Key control points for boiler installation

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I. Visual inspection of the steel frame A, columns, and beams: There should be no cracks, sand holes, peeling, uneven surfaces, bending, or twisting and other visual defects; the allowable values for such defects shall comply with the provisions of the \"Technical Specifications for Construction and Acceptance of Electric Power Projects.\" If any such defects are present, corrective actions must be taken. B. The material shall meet the design requirements. C. Marking of the boiler foundation: The vertical and horizontal center lines must be accurate and checked against the standard points of the plant building; before each construction phase, these center lines should be verified using a plumb line. Its allowable deviation meets the requirements specified in the \"Technical Specifications for Power Generation Construction, Installation, and On-site Acceptance\" (Boiler Units Section) D. Lifting, alignment, and fixing of the steel frame: Control points: ① Marking of the boiler foundation and installation of the column floors. ②Perform a comprehensive inspection and adjustment of the boiler as a whole. ③The tightening torque of high-strength bolts. ④, secondary grouting. II. Installation of the boiler’s heating surfaces: A. The materials of all components of the heating surfaces must meet the design requirements. In addition to conducting the necessary written inspections, a visual inspection should also be carried out on the welds of key components such as the water wall, superheater, reheater, and economizer, including the manifolds. Alloy steel components must undergo spectral analysis one by one. B. Strict control over welding processes is required, and welders must hold valid certificates to work. C. The balls used in the ball-passing test must be strictly managed and coded to prevent them from being left inside the tubes. D. Requirements for the installation quality of the water wall and key points for quality control: ① Quality requirements. Check whether the tubes and dimensions of the header are in accordance with the drawings, ensure that the interior of the header and pipe joints is clean, verify the external dimensions of all tubes on the heat-exchanging surfaces, the material of the alloy steel components, and whether the rigid beams are twisted; any defects found should be recorded and corrected promptly. ②, quality standards. Refer to DL/T5047-95 \"Technical Specifications for Construction and Acceptance of Electric Power Projects\" (Boiler Unit Section), E. Precautions for the vertical installation of superheaters and reheaters: ① The dimensions of the coiled tubes should be checked one by one and corrected, while ensuring that the lower elbows are properly aligned to prevent interference with expansion and short-circuiting of flue gas. ②Before assembling the header, desuperheater, and coiled tubes, they must be thoroughly cleaned with compressed air, and the tube ends must be sealed. The coiled tubes should be assembled as the ball is passed through; separate teams should use separate balls for passing. ③Heat treatment is carried out immediately after welding. ④When assembling, a row should be installed in the middle or on one side first as the reference tube row. When installing the reference tube row, it is necessary to check the perpendicularity between the axis of the header and the tube row, as well as its geometric dimensions. ⑤When installing the tube array, comb-shaped clamps and hanging plates should be used simultaneously; care should be taken to ensure that the tubes are arranged evenly and smoothly. After assembly, it is necessary to measure the diagonals of the tube array in all directions to prevent twisting. ⑥All alloy pipes must undergo spectral analysis. ⑦Under water pressure, the water in the serpentine tube is difficult to discharge; therefore, anti-corrosion and anti-freezing measures must be taken. F. Quality requirements and key quality control points for superheater installation: ① When installing and assembling the superheater serpent tubes, the header should first be aligned and fixed to serve as the reference for installing the serpent tubes. During the installation of the reference serpentine tube, it is necessary to carefully check the fit between the serpentine tube and the connectors, as well as the length deviation from the center of the manifold to the ends of the serpentine tube. After the reference serpentine tube has been aligned and fixed, the remaining rows of tubes can be installed. ②When heating and correcting alloy steel components, the heating temperature is generally kept below the critical temperature of the steel. ③The allowable tolerances for the combined installation of superheater components are as follows: the allowable tolerance for the free end of the coiled tubes is ±10 mm, the allowable tolerance for the spacing between tube rows is ±5 mm, the allowable tolerance for the flatness of the tube rows is less than 20 mm; the allowable tolerance for the flatness of the tube rows in the ceiling-mounted superheaters is ±5 mm. The gap between the tubes in the side rows and the tubes on the heat-exchanging surface must comply with the specifications given in the drawings. ④The anti-wear device of the superheater should provide expansion gaps at the joints as indicated in the drawings; the welding must be secure and even, with no areas that could obstruct the flow of flue gas. ⑤Before installation, the spray water cooler should be checked for the assembly and sealing certificate provided by the manufacturer, as well as undergo an external inspection. ⑥For superheater tubes that develop defects after installation and cannot be repaired, a single-tube hydrostatic test or non-destructive testing should be conducted prior to tube replacement. ⑦When the superheated gas pipes are aligned, the groove shape shall meet the requirements specified in the drawings. Within a range of 10–15 mm inside and outside the tube, there should be no rust, grease, or other contaminants, and the metal surface should show its natural luster. The misalignment at the joint should be less than 10% of the wall thickness and less than 1 mm; the deflection of the joint at a distance of 20 mm from the weld center should be less than 2 mm. ⑧ The installation of the manway should meet the following requirements: the vertical and horizontal deviations of the manway should be less than 3 mm, while the deviation of its longitudinal centerline from being vertical and the horizontal distance deviation should be ±3 mm. The allowable deviation for the manway diagonals is less than 5 mm; the elevation deviation of the manway is ±3 mm, while the deviation between the longitudinal and transverse centerlines of the manway and the center of the furnace is also ±3 mm. ⑨All seals must be installed in accordance with the drawings; the welds should be firm and even, and the sealing areas must be tight to prevent leaks. G. Quality requirements and key quality control points for reheater installation ①. Quality requirements. Check whether the positions of each header pipe seat conform to the drawings ； Clean the inside of the header and pipe fittings; check whether the dimensional specifications and material of each heating surface tube are in accordance with the requirements ； Any issues found should be recorded and addressed promptly. ②, quality standards. Refer to Table 3.4.3 of DL/T5047-95 \"Technical Specifications for Construction and Acceptance of Electric Power Projects\" (Boiler Units Section), in accordance with the allowable deviation rules specified in 3.1.6. H. Quality requirements for economizer installation and key points for quality control 1) Quality requirements ① The width deviation shall not exceed ±5mm. ②The diagonal deviation shall not be greater than 10 mm. ③The gaps between various tube rows should be uniform, with an error not exceeding ±5mm; the protrusion of individual tubes within a tube row should not be more than 20mm. ④The allowable horizontal deviation of the junction box is ±2 mm, while the allowable elevation error is ±5 mm. ⑤The allowable deviation in the centerline distance between the inlet and outlet manifolds shall not be greater than 3 mm. ⑥The gap between the edge tube and the furnace wall shall meet the requirements specified in the drawings. 2) Key points of quality control: ① All pipe arrays must undergo a ball-passing test, and they should be sealed promptly after the test is completed. ②The gaps between each row of pipes should be even, and the upper surface should be smooth. III. Installation quality requirements and quality control points for the drum: ① The elevation deviation of the drum’s center is ±3mm. ②The deviation in vertical and horizontal alignment is ≤1mm. ③Axial center position deviation ±3mm. ④The vertical centering deviation shall be ±3 mm. The suspension ring of the drum shall be in contact with the outer circumference of the drum: the arc at a 90° contact angle shall fit perfectly, with individual gaps not exceeding 2 mm. The drum shall be cleaned and sealed. IV. Procedure for hydrostatic testing: Ensure the valve is in the appropriate open or closed position → Start the feed water pump or drain pump to slowly fill the boiler with water → Continuously check whether air vents are releasing steam → Once the boiler is filled with water, stop adding water and conduct a thorough inspection of the boiler → Increase the pressure (the rate of pressure increase should not exceed 0.3 Mpa/min before reaching the operating pressure) → When the pressure reaches 10% of the operating pressure, pause the pressure increase and carry out a comprehensive inspection; if there are leaks in the heating surfaces, stop increasing the pressure and address the issues; if no leaks are found, continue increasing the pressure → If any leaks are detected at higher pressures and the leakage is severe, stop increasing the pressure; after fixing the issues, proceed to reach the operating pressure → Pause the pressure increase again, and after confirming that there are no leaks or abnormalities, increase the pressure to the test pressure. After that, maintain this pressure for 20 minutes before reducing it back to the operating pressure. At this point, the person monitoring the pressure gauge should immediately record the time when pressure increase was stopped, and monitor the pressure drop over the next 20 minutes → Conduct a thorough inspection at the operating pressure, and clearly mark the locations of any leaks → After the inspection is complete, start reducing the pressure at a rate of 0.4–0.5 Mpa/min → When the pressure reaches zero, drain the water from the boiler. The passing criterion for the hydrostatic pressure test is: no water droplets or mist on the metal walls and welds of the pressure-bearing components ； When the pressure is reduced to the operating level, no water droplets appear at the flared area ； No residual deformation was found after the hydrostatic pressure test. Installation process of large boilers: assembly of main components → transportation → lifting → positioning → alignment → hydrostatic test → construction of furnace walls and insulation → preparation for startup and trial operation. I. Assembly of main boiler components A. Assembly of the boiler steel frame B. Assembly of the water wall C. Assembly of the superheater D. Assembly of the reheater E. Assembly of the economizer F. Assembly of the suspension tubes G. Assembly of the steam drum and large-diameter downcomers H. Hydrostatic test of the assembled structure. II. Transportation and Lifting of Boiler Components A. For various components, it is necessary to consider measures for reinforcement during transportation and lifting; a practical plan for lifting, reinforcement, and transportation must be in place to primarily prevent deformation and damage. B. The principles that should be followed for the lifting sequence are: primarily taking into account the structure of the boiler and the capacity of the lifting equipment, as well as the stability of the steel frame after it bears load. III. Installation of Boiler Pipes and Valves A. In large boilers, the air, flue gas, and coal pipes are usually combined and insulated on the ground before installation. B. The valves must undergo inspection prior to installation, and this inspection must be carried out accurately depending on the different media, temperature requirements, connection types, and flow direction. IV. Boiler water pressure test: A. The steam and water pipelines, as well as the valves, from the feedwater inlet to the steam outlet, must undergo a comprehensive overpressure water test to verify that the tightness and strength of all pressure-bearing components under cold conditions meet the required standards. Prior to this test, a pressure test at 3–5 kg/cm² can be conducted. V. Construction of the furnace wall and insulation The furnace wall is the outer shell of the boiler; it separates the boiler’s combustion chamber and flue from the outside environment. When constructing this wall using water-resistant materials, it is necessary to strictly follow the design specifications as well as the construction requirements provided by the manufacturer for such materials. Especially in large circulating fluidized bed boilers, attention should be paid to the installation of water-resistant materials in the swirl separator, return conveyor, and cold slag holder located in the upper part of the furnace, as these components are prone to collapse under the combined effects of thermal cycling and mechanical vibrations. VI. Boiler startup preparation and trial operation: After the boiler is installed, it is necessary to carry out partial trial operations and tests for each system of the boiler equipment. After all the distribution work is completed, 72 hours of trial operation are carried out. A. Boiler testing: This involves checking the integrity of the combustion chamber, coal grinding system, cold and hot air systems, as well as the flue gas system. For parts such as the combustion chamber flues, an exhaust fan can be started to maintain a certain negative pressure in the system; a lit candle can then be brought near the joints – if the flame is drawn towards that area, it indicates a leak. For the coal grinding system, air ducts, and air preheaters, an exhaust fan can be used to maintain a positive pressure in the system; flour can be scattered at the outlets of these fans to identify any leaks, as flour will appear at the locations where there are leaks.

B. Oven drying: After construction, the oven walls contain moisture. If such moist walls come into contact with hot flue gas at a large temperature difference, the moisture within the walls will evaporate rapidly, producing large amounts of steam. The effect of this steam can cause cracks to form in the oven walls. Methods of oven drying include: fuel drying, hot air drying, and steam drying. Large boilers are dried using steam; initially, saturated steam (3-4 kg/cm*cm) is introduced into the boiler’s heating surfaces through the drain valves located beneath the water wall, gradually heating the water to around 90° while maintaining an appropriate water level. This process of drying continues until the desired standards are met. C. Chemical cleaning: Chemical cleaning generally involves alkali cleaning and acid cleaning. Alkali cleaning is mainly used to remove oil residues, and it also helps to loosen adhering substances such as SiO2 and scale. Pickling is primarily used to remove iron oxide, copper, and dirt, as well as adhering substances such as SiO2 and scale (mainly found in components like heat-exchanging surfaces, header connection pipes, and steam drums). D. Pipe flushing: In boilers, for systems such as feedwater, desuperheating water, pressure-reducing loops, superheaters, reheaters, their associated pipes, and other low-pressure pipes, chemical cleaning may not be appropriate due to structural considerations. For newly installed boilers, before they are put into use for supplying water and steam, the pipes are flushed using steam generated by the boiler itself to eliminate any residues remaining inside them. E. Steam tightness test and safety valve adjustment: The steam tightness test is conducted at operating temperature, using steam at the working pressure to check the tightness of all pressure-bearing components and pipelines, while also determining the degree of thermal expansion of these components under heat. After the tightness test is completed, the safety valve can be adjusted for pressure elevation calibration. F. The boiler undergoes a 72-hour trial run; this 72-hour trial run is carried out after the aforementioned tests are completed.