Valve pressure temperature rating valve electric hydraulic actuator introduction
The valve pressure – temperature rating is a higher allowable operating pressure at a specified temperature expressed as gauge pressure. As the temperature increases, the higher the allowable working pressure decreases. Pressure-temperature rating data is the main basis for the correct selection of flanges, valves and pipe fittings under different working temperatures and pressures, as well as the basic parameters in engineering design and manufacturing. ASME/ANSI B16.5A-1992 flange pressure-temperature ratings for American Petroleum Institute, Japanese Petroleum Institute, French Petroleum Institute and BS1560 Part II are formulated in accordance with ASME/ANSI B16.5A-1992 pressure-temperature ratings.
Pressure temperature rating
The valve pressure – temperature rating is a higher allowable operating pressure at a specified temperature expressed as gauge pressure. As the temperature increases, the higher the allowable working pressure decreases. Pressure-temperature rating data is the main basis for the correct selection of flanges, valves and pipe fittings under different working temperatures and pressures, as well as the basic parameters in engineering design and manufacturing.
The pressure-temperature rating and data for various materials are shown in Chapter 4. Many countries have formulated pressure-temperature rating standards for valves, fittings and flanges.
I. American standards
In the American standard, the pressure to temperature ratings for steel valves are in accordance with ASME/ANSI B16.5A-1992,ASMEB 16.34-1996; Pressure to temperature ratings for cast iron valves as per ANSI 816.1-1989} B16.4-1989} ANSI B16.42-1985: Pressure to temperature ratings for bronze valves as per ASME/ANSI B16.15A-1992,ASME Provisions of B16.24-1991.
1) ASME/ANSI B16.5A-1992 prescribes two series of flange sizes in English and metric units, and lists the flange pressure and temperature ratings applicable to the two systems respectively. A method for determining the British unit pressure – temperature rating is given in Appendix D of the Standard.
Taking metric units as an example, the formula for determining pressure-temperature ratings for different materials is:
Where PT is the relatively large allowable working pressure (MPa) at the specified temperature;
PN — Nominal pressure (MPa);
σ- – The allowable stress (MPa) of the material at a specified temperature.
Where, the value 148 is the allowable stress value of carbon steel material at room temperature, known as reference stress coefficient.
σ in the formula is influenced by the temperature characteristics of the material, the allowable stress and yield strength of the material at different temperatures, and the bolt load. The value of σ S is specified in ASME/ANSI B16.5A-1992. As many as 100 kinds of French blue materials are included in the standard, which are grouped according to similar chemical composition and mechanical properties.
ASME/ANSI B16.5A-1992 flange pressure-temperature ratings for American Petroleum Institute, Japanese Petroleum Institute, French Petroleum Institute and BS1560 Part II are formulated in accordance with ASME/ANSI B16.5A-1992 pressure-temperature ratings.
2) The American ANSI B16.42-1985 “ductile iron pipe Flanges and Flanged Fittings” standard provides CL150 and CL300 (PN2.0 and PN5.0mpa) ductile iron flange pressure temperature rating in the appendix of the standard also provides the formulation method of pressure temperature class, Its basic principle, scope of use, restrictions and procedures are basically consistent with ASME/ANSIB 16.5A-1992.
3) ASME B16.34-1996 incorporates temperature pressure rating data for flanged valves in ASME/ANSI B16.5A-1992. The pressure-temperature ratings for flanged valves in this standard follow the formulation method of ASME/ANSI B16.5A-1992. This standard lists pressure – temperature rating data tables for flanged and butt-welded standard class valves and for butt-welded special class valves. There are more than 100 valve materials listed in the standard, divided into 27 groups.
Ii. German standards
German standard DIN2401-1977, Part II, Permissible Working Pressure for Pipe Pressure Classes, Steel and cast iron pipe parts, is a relatively comprehensive standard for pressure-temperature rating. Among them, the allowable working pressure of seamless pipe, welded pipe, flange, valve, pipe fitting and bolt under different materials and different temperature conditions is listed. This standard includes 6 kinds of flanged materials, 4 kinds of flanged cast iron valve materials, 5 kinds of cast steel, 5 kinds of forged steel, all of which are original materials. All steels are carbon steel and low alloy steel, stainless steel is not included.
It is clearly stipulated in the standard that when other materials different from the original materials are selected, the allowable working pressure shall be calculated according to the ratio between the strength characteristic value of the materials used and the strength value of the original materials specified in the standard at 20℃.
For stainless steel material pressure – temperature rating, ISO/DIS70651 “steel flange” is supplemented. The formula for determining the pressure-temperature rating of stainless steel material is:
Where PT is the allowable working pressure (MPa) of the newly specified material at temperature T;
PN — Nominal pressure (MPa);
σs- – yield strength of the material at temperature T, i.e
Sigma, sigma 0.1 0.2 (MPa).
Where, value 205 is the yield strength value of Cr18Ni8Mo steel at 20℃, known as reference stress coefficient.
Third, the former Soviet standard
The former Soviet standard TOCT356-1980 “Valve and pipeline accessories nominal pressure, test pressure and working pressure series”, all in line with cMIAC standard RTAB253-19760
The relationship between working pressure and nominal pressure is expressed by the following formula:
Where PT — the working pressure of the specified material at temperature T, (MPa);
PN — Nominal pressure (MPa);
σ20 — Allowable stress (MPa) of material at 200℃;
Allowable stress of material at σ S – — temperature (MPa)
In the former Soviet standard TOCT356-1980, materials are grouped. In this standard, the relatively large permissible working pressure below 200℃ is regarded as the working pressure under normal temperature, and equal to the nominal pressure.
International standards
The international standard ISO/DIS7005-1-1992 “Common Pipe Flanges” is a combination of the American standard ASME/ANSI B16.5A-1992 and the German standard nominal pressure class flange standard. Pressure, therefore, a temperature rating standards are respectively adopted in the United States and Germany two countries a flange pressure temperature rating standard setting method and the corresponding ISO/DIS7005-1-1992 in the nominal pressure PN0.25, such as 0.6, 1.0, 1.6, 2.5, 4.0 MPa is a German flange system; PN2,5,10,15,25,42MPa belong to American flange system. The pressure-temperature rating standard for each system applies only to the flange standard for the respective system.
Fifth, China’s national standards
The national standard GB/T9124-2000(Appendix A) “Technical Conditions for Steel Pipe Flanges” refers to the principles and methods for formulating pressure and temperature ratings in German DIN2401-1977 and American ASME/ANSI B16.5A-1992, and uses commonly used flange materials in China. According to the international standard ISO/DIS7005-1-1992, the flange pressure-temperature rating for two nominal pressure series (PNO.25~ 4.0mpa, PN2.0 ~ 42.0mpa) was formulated respectively.
The standard specifies 13 kinds of flange materials in 12 nominal pressure grades, operating temperature of 20~530℃ relatively large allowable working pressure.
Single piston rod hydraulic cylinder Figure 2-23 shows the schematic diagram of a single piston rod hydraulic cylinder. This hydraulic cylinder has a piston rod in only one chamber. Its installation method has two kinds of cylinder fixed and piston rod fixed. In order to output linear displacement, cylinder fixation is used most frequently. The effective working area of single piston rod hydraulic cylinder with rod cavity and no rod cavity is not equal. Therefore, when the pressure oil enters the two cavities of the cylinder at the same pressure and flow rate, the speed and thrust of the piston in the two directions are not equal. Oscillating cylinder can achieve oscillating reciprocating motion, its oscillating Angle is less than 360°.
The application of hydraulic actuator in regulating valve is not as good as pneumatic and electric actuator. In principle, as long as the power source of the pneumatic actuator is changed to the hydraulic power source, it can become the hydraulic actuator. Hydraulic actuator is actually a hydraulic cylinder, used in hydraulic actuator hydraulic cylinder, mainly single piston rod hydraulic cylinder and swing hydraulic cylinder.
1 hydraulic cylinder
(1) Single piston rod hydraulic cylinder Figure 2-23 shows the schematic diagram of single piston rod hydraulic cylinder. This hydraulic cylinder has a piston rod in only one chamber. Its installation method has two kinds of cylinder fixed and piston rod fixed. In order to output linear displacement, cylinder fixation is used most frequently. The effective working area of single piston rod hydraulic cylinder with rod cavity and no rod cavity is not equal. Therefore, when the pressure oil enters the two cavities of the cylinder at the same pressure and flow rate, the speed and thrust of the piston in the two directions are not equal.
Figure 2-23 Schematic diagram of single piston rod hydraulic cylinder
A) when oil is fed without rod cavity b) when oil is fed with rod cavity c) when differential connection of hydraulic cylinder is carried out
In FIG. 2-23, in figure A, when oil is fed without rod cavity, its speed is output force; in figure B, when oil is fed with rod cavity, its speed is output force; C shows the differential connection of the hydraulic cylinder, and its speed is: the output force is.
(2) Swing cylinder can achieve swing reciprocating motion, its swing Angle is less than 360°. Single blade type and rack and pinion type are more commonly used oscillating cylinders. A rack and pinion swing cylinder makes a rack on the piston rod between two pistons. The rack meshed with the gear to change the reciprocating motion of the piston rod into the rotation of the output shaft, as shown in Figure 24. Single blade plate swing cylinder as shown in Figure 2-25A, it relies on fluid to push the blade plate in the cylinder to achieve swing. In this swinging cylinder, the rotational torque of the medium pressure P on the pendulum shaft is shown in Figure 2-25b, and its value is the product of pressure P and distance R.
The traction torque generated by the medium pressure acting on the left side of the whole blade plate is
In the formula, D — cylinder body diameter (cm);
D — Diameter of swing axis (cm);
P — Inlet working pressure (MPa);
H — Blade width (cm);
Qu — Displacement per revolution of the swinging cylinder (CM3 / R)
η – mechanical efficiency of swing cylinder η=0.8~0.85
If the average rotation speed of the swinging shaft is known as N (r/min), then the volume flow of the swinging cylinder. Qu (L/min)
Figure 2-24 Pinion and rack type swing cylinder
1.1 ‘one nut 2.2′ one bolt 3 one end cover 4,4 ‘one end cover sealing ring 5.5′ one spring/spring seat 6,6 ‘one rack piston 7 one shell 8.21 one washer 9 one elastic retaining ring 10 one flat washer 11.13.17.20.24 — 0 ring 12.25 — end cover flat washer
Adjusting bolt 15 – Piston bush 16 – piston guide ring 18- Gear shaft 19 – lower bearing 22 – Upper bearing
Post time: Jun-22-2022
