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2023 / 04 / 27
Introduction to tubular reactors 1.1 Difference between tubular reactor and kettle reactor (1) Tubular reactors are flat push flow reactors with no return mixing, while kettle reactors are fully mixed flow reactors; (2) The residence time of the medium in the reactor is shorter in the tubular reactor, while the residence time in the kettle reactor is unstable; (3) The tube reactor has a stronger ability to dissipate reaction heat, while the kettle reactor has a poorer ability to dissipate reaction heat, and can be equipped with a jacket outside the kettle reactor or with coils inside the kettle to strengthen heat exchange; 1.2 Features of tubular reactors 1) equal reaction times for all parts of the reactant in the reactor, the concentration of reactants and the rate of chemical reaction at any point in the reactor do not change because of time 2) narrow working chamber, large specific surface area, internal and external heat transfer structure, high heat transfer efficiency, especially suitable for reactions with large thermal effects 3) as the tubular reactor is a flat push flow reactor, the material re-mixing in the tubular reactor is smaller and in this respect it has an advantage over the kettle reactor in that the fluid in the tubular reactor can be seen as an ideal fluid when the flux is small; 4) It is suitable for both gas-to-gas reactions and liquid-to-liquid reactions, which can also be carried out in pressurised environments, and is equally suitable for highly viscous materials; 5) extremely high control accuracy for the time control of the medium staying in the reactor, and also the operation of sectional temperature control; 6) the large capacity per unit volume of the tubular reactor makes it suitable for large continuous production with high reaction rates; Types of tubular
Reactor simple faults and handling
2023 / 04 / 18
The reactor is the most commonly used physical mixing or chemical reactor, through the structural design and parameter configuration of the vessel, to achieve the process requirements on heating, evaporation, cooling and low-speed mixing functions. It is widely used in medicine, food, chemical industry, rubber, pesticides, dyestuffs, and is a pressure vessel used to complete the process of synthesis, oxidation, sulphidation, nitration, hydrogenation, hydrocarbonisation, polymerisation, condensation, etc. For the application of the reactor, we often encounter such and such abnormal phenomena, the following combined with the actual process of chemical production summed up the reactor common 8 kinds of failure and elimination methods. one. Failure phenomenon: shell damage (corrosion, cracks, perforation) Failure causes. 1. by the medium radiation (pitting, intergranular corrosion). 2. The impact of thermal stress to produce cracks or alkali brittle. 3. Wear thinning or uniform corrosion. Treatment methods. 1. the use of corrosion-resistant materials lining the shell need to be relined or local patch welding. 2. After welding, stress should be removed and cracks should be repaired. 3. More than the minimum allowable thickness of the design, the body needs to be replaced. Second, the phenomenon of failure: over temperature and over pressure Cause of failure. 1. Instrument failure, control is not strict. 2. Misoperation; improper proportioning of raw materials; violent reaction 3. Poor heat transfer or stirring performance, resulting in side reactions. 4. Inlet valv
Multi-effect evaporation, MVR, multi-stage flash evaporation
2023 / 04 / 07
From emission reduction to emission limitation to zero emission, the standard of wastewater discharge is gradually rising. To achieve "zero discharge", the focus is on the full recovery of highly saline wastewater, which essentially means separating water and salts from the wastewater. Currently, concentration and crystallisation technologies, as well as coupled and synergised technologies, are more often used to achieve zero discharge of highly saline wastewater. Of course, sometimes, depending on the actual situation of the high-salt wastewater, it is necessary to add pre-treatment technology before the technology in order to provide better treatment conditions for the subsequent process. Concentration, the core process for the resource treatment of high-salt wastewater, is divided into thermal concentration and membrane concentration depending on the target and the scope of application. Among them, thermal concentration technology is suitable for treating wastewater with high TDS and COD of up to several hundred grams per litre, by heating to concentrate the ions in high-salt wastewater at a high rate, mainly including multi-stage flash evaporation MSF, multi-effect evaporation MED and mechanical vapour recompression evaporation MVR. Multi-stage flash evaporation (MSF) Multi-stage flash technology began in the 1950s as a process whereby highly saline wastewater heated to a certain temperature is sequentially flash vaporised in a series of vessels at progressively lower pressures, before the vapour is condensed to give fresh water. As the first distillation technology to be applied, multi-stage flash MSF is a mature process, reliable in operation and suitable for large-scale, but with relatively low thermodynamic efficiency, high energy consumption and the presence of equipment fouling and corrosion limiting the MSF first effect steam temperature and affecting
Shell and tube heat exchanger leakage treatment
2023 / 03 / 31
Preface: Shell and tube heat exchanger is currently the most widely used kind of heat exchange equipment. Compared with several other inter-wall heat exchangers, the unit volume of equipment can provide a much larger heat transfer area, the heat transfer effect is also better. Due to the compact structure of the equipment, solid, and can choose a variety of materials to manufacture, it is more adaptable, especially in large installations and high temperature, high pressure is widely used. 1.. Introduction to tubular heat exchangers Over the years, the plant to a variety of water heat exchanger failure, the largest proportion of leakage of the tube system. Surface heat exchanger water-side pressure is greater than the steam-side pressure, once the tube system leaks, the feed water will rush into the shell, causing the steam side full of water. Water will likely be backed up along the pumping pipeline to the turbine, resulting in deformation of the turbine cylinder, expansion of the difference between changes in the unit vibration, and even blade fracture and other accidents. This type of heat exchanger leakage caused by the entire unit to stop and the turbine into the water accident in the plant occurred in many cases. Therefore, analysis of heat exchanger leakage causes, to find countermeasures to reduce leakage as much as possible is very important. 2, the cause of leakage analysis Tube heat exchanger internal tube system leakage is mainly divided into tube leakage and port leakage. 1 tube port leakage causes 1.1 Excessive thermal stress Shell and tube heat exchanger in operation, due to the cold, hot fluid temperature differences, so that the shell and tube wall temperature differences between each other. This difference makes the shell and tube thermal expan
12 types of tower equipment working principle (collection)
2023 / 03 / 23
Tower equipment is the most notable equipment in the petrochemical industry, in the tower equipment can be gas-liquid or liquid-liquid full contact between the two phases, the implementation of inter-phase mass transfer, so in the production process commonly used in the tower equipment for distillation, absorption, desorption, gas humidification and cooling and other unit operation process 1. Packed Absorption Tower Introduction: The packed tower is a mass transfer equipment using the packing in the tower as the contact member between the two phases of gas and liquid. The tower body is a vertical cylinder, the bottom is equipped with packing support plate, packing in a messy pile or the whole way placed on the support plate. The packing is installed above the packing pressure plate to prevent it from being blown by the rising airflow. Liquid is sprayed onto the packing from the top of the tower via a liquid distributor and flows down the surface of the packing. The gas is fed from the bottom of the tower, the gas distribution device (small diameter tower is generally not set up gas distribution device) distribution, and the liquid is counter-current continuous through the gap in the packing layer, on the surface of the packing, gas-liquid two-phase close contact for mass transfer. Packed tower is a continuous contact gas-liquid mass transfer equipment, the composition of the two phases along the tower height continuous change, in the normal operating state, the gas phase for the continuous phase, the liquid phase for the dispersed phase. Advantages: large production capacity, high separation efficiency, small pressure drop, small liquid holding capacity, large operating flexibility, etc. Disadvantages: high packing cost; when the liquid load is small can not effectively wet the packing surface, so that the mass transfer efficiency is reduced; can not be used directly for suspended matter or easy polymerisation of materials; side l
What are the special requirements for cryogenic pressure vessels
2023 / 03 / 13
Structural design The structural design of cryogenic pressure vessels should be considered sufficiently flexible, with the following main requirements. ① The structure should be as simple as possible to reduce the constraints between the welded parts. ② The structure should be designed to avoid excessive temperature gradients. ③ Sharp changes in the cross-section should be avoided as far as possible to reduce local stress concentrations and the inner end of the inserted receiver should be polished to a rounded angle to make a smooth transition. ④ The connecting welds of accessories should not be discontinuous or spot welded. ⑤ The saddle seat, ear seat, legs (except for spherical tanks) or skirt seat of the vessel should be set with a pad or connection plate to avoid welding directly with the vessel shell as far as possible, and the pad or connection plate should be considered according to the low temperature material. (vi) joint reinforcement should be used as far as possible as a whole reinforcement or thick-walled tube reinforcement, if the reinforcement plate is used, the weld seam should be rounded and smooth transition. (vii) For vessels that cannot be heat-treated as a whole, if the parts to be welded with them need to be stress relieved, the parts should be considered to be able to be heat-treated separately. Tube openings Low temperature pressure vessels should try to avoid the main weld and its nearby area, such as must be opened in the weld area, should meet the requirements of the relevant standards. The receiver on the low temperature pressure vessel should meet the following requirements. ① with the shell welded pipe section, the wall thickness should be not less than 5mm, of which the diameter DN ≤ 50mm receiver, it is appropriate to use thick-walled pipe, its extension using ordinary wall thickness seamle
Super complete! Multiple reactor forms and characteristics
2023 / 03 / 03
Chemical reactor is the core equipment of chemical production, the form of reactor has a very important impact on chemical production, can directly affect the production safety and product quality. According to the characteristics of the reactor form, it can be mainly divided into kettle reactor, tube reactor, tower reactor, bed reactor, micro reactor and so on. Kettle reactor The kettle reactor is also known as reactor and pot reactor. It is the simplest and most widely used of all types of reactors, and is widely used in petroleum, chemical, rubber, pesticide, dye, pharmaceutical and other fields. It can be used to carry out homogeneous reactions or non-homogeneous reactions mainly in liquid phase, such as liquid-liquid phase, liquid-solid phase, gas-liquid phase, gas-liquid-solid phase, etc. Kettle reactors are characterised by a wide range of temperatures and pressures, adaptability, flexibility of operation, easy control of temperature and concentration during continuous operation and homogeneous product quality. These reactors are usually most commonly used under relatively mild operating conditions, such as atmospheric pressure, low temperature and below the boiling point of the material. When the reaction conditions are more severe (e.g. high temperature, high pressure, strong corrosion, etc.), special kettle reactors can also be used for production. The main structure of the kettle reactor consists of the kettle body, stirring device, transmission device, shaft sealing device and heat exchange device. Kettle reactors can be divided according to their mode of operation into (1) Intermittent kettle, also known as intermittent kettle reactor, is characterised by flexible operation and can be adapted to different operating conditions and product varieties, and is particularly suitable for the production of small batches, multiple varieties and long reaction times. The disadvantage of intermitten
Maintenance of pressure vessels during decommissioning
2023 / 02 / 24
01 Keep the pressure vessel dry and clean to prevent atmospheric corrosion. Scientific practice has proved that dry air, carbon steel and other iron alloys generally do not produce corrosion, only in the case of moisture (relative humidity of more than 60%), and the metal surface with dust, dirt or old corrosion products exist, corrosion began to take place. Therefore, in order to reduce the corrosion of the atmosphere on the external surface of the decommissioned pressure vessel, the surface of the vessel should be kept clean, often scattered on the surface of the pressure vessel dust, ash and other dirt scrubbed clean, and keep the pressure vessel and the surrounding environment dry. 02 Paint the outer wall of the pressure vessel to prevent atmospheric corrosion, also pay attention to the insulation layer under and pressure vessel support at the anti-corrosion, etc. 03 The pressure gauge should be kept clean, the glass on the dial must be bright and clear so that the pressure reading indicated by the pointer in the gauge is clear and easy to see. Found that the pressure table (including taking the pressure tube) should be dealt with in a timely manner when there is a fault, the pressure table of the indicated value of doubt, should be promptly calibrated with the standard table, incorrect when it should be replaced. Pressure gauge to be regularly calibrated, calibration cycle of not less than 6 months, after the calibration of the pressure gauge should be affixed with a certificate of conformity and sealed. 04 Pressure table has one of the following conditions, should stop using and replace: limited stop nail pressure table, in the absence of pressure, the pointer can not return to the limit stop nail; unlimited stop nail pressure table (limited to the positive pressure table), in the absence of pressure, the value of the pointer from the zero position
[Knowledge]Commonly used chemical equipment cleaning how to clean? Super comprehensive summary!
2023 / 02 / 17
Chemical equipment cleaning technology Chemical equipment cleaning consists of both online and offline cleaning. Online cleaning The cooling water tower in the circulating water system is used as a dosing tank to fill the system with chemicals for natural circulation. Advantages: the equipment does not have to stop, does not affect the normal production use. Disadvantages: the cleaning effect is not very good compared to offline cleaning. The cleaning time is long and the corrosion hazard to the equipment is high. Offline cleaning Offline cleaning can be divided into physical cleaning and chemical cleaning. Physical cleaning: the use of high-pressure water to clean the equipment. High pressure cleaning equipment is required. Chemical cleaning: the heat exchanger is taken out separately and the inlet and outlet pipes of the circulating water are connected to the cleaning vehicle for circulation. Advantages: reduces the amount of chemicals used, good cleaning effect. Disadvantages: corresponding equipment is required, such as cleaning vehicles or cleaning water tanks, high-pressure pumps, various sizes of connection valves, welding equipment, etc. Chemical cleaning has two forms: acid cleaning and alkaline cleaning. Alkaline washing: mainly to remove organic matter, micro-organisms, oil and other adhesions inside the equipment, such as rust inhibitors when the equipment is installed. Alkali washing can also play the role of loosening, loosening, emulsifying and dispersing inorganic salts. Commonly used cleaning agents are sodium hydroxide, sodium carbonate, trisodium phosphate, etc. Acid washing: mainly to remove inorganic salts deposited, such as carbonate, sulfate, silica scale, etc.. Commonly used cleaning agents are hydrochloric acid, sulphuric acid, hydrofluoric acid and other organic acids. Citric acid, sulfamic aci
2023 / 02 / 10
Manufacturing process The manufacturing process of pressure vessels includes preparation of raw materials, scribing, undercutting, bending, forming, edge machining, assembly, welding, inspection, etc. Preparation of raw materials Before scribing the steel, the steel should first be pre-treated. The pre-treatment of steel refers to the purification, straightening and application of protective primer to materials such as steel plates, pipes and sections. Decontamination is the removal of rust, oxidation, oil and welding slag from the surface of steel plates, pipes and sections before scribing, cutting and welding and after cutting, beveling, forming and welding. Straightening is the process of correcting the deformation of steel produced during transport, lifting or storage. Protective coating is mainly applied to the surface in order to improve the corrosion resistance of steel, prevent oxidation and extend the life of parts and equipment. Scribing Scribing is the first process of the pressure vessel manufacturing process, it directly determines the dimensional accuracy and geometric shape accuracy of the parts after forming, and has a great impact on the subsequent grouping and welding process. Scribing is in the raw material or by the initial processing of the billet scribed out of the material line, processing line, a variety of location lines and inspection lines, and hit (or write on) the necessary signs, symbols. The scribing process usually includes the unfolding, placing and marking of the part. The billet size should be determined before scribing. The dimensions of the blank consist of the unfolded dimensions of the part and various machining allowances. Determine the size of the part unfolded mainly the following methods. 1) drawing method: refers to the use of geometric drawing method to expand the part into a plane figure. 2) cal
What do chemical plants need to be purged?
2023 / 02 / 03
Chemical plant purging is an important and indispensable part of chemical production, mainly to eliminate hidden dangers and avoid unnecessary losses in order to check the construction quality of the cleanliness of the piping system so that system operation can proceed smoothly. Today we introduce you to three common chemical plant blowing methods, their flushing principles and requirements, preparation conditions, operating points, qualified standards and precautions! The purpose of blowing: before the start of the device, it is necessary to blow and clean the pipeline and equipment after its installation and inspection is qualified, the purpose is to use air (nitrogen), steam, water and chemical solutions and other fluids, blowing and flushing to remove residual impurities in the construction process to ensure the smooth start of the device. There are usually several methods such as water flushing, air (nitrogen) blowing and oil cleaning. Water flushing Water flushing is a method of flushing pipes and equipment with water as the medium and under pressure by means of a pump. For example: flushing of circulating water systems. 1. Flushing principles and requirements ❶ Water flushing of pipes should be carried out at the maximum possible flow rate in the pipe or at a flow rate of not less than 1.5 m/s, with the flow direction from high to low. ❷ The water quality for flushing should meet the requirements for flushing pipes and equipment materials. General equipment and pipeline flushing is commonly used with a turbidity level of less than 10mg/L and a chloride ion content of less than 100ppm. The water is not only used for the flushing of the pipes, but also for the flushing of the pipes. ❹ Where pipes and equipment are connected, a blind must be added to the inlet and outlet of the equipment when flushing, and only after this pipeline has been flushed
2023 / 01 / 18
What disciplines are involved in the design of a process package? The development of a process package is a systematic project. It involves a number of disciplines and specialisms and is difficult to complete on your own. Generally speaking, process package development and design is a joint effort between R&D, chemical process, process systems, analysis and laboratory, automation, materials, safety and health, environmental protection and other disciplines to complete the process package design for the chemical product. What design documents should be included in the finished process package? The finished process package should include instructions, a process flow diagram (PFD), a preliminary piping and instrumentation flow diagram (P&ID), a proposed equipment layout, a list of process equipment, a process equipment data sheet (with equipment sketches), a summary of catalysts and chemicals, a summary of sampling points, a materials manual (if required), a safety manual (including occupational health, safety and environmental protection), an operations manual (including an analysis manual ), physical data manuals and relevant calculations. The quality control of the process package design is the same as the quality control requirements for the basic/preliminary design phase for all relevant disciplines as defined in the company's design standards. Detailed specification of the content and depth of the process package design 1 Specification The process package design specification is an important part of the process package design and should include the following a) Production methods, plant characteristics; depicting the advancedness, reliability and plant characteristics of the process production methods used in the process package design. b) Name and size of product, annual operating hours, and mode of opera
Discussion of issues related to post-weld heat treatment
2023 / 01 / 11
Heat treatment as a traditional and effective method of improving and restoring metal properties in the pressure vessel design, manufacturing and other links has been a relatively weak link. Pressure vessels involve four types of heat treatment: post-weld heat treatment (stress relief heat treatment); improve material properties heat treatment; restore material properties heat treatment; post-weld hydrogen elimination treatment. Here the focus on the pressure vessel design is widely used in the post-weld heat treatment of the relevant issues to be discussed. 1 post-weld heat treatment (stress relief heat treatment) purpose 1. Relaxation of welding involved in stress. 2. Stabilize the shape and size of the structure and reduce distortion. 3. improve the performance of the base material, welding area, including a. improve the plasticity of the weld metal. b. reduce the heat affected zone hardness. c. improve fracture toughness. d. improve fatigue strength. e. restore or improve the yield strength reduced in cold forming. 4. Improve resistance to stress corrosion. 5. Further release of harmful gases, especially hydrogen, from the weld metal to prevent delayed cracking. 2 austenitic stainless steel pressure vessel whether the need for post-weld heat treatment Post-weld heat treatment is the use of metal materials at high temperatures to reduce the yield limit, so that the stress of high places to produce plastic rheology, so as to achieve the purpose of eliminating residual stress in welding, while improving the plasticity and toughness of the welded joint and heat-affected zone, to improve the ability to resist stress corrosion. This method of stress relief is widely used in carbon steel and low-alloy steel pressure vessels with a body-centred cubic crystal structure. Austenitic stainless steel crystal structure is fa
Chemical equipment layout requirements
2023 / 01 / 03
There are various types of equipment in chemical plants, and because of the large number of various types of equipment and the specificity of the equipment itself, there are specific rules and requirements for the layout of each type of equipment, and the design of the piping layout of the equipment is also extremely important. Today, we will explain in detail the specific requirements for the layout of various types of chemical equipment! 01 What are the several types of tower arrangements? Specific requirements for? (1) single-row arrangement, in general more single-row arrangement, one side of the corridor with two or more towers or vertical containers, general centerline alignment, such as two or more towers set up a joint platform, the appropriate centerline alignment or tangential alignment;. (2) multi-row arrangement, for the smaller diameter of the body higher tower, can be double row arrangement or into a triangular arrangement, so that the platform can be used to link the tower together, to improve its stability. However, guiding nodes that can slide should be used for platform rooting members to accommodate the thermal expansion effects of different operating temperatures. (3) frame arrangement, for the diameter DN ≤ 1000mm tower can also be arranged in the frame or the side of the frame. For the use of the frame to improve its stability and set the platform, ladder. For the segmental tower arranged on the frame, when it is not possible to use the motorized lifting machine, the maintenance lifting facilities should be set up on the frame. 02 What are the requirements for the arrangement of the tower and its associated equipment? The tower and its associated equipment such as feed heater, non-open flame heating reboiler, tower top condensing cooler, reflux tank, tower bottom pumping, etc., should be arranged close to each other acco
Causes of vibration and noise in shell and tube heat exchangers and preventive measures
2022 / 12 / 21
Heat exchanger vibration As the scale of production increases, the size of the heat exchanger, the flow rate of the fluid and the span of the support all increase, even beyond the permissible limits, thus reducing the rigidity of the tube bundle and increasing the potential for vibration. Vibration can cause tube leakage, wear, fatigue, fracture and even accompanying ear-splitting noise, which not only reduces the life of the equipment, but is also detrimental to people's health. Once an incident has occurred, vibration often takes a long time to analyse and repair. Due to the complexity of the factors affecting vibration, the difficulty in estimating the magnitude of the damping effect and the difficulty in determining the rate of tube wear and damage, which cannot yet be described by simple mathematical equations, it can be said that the theoretical calculation methods used so far cannot be used to analyse vibration accurately in engineering practice. The existing codes for heat exchangers also lack clear regulations on vibration analysis methods and design guidelines for vibration prevention. However, it has been proven that if the existing research results can be used to make the necessary estimates and analyses of vibration during design, and some vibration prevention measures can be taken, then some destructive vibrations can mostly be avoided. Causes of fluid-induced vibration The tube bundle of the heat exchanger belongs to the elastomer and is disturbed by the fluid flowing through it, leaving its equilibrium position, the tube produces vibration, this vibration is called flow-induced vibration. In fact, each heat exchanger in the work of more or less vibration, the source of vibration may be the shell side or tube side of the fluid flow caused by vibration; fluid velocity fluctuations or pulsation caused by vibration; through the pipe or support propagation of power mechanical vibration and so on. Sometim
Welding of low carbon tempered steel
2022 / 12 / 12
Welding of low carbon tempered steel This type of steel as a high-strength welded structural steel, the carbon content is limited to low, usually less than 0.18% carbon mass fraction, and in the design of the alloy composition are also considered the requirements of weldability, so low carbon tempered steel welding is basically similar to normalized steel. The following problems mainly occur when welding. ① thermal cracking in the weld and liquefaction cracking in the heat affected zone. Low-carbon tempered steel generally contains low carbon and high manganese content, and the control of S, P is also more stringent, so the tendency of thermal cracking is smaller, but high nickel and low manganese type of low-alloy high-strength steel, it will increase the tendency of thermal cracking and liquefaction cracking. ② Cold cracking. As these steels contain more alloying elements that improve hardenability, they have a high tendency to cold crack. However, due to the high Ms point of this type of steel, if the joint can be made to cool more slowly at that temperature, so that the generated martensite has time to carry out a "self-tempering" treatment, to a certain extent to reduce the tendency of cold cracking, so the actual tendency of cold cracking is not necessarily very large. ③ Reheat cracking. Low carbon tempered steels contain V, Mo, Nb, Cr and other strong carbide forming elements, and therefore have a certain tendency to reheat cracking. ④ Softening of the heat-affected zone. Softening occurs when welding the heating temperature for the original tempering temperature of the base material has been to the region between Ac1. The lower the original tempering temperature, the greater the range of softening zone, the more severe the degree of softening. ⑤ heat-affected zone embrittlement. If in the superheated zone to produce low carbon martensite and volume fraction of 10%-30% of the lower bainite, you can get high
Safety management points in the process of chemical equipment maintenance
2022 / 12 / 02
I. Safety requirements before overhaul 1.1 The inspection and construction unit shall carry out the inspection and construction work within the scope of its class licence. 1.2 When signing an equipment overhaul contract, a safety management agreement should be signed at the same time. 1.3 According to the requirements of the equipment overhaul project, the overhaul construction unit shall develop an equipment overhaul programme, which shall be audited by the equipment using unit. There should be safety technical measures in the overhaul programme and the person responsible for the safety of the overhaul project should be clearly defined. The overhaul construction unit shall designate a person to be responsible for the specific safety work during the whole overhaul operation. 1.4 Before the overhaul, the equipment using unit should participate in the safety education of the personnel of the overhaul operation, safety education mainly includes the following contents: 1) Safety rules and regulations on overhaul operations. 2) The risk factors and possible problems and countermeasures that exist at the overhaul site and during the overhaul process. 3) The use of personal protective equipment and precautions for its use during overhaul operations. 4) Relevant accident cases, experiences and lessons learned. 5)The maintenance site should be set up with appropriate safety signs in accordance with GB2894. 6)The person in charge of the overhaul project should organise the overhaul operators to the site for the overhaul programme handover 7) The construction unit should implement the overhaul organization, overhaul personnel and overhaul safety measures before the overhaul. 8) When the equipment overhaul involves high work, fire work, earth moving work, disconnection work, lifting work, extraction of blind work and restricted space work, should be implem
The ten most overlooked problems in welding, the details make the difference
2022 / 11 / 22
1 . Welding construction does not pay attention to choose the best voltage [phenomenon]welding whether bottoming, filling, cover, regardless of the size of the bevel, are selected the same arc voltage. This may not achieve the required melt depth, melt width, edge biting, porosity, spatter and other defects. [Measures] Generally for different situations should be selected for the corresponding long arc or short arc can get better welding quality and work efficiency. For example, bottoming welding in order to get a better melt depth should be used to operate a short arc, filler welding or cover welding in order to get a higher efficiency and melt width can be properly increased arc voltage. 2 . Welding without control of welding current [Phenomenon]Welding, in order to seize the progress, for the thick plate butt welding seam to take no open bevel. Strength indicators decline, and even fail to meet the standard requirements, bending test cracks, which will make the performance of the welded joint can not be guaranteed, posing a potential hazard to structural safety. Measures] Welding should be controlled according to the welding current in the process assessment, allowing 10-15% floating, the blunt edge size of the bevel should not exceed 6mm. butt joint, the plate thickness exceeds 6mm, to open the bevel for welding. 3 . Do not pay attention to the welding speed and welding current, welding rod diameter coordinated use Phenomenon]Welding does not pay attention to the control of welding speed and welding current, welding rod diameter, welding position to coordinate the use. Such as full penetration of the corner seam bottoming welding, due to the narrow size of the root, such as welding speed is too fast, the root gas, slag does not have enough time to discharge, easy to make the root of the
Welding quality inspection - sealability inspection
2022 / 11 / 18
Welding quality inspection refers to the testing of welding results with the aim of ensuring the integrity, reliability, safety and serviceability of the welded structure. In addition to the requirements for welding technology and welding processes, welding quality inspection is also an important part of the quality management of welded structures. This time we will talk about the welding quality inspection method: sealing inspection. So how do you test the hermeticity of a welded joint? In general, the following methods can be used for testing. 1.Sinker test For small vessels or pipelines subject to smaller internal pressure. Before the test, the container or pipe is filled with compressed air at a certain pressure (0.4-0.5MPa) and then submerged in water to test the seal, such as right leakage; there must be bubbles in the water. This is also a common test to check whether the bicycle inner tube is leaking or not. 2.Water test The hydrostatic pressure generated by the weight of the water is used to test the structure for leaks. It is mainly visual and is suitable for general welded structures that are not under pressure but require sealing. 3.Ammonia leakage test The use and coal pumping leakage test is the same, its sensitivity is higher than the paraffin leakage test. Test before the weld is easy to observe the side of the paste soaked with a 5% mass fraction of HgNO3, aqueous solution or phenolphthalein reagent of white paper or bandage, and then in the container filled with ammonia or compressed air with a volume fraction of 1% nitrogen. If there are any leaks, the strips of paper or bandages will be discoloured. Soak through the mass fraction of 5% HgNO3 aqueous solution for the black spot, soaked through the phenolphthalein reagent for the red spot. 4.Kerosene leakage test It is used for welded structures that are subject to small internal pressure and require a certain degre
Common safety hazards in chemical plants
2022 / 11 / 11
In chemical production, there are many safety hazards associated with chemical plants, are you aware of them all? This article provides an inventory of 300 hazards, from facilities and equipment to production sites, so check yourself! Equipment and facilities Reactors and reactors 1) Abnormal noise from speed reducer 2) Oil stains on the speed reducer or frame 3) Hot melt deformation of the plastic airfoil of the speed reducer 4) Lack of oil on machine seal and reducer 5) Gasket leakage 6) Damaged anti-static earth wire, not installed 7) Safety valve not inspected annually, leaking, no account established 8) Thermometer not inspected annually, damaged 9) Pressure gauge not inspected annually, damaged or blocked by material 10) The key reactor does not adopt double sets of temperature and pressure display and record alarm 11) Rupture discs not replaced when due, leaking, no account established 12) Rupture disc lower valve not opened 13) Rupture discs not installed in reactors with explosion hazard 14) High temperature, interruption of stirring, etc., abnormal pressure increase or material flushing 15) The bottom valve is easily blocked when discharging material 16) Acid corrosion in stainless steel or carbon steel kettle 17) Overloading of the kettle, e.g. with a charge exceeding the prescribed limit 18) The enamel in the kettle is broken and still used in corrosive, flammable and explosive places 19) The inner liner of the reactor is damaged by erosion at the steam inlet of the jacket 20) The pressure vessel is older than its service life, poor manufacturing quality and still leaks after repeated repairs 21) Pressure vessel without nameplate 22) Missing or unclear identification of position number 23) Failure to effectively isolate explosion-sensitive reactors 24) No safe
Defects in aluminium welded joints
2022 / 11 / 03
When MIG welding of aluminium and aluminium alloys, the common defects in welded joints are poorly formed welds, cracks, porosity, burn-through, failure to weld through, failure to fuse and slag. I. Poor weld seam formation Poor weld formation is mainly manifested in the weld ripple is not beautiful, and not bright; weld bending is not straight, the width is not the same, too many joints; weld centre protrusion, both sides flat or depressed; weld overflow, etc.. 1. Causes a. Improper choice of joint specification. b. Incorrect angle of the welding gun. c. Unskilled welders. d. Conductive nozzle aperture is too large. e. welding arc is not strictly aligned with the bevel centre. f. Moisture in the welding wire, welding parts and shielding gas. 2. Preventive measures a. Repeated debugging to select the appropriate welding specification. b. Maintain a suitable inclination of the welding torch. c. Strengthen the skills training of welders. d. Select the appropriate conductive nozzle diameter. e. Strive to make the welding arc and the bevel strictly centered. f. Carefully clean the welding wire and welding parts before welding; ensure the purity of the shielding gas. II. Cracking Cracks in aluminium and aluminium alloy welds are produced during the crystallization of the weld metal and are called thermal cracks, also known as crystallization cracks. It takes the form of longitudinal cracks, transverse cracks (often extending to the base metal), as well as root cracks, arc pit cracks and so on. Cracking will reduce the strength of the structure or even cause sudden damage to the whole structure and is therefore totally unacceptable. 1. Causes a. Excessive depth to width ratio of the weld gap. b
The basics of heat exchanger failure
2022 / 10 / 29
Today will be a summary of common heat exchanger failures, and with a detailed solution. A, two media string each other (internal leakage) 1 Causes ① heat exchanger tube corrosion perforation, cracking. ② heat exchanger tube and tube plate expansion mouth (welded mouth) cracked. ③ floating head type heat exchanger floating head flange seal leakage. 2 processing methods ① replace or plug the leaky heat exchanger tube. ② heat exchanger tube and tube plate re-expansion (welding) or plugging. ③ tighten the bolts or replace the sealing gasket. Second, the flange at the seal leakage 1 Cause ① gasket under pressure, corrosion, deterioration. ② Insufficient bolt strength, loosening or corrosion. ③ flange rigidity and sealing surface defects. ④ flange is not flat or misaligned, gasket quality is not good. 2 Processing method ①Tighten the bolts and replace the gaskets. ②Upgrade the bolt material, tighten the bolt or replace the bolt. ③Replace the flange or deal with the defect. ④Reassemble or replace the flange and replace the gasket. Poor heat transfer 1 Causes ①Heat transfer tube fouling. ②Bad water quality, oil and microorganisms. ③Separator short circuit 2 Treatment method ①Chemical cleaning or jet cleaning of dirt and grime. ②Strengthen filtration, purify media and strengthen water quality management. ③Replace the tube box gasket or replace the bulkhead. Fourth, the resistance drop exceeds the allowable value 1 Cause Scaling inside the shell, inside and outside the tube 2 Treatment method Use jet stream or chemical cleaning scale V. Serious vibration 1 Generated by ① Resonance caused by the frequency of the medium.
Distillation columns with automatic control
2022 / 10 / 21
1. Distillation principle The basic principle of distillation is the partial gasification and partial condensation of the liquid mixture several times, using the different volatility of the components (relative volatility, α) of the characteristics of the unit operation to achieve the purpose of separation. Distillation can be classified according to its operation method: simple distillation, flash distillation, distillation and special distillation, etc. 2. Brief description of the process The vapour enters from the bottom of the tower. Evaporation of the gas phase and down liquid counter-current contact, two-phase contact, down liquid in the easy to volatile (low boiling point) components continue to transfer to the gas phase, gas phase in the difficult to volatile (high boiling point) components continue to transfer to the down liquid, the closer the gas phase to the top of the tower, the higher the concentration of its easy to volatile components, and down liquid closer to the bottom of the tower, the more difficult to volatile components are enriched, so as to achieve the purpose of component separation. The gas phase rising from the top of the tower enters the condenser, and part of the condensed liquid returns to the top of the tower as reflux into the distillation column, while the rest is taken out as distillate. The liquid flowing from the bottom of the tower, part of which is sent to the reboiler, heated and evaporated into the gas phase to return to the tower, and the other part of the liquid is taken out as kettle residue. 3. Problems However, throughout the chemical process, it is difficult to achieve fine temperature control of the entire condensing system. This can cause some substances as well as impurities to exhibit physical and chemical properties that are difficult to distinguish. That is, the system needs to be inevitably mixed with other impurities, there is no doubt that the purpose of the entire disti
Main causes of thermal cracking and preventive measures
2022 / 10 / 15
Cracking is one of the most dangerous welding defects that reduce the performance of a welded structure, and any form of cracking in the weld is prohibited. Welding cracks are gaps created by the joint action of welding stresses and other embrittlement-causing factors that break the atomic bond of the material and form a new interface. According to the conditions of welding cracks, it can be divided into hot cracks, cold cracks, reheat cracks, laminar tears and stress corrosion cracks, the following focus on the most common form of cracking - welding hot cracks. A. What is thermal cracking Thermal cracking is a crack that occurs during the solidification process at high temperatures and molten pools, and is the most common type of cracking in the welding process, from mild steel, low-alloy high-strength steel, to austenitic stainless steel, aluminium alloys and nickel-based alloys have the potential to produce welded thermal cracking. Thermal cracks are most commonly found in the centre of the weld and are crystalline cracks, the formation of which is mainly related to low melting point eutectics and tensile stresses. Second, the main factors affecting the thermal cracking 1, the chemical composition of the weld metal Weld metal in C, S, P, Cu, Zn and other low melting point elements and their compounds are more, will promote the formation of hot cracking. During the solidification process of the weld, these low melting point substances are easy to gather in the centre of the weld and deviate, when the edge of the weld crystallizes and solidifies, the impurities between the grains in the centre of the weld are still in the liquid film state, and cracks are produced under the action of the stress generated by the shrinkage of the weld. 2, weld cross-sectional shape When the depth of the weld is larger than the width, it will make the solidification particles grow
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