HG/T 20507-2000 Specification for selection and design of automation instruments (with clause explanation)
Some standard content:
Industry Standard of the People's Republic of China
Design Code for Selection of Instrument Type
Design Code for Selection of Instrument TypeHG/T20507-2000
Editor: China Huanqiu Chemical Engineering Company China Wuhuan Chemical Engineering Company
Approval Department: State Administration of Petroleum and Chemical Industry Implementation Date: June 1, 2001 National Chemical Engineering Construction Standard Editing Center (formerly the Engineering Construction Standard Editing Center of the Ministry of Chemical Industry) 2001 Beijing
Scope of Application
Temperature Instruments
1.1 General
This regulation applies to the selection of temperature instruments for chemical plants. 1.1.2
Unit and Scale (Graduation)
The scale (graduation) unit of the temperature instrument shall be Celsius (℃). The selection of scale (gradient) and measuring range should be consistent with the standard series of the finalized product in general. The selection of the insertion length of the detection (measurement) element should be based on the principle that the detection (measurement) element is inserted to the 1
position where the temperature change of the measured medium is sensitive and representative. Generally, when installed vertically or at a 45-degree angle to the pipe wall, the end of the detection (measurement) element should be located in the middle third of the pipe, but in general, in order to facilitate interchangeability, the entire device is often uniformly selected for one or two gears of length.
2 When installed on flues, furnaces and insulation material masonry equipment, it should be selected according to actual needs. In general, in order to facilitate interchangeability, a length of 250mm deep inside can be selected. 1.1.4 The material of the protection cover of the detection (measurement) element shall not be lower than that of the equipment or pipeline. If the protection cover of the finalized product is too thin or not corrosion-resistant (such as armored thermocouple), refer to Appendix A and add a protective sleeve. 1.1.5 Detection (measurement) element protection sleeve
For medium and low pressure media, it is advisable to use a steel pipe straight protection sleeve. For high pressure media or when the temperature measuring element does not need to be stopped when it is taken out, an integrally drilled straight or tapered protection sleeve should be used.
For the occasions where the flow rate of the measured medium is high or the protective sleeve requires high strength, an integrally drilled tapered protection sleeve should be used.
1.1.6 For temperature instruments, temperature switches, temperature detection (measurement) elements and transmitters used in local electrical contacts in explosive hazardous places such as flammable gas, steam and flammable dust, etc., appropriate explosion-proof structural forms or other explosion-proof measures should be selected according to the determined category of hazardous places and the degree of danger of the measured medium. 1.1.7 For temperature instruments used in places such as corrosive gases and harmful dust, the appropriate shell protection level should be selected according to the use environment conditions.
1.1.8 When implementing this provision, the provisions of the relevant national standards in force shall also be met. 1.2 Local temperature instrument
Accuracy levelbzxZ.net
General industrial thermometer: select 1.5 or 1 level. 1
Precision measurement thermometer: select 0.5 or 0.25 level. 1.2.2 Measuring range
1The highest measurement value shall not exceed 90% of the upper limit of the instrument's measuring range, and the normal measurement value shall be about 1/2 of the upper limit of the instrument's measuring range.
The measurement value of the pressure thermometer shall be between 1/2 and 3/4 of the upper limit of the instrument's measuring range. 1.2.3
Bimetallic thermometer
When meeting the requirements of measuring range, working pressure and accuracy, it shall be preferred for local display. 2The case diameter is generally selected as b100mm. In places with poor lighting conditions, high positions or long observation distances, medium Φ150mm should be selected.
3 The connection method between the instrument housing and the protection tube is generally the universal type, and the axial type or radial type can also be selected according to the principle of convenient observation.
1.2.4 Pressure thermometer
Applicable to local or local display at low temperatures below -80℃, where close observation is not possible, there is vibration, and the accuracy requirement is not high.
1.2.5 Glass thermometer
Only used in special occasions with high measurement accuracy, small vibration, no mechanical damage, and convenient observation. Glass mercury thermometers shall not be used.
1.2.6 Base-type instrument
Base-type temperature instruments should be selected for local or local installation of measuring, control (regulating) instruments. 1.2.7 Temperature switch
Applicable to occasions where contact signal output is required for temperature measurement. 1.3 Centralized temperature instrumentation
1.3.1 Detection (measurement) elements
According to the temperature measurement range, refer to Appendix A to select thermocouples, thermal resistors or thermistors with corresponding graduation numbers. 48
2 Prefabricated thermocouples are suitable for general occasions: Prefabricated thermal resistors are suitable for vibration-free occasions: Thermistors are suitable for occasions with fast measurement response speed. Armored thermocouples and armored thermal resistors are suitable for occasions that require vibration resistance or impact resistance, as well as those that require improved response speed.
3 According to the requirements of the measured object for response speed, the following detection (measurement) elements with time constants can be selected: (1) Thermocouples: 600s, 100s and 20s; (2) Thermal resistors: 90~180s, 30~90s, 10~30s and <10s; (3) Thermistors: <1s.
Choice of thermocouple measuring end form:
(1) In general, when the response speed requirements are met, the insulated type should be selected. (2)
In order to ensure that the response speed is fast enough or to suppress the interference of interference sources on the measurement, the shell type should be selected. According to the use environment conditions, the junction box should be selected according to the following principles: 5
Ordinary type: places with better conditions:
Splash-proof type, waterproof type: humid or open-air places: (3) Explosion-proof type: flammable and explosive places. 6 In general, the threaded connection method can be selected, and the flange connection method should be selected for the following occasions: (1) Installation on equipment, lined pipes, non-metallic pipes and non-ferrous metal pipes: (2) Crystallization, scarring, blockage and highly corrosive media; (3) Flammable, explosive and highly toxic media.
7 Thermal resistors and thermocouples used in special occasions: (1) For reducing gases, inert gases and vacuum occasions with a temperature higher than 870°C and a hydrogen content greater than 5%, tungsten thermocouples or air-blowing thermocouples should be used:
(2) For the temperature of the outer wall of equipment, pipelines and rotating surfaces, end (surface) type, spring-fixed or armored thermocouples and thermal resistors should be used:
(3) For media containing hard solid particles, wear-resistant thermocouples should be used; (4) When multiple points are required in the same detection (measurement) element protection tube, multi-point (branch) thermocouples should be used; (5) In order to save special protection tube materials (such as molybdenum), improve response speed or require the detection (measurement) element to be installed in a bent manner, armored thermal resistors and thermocouples can be used: (6) For blast furnace and hot blast stove temperature measurement, special thermocouples for blast furnaces and hot blast stoves can be used. 1.3.2
Transmitter
1. The measurement or control system matched with the receiving standard signal display instrument can choose a transmitter with analog signal output function or digital signal output function. 49
2. In general, a field transmitter should be selected. 1.4 Accessory equipment
1.4.1 When using thermocouples to measure temperatures below 1600℃, when the cold end temperature changes so that the measurement system cannot meet the accuracy requirements, and the matching display instrument does not have the cold end temperature automatic compensation function, a cold end temperature automatic compensator should be selected.
1.4.2 Compensation wire
1 According to the number of thermocouples, graduation number and use environment conditions, the compensating compensation wire, compensating compensation cable or extended compensation wire or extended compensation cable that meets the requirements should be selected. Generally, compensating compensation wire or compensating compensation cable should be selected. When the compensating compensation wire or compensating compensation cable cannot meet the requirements, the extended compensation wire or extended compensation cable should be selected. 2 Select different levels of compensation wires or compensation cables according to the ambient temperature: (1) Ordinary grade for -20℃~+100℃; (2) Heat-resistant grade for 40℃~+250℃. Flame-retardant compensation wires or flame-retardant compensation cables should be selected according to the ambient conditions; 3
Intrinsically safe compensation wires or intrinsically safe compensation cables should be selected according to the design requirements of the measurement or control system. 5 Shielded compensation wires or shielded compensation cables should be selected for places with intermittent electric heating or strong electric or magnetic fields. The cross-sectional area of the compensation wire should be determined according to the reciprocating resistance value of its laying length and the external resistance allowed to be input by the matching display instrument, transmitter or measurement and control system interface. 50
Scope of application
Pressure instrument
This regulation applies to the selection of pressure instruments for chemical plants. 2.1.2 Units and scales (gradients)
Pressure instruments shall all use legal measurement units. That is: Pa, kilopascal (kPa) and megapascal (MPa). For foreign-related design projects, international general standards or corresponding national standards can be adopted. 2
2.1.3 When implementing this provision, the relevant national standards in force shall also be complied with. 2.2 Selection of pressure gauges
Select according to the use environment and the nature of the measured medium. In harsh environments such as those with strong atmospheric corrosion, high dust content, and easy spraying of liquids, the appropriate shell material and protection level shall be selected according to environmental conditions. 2 Measurement of general media
(1) When the pressure is between -40kPa~0~+40kPa, a diaphragm pressure gauge should be selected. When the pressure is above +40kPa, a spring tube pressure gauge or a bellows pressure gauge is generally selected. (2)
(3) When the pressure is between -100kPa~0～+2400kPa, a pressure vacuum gauge should be selected. (4) When the pressure is between -100kPa~CkPa, a spring tube vacuum gauge should be selected. 3
For dilute nitric acid, acetic acid and other general corrosive media, acid-resistant pressure gauges or stainless steel diaphragm pressure gauges should be used. 4 For dilute hydrochloric acid, hydrochloric acid gas, heavy oil and similar media with strong corrosiveness, containing solid particles, viscous liquids, etc., diaphragm pressure gauges or diaphragm pressure gauges should be used. The material of the diaphragm and diaphragm must be selected according to the characteristics of the measured medium.
5 For crystallization, scarring and high viscosity media, flange diaphragm pressure gauges should be used. 6 In occasions with strong mechanical vibration, shock-resistant pressure gauges or marine pressure gauges should be used. 7 In flammable and explosive occasions, if electric contact signals are required, explosion-proof pressure controllers or explosion-proof electric contact pressure gauges should be used.
8 For pressure gauges measuring high and medium pressures or highly corrosive media, it is advisable to select pressure gauges with overpressure release facilities on the shell.
Special pressure gauges should be used for the following measuring media: (1)
Gaseous ammonia, liquid ammonia: ammonia pressure gauge, vacuum gauge, pressure vacuum gauge; (2)
Oxygen: oxygen pressure gauge;
Hydrogen: hydrogen pressure gauge;
Chlorine: chlorine-resistant pressure gauge, pressure vacuum gauge; Acetylene: acetylene pressure gauge;
Hydrogen sulfide: sulfur-resistant pressure gauge;
Alkali liquid: alkali-resistant pressure gauge, pressure vacuum gauge. When measuring differential pressure, a differential pressure gauge should be used. Selection of accuracy level
General measurement pressure gauges, diaphragm pressure gauges and diaphragm pressure gauges should be of level 1.5 or 2.5. Precision measurement pressure gauges should be of level 0.4, 0.25 or 0.16. Selection of external dimensions
The dial diameter of pressure gauges installed on pipelines and equipment is Φ100mm or Φ150mm. The pressure gauge installed on the instrument pneumatic pipeline and its auxiliary equipment has a dial diameter of Φ60mm. 2
The pressure gauge installed in places with low illumination, high position or where the indication is difficult to observe has a dial diameter of 3
Φ150mm or Φ200mmc
Choice of measurement range
When measuring stable pressure, the normal operating pressure value should be 1/3~2/3 of the upper limit of the instrument measurement range.1
2When measuring pulsating pressure (such as: pressure at the outlet of pumps, compressors and fans, etc.), the normal operating pressure value should be 1/3~1/2 of the upper limit of the instrument measurement range.3When measuring high and medium pressures (greater than 4MPa), the normal operating pressure value should not exceed 1/2 of the upper limit of the instrument measurement range.
2.3 Choice of transmitter
When transmitting with standard signals, a transmitter should be selected. 2.3.1
2.3.2 In flammable and explosive situations, pneumatic transmitters or explosion-proof electric transmitters should be used. 2.3.3 For crystallized, scarred, blocked, viscous and corrosive media, flange transmitters should be used. The material in direct contact with the medium must be selected according to the characteristics of the medium. 2.3.4 When the measurement accuracy is high and it is difficult for general analog instruments to achieve it, it is advisable to use intelligent transmitters, whose accuracy is better than 0.2 level or above. When the measurement point is not close or the environmental conditions are bad, it is also advisable to use intelligent transmitters.
In situations where the use environment is good and the measurement accuracy and reliability requirements are not high, resistive, inductive 2.3.5
remote pressure gauges or Hall pressure transmitters can be used. 2.3.6
Measures.
When measuring small pressures (less than 500Pa), micro differential pressure transmitters can be used. When measuring the differential pressure of equipment or pipelines, a differential pressure transmitter should be used. In places with good operating environment and easy access, a direct installation type transmitter can be selected. 2.4 Selection of installation accessories
When measuring water vapor and media with a temperature greater than 60°C, a condenser or siphon should be used. When measuring easily liquefied gases, if the pressure point is higher than the instrument, a separator should be used. When measuring dusty gases, a dust collector should be used. When measuring pulsating pressure, a damper or buffer should be used. When the ambient temperature is close to or lower than the freezing point or solidification point of the measured medium, adiabatic or heating should be adopted. 53
Flowmeter
3.1.1 These regulations apply to the selection of flowmeters for chemical plants, including flowmeters that have been finalized and proven to be reliable in practice, mainly including:
Throttling devices and differential pressure gauges:
Velocity flowmeter;
Positive displacement flowmeter;
Variable area flowmeter (rotor flowmeter); mass flowmeter;
Wedge flowmeter;
Open channel flowmeter, etc.
3.1.2 Scale selection
The scale of the instrument should meet the requirements of the instrument module. When the scale reading is not an integer, it can also be selected as an integer for the convenience of reading conversion.
1 Square root scale range
Maximum flow rate does not exceed 95% of the full scale;
Normal flow rate is 70%~85% of the full scale;
Minimum flow rate is not less than 30% of the full scale.
2 Linear scale range
Maximum flow rate does not exceed 90% of the full scale;
Normal flow rate is 50%~70% of the full scale;
Minimum flow rate is not less than 10% of the full scale.
3.1.3 Instrument accuracy
Flowmeters used for energy measurement shall comply with the State Economic Commission’s notice on the issuance of the “General Rules for the Allocation and Management of Energy Metering Instruments in Enterprises (Trial)”. For the provisions of Document No. 244 of the State Economic and Management Commission [1983], please refer to Table 3.1.3. 54
Name of measuring instruments
Various scales
Water flow
Steam flowmeter
Gas flowmeter such as coal gas
Oil flowmeter
Other energetic working fluids
Requirements for the accuracy of energy measuring instruments
Classification and use
Static: used for the measurement of fuel in and out of the factory Dynamic: used for the measurement of bulk low-value fuel in and out of the factory after agreement between the supply and demand parties Accuracy
Dynamic: used for the measurement of technical and economic analysis of workshops (teams) and process ±0.50%~±2.00% for industrial and civil water measurement
used for steam measurement including superheated steam and saturated steam for natural gas, gas and household gas for international trade accounting
used for domestic trade accounting
used for workshops (teams), key energy-consuming equipment and process control Quantity (such as compressed air, oxygen, nitrogen, hydrogen, water, etc.) 3.1.4 Flow unit
Volume flow is m/h1/h;
Mass flow is kg/h, t/h;
Gas volume flow under standard conditions is m/h (P=0.1013MPa, T=0℃). When implementing this regulation, it shall also comply with the provisions of the relevant national standards in force. 3.1.5
3.2 Selection of general fluid, liquid and steam flow measurement instruments 3.2.1
Differential pressure flowmeter
1 Throttling device
(1) Standard throttling device
For general fluid flow measurement, standard throttling devices should be used. The selection of standard throttling devices must comply with the provisions of GB/T2624~93 or IS05167-1 (1991). When implementing these regulations, the requirements of the relevant national standards in force shall also be met.
(2) Non-standard throttling devices
If the following conditions are met, a Venturi tube may be used: 1. Accurate measurement with low pressure loss is required; 2. The measured medium is clean gas or liquid; 3. The inner diameter of the pipe is in the range of 100~1200mm; 4. The fluid pressure is 1.6MPa or less.
Double orifice plate can be selected if the following conditions are met: 1. The measured medium is clean gas or liquid; 2. The Reynolds number is greater than (equal to) 3000 and less than (equal to) 300000. 3. 1/4 round nozzle can be selected if the following conditions are met: 4. The measured medium is clean gas or liquid; 5. The Reynolds number is greater than 200 and less than 100000. (3) Segmental orifice plate can be selected if the following conditions are met: 6. The measured medium is a dirty medium (such as blast furnace gas, mud, etc.) that may produce sediment before and after the orifice plate; 7. The pipeline must be horizontal or inclined. (4) Selection of pressure taking method
The whole project should be considered to adopt a unified pressure taking method as much as possible. 8. Generally, angle pressure taking or flange pressure taking method is used. According to the use conditions and measurement requirements, other pressure taking methods such as diameter pressure taking can be used. 2. Selection of differential pressure range of differential pressure transmitter
The selection of differential pressure range should be determined by calculation. Generally, it is appropriate to select according to the working pressure of the fluid: low differential pressure: 6kPa, 10kPa;
medium differential pressure: 16kPa, 25kPa;
high differential pressure: 30kPa, 60kPa.
3. Measures to improve measurement accuracy
(1) For fluids with large temperature and pressure fluctuations, temperature and pressure compensation measures should be considered: (2) When the straight pipe section of the pipeline is insufficient or a rotating flow is generated in the pipeline, fluid correction measures should be considered and a rectifier of the corresponding pipe diameter should be selected.
4 Special differential pressure flowmeter
(1) Integrated throttling flowmeter
For steam, gas, liquid, pressure is 20MPa (related to the diameter, the larger the diameter, the lower the pressure resistance), temperature is below 700℃, range ratio reaches 10:1, accuracy requirement is ±1.00%, diameter is 15~1500mm, you can choose an integrated throttling flowmeter.
(2) Built-in orifice flowmeter
For the measurement of small flow of clean liquid, steam, gas without suspended matter, when the range ratio is not greater than 3:1, the measurement accuracy requirement is not high, and the pipeline diameter DN<50mm, you can choose a built-in orifice flowmeter. When measuring steam, the steam temperature is not greater than 120℃.
(3) Model flowmeter
For flow measurement of high-viscosity liquids, steam and gas containing suspended matter, wedge flowmeter can be selected when Reynolds number is greater than 500. 3.2.2: Variable area flowmeter (rotameter) When the accuracy is required to be no better than ±1.50% and the range ratio is no greater than 10:1, a rotameter can be selected. 1
Glass rotameter
For on-site indication of flow of clean, transparent, non-toxic, non-flammable and non-explosive fluids with small and micro flows, pressure less than 1MPa, temperature below 100℃, and no corrosion or adhesion to glass, glass rotameter can be used. 2 Metal tube rotor flowmeter
(1) Ordinary metal tube rotor flowmeter
For the measurement of small and medium flow of fluids that are easy to vaporize, easy to condense, toxic, flammable, explosive, and do not contain magnetic substances, fibers and abrasive substances, as well as fluids that are non-corrosive to stainless steel, when local indication or remote signal transmission is required, ordinary metal tube rotor flowmeter can be selected.
(2) Special metal tube rotor flowmeter
A metal tube rotor flowmeter with a jacket
When the measured medium is easy to crystallize or vaporize or has high viscosity, a metal tube rotor flowmeter with a jacket can be selected. A heating or cooling medium is passed through the jacket.
A corrosion-resistant metal tube rotor flowmeter
For the flow measurement of corrosive media, an corrosion-resistant metal tube rotor flowmeter can be used. The rotor flowmeter is required to be installed vertically with an inclination of no more than 5°. Most fluids flow from bottom to top. Special metal tube rotor flowmeters can be connected to horizontal pipelines. The installation position should have less vibration and be easy to observe and maintain. Upstream and downstream cut-off valves and bypass valves should be installed. For dirty media, filters must be installed at the inlet of the flowmeter. 3.2.3 Velocity flowmeter
1 Target flowmeter
Measurement of liquid flow with high viscosity and a small amount of solid particles. When the accuracy is required to be no better than ±1.00% and the range ratio is no more than 10:1, a target flowmeter can be used. Target flowmeters are generally installed on horizontal pipelines, with the length of the front and rear straight pipe sections being 10D/5D. 2 Turbine flowmeter
Measurement of the flow of clean gases and clean liquids with low kinematic viscosity (the greater the viscosity, the smaller the range ratio). When more accurate measurement is required and the range ratio is no more than 10:1, a turbine flowmeter can be used. The turbine flowmeter should be installed on a horizontal pipeline so that the liquid fills the entire pipeline, and is equipped with upstream and downstream stop valves and bypass valves, as well as filters upstream and discharge valves downstream. The straight pipe length is not less than 20D upstream and not less than 5D downstream.
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