Basic concepts of pressure vessels

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　Basic Concepts of Pressure Vessels I. Terminology Explanation Pressure: A force that acts vertically on the surface of an object is called pressure. Pressure: The force exerted per unit area is called pressure. Atmospheric pressure: The atmosphere is subjected to the gravitational pull of the Earth’s core, which generates gravity; as a result, objects surrounding the Earth’s surface are subjected to atmospheric pressure. Pressure of pressure vessels: In pressure vessels or in general engineering practice, people *tend to refer to pressure intensity as pressure. Design pressure: refers to the pressure at the corresponding design temperature that is used to determine the calculated wall thickness of the vessel and the dimensions of its components. Generally, the design pressure is set to be equal to or slightly higher than the maximum operating pressure. Operating pressure: Also known as process pressure, it refers to the pressure at the top of the container during normal operational conditions (i.e., excluding the hydrostatic pressure of the liquid). Strength: For a given material, there is a certain limit to the stress it can withstand; once this limit is exceeded, the material will break. This limit is known as strength. Stress: The additional internal force exerted per unit area on a material. Allowable stress: The maximum safe stress that a particular material can withstand. Standard boiling point: Pressure vessels: All sealed containers that are under pressure are referred to as pressure vessels. The process parameters of pressure vessels are determined by the requirements of the production process, and they serve as the main basis for the design of pressure vessels and their safe operation. The primary process parameters are pressure and temperature. Tensile strength: The maximum stress that a steel specimen can withstand before breaking during a tensile test. Yield limit: Also known as yield strength, it is the minimum stress at which a specimen continues to deform significantly during tensile testing, even though the pulling force does not increase (or may even decrease). Creep limit: It refers to the maximum stress at which, under a certain temperature and constant tensile load, the creep deformation or creep rate of the specimen does not exceed a specified value within a given time interval. Endurance strength: The stress at which the specimen fractures after a specified period of time at a given temperature. Plasticity: refers to the ability of metal materials to undergo plastic deformation. Toughness: To prevent or reduce brittle failure of pressure vessels (failure that occurs at low stress levels without significant plastic deformation), the steel used in such vessels is required to possess good toughness at the operating temperature; this property indicates the material’s ability to resist impact energy. Processability of pressure vessels: Most pressure vessels are manufactured by rolling or stamping steel plates and then welding them, so they require good processability, that is, cold formability and weldability. Load: During operation, pressure vessels are subject to various forms of deformation factors. We classify these deformation factors as being caused by equivalent forces, that is, the force exerted on a unit of material; this is referred to as load in the field of mechanics of materials. Loads are classified into pressure loads, temperature loads, wind loads, seismic loads, etc. II. Unit conversions: 1 Kgf/cm2 = 1 engineering atmosphere = 735.6 mmHg = 10 mm of water column. 1 MPa = 10^6 Pa = 10 Kgf/cm2. III. Pressure sources for pressure vessels: The sources of pressure can be categorized into two types: the generation of gas pressure, and increases in pressure that occur either inside or outside the vessel. IV. Boundaries of pressure vessels The \"Regulations on Safety Supervision of Pressure Vessels\" classify vessels into three categories: I. Vessels that fall under one of the following conditions are classified as Category I vessels: 1. Low-pressure vessels containing non-flammable or non-toxic media (0.1 Mpa ≤ p ≤ 1.6 Mpa) ； 2. Low-pressure separation vessels and heat exchange vessels for flammable or toxic media (0.1 Mpa ≤ p ≤ 1.6 Mpa). II. Containers that fall under one of the following situations are classified as Category II containers: 1. Medium-pressure containers (1.6 Mpa ≤ p ≤ 10.0 Mpa) ； 2. Low-pressure containers for highly toxic media (0.1Mpa≤p≤1.6Mpa) ； 3. Low-pressure reaction vessels and storage/transmission vessels for flammable or toxic media (0.1 Mpa ≤ p ≤ 1.6 Mpa). 4. Low-pressure waste heat boilers with an inner diameter of less than 1 meter. III. Containers that fall under one of the following categories are classified as Category III containers: 1. High-pressure and ultra-high-pressure containers (①High pressure: 10 Mpa ≤ p ≤ 100 Mpa; ②Ultra-high pressure: 1.6 Mpa ≤ p ≤ 10.0 Mpa). 2. Low-pressure containers containing highly toxic substances where pw × V ≥ 0.2 m3•Mpa, or medium-pressure containers containing highly toxic substances (pw is the operating pressure in Mpa; V is the volume in m3) ； 3. Medium-pressure reaction vessels containing flammable or toxic media with pw×V≥0.5 m3•Mpa, or medium-pressure storage and transportation vessels with pw×V≥5 m3•Mpa ； 4. Medium-pressure waste heat boilers or low-pressure waste heat boilers with an inner diameter greater than 1 meter. *Containers are typically classified into four categories based on the pressure level (with p representing the design pressure): ㈠ Low-pressure containers: 0.1Mpa≤p≤1.6Mpa; ㈡ Medium-pressure containers: 1.6Mpa≤p≤10.0Mpa; ㈢ High-pressure containers: 10Mpa≤p≤100Mpa; ㈣ Ultra-high-pressure containers: p≥100Mpa. Lecture 2: Structure of Pressure Vessels. The structural forms of pressure vessels are diverse, and they are determined based on factors such as the function of the vessel, process requirements, processing equipment, and manufacturing methods. The structure of a container mainly consists of key components such as the ① housing for withstanding pressure, ② connectors, ③ sealing elements, and ④ supports. 　Safe Operation of Pressure Vessels, Lecture 4: Introduction to Pressure Vessel Design. In China, the standard used for the conventional design of pressure vessels is the **standard for steel pressure vessels**. The strength criterion adopted in this standard is elastic failure, that is, the basic (film) stress in the shell body is required not to exceed the allowable stress value of the material, and due to the additional stresses resulting from structural discontinuities, a stress enhancement factor is used in the wall thickness calculation. ①1. Calculation of cylinder wall thickness 2. Calculation of head wall thickness 3. Bolt design 4. Flange design 5. Support design 6. Welded structure design of the container