HG/T 20515-2000 Instrument Isolation and Purging Design Specifications (with clause explanation)
Some standard content:
Industry Standard of the People's Republic of China
Design Code for Instrument Seal and Purge
Design Code for Instrument Seal and Purge HG/T20515-2000
Editor: China Wuhuan Chemical Engineering Company Approval Department: State Administration of Petroleum and Chemical Industry Implementation Date: June 1, 2001 1 General Principles
1.0.1 This regulation applies to the design of isolation and purge of differential measurement and control instruments in chemical industry, including application scope, use requirements, material selection, replacement methods, etc. 1.DZ Isolation or purge is a method to prevent corrosive, high viscosity, precipitation and vaporized and condensed process media from entering the instrument or its pipeline, to protect the instrument and to achieve various measurements. 1.0.3 Isolation and purge are interrelated. Sometimes one measurement method can be replaced by another method. When necessary, the two methods can also be used together. Therefore, it is very necessary to conduct a detailed analysis before selecting a measurement method. 1.0.4 For the measurement of high viscosity, process media that may precipitate, vaporize, or condense, the instrument should be installed nearby. 1.0.5 When implementing this provision, the provisions of the relevant national standards in force should also be followed. 305
2.1 Scope of application
2.1.1 Isolation is a method of using a barrier fluid and an isolation diaphragm to prevent the measured medium from directly contacting the instrument sensor element, so as to protect the instrument and achieve quality.
2.1.2 For corrosive media, when the material of the measuring instrument cannot meet the requirements of corrosion resistance, a trap should be used to protect the instrument.
2.1.3 For measuring viscous media, solid-containing media, toxic media, or media that may vaporize, condense, crystallize, or precipitate at ambient temperature, the barrier method can also be used. 2.2 In-pipe isolation method
2.2.1 In-pipe isolation method is an isolation method that uses an isolation tube filled with a barrier fluid. In this way, the pipes of the measuring tube and the isolation tube should be properly arranged to facilitate the filling of the required liquid and ensure reliable storage. 2.2.2
In-pipe isolation is suitable for instruments with stable pressure of the measured medium and small discharge volume. 2.2.3
The diameter and material of the isolation tube are generally the same as those of the measuring pipeline. 2.3Container isolation method
Container isolation is an isolation method that uses an isolation container to fill the isolation liquid. The container isolation method is suitable for instruments with obvious pressure fluctuations of the measured medium and large discharge volume. 2.3.2
Selection of isolation container
The structural type of the isolation container should be selected according to the relative density of the measured medium and the isolation, the relative position of the instrument and the isolation container, and other factors. The isolation container should have good sealing performance, simple structure, easy cleaning, and strong replacement performance. 2
3The material of the isolation container should be selected according to the corrosiveness of the measured medium at the working temperature and concentration. 306
2.4 Diaphragm isolation method
Diaphragm isolation is an isolation method that uses a corrosive diaphragm to isolate the isolation liquid from the measured medium. It is used for highly corrosive media, viscous media with strong adhesion, and other occasions where it is difficult to use pipe isolation or container isolation.
When the diaphragm isolation method is selected for measurement, it is recommended to use an instrument with diaphragm isolation. 2.4.3
Selection of isolation diaphragm
The material of the isolation diaphragm should be selected according to the corrosiveness of the measured medium at the working temperature and concentration. 1
2The diaphragm must be elastic and impermeable, and have a sufficiently large displacement volume to reduce the measurement error. 2.5
Technical requirements for the trapping liquid
Good chemical stability, no chemical reaction with the measured medium. It is not miscible with the medium being measured.
3 It has a different density from the medium being measured, and the density difference is as large as possible, and the stratification is obvious: high boiling point, low volatility.
When the ambient temperature changes, it does not stick or condense: 6 It is non-corrosive to instruments and measuring pipelines:
The properties and uses of commonly used separation fluids are shown in the appendix. 2.5.2
3 Flushing
3.1 Scope of application
3.1.1 Flushing is used for the separation and pressure flow measurement of corrosive, high-viscosity, fusible, and precipitating media.
3.1.2 Flushing referred to in this regulation does not include the use of air or gas to blow into the instrument housing and transmitter box for anti-corrosion or anti-drying, and the use of water or steam to clean the measuring pipelines and control lines. Flushing fluid
Flushing fluid must be the fluid medium allowed by the process to be measured, and generally should meet the following requirements: 3.2. 1
No chemical reaction with the process medium of the measured object: clean, no solid matter, no contamination of process medium; 2
When the flushing fluid is liquid, no phase change occurs after pressure reduction: 3
4 Non-corrosive;
5 Good fluidity.
Flushing fluid usually uses air, nitrogen, steam condensate and other fluids allowed by the process to be measured 3.2.2
Medium.
The flushing fluid source should be fully reliable, continuous and stable, and not affected by the process state and process. Pressure and flow rate of purging fluid
3.3.1 The pressure of purging fluid should be higher than the pressure of the object to be measured to ensure continuous and stable purging according to the predetermined flow rate during the purging process.
3.2.2 The reverse flow rate should be selected according to the type of purging fluid, the characteristics of the measured medium, and the measurement requirements. The purging volume in various cases can refer to the following values: 1 Fluidized bed: When the purging fluid is air or other gases, it is generally 0.85~3.4m/h. 2 Low-pressure sugar storage liquid level: When the purging fluid is air or other gases, it is generally 0.03~0.045m/h. 308
3.-General flow measurement: When the purging fluid is air or other gases, it is 0.03-.0.14m/h. When the purge fluid is against the object, it is generally 0.014~0.035m/h3.3.3 The control and indication of the purge flow are generally carried out by using orifice plate, shaped body, drilled orifice valve, constant difference relay, constant difference flow regulator and rotor flowmeter. When the pressure fluctuation of the object or the pressure fluctuation of the purge fluid is obvious, the pressure should be adjusted steadily. 3.4
Purge flow limiting orifice
The aperture of the closed flow limiting orifice can be calculated by the calculation method of the general flow limiting orifice. 3.4.11
Connection of purge pipeline
The material of the purge pipeline should be selected according to the properties of the working medium and the measurement requirements. 3.5.1
3.5.2 The entry point of the purge fluid into the Sheppard line should be as close as possible to the instrument source component to keep the pressure drop caused by the purge in the measuring pipeline to a minimum. 3.5.3 When selecting the installation location of the measuring instrument and designing the measuring pipeline, try to avoid condensation or infiltration of the measuring medium to avoid measurement errors or damage to the instrument. 3.5.4 For the connection diagram of the pipelines for pressure, flow and level measurement by monthly flushing, please refer to the automatic control installation atlas\ (HIG21581-95)
H Oil-water solution
Density ratio 50%
Ethylene glycol water solution
Density ratio 50%
Ethanol solution
2. Diisocyanate
Glycerol ratio 36%
Carbon tetrachloride
Sulfonated kerosene
Specific density
15℃／
Appendix
Appendix A
Properties and uses of commonly used isolation fluids
Properties and uses of commonly used isolation fluids List of viscosity (nP·s
[25. 66]20.9
1.068! 4. 36
Vapor pressure
[15℃]
0.63810159
145000
Freezing point
[197. 8| - 12. 95bZxz.net
Properties and uses
Applicable to oils and water insoluble in water, suitable for the like, hot steam,
water, coal, gas, semi-water bath, gas, etc., hydrocarbons, oxygen
Has water absorption, can be dissolved in water, aldehyde and
ether. Applicable to oily substances and
reduced gas, ammonia
falls into water, alcohol and ether. Applicable to the like|| tt||Material and liquefied gas
Soluble in water, suitable for propane, alkane
and other complete substances
Not soluble in water, suitable for dry salts, acids
and other water-soluble and saturated ammonia, carbon dioxide
chemical gas medium
Soluble in water, suitable for dry propane, alkane
and other substances
Slightly soluble in water, with aldehydes, alcohols, lactones,
11. 1:Carbon tetrachloride and acetic acid can be mixed arbitrarily. Applicable to nitrogen and other media. Insoluble in water. Can be mixed arbitrarily with aldehydes, enzymes, benzene, oil, etc. Applicable to age-related media. Insoluble in water. Suitable for corrosive non-organic waves. Sulfonated oil. Applicable to
acetylene, hydrogen and other interfaces
pentachloroethane
methyl silicone socks
gold fluorine rubber
transformer oil
5% alkali drop
40%CaCtr
aqueous solution
specific density
（mPat
(25℃
(25%)
25%℃)
10 ±1%
20
rara/e
(23℃)25
Continued in the attached table
Vapor pressure
(20℃
Pu solid pointFlash point
Properties and uses
Insoluble in water, can be mixed with alcohol, aldehyde and other organic substances, toxic. Suitable for
Its cloth has excellent electrical insulation,
water-increasing and moisture-proof properties, small viscosity-temperature
coefficient, small volatility, large compression
rate, small surface tension, can be used at -50
+200℃, suitable for gases and liquids other than oxygen, suitable for condensing gas, non-combustible, insoluble in water and general decomposing agents, and unresponsive to nitric acid, sulfuric acid, aqua regia, salt alcohol, and burning. Suitable for strong acid, ammonia, concentrated hydrogen, ammonia water, NaOH, sulfide amine, sulfur film water gas, semi-water gas, etc. Suitable for water gas, semi-water gas, etc. Water welding gas
Applicable to propylene, benzene, petroleum gas
Explanation of the terms in this regulation
The terms in this regulation that require different degrees of strictness are explained as follows: 1 Indicates that it is very strict and must be done in this way. The positive word is "must" and the negative word is "strictly prohibited". 2 Indicates that it is strict and should be done in normal circumstances. The positive word is "should" and the negative word is "should not" or "must not". 3 Indicates that it is allowed to be optional and should be done first when conditions permit. Use the indirect positive word to lead to "should". This word uses "should not" to indicate that there is a choice. If it can be done under certain conditions, use "may". 312
Table separation and purge design regulations
HG/T20515-2000
Article explanation
1 General
1.0.3 Purge measurement is an indispensable way to carry out instrument maintenance. In many occasions, it cannot be replaced by other measurement methods. In phosphate fertilizer, urea and other projects, it is very important to measure the performance of the instrument. It is often used as the main means of preventing crystallization and corrosion in foreign imported designs. This European revision has modified the expression of "avoid using" in the regulations. 2 Isolation
24.2 The diaphragm isolation measurement method is rarely used today. From now on, this regulation recommends the use of instruments with diaphragm isolation instead.
Z.4.3 Automatic Control Design Anti-Corrosion Manual (CADC051-93) has made detailed descriptions of the anti-corrosion properties of various materials, so the anti-corrosion properties of various materials are no longer listed. 3 Flushing
31.1 Flushing includes blowing, steam blowing and flushing. "Blowing" and "steam blowing" are to continuously and quantitatively blow gas and steam into the measured object through the measuring pipeline. "Flushing" is to continuously and quantitatively flush liquid into the measured object through the measuring pipeline. The purpose of both is to prevent the measured medium from directly contacting the instrument sensor, so as to protect the instrument panel.
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