil, cutting fluid, forming lubricant, colored pen markings, and other pollutants. Annealing can cause pollutants to "burn" into the surface and must be ground, otherwise it is difficult to remove. The infiltration of carbon containing pollutants into the surface can cause carbonization or sensitization, which can easily lead to intergranular corrosion during use. Therefore, surface cleaning before heat treatment is crucial for ensuring product quality. Cleaning methods include soaking or spraying chemical reagents. The cleaning agents used for stainless steel degreasing include hot alkaline solutions and chemical solvents.
Low melting point metals such as lead, copper, and zinc must be avoided from contaminating the surface. During annealing, they can cause grain boundary infiltration, leading to so-called liquid metal embrittlement and intergranular cracking. Therefore, before high-temperature treatment such as annealing and welding, it is necessary to clean up the residual pollutants on the surface.
temperature
The minimum annealing temperature refers to the lowest temperature at which the microstructure homogenizes and dissolves carbides and intermetallic precipitates. To ensure complete dissolution of precipitates and restore corrosion resistance, the annealing temperature must be higher than this temperature. The upper limit of annealing temperature is based on no warping, avoiding excessive grain growth, and minimizing the number of difficult to clean oxide scales as much as possible. The following table lists the minimum annealing temperatures for some austenitic stainless steels. High performance austenitic stainless steel requires homogenization of its microstructure at high temperatures, so their solution annealing temperature is higher than that of standard austenitic stainless steel.
annealing time
Maintaining the solution annealing temperature for 2-3 minutes is sufficient to dissolve a small amount of carbides and other secondary phases, and can also soften the cold formed material. During solution annealing, in order to ensure that the workpiece reaches the solution annealing temperature from the outside to the inside, the insulation time is usually 2-3 minutes per millimeter of thickness. If the amount of precipitates is large, especially with χ and σ When in phase, it is necessary to extend the insulation time.
If the solution annealing time is too long or the temperature is too high, a large amount of oxide skin will be generated, making cleaning difficult and costly. Long term annealing also increases the possibility of unqualified dimensional deformation during the heat treatment process. High molybdenum and high-performance austenitic stainless steel rapidly forms oxide scales in a naturally ventilated furnace. Molybdenum trioxide usually evaporates and leaves the surface as a gas. If volatilization is inhibited, liquid molybdenum trioxide will accumulate on the surface, accelerating the oxidation process. This is what is called "intense oxidation". The measures to minimize oxidation of high molybdenum steel include:
• Avoid conditions that inhibit volatilization (filling too tightly and sealing the furnace too tightly);
• Materials with severe oxide scale cannot be re annealed;
• Avoid prolonged exposure to environments above the minimum annealing temperature;
• Use the lowest annealing temperature that can be operated;
• Use a protective atmosphere.
atmosphere
Air and oxidizing combustion gases form the most economical and effective annealing atmosphere for stainless steel. However, the oxide skin generated by air annealing must be removed to restore corrosion resistance. Protective atmospheres such as argon, helium, hydrogen, cracked ammonia, hydrogen/nitrogen mixture, and vacuum can reduce the formation of oxide scales, but the cost is relatively high. Bright annealing is generally carried out in hydrogen or cracked ammonia gas with a dew point of -40 ° C or lower. Under normal operating conditions, annealing in a protective atmosphere will not produce visible oxide skin, so there is no need to clean it after annealing.
cooling
To prevent the precipitation of chromium carbide or other intermetallic phases, austenitic stainless steel may require rapid cooling after annealing. The need for rapid cooling and the choice of cooling method depend on the cross-sectional size and grade.
In the vast majority of cases, 304L and 316L with thin sections will not precipitate harmful phases after air cooling. As the cross-sectional size, carbon content, and alloy content increase, the necessity for rapid cooling also increases. High performance austenitic stainless steel requires rapid cooling regardless of thickness. Common cooling methods include forced air cooling, water spray cooling, or water quenching cooling. After vacuum annealing, inert gas quenching will not produce oxide skin.
If the annealed material still needs to undergo hot processing such as welding, it is best to perform maximum cooling such as water quenching after annealing. This can make the material better resistant to the adverse effects generated by the subsequent thermal cycles. When selecting cooling methods, possible deformation and new residual stresses should be considered.
Cleaning after annealing
Due to the high chromium content in the heat treated oxide skin, the chromium content of the metal adjacent to the oxide skin is reduced, resulting in a decrease in corrosion resistance. To fully restore corrosion resistance, it is necessary to remove the oxide skin and poor chromium metal layer.
The most commonly used cleaning method is shot peening to remove oxide scale, followed by acid washing to remove poor chromium metal. The most common method for pickling stainless steel is immersion pickling, which can also be performed by spraying, gel and ointment.
The acid used for pickling is very harmful and must be used in accordance with safety regulations (ventilation, wearing goggles and gloves, wearing safety clothing, etc.). The workpiece after pickling must be neutralized and thoroughly rinsed with a large amount of clean low chlorine water. Collect and dispose of waste liquid separately according to local hazardous waste management regulations.
Differences Between O-Type Ball Valves And V-Type Ball Valves
Ball valve structure
There are many types of structures for ball valves, but they are basically the same. They are all round ball cores with opening and closing parts, mainly composed of valve seats, balls, sealing rings, valve stems, and other driving devices. The valve can be opened and closed by rotating the valve stem 90 degrees. They are used in pipelines to shut off, distribute, regulate flow, and change the flow direction of the medium. The valve seat uses different sealing forms according to different working conditions. The valve body of the O-ring ball valve is equipped with a ball with an intermediate through-hole inside. There is a through-hole with a diameter equal to the pipeline diameter on the ball, which can rotate in the sealing seat. There are circular elastomers on both sides of the pipeline direction to achieve sealing. The V-shaped ball valve core has a V-shaped structure, and the valve core is a 1/4 ball shell with a V-shaped notch. It has a large flow capacity, a large adjustable range, shear force, and can be tightly closed, making it particularly suitable for fluid materials with fibrous structures.
1、 O-type ball valve structure:
The valve body of the O-ring ball valve is equipped with a ball with an intermediate through-hole inside. There is a through-hole with a diameter equal to the pipeline diameter on the ball, which can rotate in the sealing seat. There are circular elastomers on both sides of the pipeline direction to achieve sealing. By rotating the ball by 90 °, the direction of the through-hole can be changed, thereby achieving the opening and closing of the ball valve. The O-type ball valve adopts a floating or fixed design, and the relative moving parts are made of self-lubricating materials with minimal friction coefficient, resulting in low operating torque. In addition, the long-term sealing of sealing grease makes operation more flexible. Its product advantages are as follows:
1. O-type ball valve has low fluid resistance
Ball valves generally have two structures: diameter reduction and diameter reduction. Regardless of which structure, the flow resistance coefficient of the ball valve is relatively small. The conventional ball valve is a straight through type, also known as a full flow type ball valve. The channel diameter is equal to the inner diameter of the pipeline, and the resistance loss is only the frictional resistance of the same length of pipeline. Among all valves, this type of ball valve has the smallest fluid resistance. There are two ways to reduce the resistance of the pipeline system: one is to reduce the fluid flow rate, and the other is to increase the pipe diameter and valve diameter, which will greatly increase the cost of the pipeline system. The second is to reduce the local resistance of the valve, and ball valves are the best choice.
2. The O-ring ball valve switches quickly and conveniently
The ball valve only needs to rotate 90 degrees to complete full opening or full closing, so it can quickly achieve opening and closing.
3. O-type ball valve has good sealing performance
The vast majority of ball valve seats are made of elastic materials such as polytetraethylene (PTFE), commonly known as soft sealed ball valves. Soft sealed ball valves have good sealing performance and do not have high requirements for the roughness and machining accuracy of the valve sealing surface.
4. Long service life of O-ring ball valve
Due to the excellent self-lubrication of polytetrafluoroethylene (PTFE or F4), the friction coefficient with the sphere is small. Due to the improved processing technology, the roughness of the ball valve has been reduced, greatly increasing its service life.
5. O-type ball valve has high reliability
The sealing pair of the ball and valve seat will not have any scratches, sharp friction, or other faults;
After the valve stem was changed to an internal type, the potential accident hazard of the valve stem flying out due to the loosening of the packing gland under fluid pressure was eliminated;
Ball valves with anti-static and fire-resistant structures can be used for pipelines transporting oil, natural gas, and gas.
The O-ring ball valve core (ball) is spherical, and from a structural perspective, the ball valve seat is embedded in the valve seat on the valve body side during sealing. The relative moving parts are made of self-lubricating materials with extremely low friction coefficient, resulting in low operating torque. In addition, the long-term sealing of sealing grease makes operation more flexible. Generally used for two position regulation, with a fast opening flow characteristic.
When the O-type ball valve is fully open, both sides are unobstructed, forming a straight pipe channel with bidirectional sealing. It has the best self-cleaning performance and is suitable for two position cutting occasions with particularly unclean and fibrous media. The ball core always rubs against the valve during the opening and closing process. At the same time, the sealing between the valve core and the valve seat is achieved through the pre tight sealing force of the valve seat pressing against the ball core. However, due to the excellent mechanical and physical properties of the soft sealing valve seat, its sealing performance is particularly good.
2、 V-shaped ball valve structure:
The V-shaped ball valve core has a V-shaped structure, and the valve core is a 1/4 ball shell with a V-shaped notch. It has a large flow capacity, a large adjustable range, shear force, and can be tightly closed, making it particularly suitable for fluid materials with fibrous structures. Generally, V-shaped ball valves are single sealed ball valves. Not suitable for bi-directional use.
V-shaped edge, cutting off impurities. During the rotation of the ball, the V-shaped blade of the ball is tangent to the valve seat, thereby cutting off fibers and solid substances in the fluid. However, ordinary ball valves do not have this function, which can easily cause fiber impurities to get stuck when closing, causing great inconvenience to maintenance and repair. The valve core of the V-shaped ball valve will not be stuck by fibers. In addition, due to the use of flange connection, its disassembly and assembly are simple, without the need for special tools, and maintenance is also simple and easy. When the valve is closed. The V-shaped notch produces a wedge-shaped scissors effect between the valve seat, which has self-cleaning function and can prevent the ball core from getting stuck. The valve body, valve cover, and valve seat respectively adopt a metal point-to-point structure, and a valve stem spring with a small friction coefficient is used. Therefore, the operating torque is small and very stable.
V-shaped ball valve is a right angle rotating structure that can achieve flow regulation. It can achieve different degrees of proportionality according to the V-shaped angle of the V-shaped ball. V-shaped ball valves are generally used in conjunction with valve actuators and locators to achieve proportional adjustment. V-shaped valve cores are most suitable for various adjustment occasions, with high rated flow coefficient, large adjustable ratio, good sealing effect, zero sensitivity in adjustment performance, small volume, and can be installed vertically or horizontally. Suitable for controlling media such as gases, vapors, liquids, etc. The V-shaped ball valve is a right angle rotary structure, composed of a V-shaped valve body, pneumatic actuator, locator, and other accessories; There is an approximate inherent flow characteristic of equal percentage; Adopting a dual bearing structure, with low starting torque, excellent sensitivity and sensing speed, and strong shear ability.
Introduction To Stainless Steel (Austenitic, Ferritic, Martensitic, PH, And Duplex Stainless Steel)
Austenite, ferrite, martensite, PH, and duplex stainless steel
What are the different types of stainless steel? Can austenitic stainless steel be heat treated? Can ferritic stainless steel be heat treated? What stainless steel can you heat treat? What makes stainless steel rust resistant?
Ordinary daily experience tells us that steel corrodes. Give it water and oxygen, and it will rust. Porous rust will continue to grow and peel off until it eventually consumes all the steel. But adding enough chromium to the steel only forms a thin layer of oxide, which will not allow corrosion to continue. Based on the chromium content in the alloy and the effects of some other elements, various components with various combination characteristics have been established as standard alloys.
The specific environment, temperature, required strength, manufacturability, and ultimately... cost all involve choosing which type of stainless steel to use in any given application.
Stainless steel is classified into austenite, ferrite, martensite, duplex or precipitation hardening according to its metallurgical structure.
austenitic stainless steel
01
The AISI 200 and 300 series... cannot be hardened through heat treatment. HT depends on the structure changing with temperature. From high temperatures up to 1900 ° C to extremely low negative 300 ° C, these grades remain in an austenitic state. Under normal conditions, there is almost no reaction to magnets. Cold working this material can make it slightly magnetic. The common types commonly referred to as "18-8" (which means that the nominal amount of CR is 18% and the nominal amount of Ni is 8%) are 303, 304, and 316. 316 also adds molybdenum, which improves corrosion performance in many environments compared to 304. In addition, 316 has stronger antioxidant properties at higher temperatures. The addition of sulfur to 303 stainless steel improves processing characteristics, but sacrifices some corrosion resistance. Annealed state is the most corrosion-resistant and commonly used. It exhibits good strength and toughness in low-temperature applications.
02
Some AISI 400 series alloys cannot be hardened through heat treatment because these stainless steels still maintain a ferrite state within the critical temperature range. Some stainless steels react to magnets much like ordinary steel. The "pure Cr" grade of 405 and 409 stainless steel has a relatively low Cr content, making it suitable for automotive exhaust applications where appearance is not important. 430 stainless steel and other alloys with higher chromium content can resist corrosion at higher temperatures and maintain a better appearance for applications such as automotive or home appliance decoration at a lower cost than austenitic grade.
Annealed state is the most corrosion-resistant.
Martensitic stainless steel composed of allowances from the AISI 400 series can be hardened through conventional heat treatment. Heat treatment is similar to the heat treatment of alloy steel. They have an austenitic structure at high temperatures and undergo rapid cooling to transform into a martensitic structure. They are usually used under fully hardened conditions to achieve optimal corrosion resistance, while also possessing high strength and hardness. According to different types, the intermediate value of HRc (Rockwell hardness) for 410 and 416 stainless steel can be 60HRc for 440c stainless steel, as the maximum hardness after heat treatment depends on the carbon content. The achievable hardness increases with the increase of carbon content. These stainless steels also react to magnets like ferrite.
PH precipitation hardened stainless steel
03
PH stands for "precipitation hardening". This means that they can be hardened through heat treatment. They usually also react to magnets. The most common alloy is 630 stainless steel, commonly referred to as "17-4". Heat treatment includes high-temperature "solution treatment" (also known as annealing or solution annealing), followed by "aging" at temperatures between 900 F and 1150 F. At 900 hours, the strength and general corrosion performance are higher. The strength decreases with the increase of temperature, while the aging temperature increases but the toughness increases. For certain specific environments, corrosion performance has also been improved. In these applications, strength and corrosion performance are factors that need to be considered.
Finally, there is duplex stainless steel, which is a type of stainless steel with a mixed structure of austenite and ferrite, used for more specific applications than in this stainless steel introduction. Many are proprietary names, while a few, such as 2205, are considered standard or universal stainless steel names.
Conversion Of PN Nominal Pressure To Class Pounds (Lb)
Conversion Of PN Nominal Pressure To Class Pounds (Lb)
The nominal pressure (PN) and Class American pound scale (Lb) are both expressions of pressure. The difference is that the pressure they represent corresponds to different reference temperatures. The PN European system refers to the pressure corresponding to 120 ℃, while the Class American standard refers to the pressure corresponding to 425.5 ℃. So in engineering exchange, pressure conversion should not be solely used. For example, the CLass300 should be converted to 2.1MPa using pressure alone. However, if temperature is considered, the corresponding pressure increases. According to the temperature and pressure resistance test of the material, it is equivalent to 5.0MPa.
There are two types of valve systems: one is the "nominal pressure" system represented by Germany (including China), which is based on the allowable working pressure at room temperature (100 degrees in China and 120 degrees in Germany). One is the "temperature pressure system" represented by the United States, which is represented by the allowable working pressure at a certain temperature. In the temperature pressure system of the United States, except for 150Lb, which is based on 260 degrees, all other levels are based on 454 degrees. The allowable stress of the No. 25 carbon steel valve in the 150 pound class (150psi=1MPa) is 1MPa at 260 degrees Celsius, and the allowable stress at room temperature is much greater than 1MPa, approximately 2.0MPa. So, generally speaking, the nominal pressure level corresponding to the American standard 150Lb is 2.0MPa, and the nominal pressure level corresponding to 300Lb is 5.0MPa, etc. Therefore, the nominal pressure and temperature pressure level cannot be arbitrarily changed according to the pressure transformation formula.
PN is a numerical code related to pressure, which is a convenient circular integer for reference. PN is an approximate pressure resistance MPa equivalent to room temperature, and is the nominal pressure commonly used in Chinese valves. For control valves with carbon steel valve bodies, it refers to the allowable high working pressure for applications below 200 ℃; For cast iron valve bodies, it refers to the allowable high working pressure for applications below 120 ℃; For control valves with stainless steel valve bodies, it refers to the allowable high working pressure for applications below 250 ℃. When the working temperature increases, the pressure resistance of the valve body will decrease. American standard valves represent nominal pressure in pounds, which is the calculation result of the combined temperature and pressure of a certain metal. It is calculated according to the standard of ANSI B16.34. The main reason why pound scale and nominal pressure do not correspond one-to-one is that the temperature reference for pound scale and nominal pressure is different. We usually use software to calculate, but we also need to know how to use tables to check the scale. Japan mainly uses K value to indicate pressure level. For gas pressure, in China, we generally use the unit of mass "kilogram" to describe it more commonly (rather than "jin"), with the unit of kg. The corresponding pressure unit is "kg/cm2", and one kilogram of pressure is the force of one kilogram acting on one square centimeter. Similarly, compared to foreign countries, the commonly used unit of pressure for gases is "psi", with the unit being "1 pound/inch2", which is "pounds per square inch" in English. But more commonly used is to directly refer to its mass unit, which is the pound (Lb.), which is actually Lb. It is the pound force mentioned earlier. Replacing all units with metric units can calculate: 1 psi=1 pound/inch2 ≈ 0.068 bar, 1 bar ≈ 14.5 psi ≈ 0.1 MPa, and countries such as Europe and America commonly use psi as the unit. In Class600 and Class1500, there are two different values corresponding to the European and American standards. 11MPa (corresponding to the 600 pound class) is a European system regulation, which is stipulated in ISO 7005-1992 Steel Flanges; 10MPa (corresponding to the 600 pound class) is an American system regulation, which is stipulated in ASME B16.5. Therefore, it cannot be absolutely said that the 600 pound level corresponds to 11MPa or 10MPa, and the regulations for different systems are different.
There are two main types of valve systems: one is the "nominal pressure" system represented by Germany (including China), which is based on the allowable working pressure at room temperature (100 degrees in China and 120 degrees in Germany). One is the "temperature pressure" system represented by the allowable working pressure at a certain temperature in the United States. In the temperature pressure system in the United States, except for 150Lb which is based on 260 degrees, all other levels are based on 454 degrees. For example, the allowable stress of a 150Lb. 25 carbon steel valve at 260 degrees Celsius is 1MPa, while the allowable stress at room temperature is much greater than 1MPa, approximately 2.0MPa. So, generally speaking, the nominal pressure level corresponding to the American standard 150Lb is 2.0MPa, and the nominal pressure level corresponding to 300Lb is 5.0MPa, etc. Therefore, the nominal pressure and temperature pressure level cannot be arbitrarily changed according to the pressure transformation formula.
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