Basic Knowledge of Construction and Installation Projects (II): Basic Knowledge of Construction Techniques

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Chapter 2: Basic Knowledge of Construction Techniques Section 1: Cutting and Welding I. Understanding the common cutting methods used in installation projects, as well as the characteristics and application ranges of these methods. The common cutting methods used in engineering include oxygen-gas cutting, plasma cutting, carbon arc gouging, and laser cutting. (1) Oxygen-gas cutting 1. Conditions that must be met for gas cutting of metals (1) The melting point of the metal oxide should be lower than that of the metal itself. (2) Metals release a large amount of heat when burning in oxygen, and they also have low thermal conductivity. 2. Application range of oxygen cutting Oxygen cutting is suitable for pure iron, low-carbon steel, medium-carbon steel, low-alloy steel, as well as titanium, etc. 3. Process parameters for oxygen cutting The process parameters for oxygen cutting include preheating flame settings, oxygen pressure, cutting speed, the distance between the cutting torch and the workpiece surface, and the angle of inclination of the cutting torch. (II) Plasma arc cutting: The plasma arc column has a high temperature, and the cutting process relies on melting; therefore, it can cut most metal and non-metal materials. The gases commonly used for plasma arc cutting include argon, nitrogen, a mixture of helium and argon, and a mixture of nitrogen and argon. The process parameters for plasma arc cutting include cutting current, no-load voltage, cutting speed, gas flow rate, and the distance between the nozzle and the workpiece. (III) Carbon arc gas gouging is a cutting method that uses a carbon rod or graphite rod as an electrode; the arc generated between this electrode and the workpiece melts the metal, and compressed air is then used to blow away the melted metal. The characteristics, application scope, process parameters, and possible defects of carbon arc gas gouging are covered on pages 71 and 72 of the textbook. (IV) Laser cutting: It is a method of cutting materials that uses a laser with high energy density as the “cutting tool”. There are laser gasification cutting, laser melting cutting, laser oxygen cutting, slitting, and controlled fracture. Information on the characteristics of laser cutting, cutting parameters, and safety measures can be found on page 72 of the textbook. II. Understanding the classification, characteristics, selection, and classification codes of welding methods (I) Classification and characteristics of welding methods (1) Arc welding includes shielded metal arc welding, submerged arc welding, tungsten inert gas arc welding, plasma arc welding, as well as fusion and gas-shielded arc welding. (2) Resistance welding includes electroslag welding, which uses the resistive heat of molten slag as an energy source, and resistance welding, which uses the resistive heat of solids as an energy source. (3) High-energy beam welding includes electron beam welding and laser welding. (4) Brazing can be categorized into flame brazing, induction brazing, furnace brazing, dip brazing, resistance brazing, etc. The above are the characteristics and applicable scopes of various welding methods. (II) Selection of welding methods and classification codes. Factors to consider when selecting a welding method include: (1) Product characteristics. These include the structural characteristics of the welded product, the thickness of the workpiece, the type of joint, the welding position, and the properties of the base material. (2) Production conditions: Welding production conditions include operational skills, welding equipment, and welding materials. (3) The welding method code is a code representing the welding method, expressed in digits or letters. Section 2: Heat Treatment
1. Familiarization with the basic concepts and significance of heat treatment
The process of heating metal to a specified temperature and holding it there for a certain period of time, followed by cooling it at a chosen rate and in a specific manner to obtain the desired microstructure and properties is known as heat treatment. Heat treatment of welded joints prevents brittle failure, delayed cracking, stress corrosion, and hydrogen corrosion in the welded area. Proper heat treatment can relieve welding residual stresses and soften the hardened zones; it can also improve the microstructure, reduce hydrogen content, and enhance corrosion resistance, impact toughness, creep limit, etc. II. Understand the functions and general requirements of pre-welding heating and post-welding heat treatment, as well as their heating methods. (1) Pre-welding heating: The purpose of preheating is to reduce the temperature difference between the weld metal and the base material, thereby reducing contraction stresses (thermal stresses). It also slows down the cooling rate of the weld, controls the structural transformation of the steel, reduces localized hardening, and improves the quality of the weld. It can also reduce defects such as pores and slag inclusions. Normally, the preheating temperature for 35# and 45# steels can be set at 150–250°C. When the carbon content is further increased or when the workpiece has very high rigidity, the preheating temperature can be raised to 250–400°C. The heating range for local preheating is 150 mm to 200 mm on both sides of the weld joint. (II) Post-weld heat treatment: The functions of post-weld heat treatment, the selection of heat treatment specifications, the general requirements for post-weld heat treatment, and the heating methods used in this process are covered on pages 78 and 79 of the textbook. (III) Overall heat treatment: Overall heat treatment is carried out to eliminate the stresses resulting from welding, stabilize various geometric dimensions, modify the microstructure of the welded material, enhance the toughness and stress resistance of the metal, and prevent the formation of cracks. Section 3: Degreasing, pickling, passivation, and pre-filming. 1. Understand the application scope of degreasing, types of degreasers, degreasing methods, and methods for inspecting the quality of degreasing. During construction, oil-sensitive systems must be degreased as required. For pipes, fittings, and valves made of carbon steel, stainless steel, and copper, industrial-grade carbon tetrachloride should be used. For those made of aluminum alloy, industrial alcohol is recommended. For non-metallic gaskets, only carbon tetrachloride may be used. (1) Degreasing methods: For the degreasing of pipes and tubing, as well as of pipe fittings and gaskets, refer to page 80 of the textbook. (II) Degreasing test: The degreasing test is divided into direct and indirect methods. II. Understanding the requirements, application scope, and common methods of acid cleaning: During construction, acid cleaning should be carried out on equipment and pipelines whose inner surfaces require special cleaning. Pickling is commonly carried out using the tank immersion method and the system circulation method. The pickling process must be carried out strictly in accordance with the requirements. Pipes and equipment after pickling must be passivated promptly. III. Understanding passivation and common methods of passivation Section 4: Insulation and corrosion protection I. Understanding the types of insulation, their purposes, the scope of application, the forms of insulation structures, and the construction methods. The insulation of equipment and pipelines can be classified into three types based on their purpose: heat retention, heating insulation, and cooling insulation. (1) Insulation range: The insulation of equipment pipes shall meet the relevant regulatory requirements. (II) Insulated structure types: In insulation projects, the insulation structure consists of an electrical anti-corrosion layer, an insulation layer, and a protective layer. The insulation structure for heat retention should also include a moisture and air barrier layer. Adiabatic structures come in various forms and installation methods, including plastering, filling, wrapping, compounding, casting, spraying, and precast blocks. (III) Insulated construction: Insulated construction includes the application of an anti-corrosion layer ； Construction of thermal insulation and cold insulation layers ； Construction of moisture and air barrier ； Construction of the protective layer. (IV) Quantity calculation of work 1. General provisions for quantity calculation of work (1) The quantity of work for pipe insulation is calculated in terms of \"length in meters\", without deducting the length occupied by valves and flanges. If the design requires insulation for valves and flanges, the quantity for such work will be calculated separately. (2) The technical specifications for thermal insulation engineering stipulate that when the thickness of the thermal insulation layer is greater than 100 mm and that of the heat-insulating layer is greater than 75 mm, construction should be carried out in layers, and the volume of work shall be calculated on a layer-by-layer basis. (3) The foaming and installation of polyurethane foam plastics are designed for direct spraying without the use of molds. If installation is carried out using molds, the cost of those molds will be calculated separately according to the construction plan. (4) The specifications for the galvanized iron sheet used as the protective layer for metal sheets are 1000mm × 2000mm and 900mm × 1800mm, with a thickness of 0.8mm or less; if other specifications are used, adjustments can be made according to actual conditions. (5) The protective layer is provided with a plaster finish. If not specified in the construction drawings, generally, when the pipe diameter is less than 200 mm, the thickness should be set at 100 mm ； If the pipe diameter is greater than 200 mm and less than 500 mm, the thickness shall be 20 mm. 2. Calculation of insulation work volume includes the calculation of insulation work volume for individual pipes ； Calculation of the workload for pipes with heating tubes, including single-tube heating and double-tube heating ； Valve insulation engineering calculations ； Calculation of flange insulation work volume ； Calculation of the thermal layer workload for end caps ； Calculation of the insulation work volume for equipment cylinders. 3. Calculation of the quantity for protective layer work: This includes the calculation of the quantity required for pipeline protective layers ； Calculation of the workload for valve protective coating installation ； Calculation of the quantity of work for flange protective coating ； Calculation of the quantity of work for the head cover protection layer. II. Understand the classification of rusting, as well as the purposes and methods of rust removal. Know the functions, composition, and classification of coatings. (I) Rust Removal 1. Purpose of rust removal: The aim is to remove all rust and impurities from the metal surface ； Increase the roughness of the metal surface ； Increase the adhesion strength between the paint film or anti-corrosion layer and the surface. 2. Grades of corrosion: The corrosion on metal surfaces is generally classified into four grades: Sa3 (Grade 1), Sa2.5 (Grade 2), Sa2 (Grade 3), and Sa1 (Grade 4). 3. Rust removal methods: There are four methods for treating metal surfaces, namely manual rust removal, semi-mechanical rust removal, mechanical rust removal, and chemical rust removal. For Grade 1 standards, the sandblasting method or mechanical rust removal methods must be used; chemical treatment methods are not permitted. For the secondary standard, sandblasting, mechanical treatment, or chemical rust removal methods should be used. For the third-level standard, manual or semi-mechanical methods can be used for rust removal. The level 4 standard can adopt manual rust removal methods. Different rust removal levels are suitable for different projects. (II) Corrosion-resistant coatings 1. Basic components of coatings Coatings can generally be divided into three parts, namely the main film-forming substance, the secondary film-forming substance, and the auxiliary film-forming substance. The main film-forming substances are oils, natural resins, and synthetic resins. Secondary film substances include rust-inhibiting pigments, extender pigments, and coloring pigments. Auxiliary film-forming agents include solvents and other auxiliary materials. 2. The function of paint. It has protective effects, color-indicating functions, and some special functional roles. (III) Application of anti-corrosion coatings: The coating application process includes: rust prevention – applying the first coat of primer – inspection and additional coating if necessary – applying the second coat of primer – inspection – sanding – applying the intermediate coat (1–2 times) – applying the topcoat (1–2 times) – inspection – additional coating if needed – curing time – final product. III. Understanding the classification, characteristics, and construction procedures of common linings and spraying projects (1) Fiberglass reinforced plastic lining projects (1) Generally, a fiberglass reinforced plastic lining consists of four layers: the base layer, the putty layer, the fiberglass reinforcement layer, and the surface layer. (2) The procedures for the fiberglass lining project are as follows: rust removal – application of the first coat of primer – applying putty – application of the second coat of paint – applying adhesive to attach the lining fabric – inspection and adjustment – applying adhesive to attach the second layer of lining fabric – inspection and adjustment. (2) Rubber sheet lining project: (1) Rubber lining involves attaching a pre-formed rubber sheet to the metal surface using adhesive, thereby separating corrosive substances from the metal substrate and providing protection. Rubber lining layers generally have high density, strong impermeability, a certain degree of elasticity, as well as good toughness, enabling them to resist mechanical and thermal shocks. Its advantages are easy construction, fast setting, and safety ； The downside is that its usage is generally low. (2) The vulcanization methods for rubber sheet linings can be divided into natural vulcanization, pre-vulcanization, and heat vulcanization; the construction procedures vary depending on the vulcanization method used. (3) Rubber-lined types can be divided into natural rubber and synthetic rubber (neoprene, butyl rubber, polysulfide rubber, etc.). Natural rubber, butyl rubber, and neoprene are commonly used in our country. (4) The sulfurization process is divided into indirect sulfurization and direct sulfurization. (III) Lead lining and lead cladding construction (1) Lead lining and lead cladding are two methods of applying a lead coating. The construction method for lining with lead is simpler than that for plating with lead; it has a shorter production cycle and lower relative costs, making it suitable for use under vertical loads, static loads, and positive pressures ； The lead plating forms a uniform and strong bond with the equipment walls, with no gaps present; it offers good heat transfer properties and is suitable for operation under negative pressure, rotational motion, and vibration. (2) Lead lining construction process. Lead lining is generally fixed using riveting, bolting, or clamping strips. Its construction procedures also vary depending on the construction method. (IV) Metal spraying project: The metal spraying project is a new technique for repairing corrosion and mechanical wear. In metal spraying, there are methods such as aluminum spraying, steel spraying, zinc spraying, and copper spraying. The spraying methods include the combustion method and the electric heating method. The construction procedure for spraying is as follows: rust removal – trial spraying – application of the first coating layer – application of the second coating layer – inspection and treatment of the coating – post-coating treatment. (5) Acid-resistant brick and plate lining project: In this process, acid-resistant bricks and plates are attached to the inner surface of metal equipment using corrosion-resistant mortar, thereby creating a thick anti-corrosion protective layer. Acid-resistant mortar comes in two types: inorganic mortar and organic mortar. Acid-resistant bricks and slabs mainly include acid-resistant ceramic tiles and slabs, acid-resistant pottery bricks and slabs, diabase slabs, impregnated graphite slabs, granite slabs, and more. The issues to be noted, as well as the construction procedures and methods for acid-resistant brick and slab linings, shall be carried out in accordance with the design or relevant specifications. IV. Become familiar with the rules for calculating the quantities involved in insulation and anti-corrosion works, and master the methods for such calculations. Section 5: Lifting Operations I. Understand the factors that need to be considered when selecting lifting equipment for formulating a lifting plan. II. Understand the selection of crane models in mechanical lifting operations, the calculation of the number of cranes required, as well as the common methods used in mechanical lifting. (a) Selection of Crane Models The principle for selecting a crane model is that the three operational parameters of the chosen crane—lifting capacity Q, lifting height H, and working radius R—must all meet the requirements for lifting the components. Based on the crane’s working radius R and boom length L, consult the crane’s lifting capacity table or curve to check the lifting capacity Q and the lifting height H. (II) Calculation of the number of cranes. The number of cranes is determined based on the workload, project duration, and the output per shift of the cranes, using the following formula: Additionally, the requirements for transporting components and carrying out assembly work must also be taken into account. (III) Mechanized lifting methods: When using crane equipment, the lifting methods can be categorized as single-crane lifting, double-crane lifting, three-crane or multiple-crane lifting, etc. Refer to Figures 2.5.1 through 2.5.10 in the textbook. III. Understand the selection of crane models for mechanical lifting, the calculation of the number of cranes required, and the common methods used in mechanical lifting. Semi-mechanical lifting primarily makes use of lifting devices such as jacks or masts, along with associated equipment like winches, pulleys, and steel cables. Refer to Figures 2.5.11 through 2.5.20. Section 6: Quality Inspection of Construction Projects I. Understand the significance, contents, and methods of quality inspection for construction projects. II. Understand the contents and methods of inspection for metal materials. The acceptance and quality inspection of metal materials are carried out in accordance with the contract signed by the supplier and the buyer, as well as three other types of documents. The inspection items include: inspection of specifications and dimensions, visual inspection, as well as inspection of composition, properties, and structure. Component, performance, and microstructural inspections include: microscopic structure inspection, macroscopic structure inspection, and non-destructive testing inspection. III. Familiarize oneself with the integrity tests in the quality inspection of equipment and pipeline installation. The quality inspection of equipment and pipelines is carried out through integrity tests. Density tests include hydrostatic testing, pneumatic testing, airtightness testing, etc. (1) Pressure testing and sealing inspection of equipment 1. Hydrostatic test The hydrostatic test is used to check the density and strength of the welds in the equipment. The most widely used is hydrostatic testing. The water quality used for hydrostatic testing and the testing methods shall comply with relevant regulations. The test pressure must meet the specified requirements. 2. Pneumatic testing: For containers that are not suitable for hydraulic testing, or those that cannot be filled with liquid due to their structure, pneumatic testing can be used as an alternative to hydraulic testing. The pneumatic testing method and test pressure shall meet the specified requirements. 3. Airtightness test: Its purpose is to check the sealing performance of the connection points. The airtightness test can be carried out only after the hydraulic test is successful. The pressure increase requirements for the airtightness test are the same as those for the pneumatic test; the pressure in the airtightness test is equal to the design pressure. 4. Leakage test The ammonia leakage test is commonly used to inspect equipment operating at near-atmospheric pressure. (II) Pressure testing and leak inspection of the piping system: After the piping is installed, a pressure test should be conducted on the system. Pressure tests can be divided into strength tests and tightness tests, which in turn can be further categorized into hydrostatic tests and pneumatic tests. In addition to complying with general regulations, pressure testing, whether hydraulic or pneumatic, must also meet the relevant specified requirements. IV. Be familiar with the contents, methods of welding quality inspection, as well as the advantages, disadvantages, and application ranges of various methods. Welding quality generally includes: the dimensional characteristics of the weld seam, the continuity of the joint, and the performance of the joint. (1) Visual inspection: Visual inspection is used to check for defects on the outer surface of the weld. This includes checking whether the weld dimensions meet the requirements, as well as looking for issues such as undercutting, weld beads, cratering, and arc damage. (II) Radiographic testing: Radiographic testing is a widely used non-destructive testing technique in construction inspections. It can accurately determine the size, location, and nature of any defects present within or on the surface of workpieces. Including X-rays, rays, and high-energy X-ray flaw detection. 1. X-ray flaw detection includes the principles of X-ray flaw detection, X-ray radiography methods, the characteristics of various weld defects, as well as the advantages and disadvantages of X-ray flaw detection. For more details, see pages 120–121 of the textbook. 2. Radiographic testing. For details, please refer to page 122 of the textbook. (III) Ultrasonic testing: For details, see page 122 of the textbook. (IV) Surface testing includes magnetic particle testing, fluorescent testing, and dye penetrant testing.