Pressure vessel is an indispensable equipment in the industrial production process. With the development of the national economy and the improvement of people's living standards, the use of pressure vessels more and more widely, it is not only used in industry and agriculture, scientific research, national defense, medical and health care and education and sports and other sectors of the national economy, but also deep into the dry household. Pressure vessels are not only the number of fast-growing, and the type of complexity, the possibility of accidents is greater. As a pressure vessel operator, to ensure the safe operation of pressure vessels is their own due diligence. In order to help operators to improve the theoretical knowledge and practical level of operation, this chapter will explain in more detail some of the basic knowledge related to pressure vessels.
Section I. Introduction to pressure vessels
I. Pressure
We call the force acting vertically on the surface of an object pressure. When people walk on the mud road, two feet often sink very deep, if the road on a wooden board, people walk from the wooden board, two feet will not sink. It can be seen that whether the road surface will be plunged into not only with the size of the pressure on the road surface and with the area of the force. Therefore, the pressure per unit area should be compared. We call the force per unit area the pressure. If we use P to denote the pressure; corpse to denote the pressure; J to denote the area subjected to the force. Then:
P (pressure) = F (pressure) / S (force area) (1-1)
The unit of force is expressed in "N (Newton)"; the unit of area is expressed in "m2" and "cm2". The unit of force is expressed in "N (Newton)"; the unit of area is expressed in "m2" and "cm2". The legal unit of measurement of pressure is "Pascal", referred to as "Pa", expressed in "h". l Pascal: 1 Newton / m ', that is, 1h two 1N / m2. 1N / m2. It is used in the past with the unit of pressure "kglTem2" conversion relationship:
lkWrm2 two 10000kgr / m2 two 9.8x104h
From the above analysis, it can be seen that the pressure and the pressure is the concept of the two different physical quantities, but in the pressure vessel or general engineering, people are accustomed to the pressure is called pressure. It is customary to refer to pressure as pressure. Therefore, in the absence of explanation, the pressure mentioned later in this book is actually the pressure.
(a) atmospheric pressure
The surface of the Earth is wrapped in a very thick layer of atmosphere. Atmosphere by the center of the earth's attraction generates gravity, so surrounded by the atmosphere outside the earth on the surface of the earth and its objects on the atmospheric pressure, that is, the so-called atmospheric pressure. The thicker the atmosphere, the greater the pressure; and vice versa, the smaller. Therefore, the atmospheric pressure is not constant, and the atmospheric pressure on high mountains is smaller than that at sea level. In order to make the calculation of a unified base, in the past, we will be the atmospheric pressure at sea level 1.033kzf/cm2 (equivalent to 0.1MPa, MPa read megapascals, 1 megabucks: 1 million), or 760 millimeters of mercury known as a standard atmospheric pressure, or - a physical atmospheric pressure.
Engineering for ease of calculation, the "gr / em2 (0.098MPa) pressure is called a project atmospheric pressure. It and the standard atmospheric pressure conversion relationship between:
Page 1 1 engineering atmospheric pressure = 0.968 standard atmospheric pressure = 735.6mlh
If the height of the water column to calculate the pressure, the conversion relationship is:
1kWm2 (9.8Pa); 1mmH20
1kgf / em2 (0.098MPa ): 1000011llllI~120 two lOmilo
(ii) absolute pressure, gauge pressure and negative pressure
The medium in the container (liquid or gas) pressure is higher than the atmospheric pressure, the medium is in a positive state; such as lower than the atmospheric pressure, the medium is in a negative state. The actual pressure inside the container is called the absolute pressure, with the symbol - Pa "said.
When the pressure of the medium in the container is equal to the atmospheric pressure, the needle of the pressure gauge in the zero position (Figure l-1 (a)). Or u-tube pressure gauge inside the liquid level is equal (Figure 1-2 (a)).
When the pressure of the medium in the container is greater than atmospheric pressure, the pointer of the pressure gauge will turn, the gauge reads (Figure 1-1 (b)). Or u-shaped tube pressure gauge of the liquid level by the container medium pressure to the end of the through atmosphere, the formation of liquid column difference "(Figure 1-2 (b)). At this time, the pressure gauge reading or liquid column difference in the pressure value is the container medium pressure exceeds the atmospheric pressure part, that is, the table pressure, referred to as gauge pressure.
When the pressure of the medium in the container is lower than the external atmospheric pressure, then the u-tube pressure gauge of the liquid surface is pressed to the end connected to the container by atmospheric pressure, the formation of a liquid column difference Hall / (Figure 1-2 (c)), the Hall of the pressure value of f that is the medium pressure is lower than the atmospheric pressure of the part known as the negative pressure or vacuum, referred to as the negative pressure.
Second, the definition of the pressure vessel
The so-called container, the usual saying is: by the curved surfaces used to contain the material space components. In layman's terms, it is the chemical industry, oil refining, pharmaceuticals, food and other production of a variety of equipment used in the external shell belongs to the container. It goes without saying that all closed containers subjected to pressure are called pressure vessels, or pressurized vessels.
Chapter 2 Pressure Vessel Structure
Section I. Basic Composition of Pressure Vessels
The structural type of pressure vessels is varied, it is based on the role of the vessel, process requirements, processing equipment and manufacturing methods and other factors to determine. Figure 2-1, Figure 2-2 shows the common cylindrical container and spherical container, respectively.
From the figure, it can be seen that the structure of the container is composed of the shell with the pressure, connectors, sealing elements and supports and other major components. In addition, as a production process equipment, some of the pressure capacity aluminum, such as for chemical reactions, heat transfer, separation and other processes of the pressure vessel, the shell is also equipped with internal parts required by the process. In this regard, this book does not make a special introduction, but only to introduce the other components of the pressure vessel.
First, the shell
Shell is the most important component of the pressure vessel, is the storage of materials or chemical reactions to complete the required pressure space, the shape of the cylindrical, spherical, conical and combined and so on a number of species, but the most commonly used is the cylindrical and spherical two.
(a) cylindrical shell
Its shape is characterized by axisymmetric, cylindrical body is a smooth curved surface, the stress distribution is relatively uniform, high load-bearing capacity, and easy to manufacture, easy to
Page 15 setup and assembly and disassembly of the inner parts, and thus gained wide application. Cylindrical shell consists of a cylindrical cylinder and two ends of the head or end cap.
1. Cylinder
Simple body diameter is small (generally "5 plus one"), can be made of seamless steel pipe; diameter is large, the available steel plate in the coiler first rolled into a cylinder, and then welded. As the container diameter increases, the steel plate needs to be spliced, and thus the number of longitudinal welds of the simplified body increases. When the shell is longer, due to the limitations of the size of the steel plate, two or more cylinders (at this time each of which is called a cylinder section) welded into the required length of the body. In order to facilitate batch production, the cylinder diameter of the second small has been standardized, according to Table 2-1, Table 2-2 shown in the nominal diameter selection (with brackets should try not to use the size). For welded body, the table nominal diameter (D.) refers to its inner diameter; while the cylinder made of seamless steel pipe, the table nominal diameter refers to its outer diameter.
Cylindrical cylinder according to its structure can be divided into two categories of integral and combined, its structural characteristics and scope of application see section II of this chapter.
2. Head and end cover
Where welded with the cylinder and not detachable, it is called head (1l, 14 in Fig.2-1); with the simplified body to flange and so on connection and detachable is called end cover (3 in Fig.2-1). According to the different geometrical shapes, the head can be divided into several kinds such as hemispherical, oval, disk, conical with folded edge, conical without folded edge and flat plate-shaped head (also called flat cover). For the container which no longer needs to be opened after assembling, such as the container without inner parts or without inner parts but not needing to be replaced or overhauled, the head and the simplified body adopt the form of welded connection, which can effectively guarantee the sealing and save steel and reduce the amount of manufacturing and processing. For the container which needs to be opened, the head (end cover) and the connection of the simplified body should adopt the detachable type, at this time, the seal must be installed between the head and the cylinder.
Characteristics and application scope of various types of heads are detailed in Section III of this chapter.
(II) Spherical shell
The container shell is spherical, also called ball tank. Its shape is characterized by center symmetry, has the following advantages: uniform force; in the same wall thickness conditions, the highest bearing capacity of the spherical shell, that is, in the same internal pressure, the spherical shell requires the thinnest wall thickness, only for the same diameter, the same material cylindrical shell wall thickness of 1/2 (not training - corrosion margin); in the same volume conditions, the spherical shell of the smallest surface area. Shell wall thin and small surface area, manufacturing can save steel, such as manufacturing volume of the same capacity
Chapter III safety accessories
Safety valves, rupture discs, pressure gauges, level gauges, thermometers, etc. is the main safety accessories of the pressure vessel, these safety accessories sensitive and reliable pressure vessel is an important guarantee of safe work.
The first section of the safety valve
The safety valve is the most commonly used safety relief device on the pressure vessel. It is through the automatic opening of the valve to discharge the medium to reduce the high pressure in the container. The advantage is: only discharge pressure vessel higher than the prescribed value of part of the pressure, when the pressure in the container falls to the normal pressure value is automatically closed, so that the pressure vessel and the safety valve to work again, so that the pressure vessel will not make the pressure vessel once the overpressure of all the media have to be discharged to cause waste and production interruptions; the structural characteristics of the safety valve so that the installation and adjustment of the relatively easy. Its shortcomings are poor sealing, even if it is a good safety valve in the normal working pressure will inevitably leak slightly; due to the spring and other inertia, the valve opens with a hysteresis phenomenon, and thus slower response to pressure relief; when the medium is not clean, the valve spool and seat will be sticking, so that the safety valve reaches the opening pressure and can not be opened, or so that the safety valve is not tight, did not reach the opening pressure has been leaked. At the same time, the safety valve on the pressure vessel medium selective, it applies to cleaner such as air, water vapor, water, etc., should not be used for toxic media, not to mention that it is not suitable for the possibility of violent chemical reactions and make the container pressure rise sharply in the medium.
First, the safety valve working principle
The safety valve is mainly composed of three parts: valve seat, valve flap and loading mechanism. Valve seat and seat body is a whole, some assembled together, connected to the container. The valve flap is usually accompanied by a valve stem, fastened to the valve seat. Above the valve flap is the loading mechanism, which is used to adjust the size of the load. When the pressure in the container within the specified operating pressure range, the medium acting on the valve flap pressure is less than the loading mechanism imposed on it above the force, the difference between the two constitutes the valve flap and the sealing force between the valve seat, so that the valve flap is tightly pressed against the valve seat, the container gas can not be discharged; when the pressure in the container exceeds the specified operating pressure and reaches the opening pressure of the safety valve, the medium acting on the flap of the valve flap is greater than the force of loading mechanism added to it above the force, so the valve flap is used to adjust the size of load. When the pressure in the vessel exceeds the specified working pressure and reaches the opening pressure of the safety valve, the force of the medium acting on the valve flap is greater than the force loaded on it by the loading mechanism, so the valve flap leaves the valve seat and the safety valve opens. If the container's safety discharge is less than the safety valve discharge, the pressure inside the device gradually decline, and soon fall back to normal working pressure, the medium acting on the valve flap on the force is less than the loading mechanism exerted on it, the valve flap and the valve seat, the gas stops being discharged, the container to maintain the normal working pressure to continue to work. Safety valve by acting on the valve flap on the unbalanced effect of the two forces, so that its opening and closing, in order to achieve automatic control of pressure vessels overpressure purpose.
Second, the type of safety valve
(a) according to the loading mechanism classification
1. Hammer lever safety valve
Hammer lever safety valve is the use of the hammer and the lever to balance the force acting on the valve flap, the structure of the valve as shown in Figure 3-1
Page 40 shown by adjusting the weight in the lever on the position or change the mass of the weight to the valve flap. Its structure is shown in Figure 3-1
Page 40, by adjusting the position of the hammer on the lever or changing the mass of the hammer to adjust the opening pressure of the corrective safety valve.
The hammer safety valve is characterized by a simple structure, easy to adjust and relatively accurate, the load will not be significantly increased with the valve flap rise, action and performance is not affected by high temperature, but its structure is relatively bulky, the weight of the hammer and the size of the valve body is not proportional to the valve sealing performance of the valve is more sensitive to vibration, the valve flap back to the seat of the valve is prone to deflection, back to the seat of the pressure is relatively low, and in some cases even down to 70% of the normal working pressure to maintain sealing, which is very difficult for the valve to open, and the valve is not suitable for the safety of the valve. Some even have to be reduced to 70% of the normal operating pressure to maintain sealing, which is unfavorable to the normal operation of the pressure vessel. Weighted lever safety valves are suitable for high temperature occasions, especially boilers and high temperature vessels.
2. Spring-loaded safety valves
Spring-loaded safety valves utilize the compressed spring force to balance the force acting on the valve flap, and its structure is shown in Figure 3-2, which is adjusted by the adjusting nut to adjust the opening (setting) pressure of the safety valve.
Spring-loaded safety valves are characterized by a lightweight and compact structure, high sensitivity, unrestricted placement, insensitive to vibration, but the load will be added with the opening of the valve to change the spring on the valve will be affected by high temperatures over a long period of time and the elasticity of the valve is reduced. Suitable for mobile equipment and medium pressure pulsating fixed equipment.
(B) according to the valve opening height classification
According to the different valve opening height, safety valves are divided into full-opening type and micro-opening type.
1. Full-opening safety valve
As shown in Figure 3-3, the safety valve is open when the valve opening height A "d / 4 (d is the minimum diameter of the flow path). Flap opening height has made its curtain area (flap rise, in its sealing surface between the formation of cylindrical or conical channel area) is greater than or equal to the area of the flow path (valve inlet end to the sealing surface between the minimum cross-sectional area of the flow path). In order to increase the opening height of the valve flap, upper and lower adjustment rings are installed. Mounted on the outside of the valve flap on the adjusting ring and the valve seat on the lower adjusting ring in the sealing surface around the formation of a very narrow gap, when the opening height is not large, the airflow twice impact valve flap, so that it continues to rise, the opening height increases, the upper adjusting ring and force the direction of the airflow to turn down, the reaction force to make the valve flap further open. This form of safety valve sensitivity is higher, the position of the adjustment circle is difficult to adjust the appropriate. In recent years, the manufacture of full-opening safety valves generally use the structure of the recoil disk, and valve flap activity connection.
2. Micro-opening safety valve
The valve opening height is very small, A; (1/40-1/20)d. In order to increase the valve opening height, generally installed on the valve seat
Chapter IV Pressure Vessel Management
Section I Pressure Vessel Technical Archives
The technical archive is a pressure vessel from the design, manufacture, use and maintenance of the whole process of textual records. The whole process of the written record, it provides people with the specifics of the process, through which the pressure vessel management and operators can fully grasp the technical status of the equipment, to understand its operating rules. A complete technical file is the main basis for the correct and reasonable use of pressure vessels. Therefore, the establishment of the technical file of the pressure vessel is an important basic work of safety and technical management. Pressure vessels should be established on a technical file, the technical file should include the original technical data of the pressure vessel, container use record data and container safety accessories technical data.
First, the original technical data of the pressure vessel
The original technical data of the pressure vessel, including the design of the pressure vessel and the pressure vessel manufacturing and installation documents and information.
(a) the design of the pressure vessel
Pressure vessel design documents, including design drawings, technical conditions, strength calculations, if necessary, should also include the design or installation, instructions.
(1) The design unit of the pressure vessel, the pressure vessel should be provided to the use of units or pressure vessel manufacturing units to set juice instructions, design drawings and technical conditions.
(2) When the user needs, pressure vessel design or manufacturing unit should also be provided to the use of pressure vessels, installation, use instructions.
(3) for mobile pressure vessels, high-pressure vessels, the third type of medium-pressure reaction vessels and storage vessels, the design unit should provide strength calculations to the use of units.
(4) When designing according to JB4732, the design unit shall provide the stress analysis report to the user.
The content of the strength calculation book, at least, should include: design conditions, the norms and standards used, materials, corrosion margins, calculated thickness, nominal thickness, calculated stress and so on.
Pressure vessels equipped with safety valves, rupture disc devices, the design unit should provide the user with a pressure vessel safety discharge, safety valve discharge and rupture disc discharge area of the calculation. Can not be calculated, should seek the views of the use of units, consultation on the choice of safety relief devices.
In the process parameters, materials used, manufacturing technology, heat treatment, inspection and other aspects of special requirements, should be specified in the contract.
(B) pressure vessel manufacturing unit should be provided to the user's technical documents and information
Pressure vessel factory, the manufacturing unit should be provided to the user at least the following technical documents and information:
(1) as-built drawings. As-built drawings should be designed unit qualification seal (compound seal is invalid). If the manufacturing occurred in the material substitution, non-destructive testing method changes, processing size changes, etc., the manufacturing unit should be in accordance with the requirements of the design modification notification
Page 60 in the as-built drawings directly on the note. The notation should be the signature of the modifier and reviewer and the date of modification. As-built drawings should be stamped with as-built stamp, as-built stamp should be the name of the manufacturing unit, manufacturing license number and "as-built drawings".
(2) product quality certification and product nameplate topography.
(3) pressure vessel product safety and quality supervision and inspection of bandits (except for the implementation of supervision and inspection of products).
(4) mobile pressure vessels should also provide product instructions (including safety instructions), with a list of tools and safety accessories, chassis instructions.
(5) This section I (a) of the strength of the required calculations.
Pressure vessel pressure components (head, forgings, etc.) of the manufacturing unit, should be in accordance with the product quality certificate of the pressure components of the relevant content, respectively, to the pressure vessel manufacturing unit and pressure vessel users to provide the quality certificate of the pressure components.
Second, the use of container record information
After the container is put into use, it should be recorded on time the use of technical files and storage containers. Records of use include records of operation and inspection and repair records.
(a) container operation record
container operation record in the main圮man container start date, each time to drive and stop the period; the actual operating pressure, operating temperature and its fluctuation range and number of times. When the operating conditions change, the date of change and the actual operating conditions after the change should be noted. Should also be deposited on the accident record information and processing reports.
(B) container inspection and repair records
container inspection and repair records are mainly recorded in the inspection or repair date, content; inspection of the defects found in the elimination of defects and inspection conclusions; container pressure test and test evaluation conclusions; container pressure components of the repair or replacement.
Pressure vessel use record by the container specialist or each regular or each open, stop the inspection truthfully fill in. If the container is transferred out of the original use of the unit, the container should be technical files, including the original technical information and the use of record information, along with the container and transfer to the new use of the unit.
Third, the safety device technical data
This type of information mainly includes the installation of technical specifications and safety device inspection or replacement record information.
(a) safety device technical specifications
Technical specifications should be the name of the safety device, form, specifications, structure, technical conditions and the scope of application of the device. Technical specifications provided by the safety device manufacturing unit.
(b) safety device inspection or replacement records
Contents include device inspection and correction date, test or adjustment results, the next calibration date, replacement date and replacement records. Calibration or replacement information by the container management personnel to fill in.
The second section of the use of pressure vessels registration
The use of pressure vessels in the pressure vessel unit, before putting into use, should be in accordance with the "Pressure Vessel Use Registration Management Rules" requirements, to the safety inspection agencies or authorized departments to handle the use of the registration procedures, to obtain the use of certificates in order to be able to put the container