What is a pressure vessel

What is a pressure vessel?

Pressure vessel is a kind of airtight equipment which contains gas or liquid and bears a certain pressure. In order to implement scientific management and safety supervision more effectively, pressure vessels are divided into three categories according to working pressure, medium harmfulness and their role in production in China’s “safety supervision regulation for pressure vessels”.

Table of Contents hide

Different regulations are made on the design, manufacturing process, inspection items, contents and methods of each type of pressure vessel. The safety and quality licensing system for imported goods has been implemented for pressure vessels, and the goods without import safety and quality licensing certificate are not allowed to be imported. It should be divided according to the latest TSG 21-2016 “Supervision Regulation on safety technology of stationary pressure vessels”, first divided into the first group of media and the second group of media according to the media, and then divided into categories I, II and III according to the pressure and volume. The so-called first, second and third categories in the old regulations are no longer applicable.

Pressure vessel is a kind of closed vessel which can bear pressure. Pressure vessel is widely used in many fields, such as industry, civil, military and scientific research. Most of them are used in chemical industry and petrochemical industry, and the pressure vessels only used in petrochemical industry account for about 50% of the total pressure vessels. In the field of chemical industry and petrochemical industry, pressure vessel is mainly used for heat transfer, mass transfer, reaction and other process, as well as storage and transportation of pressurized gas or liquefied gas; It is also widely used in other industrial and civil fields, such as air compressor. All kinds of special compressors and auxiliary machines of refrigeration compressors (coolers, buffers, oil-water separators, gas storage tanks, evaporators, liquid coolant storage tanks, etc.) are pressure vessels.

Types of Pressure Vessels

Classification overview

There are many classification methods of pressure vessels, from the perspective of use, manufacture and supervision, including the following.
(1) According to the pressure level, it can be divided into low pressure vessel, medium pressure vessel, high pressure vessel and ultra-high pressure vessel.
(2) According to the medium: non flammable, non-toxic; Flammable or toxic; Highly toxic.
(3) According to the different functions in the process, it can be divided into three parts:

  • ① Reaction vessel: it is used to complete the physical and chemical reaction of medium.
  • ② Heat exchanger: a container used to complete the heat exchange of medium.
  • ③ Separation container: it is used to complete the mass exchange of medium, gas purification, solid, liquid and gas separation.
  • ④ Storage and transportation container: it is used to hold liquid or gas materials, storage and transportation medium or to balance and buffer pressure.

Basic classification method

For pressure vessel classification, the classification diagram shall be selected according to the medium characteristics and the following requirements, and then the coordinate points shall be marked according to the design pressure P (unit: MPa) and volume V (unit: l) to determine the vessel classification.

Multicavity pressure classification

Multi cavity pressure vessels (such as tube side and shell side of heat exchanger, jacketed vessels, etc.) are classified according to the pressure chamber with high classification and managed according to the classification. However, the design and manufacturing technical requirements should be put forward according to the respective categories of each pressure chamber. When the pressure chambers are classified, the design pressure is taken as the design pressure of the pressure chamber, and the volume is taken as the geometric volume of the pressure chamber.
1. Classification of multi media containers in the same chamber
When there are many kinds of media in a pressure chamber, they are classified according to the media with high group.
2. Classification of containers with minimal medium content
When the content of a hazardous substance in the medium is very small, the medium group shall be determined by the pressure vessel design unit according to its hazard degree and content.

Pressure rating

The design pressure (P) of pressure vessel is divided into four pressure grades: low pressure, medium pressure, high pressure and ultra-high pressure

  • (1) Low pressure (code L) 0.1MPa ≤ P < 1.6Mpa.
  • (2) Medium pressure (code m) 1.6Mpa ≤ P < 10.0MPa.
  • (3) High pressure (code h) 10.0MPa ≤ P < 100.0mpa.
  • (4) Ultra high pressure (code U) P ≥ 100.0mpa.

Classification of varieties

Pressure vessels are divided into reaction pressure vessels, heat exchange pressure vessels, separation pressure vessels and storage pressure vessels according to the principle of action in the production process. The specific division is as follows:
(1) Reaction pressure vessel (code R): it is mainly used to complete the physical and chemical reaction of medium, such as reactor, reaction kettle, decomposition pot, vulcanization tank, decomposition tower, polymerizer, autoclave, ultra-high pressure kettle, synthesis tower, shift converter, digester, steam ball, autoclave, gas producer, etc.

What is a reactor

Reactor is a kind of equipment to realize the reaction process, which is widely used in chemical industry, oil refining, metallurgy and other fields. The reactor is used to realize liquid-phase single-phase reaction process and liquid-liquid, gas-liquid, liquid-solid, gas-liquid-solid multi-phase reaction process.

20210718020954 20296 - What is a pressure vessel
The application of reactor began in ancient times. The kiln used to make pottery is a kind of original reactor. There are many kinds of reactors in modern industry, such as blast furnace and converter in metallurgical industry; Fermentation tanks and burners in bioengineering are all different types of reactors.

What is a reaction still

The reaction still is a vessel with physical or chemical reaction. Through the structural design and parameter configuration of the vessel, the heating, evaporation, cooling and low-speed mixing functions required by the process can be realized.

20210718021045 26783 - What is a pressure vessel
Reaction still is widely used in petroleum, chemical industry, rubber, pesticide, dyestuff, medicine and food. It is a pressure vessel used to complete vulcanization, nitration, hydrogenation, alkylation, polymerization, condensation and other process, such as reaction still, reaction pot, decomposition pot, polymerization kettle, etc; Materials generally include carbon manganese steel, stainless steel, zirconium, nickel base (Hastelloy, Monel, Inconel) alloy and other composite materials.
Classification of reaction still
According to the manufacturing structure of the reaction still, it can be divided into three categories: open flat cover reaction still, open butt welding flange reaction still and closed reaction still. Each structure has its application scope, advantages and disadvantages. According to the material and application, the reaction still can be divided into the following types:
stainless steel reaction still
Stainless steel reaction still is composed of reaction still body, reaction still cover, jacket, agitator, transmission device, shaft seal device, support, etc. Materials generally include carbon manganese steel, stainless steel, zirconium, nickel base (Hastelloy, Monel) alloy and other composite materials.
Generally, the stirring forms of stainless steel reaction still include anchor type, paddle type, turbine type, propulsion type or frame type. When the height diameter ratio of the stirring device is large, multi-layer stirring paddles can be used, or it can be selected according to the user’s requirements
The seal types of stainless steel reaction still are different, which can be divided into packing seal, mechanical seal and magnetic seal. The heating methods include electric heating, hot water heating, heat transfer oil circulation heating, external (internal) coil heating, etc. the cooling methods are jacket cooling and coil cooling in the kettle.
Glass lined reaction still
Glass lined reaction still is a kind of composite material product, which is made of glass containing high silicon dioxide lining on the inner surface of steel vessel and firmly adhered to the metal surface by high temperature burning. Therefore, the glass lined reaction still has the double advantages of glass stability and metal strength, which is an excellent corrosion-resistant equipment.
Magnetic stirring reaction still
The static seal structure is adopted, and the magnetic coupling is used between the agitator and the motor drive. Because of its non-contact transmission torque, the static seal is used to replace the dynamic seal, which can completely solve the leakage problem that can not be solved by the mechanical seal and the packing seal before, and make all the mixing parts of the whole medium work in the absolutely sealed state. Therefore, it is more suitable for various flammable and explosive materials It is the most ideal leak free reaction equipment in petroleum, chemical, organic synthesis, polymer polymerization, food and other processes for sulfidation, fluorination, hydrogenation, oxidation and other reactions.

What is a vulcanizer

20210718021102 37056 - What is a pressure vessel

Vulcanization tank refers to the equipment that vulcanizes rubber products with steam. It is a fast opening pressure vessel which needs to be opened frequently. The vapor pressure during vulcanization is generally less than 1MPa gauge pressure and the temperature is below 180 ℃. The structure of vulcanization tank is cylindrical vessel with convex head. There are vertical and horizontal, one end of the head for quick open. The small curing tank is opened and closed by hand, and the large one is opened and closed by hydraulic method. When the hydraulic cylinder is used to push the head to rotate a certain angle, the locking teeth of the connection part between the head and the cylinder body can be locked or retracted. A rocker arm is connected between the head and the barrel. A conveying track is arranged at the bottom of the horizontal vulcanizing tank to facilitate the entry and exit of the trolley with vulcanized rubber products. When the vulcanizing tank bears alternating load, cracks often appear at the tooth root of quick opening. During operation, the end cover can only be opened after the internal pressure is completely relieved. Therefore, the interlock device of pressure relief and quick opening must be installed to prevent safety accidents caused by opening the quick opening before the pressure is completely relieved.

What is polymerizer

20210718021238 67980 - What is a pressure vessel

Polymerizer is the main equipment for preparing polymer compounds. Generally, it is a vertical cylindrical autoclave with jacket for heating or cooling by steam or cold water.

What is autoclave

Autoclave is a kind of reactor operated under high pressure. According to the process requirements, there are two kinds of autoclaves with agitator and without agitator, and the structure of the former is the same as that of the mixing equipment.

20210718021813 17844 - What is a pressure vessel
Its structural features are as follows:

  • (1) The kettle body is a high-pressure cylinder with a thick shell. In order to resist high temperature and corrosion, stainless steel is commonly used. Carbon steel or low alloy steel is also used as the shell. Stainless steel is the inner material, which can be directly made of composite plate or lining;
  • (2) Generally, there is no hole on the kettle body, and the connecting pipe, interface and accessories are set on the kettle cover;
  • (3) The top of the kettle is equipped with a safety relief device, such as a safety valve, a bursting disc device or a combination of the two devices.

What is a synthetic tower

Synthetic tower is a kind of gas-liquid mass transfer equipment widely used in oil refining, chemical industry, petrochemical industry, biochemical industry and pharmaceutical industry. According to the structure of gas-liquid contact parts in the tower, it can be divided into two categories: plate tower and packed tower.

20210718021937 30575 - What is a pressure vessel
Plate column
Plate column is a kind of mass transfer equipment used in gas-liquid or liquid-liquid system. It is composed of cylindrical column and several plates horizontally installed in the column according to certain spacing. A certain number of trays are built in the tray column. The gas passes through the liquid layer on the tray in the form of bubbling or jet for mass and heat transfer. The gas-liquid phase composition changes in a step-by-step manner, which is a step-by-step contact countercurrent operation process.
Packed tower
There is a certain height of packing layer in the packed tower. The liquid flows down from the top of the tower along the packing surface, and the gas contacts the liquid upstream for mass and heat transfer. The gas-liquid phase composition changes continuously along the tower height, which is a differential contact operation process.

What is a shift converter

20210718022140 73688 - What is a pressure vessel

Shift converter is a key equipment in the production of carbon monoxide in ammonia plant. Whether the structure of shift converter can meet the process requirements, calculation equipment and reliability directly affect the output, energy consumption, conversion rate, catalyst consumption and investment cost. With the development of modern technology and the demand of modern ammonia production, the structure of shift converter has been developing continuously.

What is steamed ball

20210718022308 72633 - What is a pressure vessel

Steaming ball is a kind of rotary batch cooking and pulping equipment. It is spherical, mainly composed of sphere, base, transmission device and other parts. The sphere is made of steel plate by welding or riveting. A charging hole is arranged at the position of the vertical center line of the sphere for charging and feeding the cooking liquid. Steam for cooking and heating is fed into the hollow journal and condensed water is discharged. The advantages of steaming ball are that the raw materials in the ball are fully mixed with the liquid medicine, the quality of the pulp is relatively uniform, the liquid ratio is low, the concentration of the liquid medicine is high, the cooking time can be shortened, the equipment is simple, the investment is less, and the management and maintenance are easy. The disadvantages are large area, direct steam, and large concentration change. It is mostly used in medium and small straw pulp mills. There are 14 m3, 25 m3 and 40 m3 steam balls produced in China.

What is autoclaved kettle

20210718022532 20438 - What is a pressure vessel

Autoclaved kettle, also known as autoclave. Autoclave, is a large pressure vessel with large volume and heavy weight. Autoclave is widely used in autoclave curing of building materials such as aerated concrete block, concrete pipe pile, lime sand brick, coal ash brick, microporous calcium silicate board, new lightweight wall material, heat preservation asbestos board, high strength gypsum, etc. it can complete the hydrothermal reaction of Cao—Si02—H2O in autoclave. At the same time, it is also widely used in rubber products, wood drying and anti-corrosion treatment, heavy metal smelting, refractory brick oil penetration and coal penetration, glass steaming, high-pressure treatment of chemical fiber products, high-temperature and high-pressure treatment of food cans, pulp cooking, cable vulcanization, fishing net shaping, chemical industry, medicine, aerospace industry, thermal insulation materials, textile industry Military and other production projects that need pressure steam curing production process.

What is a Gasifier

20210718022709 53489 - What is a pressure vessel

Gasifier refers to the reaction furnace used to produce gas, water gas and semi water gas. The furnace body is cylindrical, the shell is made of steel plate or brick, lined with refractory brick, and equipped with feeding equipment, blast pipe and gas pipe. According to the structure, it can be divided into mechanical generator, step generator, shaft rotating generator and two-stage generator. According to the process, it can be divided into fixed bed or fluidized bed gasifier.

(2) Heat exchange pressure vessel (code E): it is mainly used to complete the heat exchange of medium, such as shell and tube waste heat boiler, heat exchanger, cooler, condenser, heater, disinfector, Dyer, dryer, steamer, preheater, solvent preheater, steamer, steam off-line, electric steam generator, water jacket of gas generator, etc.

What is a heat exchanger

20210718022907 33450 - What is a pressure vessel

Heat exchanger (also known as heat exchanger or heat exchange equipment) is used to transfer heat from hot fluid to cold fluid to meet the specified process requirements. It is an industrial application of convective heat transfer and heat conduction. Heat exchangers can be classified in different ways. According to its operation process, it can be divided into three types: inter wall type, hybrid type and regenerative type; According to the compactness of its surface, it can be divided into compact type and non compact type.

What is a cooler

Cooler is a kind of heat exchange equipment, used to cool the fluid. Usually water or air is used as coolant to remove heat. It can be divided into tubular cooler, plate cooler and air-cooled cooler. Cooler is a heat exchange device widely used in metallurgy, chemical industry, energy, transportation, light industry, food and other industrial sectors.

20210718023024 90249 - What is a pressure vessel
It is suitable for different working conditions such as cooler, condensation, heating, evaporation and waste heat recovery. Therefore, in many kinds of heat exchanger, cooler and tube heat exchanger still occupy an important position.

What is a condenser

Condenser, as a part of refrigeration system, is a kind of heat exchanger. It can convert gas or steam into liquid and transfer the heat in the pipe to the air near the pipe in a fast way. The working process of condenser is an exothermic process, so the temperature of condenser is higher.

20210718023644 51918 - What is a pressure vessel
Many condensers are used in power plants to condense steam from turbines. Condensers are used in refrigeration plants to condense refrigeration vapors such as ammonia and Freon. Condensers are used in the petrochemical industry to condense hydrocarbons and other chemical vapors. In the distillation process, the vapor into a liquid device, also known as the condenser. All condensers operate by taking away the heat of gas or steam.

What is a heater

20210718023733 83826 - What is a pressure vessel

Electric heater refers to the use of electrical energy to achieve heating effect of electrical appliances. It has the advantages of small volume, high heating power, wide application, intelligent control mode, high temperature control precision, and can be connected with computer. It has wide application range, long service life and high reliability. The core of the heater principle is energy conversion, the most extensive is the conversion of electric energy into heat energy.

What is the dryer

20210718023858 80607 - What is a pressure vessel

The dryer is a hollow cylinder made of cast iron with covers at both ends. It is composed of the cylinder and the cylinder heads at both ends. Its outer diameter is mostly 1000-3000mm. In the process of operation, the paper is dried and ironed by steam.

What is a steamer

Electric steamer, also known as electric steamer, is a kind of kitchen appliance developed on the traditional wood steamer, aluminum steamer and bamboo steamer, which uses the principle of electric steam to directly steam all kinds of delicious food.

20210718024224 96486 - What is a pressure vessel
Pay attention to safety in use, do not leave people in the process, if necessary, make sure that people walk and power off.

What is an electric steam generator

20210718024519 15080 - What is a pressure vessel

The electric steam generator is an electric boiler which supplies steam to ironing table and iron. It consists of water tank, electric heater, water injection pump, steam supply valve, pressure gauge, safety valve, steam regulating valve, etc. The full-automatic electric steam generator has a perfect automatic control system. The water level detector in the furnace automatically controls the water injection pump to ensure the water level in the boiler. When the water level is lower than the police line, the heating power will be cut off automatically. The pressure sensor strictly controls the boiler steam pressure, and the pressure is displayed by the steam pressure gauge. The steam supply pressure, quantity and temperature of the boiler can be adjusted. The pressure relay, temperature relay and boiler safety valve can ensure the production safety. Because of its small volume, light weight and flexible mobility, the electric steam generator is a kind of hot and humid processing equipment suitable for intermediate ironing.

(3) Separation pressure vessel (code s): it is mainly used for fluid pressure balance buffer and gas purification separation of medium, such as separator, filter, oil collector, buffer, scrubber, absorption tower, copper scrubber, drying tower, stripper, cylinder separator, deaerator, etc.

What is a separator

20210718024720 19285 - What is a pressure vessel

A separator is a machine that separates mixed substances into two or more different substances. The common separators are centrifugal separator and electrostatic separator.

What is a filter

20210718025627 52965 - What is a pressure vessel

Filter is an indispensable device in the medium pipeline. It is usually installed at the inlet of pressure reducing valve, pressure relief valve, constant water level valve, square filter and other equipment. The filter is composed of cylinder, stainless steel filter screen, blowdown part, transmission device and electrical control part. After the water to be treated passes through the filter cartridge of the filter screen, its impurities are blocked. When it needs to be cleaned, as long as the detachable filter cartridge is taken out and re loaded after treatment, it is very convenient to use and maintain.

What is an oil collector

20210718025636 22521 - What is a pressure vessel

Oil collector is a container for collecting lubricating oil, which is mostly used in refrigeration ammonia system. In the refrigeration ammonia system, a small amount of refrigerant oil will be brought into the refrigeration pipeline and heat exchange equipment by high-speed refrigerant from the refrigeration compressor oil system, and the fouling such as oil film will adhere to the heat exchange pipe, which will reduce the heat exchange effect of the equipment. If the lubricating oil in the oil system runs too much, it will affect the normal operation of the compressor. Therefore, the lubricating oil that runs away either returns to the refrigeration compressor oil system automatically through venturi and other oil return parts, or is collected together through the oil collector.

What is an absorber

20210718025648 56876 - What is a pressure vessel

Absorption tower is the equipment to realize absorption operation. It can be divided into three types according to the gas-liquid contact morphology. The first type is plate column, bubble absorption column and agitated bubble absorption column in which gas is dispersed in liquid phase in the form of bubbles; The second type is the ejector, venturi tube and spray tower dispersed by liquid in the gas phase. The third type is packed absorption tower and falling film absorption tower in which the liquid moves in film form and contacts with the gas phase. The gas-liquid two-phase flow in the tower can be either countercurrent or cocurrent. Generally, countercurrent operation is adopted. The absorbent is added at the top of the tower and flows from top to bottom. It contacts with the gas flowing from bottom to top. The liquid absorbed by the absorbent is discharged from the bottom of the tower, and the purified gas is discharged from the top of the tower.

What is a stripper

20210718025700 87210 - What is a pressure vessel

Stripping is a unit operation used to recover the absorbed solute and separate the absorbent and solute to obtain regeneration. At the same time, in some cases, stripping is also used to remove the light components in liquid. For example, in oil refining industry, steam is often used as stripping agent to remove the light components of oil varieties. Therefore, stripping can be used in combination with absorption or alone.
Stripper can be plate column or packed column. No matter what kind of tower, raw materials enter the tower from the top and leave the tower from the bottom; The desorber enters the tower from the bottom of the tower, contacts with the liquid raw material countercurrent in the tower, and leaves the tower at the top together with the distillate. In contrast to the absorption tower, the concentrated end is at the top of the tower, and the dilute end is at the bottom of the tower. In the stripper, the equilibrium partial pressure of solute in the liquid phase is greater than that in the gas phase. In the stripping process, solute molecules need to be transformed into gas, so it is an endothermic process, so the temperature of stripper is generally equal to or greater than the temperature of raw material, otherwise the stripping effect will be reduced.

What is a cylinder

20210718025713 42985 - What is a pressure vessel

The sub cylinder is the main supporting equipment of the boiler, which is used to distribute the steam generated during the operation of the boiler to various pipelines. The sub cylinder is pressure bearing equipment and belongs to pressure vessel. Its pressure bearing capacity and capacity should correspond to the supporting boiler. The main pressure parts of the cylinder are: head, shell material, etc.

What is a deaerator

20210718025725 83592 - What is a pressure vessel

Deaerator is one of the key equipment of boiler and heating system. If the deaerator has poor deaeration capacity, it will cause serious loss to the corrosion of boiler water supply pipeline, economizer and other auxiliary equipment, and the economic loss will be dozens or hundreds of times of the cost of deaerator. Therefore, the Ministry of electric power of the people’s Republic of China has put forward some standards for the oxygen content of deaerator, That is to say, the oxygen content of feed water of atmospheric deaerator should be less than 15 цɡ/50. The oxygen content in feed water of pressure deaerator should be less than 7 цɡ/L.
Law of deaeration – gelussack’s Law:
When the pressure is constant, the volume of a certain mass of gas increases by 1 ° C, which is equal to 1/273 of its volume at 0 ° C; Or when the pressure is constant, the volume of a certain mass of gas is directly proportional to the thermodynamic temperature. It was discovered in the experiment by the French scientist geluzak, so it was named. It is suitable for ideal gas and also for real gas under high temperature and low pressure.
According to Henry’s law, when the total pressure of gas phase is not high at a certain temperature, for dilute solution, the concentration of solute in solution is proportional to its partial pressure in gas phase; According to Dalton’s partial pressure law, when the temperature and volume are constant, the total pressure of the mixed gas is equal to the sum of the component pressures of the component gases, and the component pressure of each component gas is equal to the pressure of the gas when it occupies the total volume alone.

(4) Storage pressure vessel (code C, including spherical tank code B): it is mainly used to store and hold gas, liquid, liquefied gas and other media, such as various types of storage tanks.
In a pressure vessel, if it has more than two process action principles, it should be classified according to the main role in the process.

Manufacturing process of pressure vessel

Most pressure vessels used for private and industrial purposes use various types of steel, especially carbon steel and stainless steel. Individual steel parts are welded together to form a cylinder or sphere of the pressure vessel. In order to avoid mechanical damage during welding, special preventive measures are taken to determine the properties of steel used for forging. These precautions ensure the mechanical strength of the material and the soundness of the finished pressure vessel. For example, engineering standards currently require that only steel with high impact resistance be used in the manufacture of pressure vessels. For some applications of steel pressure vessels, engineering standards also specify the use of special corrosion resistant materials.
Pressure vessels are also made of partially loaded liners made of metal, ceramic or polymer. This kind of liner not only helps to bear the load of internal pressure, but also protects the container from the influence of the contained substances and prevents leakage. The manufacturing of pressure vessels must follow strict manufacturing standards.
The manufacturing specifications are developed by a number of authorities, including the American Society of mechanical engineers, the National Board of boiler and Pressure Vessel Inspectors, and the European Pressure Equipment Directive. The pressure vessel manufacturer shall comply with one or more of these regulations.

The manufacturing process of pressure vessel includes raw material preparation, marking, blanking, bending, forming, edge processing, assembly, welding, inspection, etc.

Preparation of raw materials

Before marking, the steel should be pretreated first. The pretreatment of steel refers to the purification, rectification and application of protective primer to steel plate, pipe and section steel.
Purification treatment is mainly to remove rust, oxide scale, oil and welding slag on the surface of steel plate, pipe and section steel before marking, cutting and welding, and after cutting, beveling, forming and welding.

Orthopedics is the process of correcting the deformation of steel in the process of transportation, hoisting or storage.

20210718012758 68382 - What is a pressure vessel

The main purpose of applying protective paint is to improve the corrosion resistance of steel, prevent oxidation and prolong the service life of parts and equipment.

Scribing

Marking is the first working procedure in the manufacturing process of pressure vessel, which directly determines the dimensional accuracy and geometric accuracy of parts after forming, and has a great influence on the later assembly and welding process.
Scribing is to draw the blanking line, processing line, various position lines and inspection lines on the raw materials or billets, and mark (or write) the necessary signs and symbols. The marking process usually includes unfolding, lofting and marking of parts. The blank size should be determined before marking. The blank size is composed of unfolding size and various machining allowance. There are several methods to determine the unfolding size of parts

  • 1) Drawing method: refers to the use of geometric drawing method to expand parts into plane graphics.
  • 2) Calculation method: the calculation formula is derived according to the principle of unfolding or the principle of invariable area before and after compression (stretching) deformation.
  • 3) Test method: it means to determine the blank unfolding size of complex parts by test formula. This method is simple and convenient.
  • 4) Comprehensive method: it refers to the drawing method and calculation method can be used to determine the blank unfolding size for different parts of excessively complex parts, and sometimes the test method can be used for verification.
  • The parts for manufacturing containers can be divided into two categories: Deployable parts and non deployable parts. For example, circular cylinder and elliptical head belong to deployable and non deployable parts respectively.

Cutting

Cutting, also known as blanking, refers to the process of separating the required blank on the raw materials crossed the line. There are two cutting methods: mechanical cutting and thermal cutting.

Mechanical cutting

Mechanical cutting mainly includes cutting, sawing, milling and punching. Its characteristic is that the mechanical force plays a major role in the cutting process.
(1) Shear
Shearing is to press the scissors into the workpiece, so that the shear stress exceeds the shear strength of the material to achieve the purpose of shearing. This method has high efficiency and high cutting accuracy. It can be used as long as the hardness and size of the material are suitable, but the metal 2 ~ 3mm away from the cutting has obvious hardening phenomenon. According to the plane shape to be cut, it can be divided into straight line cutting and curve cutting.
1) Linear cutting
There are two kinds of shears using linear long cutting edge for cutting, which are flat shear and inclined shear.
In the flat shear, the two straight cutting edges are parallel, and the shearing process is carried out simultaneously along the length of the cutting edge, so the shearing force is large and the impact is strong, which is suitable for cutting thick and narrow strips.
In the oblique shear, the two straight cutting edges are obliquely intersected at a certain angle, and the shearing process is gradually carried out along the length of the cutting edge, so the shearing force is smaller than that of the flat shear when cutting the workpiece with the same thickness, and the impact is reduced, which is suitable for cutting thin and wide sheet metal.
In equipment manufacturing, gantry shears are often used to cut linear workpieces. The shearing machine has the advantages of convenient use, simple feeding, fast shearing speed and high precision.
(2) Sawing
Sawing belongs to cutting processing, and the equipment used includes grinding wheel saw, disc saw, etc. Sawing is usually used for cutting pipe fittings and profiles.

Oxygen cutting

Oxygen cutting is also called flame cutting. Oxygen cutting belongs to thermal cutting, which needs a preheating flame, but only flame can’t realize cutting. The key is to have high-speed pure oxygen flow.

Plasma cutting

Plasma is a state of matter, which is ionized into positive and negative ions. Plasma cutting is the use of high-temperature, high-speed plasma flame to fuse materials to form a cut, which belongs to the high-temperature melting cutting in thermal cutting. It is not limited by physical properties, and can cut metal or nonmetal, but it is mainly used for cutting stainless steel, aluminum, copper, nickel and their alloys.

Forming

Forming of cylinder

The cylinder body is composed of a number of cylinder sections welded by circumferential welds, and the cylinder sections are welded by plate rolling and longitudinal welds. This is the basic manufacturing method of cylinder section. The principle of roll bending is to apply continuous and uniform plastic bending to the steel plate by using the plate bending machine to obtain the cylindrical surface.

Forming of head

There are three main forming methods of head: stamping, spinning and explosive forming. At present, the commonly used methods are stamping and spinning.

Welding

Welding is a process which makes the weldment combine with atoms and form a permanent joint by heating or pressing, or both. Welding process takes part in 50% of the annual steel consumption in the world.
Welding can be divided into three categories: fusion welding, pressure welding and brazing.

Fusion welding

The processing method is that the workpiece to be welded is locally heated to melt, and the welding seam is formed after condensation, so that the components are connected together. Including arc welding, gas welding, electroslag welding, electron beam welding, laser welding, etc. Fusion welding is a widely used welding method. Most low carbon steel and alloy steel are welded by fusion welding. Special fusion welding can also weld ceramics, glass and other non-metal.

Pressure welding

Welding process must be applied pressure, may or may not be heated to complete the welding. The main purpose of its heating is to soften the metal by applying pressure to make the metal plastic, so that the atoms are close to the distance of mutual stable attraction, which is essentially different from the heating in fusion welding. Pressure welding includes resistance welding, friction welding, ultrasonic welding, cold pressure welding, explosion welding, diffusion welding and magnetic welding. It is characterized by small welding deformation, less cracks and easy automation.

Brazing

The solder with lower melting point than the base metal is heated to melt, but the heating temperature is lower than the melting point of the base metal. Brazing is divided into two categories: brazing and soldering. The heating temperature of brazing is more than 450 ℃, and the tensile strength is more than 200MPa. Silver based and copper based brazing filler metals are often used, which are suitable for the occasions with high working stress and high ambient temperature, such as the welding of cemented carbide turning tools and geological drills. The heating temperature of soldering is less than 450 ℃ and the tensile strength is less than 70MPa, which is suitable for the environment with low stress and low working temperature, such as tin based soldering of circuit.

Development of pressure vessel industry

  • (1) Encouraged by the national industrial policies, the metal pressure vessel industry is encouraged by the relevant national industrial policies listed in the relevant industrial policies, and a good industrial policy environment is conducive to the sustainable development of the industry in the future.
  • (2) The upgrading of the equipment manufacturing industry is the only way for China to become a manufacturing power. The technical level and strength of the equipment manufacturing industry directly affect and determine the competitiveness of its downstream industries and products, and it is an important embodiment of the country’s comprehensive national strength. Throughout the world’s industrial powers, without exception, are powerful in the equipment manufacturing industry. Benefiting from the sustained and rapid development of China’s national economy and the strong support of the state, China’s transformation from a big manufacturing country to a powerful manufacturing country has become an inevitable trend. Under the background of China’s industrial equipment upgrading, the important application fields of metal pressure vessels, such as clean energy application, new energy manufacturing, and seawater desalination equipment manufacturing, have been listed in the current high-tech industrialization key areas Guide (2007) and industrial structure adjustment guide directory (2005), The upgrading of downstream industry will bring huge development opportunities and market prospects for metal pressure vessel manufacturing industry.
  • (3) The development focus of equipment manufacturing industry is gradually shifting to the Asia Pacific region
  • Affected by economic globalization and increasing labor costs, the focus of the world’s manufacturing industry is gradually shifting to the Asia Pacific region. As the most widely accepted and applied pressure vessel standard in the world, American ASME certification has been studied and promoted by more and more enterprises in China. According to the statistics of China Chemical Equipment Association, there were 260 ASME licensed manufacturers in China in 2007, an increase of 33% over the previous year; As of June 2009, the number has increased to 390, ranking second in the world. Among them, there are 126 enterprises with certificates in Jiangsu Province. After years of development, China’s manufacturing industry has a considerable scale and strength foundation, which provides a realistic possibility for foreign countries to transfer equipment manufacturing industry to China.
  • (4) On the basis of introduction, absorption, digestion and innovation, we have developed new technologies and processes suitable for China’s national conditions, trained a large number of technical backbones and experienced managers, and possessed the core competitiveness of opening up domestic and foreign markets.

It is a sealed container which can bear gas or liquid pressure inside or outside and has high safety requirements. In the early chemical industry, the reaction pressure was mostly below 10 MPa. However, after the emergence of high-pressure production processes such as synthetic ammonia and high-pressure polyethylene, the pressure of pressure vessel is required to be more than 100 MPa. With the development of chemical industry and petrochemical industry, the working temperature range of pressure vessels is wider and wider, the capacity is increasing, and some of them need to be resistant to medium corrosion. Since the 1960s, the development of nuclear power plants has put forward higher safety and technical requirements for reactor pressure vessels, which promotes the further development of pressure vessels and is widely used in various industrial sectors. Pressure vessels are mainly cylindrical, but also spherical or other shapes. According to the structure, it can be divided into multilayer pressure vessels, wound plate pressure vessels, groove wound belt pressure vessels, hot sleeve pressure vessels, forging welding pressure vessels and thick plate rolling welding pressure vessels. Most pressure vessels are made of steel, some are made of non-ferrous metals such as aluminum and titanium, and non-metallic materials such as glass fiber reinforced plastics and prestressed concrete. If the pressure vessel explodes in use, it will cause catastrophic accidents. In order to ensure the safety of pressure vessels, the design is advanced, the structure is reasonable, the manufacture is easy, the use is reliable and the cost is economical. According to the specific situation of each country, the standards, specifications and technical conditions of pressure vessels are formulated, and the specific and necessary regulations for the design, manufacture, inspection and use of pressure vessels are put forward.

Application of pressure vessel

Most pressure vessels are industrial. Some private sector uses include hot water tanks and diving tanks. Industrial applications of pressure vessels include distillation tower, hydraulic oil tank and liquefied gas container. In industry, pressure vessels can be used for high pressure or low pressure containment, depending on the customer’s needs and materials used. They can also be used for cooling and process heating. As well as in the processing of materials to achieve secondary containment means.
For gases or liquids, pressure vessels can be used with immersion electric heaters. Industrial versions of these heaters heat various substances (water, oil, gases and solvents) through direct contact. The immersion heater can be installed on the pressure vessel by flange, welding or threaded connection. The combination of immersion electric heater and pressure vessel is an ideal choice for heating gas and liquid and generating steam.

Inspection of pressure vessels

External inspection

Also known as in-service inspection, the main contents of the inspection are: whether there are cracks, deformation, leakage, local overheating and other abnormal phenomena on the external surface of the pressure vessel; Whether the safety accessories are complete, sensitive and reliable; Whether the fastening bolts are in good condition and fully tightened; Whether the foundation sinks, inclines and whether the anticorrosive coating is damaged. External inspection is not only the work of inspectors, but also the daily patrol inspection items of operators. In case of safety endangering phenomena (such as cracks, deformation and serious leakage of pressure parts), stop operation and report to relevant personnel in time.

Internal and external inspection

The internal and external inspection of pressure vessel can only be carried out after shutdown and cleaning of the vessel. The main contents of the inspection include not only all the contents of external inspection, but also the corrosion and wear of internal and external surfaces; All welds, head transition zone and other stress concentration parts shall be inspected for cracks with naked eyes and magnifier. If necessary, the internal quality of welds shall be inspected by ultrasonic or radiographic inspection; Measure the wall thickness. If the measured wall thickness is less than the minimum wall thickness of the vessel, the strength should be checked again, and the use or repair measures should be put forward; If necessary, metallographic examination should be carried out for vessels that may cause changes in the metallographic structure of metal materials; The main bolts of high pressure and ultra-high pressure vessels shall be inspected for cracks by magnetic powder or coloring. Through the internal and external inspection, analyze the causes of the defects and put forward the treatment suggestions. Re inspection shall be carried out after repair. The internal and external inspection cycle of pressure vessels is once every three years, but the inspection cycle of vessels with strong corrosive medium and highly toxic medium should be shortened. The inspection period should also be shortened for the vessels with serious defects, poor welding quality and unclear material corrosion resistance.

Comprehensive inspection

In addition to the above inspection items, pressure test is also required for the overall inspection of pressure vessels (generally hydraulic test). Carry out NDT spot check on main welds or all welds. However, for the vessels with low pressure, non flammable, non-toxic and non corrosive media, if no defects are found, the nondestructive testing may not be carried out after obtaining certain experience. The overall inspection cycle of the container is generally at least once every six years. For the qualified containers containing air and inert gas, the overall inspection period can be appropriately extended after obtaining the use experience and one or two internal and external inspection to confirm that there is no corrosion.

Material substitution of pressure vessel

Attention should be paid to the following matters in substitution of materials:

Regulations on material substitution

In the process of equipment design and manufacturing, material substitution is widely used in the design of pressure vessels due to the difficulty of material procurement and selection or the lack of economic consideration and analysis《 In the design and manufacture, the main requirement is that the material selection of pressure parts of pressure vessels should not only be similar to the appearance and quality of the substituted material, but also take full account of the chemical composition, dimension standard, material quality, etc Performance indicators and monitoring methods should be replaced reasonably. The most basic principle of material substitution is to eliminate the application of substandard materials in substitution, strictly ensure the quality of materials and achieve absolute guarantee. Technically, the technical requirements of substitute materials can not be lower than that of the substituted materials, and the materials can be detected and tested through a variety of material selection methods.
The procedure requirements for material substitution are as follows:

  • (1) The substitution of pressure containing parts of vessels shall be strictly carried out, which shall be approved by the technical department of the substitute unit, and the re inspection report or quality certificate of the substitute materials shall be submitted, which shall be approved by the person in charge;
  • (2) Only after obtaining the permission of the original design unit and obtaining the supporting documents, can material substitution be carried out in the manufacture of pressure vessels;
  • (3) The specification, position, material and specification of the substitute material shall be carefully marked in the design drawing, construction drawing and factory quality certificate of the pressure vessel.

Replace the inferior with the superior

All metal materials used in pressure vessels should have excellent properties, including mechanical properties, corrosion resistance, high temperature resistance and manufacturing process. The performance of each material is fixed. From the point of view of performance comparison, there are often problems of “excellent” and “bad” between materials. However, the requirements of each kind of pressure vessel for material properties are different in different cases. Therefore, the judgment of “excellent” and “bad” in material substitution is based on the reality, and the specific problems are analyzed in detail. Next, based on my own work experience, the author mainly discusses several typical problems of “replacing the inferior with the superior”.
In the manufacture of pressure vessel, the low alloy steel is better than carbon steel in strength, mechanical characteristics and other mechanical energy, but its cold workability and weldability are not as good as carbon steel. Generally speaking, the cold workability and weldability of high strength steel are poor, and the two are negatively correlated. Therefore, the welding process should be adjusted accordingly when substituting in this aspect, and there may be corresponding changes during heat treatment, which should be given full attention.
The material substitution should be considered carefully and comprehensively, otherwise various potential safety hazards may appear in the actual use of pressure vessels. For example, in the wet hydrogen sulfide environment and the equipment with the risk of stress corrosion cracking, the sensitivity of the vessel to stress corrosion cracking increases with the increase of the strength level of the steel used in the vessel, and the two are positively correlated. At this time, it is very easy to cause problems if low alloy steels such as 16MnR are used for 20R, Q235 and 20R series steels. Therefore, this kind of practice of “replacing inferior with superior” is not feasible in principle and should be prohibited. Killed steel has more advantages than rimmed steel in many aspects of properties, but the enameling effect of killed steel is not as good as rimmed steel in the manufacture of glass lined vessels.
Generally speaking, the corrosion resistance of stainless steel is better than that of low alloy steel and carbon steel in the environment containing chloride ion.
Compared with ordinary stainless steel, ultra-low carbon stainless steel has more excellent high temperature thermal strength although it has price advantage and good corrosion resistance. In general, in order to improve the corrosion resistance, it is necessary to reduce the carbon content, and in order to improve the high temperature performance, it is necessary to increase the carbon content. Therefore, in this case, it is necessary to accurately design the equipment temperature and recalculate it if necessary.
Replace thin with thick
“Replacing the thin with the thick” often changes the stress state of the shell from plane stress to plane strain state, which is harmful but not beneficial to the stress state of the container. Generally, the thick wall container is more likely to produce three-dimensional tensile stress than the thin wall container, and then produce plane stress brittle fracture.
For the vessel with equal thickness welding between the head and the cylinder in the original design, if the thickness of individual parts of the vessel shell is replaced by the thickness, it is easy to increase the geometric discontinuity of the shell, thus increasing the local stress on the joint between the head and the cylinder. At this time, it will cause great damage to the vessel with stress corrosion tendency. It may lead to fatigue crack, and serious may cause fatigue fracture.
When the thick plate replaces the thin plate, the connection structure often changes accordingly. For example, when the cylinder is connected with the thickened head, it is usually necessary to cut the edge of the head. For the equipment with pipe as the main cylinder, if the thickness of the cylinder wall is increased, the inner trimming treatment should also be carried out on the cylinder side at the connection part between the head and the cylinder. When the thickness increases greatly, it is often related to the change of welding process.
Although the “replacing thin with thick” on the overall level of the vessel shell will not increase the local stress at the connection of the cylinder and the head, it will inevitably lead to adverse effects:

  • (1) With the increase of thickness, the flaw detection method and welding process in the original shell design should be changed accordingly, which increases the difficulty;
  • (2) The increase of shell thickness will inevitably increase the weight of the container. When the weight of the container increases too much, the foundation and support of the container will be adversely affected;
  • (3) The increase of shell thickness will definitely affect the heat transfer effect of the vessel with shell heat transfer function at the same time.

Other considerations

When substituting materials, the welding process should be properly adjusted according to the actual situation of materials. The general adjustment principle is: when using high-grade materials to replace low-grade materials, the standard of low-grade materials can still be used in the test and acceptance, and there is no need to improve the standard; When the high temperature resistance and toughness of different materials are different, the corresponding temperature may also change during the minimum water pressure test. At this time, the relevant provisions of GB150 shall be strictly followed; When the plate thickness increases beyond the cold coil thickness specified in GB150, the cylinder must be heat treated to eliminate stress; When the thickness of steel plate reaches a certain level, ultrasonic flaw detection should be carried out. If necessary, the pressure of water test should be increased.
Conclusion the design and manufacture of pressure vessel based on the main material just now is the basis of the current application of pressure vessel, and it is also the key and difficult point in the reasonable requirements of neutral energy in the material substitution of pressure vessel. As for the mechanical properties of materials, the toughness should be considered when the strength of materials is tested twice. If the toughness is satisfied, the strength should be improved as much as possible. From this point of view, it is necessary to correctly define “excellent” and “inferior” in the selection of pressure vessel materials, not only from the thickness and strength of materials, but also from a comprehensive analysis and consideration.

Design requirements of pressure vessels

Design pressure

The pressure of pressure vessel can come from two aspects, one is that the pressure is generated (increased) outside the vessel, the other is that the pressure is generated (increased) inside the vessel.
The maximum working pressure refers to the maximum pressure that may appear on the top of the vessel under normal operation.
The design pressure refers to the pressure used to determine the thickness of the vessel shell at the corresponding design temperature, that is, the design pressure of the vessel marked on the nameplate. The design pressure of the pressure vessel shall not be lower than the maximum working pressure; When the static pressure of the liquid column on each part of the vessel or pressure element reaches 5% of the design pressure, the sum of the design pressure and the static pressure of the liquid column should be taken for the design calculation of the part or element; The design pressure of pressure vessel with safety valve shall not be lower than the opening pressure or bursting pressure of safety valve. The design pressure of the vessel should be determined according to the corresponding provisions of GB150.

Design temperature

Metal temperature refers to the average temperature of the pressure parts of the vessel along the section thickness. In any case, the surface temperature of element metal shall not exceed the allowable service temperature of steel.
Design temperature refers to the maximum or minimum temperature that the shell wall or element metal may reach under the corresponding design pressure under normal operation of the vessel. When the temperature of shell wall or element metal is lower than – 20 ℃, the design temperature is determined according to the minimum temperature; In addition, the design temperature is selected according to the highest temperature. The design temperature value shall not be lower than the maximum metal temperature that the element metal may reach; For metal temperatures below 0 ℃, the design temperature shall not be higher than the minimum metal temperature that the element metal may reach. The design temperature of the vessel (i.e. the design medium temperature marked on the vessel name plate) refers to the design temperature of the shell.

Medium

There are many kinds of media involved in the production process, and there are many kinds of classification methods. According to the material state, there are gas, liquid, liquefied gas, simple substance and mixture, etc; According to the chemical characteristics, there are four types: combustible, flammable, inert and combustion supporting; According to the degree of their toxicity to human beings, they can be divided into four levels: extreme harm (I), high harm (II), moderate harm (III) and mild harm (IV).
Flammable medium: refers to the gas mixed with air with lower explosion limit less than 10%, or the difference between upper explosion limit and lower explosion limit greater than or equal to 20%, such as methylamine, ethane, ethylene, etc.
Toxic media: according to GB 5044 classification of occupational exposure to toxic substances, the toxic degree of media is divided into four levels according to the regulations on safety technology supervision of pressure vessels (hereinafter referred to as “volume regulations”). The maximum allowable concentrations were: extremely hazardous (grade I) < 0.1mg/m3; High hazard (grade II) 0.1 ~ < 1.0mg/m3; Moderate hazard (grade III) 1.0 ~ < 10mg/m3; Mild hazard (1V level) ≥ 10mg/m3.
When the medium in the pressure vessel is a mixture, it should be determined by the process design department of the design unit or the production technology department of the user unit according to the composition of the medium and the principle of dividing the toxic degree or flammable medium.
Corrosive media and petrochemical media have corrosion resistance requirements for pressure vessel materials. Sometimes there are impurities in the medium, which aggravates the corrosivity. The types and properties of corrosive media are different, and the corrosivity of media is also different due to different process conditions. This requires the pressure vessel in the selection of materials, in addition to meet the requirements of mechanical properties under the use conditions, but also have enough corrosion resistance, if necessary, also take certain anti-corrosion measures.

Accident rate of pressure vessel

The size of equipment accident rate is influenced by many factors and is very complex. It is not only related to the technical level of the whole industrial field, but also related to social culture and human quality.
Under the same conditions, the accident rate of pressure vessel is much higher than other mechanical equipment. Originally, most pressure vessels bear static and relatively stable load, which is not as easy to failure due to excessive wear as general rotating machinery, nor as easy to fatigue failure due to high cycle repeated load as high-speed engine. The main reasons are as follows.

Technical conditions

  • 1) The service conditions are rather harsh. Pressure vessels not only bear different pressure loads (pulsating load in general) and other loads, but also operate under high temperature or cryogenic conditions. The working medium is often corrosive and the working environment is relatively harsh.
  • 2) It is easy to overload. The pressure in the container often rises rapidly due to misoperation or abnormal reaction, and the container is often broken even if it has not been found.
  • 3) The local stress is complex. For example, high local stress and repeated loading and unloading often lead to fatigue fracture around vessel openings and other structural discontinuities.
  • 4) It often has serious defects. Welding or forging vessels often leave serious defects such as tiny cracks during manufacturing. If these defects continue to expand in operation, or under appropriate conditions (such as service temperature, working medium properties, etc.), the vessel will burst suddenly.

Usage management

  • 1) Illegal use. Purchase some equipment produced by factories without pressure vessel manufacturing qualification as pressure bearing equipment, and illegally use it as pressure vessel, so as to avoid safety supervision and management such as loading, use registration and inspection, leaving endless future trouble.
  • 2) Although the container is legal, the management operation does not meet the requirements. Enterprises are not equipped with or lack of technical management personnel who understand the professional knowledge of pressure vessels and the relevant national regulations and standards for pressure vessels. Pressure vessel operators without necessary professional training and assessment, without a license, it is easy to cause operational accidents.
  • 3) The management of pressure vessel is in “four no” state. That is, there are no safety operation procedures, no technical files for pressure vessels, no personnel with certificates and relevant management personnel for pressure vessels, and no regular inspection management. The pressure vessel and safety accessories are out of control of blind use and management.
  • 4) Change the conditions of use, repair and reform without authorization. Operators ignore the safety of pressure vessels, arbitrarily change the use and use conditions of pressure vessels in order to meet the needs of a certain process, even “sick” operation, illegal overload and overpressure production, resulting in serious consequences.
  • 5) The local government’s safety supervision and management departments and relevant administrative law enforcement departments are not in place. The work of safety supervision and management departments and relevant administrative law enforcement departments failed to take advantage of the development of socialist market economy, especially the proliferation of small-scale and widely distributed private and private enterprises, which made the safety supervision and management of pressure vessels have blind spots and inadequate management, and helped the illegal use and management of pressure vessels.

Deformation and prevention of pressure vessel

Stress deformation and Prevention

Flame cutting deformation

  • (1) Cylinder section: when the short cylinder section of large diameter shell is blanking (long and narrow), the flame cutting edge of its port is easy to deform. After the cutting temperature is cooled, the processing edge shrinks, and the straight edge becomes “arc” edge. After the cylinder section roll is round, its port is not on a horizontal plane, and when the error is large, it can not meet the requirements of assembly and welding. Symmetrical cutting or machining should be adopted to avoid deformation.
  • (2) Head: after the flame cleaning material cutting of the formed head, the periphery of the port will shrink, making the diameter of the head smaller. In severe cases, the diameter of the head after shrinkage can not meet the size requirements. If flame cutting is adopted in the processing of integral forming head port, the shrinkage after cutting should be considered in the design of forming die; If flame cutting is adopted for the port processing of the combined head, the diameter of the head should be enlarged properly to make up for the shrinkage after cutting. The deformation can also be avoided by machining.
  • (3) Machining blank (mainly steel plate blank): this blank is mostly used for large flange or sealing ring on pressure vessel. After flame cutting, the uneven expansion and contraction of the steel plate results in uneven surface of the blank, and in serious cases, the processing capacity of the blank surface is not enough. After cutting, the blank plate should be leveled and straightened. For the blank plate which is difficult to be straightened, the machining allowance can be increased appropriately.

Machining instability deformation

The instability deformation is usually caused by opening large holes on the formed head or cylinder section (such as the loading and unloading holes of the container). The stability of the opening area and its vicinity is weakened, resulting in the deformation of the shell or parts. Try to avoid directly opening large holes on individual cylinder sections or heads, and open large holes after assembling the shell into large sections or whole as appropriate; Before opening the large hole, the opening area is strengthened with the rib plate close to the shell. After assembling the welded pipe, when the shell is in the overall stable state, the reinforcing plate is removed.

Welding deformation

Welding process is the technical requirements and operation regulations of vessel welding, including welding method, welding groove, type and diameter of welding rod, welding process parameters, welding sequence, number of weld pass layers, treatment before and after welding, welding environment requirements, anti deformation and anti deformation measures, etc. The welding process must pass the process qualification, and the process requirements must be strictly implemented in the welding operation.
According to the welding conditions and welding quantity of pressure vessel and large parts, the deformation size and shape of welding are analyzed in advance, and the control measures are formulated

  • (1) Large pressure vessels with multiple welding passes, such as spherical vessels, shall be assembled and connected as a whole before welding. The welding shall be carried out symmetrically and the specified welding sequence shall be observed.
  • (2) For large parts with multiple welding passes, such as melon flap combined head and shell transition section combined by flap, in addition to the above requirements, mouth shaped fixing fixture shall be set at the welding site.
  • (3) For the pressure vessel with long length and multi section welding, the welding shrinkage should be properly released when the cylinder section is blanking, so as to avoid the shortening of the shell after welding.
  • (4) For the assembly and welding of pressure vessels, especially those with complex structure, reasonable assembly sequence and welding deformation prevention measures should be taken to ensure no deformation during manufacturing.
  • (5) Anti deformation measures: according to the practical experience or calculation, the pre deformation is given to the weldment in the opposite direction of welding deformation in advance, and the pre deformation is just offset after welding. The specific methods are as follows: when the two ends of the longitudinal seam butt joint of the pressure vessel cylinder section are arced, the anti deformation is reserved in the opposite direction of welding deformation; The reverse deformation of offset welding deformation is considered in the die size of combined flap head and transition section.

Preventive measures for heat treatment deformation

  • (1) The heat treatment furnace must meet the requirements of the specification, the temperature in the furnace must be uniform and accurate, the flame nozzle on the furnace wall shall be set with a fire wall, and the flame shall not directly contact or approach the heat treatment parts.
  • (2) After the pressure vessels with large length are put into the furnace, the temporary support pads should be added, and the quantity used depends on the specific dimensions of the vessels.
  • (3) Generally, the shell with larger diameter and thinner thickness should be strengthened internally.
  • (4) For the pressure vessel prefabricated in sections, the reinforced support should be set at the section port.
  • (5) The pressure vessel parts which are easy to lose stability under high temperature should also be strengthened according to the specific situation.

Machining error and deformation

Cutting error and deformation

Due to the inaccuracy of blanking size, the shape of formed parts exceeds the standard. The inaccuracy of cutting size is mainly due to errors in calculation or detailed drawing. In addition to improving the technical level of cutting personnel, the checking system of cutting size should be implemented, and the computer software management of cutting size should be adopted as far as possible.

Forming error and deformation

In the process of pressure vessel parts forming, due to improper operation or mold nonstandard deformation: there are certain requirements for the demoulding temperature of the hot forming head, if the temperature is still high, demoulding too early will cause the head shrinkage, and if it is serious, its geometric dimension will exceed the standard; The container parts made by mechanical roller or pressing are deformed due to improper operation; The geometric dimension of the formed pressure vessel parts does not meet the requirements due to the improper or wrong design of the die. The main preventive measures are as follows:

  • (1) Molding operation is carried out in strict accordance with the technical requirements.
  • (2) Strictly control the shape of workpiece with inspection template.
  • (3) Based on the theoretical size and shape of the processed parts, the changes of the pressure vessel parts during and after processing should be fully considered in the mold design. The springback of the formed parts should be considered in the cold forming mold, and the shrinkage of the formed parts after cooling should be considered in the hot forming mold.

Assembly error and deformation

During the assembly of pressure vessel shell, the deformation caused by misalignment or out of straightness error is called assembly deformation. The preventive measures are as follows

  • (1) Positioning fixture shall be used for shell assembly. For shell with larger diameter and thinner thickness, support shall be added to the shell section during assembly to strictly limit the staggered joint of shell butt joint.
  • (2) The horizontal assembly of the shell should be carried out on the idler, and its straightness should be checked with a straight line.
  • (3) The pressure vessel prefabricated in sections shall be installed with positioning fixture, and its straightness shall be checked with theodolite.

Source: Network Arrangement – China Pressure Vessels Manufacturer  www.secmachinery.com

www.secmachinery.com is one of the leading china filtration equipment & sanitary stainless steel pressure vessels manufacturer, with professional factory. We focus on the sanitary pressure vessels, filtration equipment research and development, manufacturing, sales and service since the company been established. Our products is widely used on bio-pharmaceutical, food and beverage, fine chemical industry. 

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@secmachinery.com

Related News

العربيةБългарски简体中文繁體中文DanskNederlandsEnglishFrançaisDeutschBahasa IndonesiaItaliano日本語한국어LatinPortuguêsРусскийEspañolதமிழ்ไทยTürkçe