Measures for safety, technology and welding quality in boiler and pressure vessel inspection

Gansu Lanzhou No. 2 Thermal Power Plant Zhang Hongyu Gansu Electric Power Research Institute Song Shaohe 6471998 Boiler and Pressure Vessel Inspection Regulations, combined with equipment overhaul, if some technical inspections are missed during the inspection or the quality of the overhaul is poor, overhaul will occur. A series of problems such as water and oil system failure and valve leakage. Therefore, the formulation of technical requirements and welding quality assurance measures in comprehensive inspection and overhaul can effectively prevent the occurrence of some equipment accidents during operation.

1 Overview 1.1 The defects of in-service boilers and pressure vessels have to go through a process from occurrence to development to an accident. Such as cracks, corrosion, deformation, etc. of the pressure element did not happen suddenly. If technical inspections are carried out during the overhaul, that is, internal and external inspections, defects can be found in time, its development trend can be grasped, and corresponding measures can be taken to prevent accidents.

1.2 If the minor defects found in the inspection of boilers and pressure vessels are not repaired in time and correctly according to quality construction measures, the damage speed will be accelerated and the service life will be shortened. Otherwise, the service life of boilers and pressure vessels will be increased.

3 Defects found in the inspection of boilers and pressure vessels shall be handled in accordance with the provisions of DL612-1996 Boiler and Pressure Vessel Supervision Regulations.

This article is the author's experience and summary of implementing DL / T6471998.

1.4 The technical inspection items in this article, as the content of leak-proof and explosion-proof inspections during the comprehensive inspection of boilers and pressure vessels, help boiler and pressure vessel inspectors to supervise and guide the leak-proof and explosion-proof inspections of power plants.

2 Safety 2.1 Safety matters for internal inspection of the boiler The blocking board is cut off, and the related valves have been closed, locked, and warning signs have been hung. The electric door has cut off the power supply, and the warning signs have been hung to prevent sudden steam and water.

2.1.2 Before entering the combustion chamber and flue, it should be fully ventilated. The repaired furnace should not leak into the furnace smoke, hot air, pulverized coal or oil, steam, and the coke residue and ash in the combustion chamber must be cleaned.

3 When inspecting various hole doors, care should be taken to prevent burns caused by the high temperature steam and water accumulated inside.

2 Safety matters for internal inspection of steam drums and pressure vessels 2.2.1 All soda water connection doors should be closed and locked. Make sure there is no steam or water before entering the steam drum or pressure vessel, and then cover the tube with a special tube cover and lay a rubber pad to prevent objects from falling into the tube.

2.2.2 There should be good ventilation in the steam drum and pressure vessel, the internal temperature is> 40C, and the air is clean.

2.2.3 12V running lights or flashlights are used in steam drums and pressure vessels, but running light transformers cannot be placed in steam drums or vessels.

2.2.4 When entering the steam drum and pressure vessel for inspection, there should be someone outside to supervise and frequently contact with external personnel.

2.5 The tools and materials brought into the steam drum or container must be registered, and the inspector's clothing bag must not contain sporadic objects to prevent falling.

3 Technical inspection 1 The steam drum connection pipe and deaerator a, the upper and lower tile-shaped pads and inclined pads are intact. b Pin nut should be tightened.

c. The lower part of the hanger should be in full contact with the steam drum. The d support hanger is complete, and the bearing capacity is balanced without corrosion.

a. Check the corrosion of the inner wall, and record the remaining wall thickness at the corrosion site, depth, shape, area, etc. of uniform corrosion or pitting pits not less than the design wall thickness.

b. Take out the rust and scale cleaned from the inner wall of the steam drum and downcomer or container, analyze the chemical composition, determine the nature of the scale sample, the content of the chemical composition, etc., count the total scale and make a record

c. Check the thickness of the cylinder wall with an ultrasonic thickness gauge to check whether there are defects such as interlayers and cracks.

d. There should be no defects such as cracks in the vicinity of the opening. The inner edge of the pipe with a diameter of D> 159 should be rounded with R> 15mm, and no sharp corners are allowed.

a. The longitudinal and girth welds of the steam drum and pressure vessel and the heat-affected zone should be free of cracks and other over-standard defects. X-ray spot checks should be made at the T-shaped joints.

b. Near the welding seam of the reinforcement ring of the head, saddle and nozzle (especially the lower nozzle, feed water inlet, dosing pipe, recirculation pipe), there is no crack and other defects exceeding the standard by visual inspection. After surface nondestructive inspection.

c. The distance between the buried parts of the equipment inside the steam drum and the edge of the pipe hole or the weld of the pipe hole should be greater than 50mm. d. The monitoring operation or repaired parts should be subject to key inspection, and the position, size and nature should be done. According to the comparison record, if the defect develops, it should be dealt with in time.

1.4 Various connecting pipes a, the connecting pipes of the steam drum (such as water level gauge pipe, pressure gauge pipe, soda water sampling pipe, dosing pipe, continuous exhaust pipe, sewage pipe, water supply pipe, etc.) are required to be unobstructed. If there is rust and mud to be removed, the connected bracket must be intact, and if necessary, check whether the zero position of the local water level gauge is correct.

5 Key inspection parts of the deaerator 1 Requirements for external inspection of the water wall a. Irradiation with strong parallel light, touch by hand, sight and measurement with inspection model, etc., to check for swelling and bulging.

b. For the pipe sections and adjacent areas where tube explosion, bulging and bulging have occurred before, as well as overloading during operation, local heat load is too high, or the inner wall may be scaled, the inspection should be focused.

c. When the swelling exceeds 3.5% of the original diameter, a new tube should be replaced.

For the partially swollen pipe, although the above standards are not exceeded, but the metal overheating can be clearly seen, the pipe should also be replaced.

d. Check whether the expansion of the four corners of the combustion chamber is deformed and bent; whether the water-cooled wall hanger, hook, and pipe clamp are jammed or burned; if something is stuck in the expansion gap between the water-cooled wall and the burner, it should be cleaned.

e. There is no crack in the welding seam and heat-affected zone of the fins and tubes, especially the welded joints of the water wall of the burner support are not cracked.

2.2 The inspection of the inner wall of the water cooling wall requires two long pipe sections, and then a certain length is cut from the cut pipe section, and the scale is washed with acid wash to remove the scale, and the amount of scale per unit area of ​​the inner diameter is calculated.

Above, otherwise it should be pickled.

a. Check if there is any crack or deformation at the nozzle of the downcomer, steam drum and lower header.

b. Check whether there are any cracks, deformation and ellipticity changes inside and outside the elbow of the outlet pipe elbow of the descending pipe distribution header. Regularly perform pipe cutting to check the changes in mechanical properties.

c. Working condition and expansion gap of downpipe support and hanger.

3 Superheater 3.3.1 Check the tube expansion, bulging, bending and wear.

a. The expansion of the alloy steel pipe cannot be greater than 2.5% of the original diameter; the expansion of the carbon steel pipe cannot be greater than 3.5% of the original diameter. b. The local wear area should not be greater than 10cm2, and the wear thickness must not exceed 1 / 3. C. If it exceeds the above standard, it should be recorded and replaced. Metallographic inspection of the swollen and bulged pipe sections to find out the cause and solve it.

d. There should be no cracks and other damage on the outer surface of the pipe, and no obvious bending deformation.

3.2 The key inspection site a, the high temperature part of the superheater, the elbow and the place where the flow velocity of the flue gas is large should be provided with fixed inspection points.

b. When the ash blocking is serious, it is necessary to check the expansion of the pipe in the part of the flue that is not blocked.

c. From bottom to top and from left to right during inspection, see the corners and ash-blocking places, elbows and straight pipe sections.

3.3 Check the corrosion situation a. The personnel of the boiler inspection center and the boiler supervisory engineer of the power plant, together with the metal inspectors and chemists, determine the high-temperature section and low-temperature section superheater outlet serpentine pipe cutting elbows one and two each.

Perform detailed inspection and check the changes in the metallographic structure of the monitoring section.

c. For the cut pipe section, the location and location should be marked and registered. If the pipe cannot be welded immediately after cutting, a plug should be added.

4 Desuperheater 3.4.1 Check the inner bushing and nozzle with endoscope for cracks, severe wear, and no displacement of the inner bushing.

3 If necessary, use non-destructive testing to determine whether the inner wall is cracked.

4 If you suspect that there is a problem with the protective sleeve, you can cut the header of the spray desuperheater header and check it.

1 Check the corrosion and wear of the outer wall of the economizer.

a. The upper three rows of tubes (the first row in the first row and the second row in the staggered row), the serpentine tube elbows, the tubes near the furnace wall and the tubes on both sides of the flue gas corridor should be inspected.

b. Check if the anti-wear protective tile has fallen off or damaged. If it falls, it should be repaired.

c. The connection between the pipe clamp and the pipe shall be good, the pipe shall not be bent and deformed, and the pitch shall be normal.

d The local wear and corrosion shall not exceed 1/3 of the original pipe wall thickness. If it exceeds and wears over a large area, it should be replaced.

a. The personnel of the boiler inspection center and the boiler supervision engineers of the power plant will work with the metal inspectors and chemists to determine the cutting of the economizer tubes 1 and 2 in the high and low temperature sections for inspection.

b. There is no ulcerative corrosion on the inner wall, the average corrosion depth is not more than 1/3 of the original wall thickness. If it exceeds the standard, it should be replaced.

It should be replaced.

6 There is no serious corrosion or scaling on the header below the water wall, the superheater header, and the economizer header. Open the hand hole of the header to check.

6.2 Applicable spectral retest materials of alloy steel headers are qualified.

3 There are no over-standard defects in the appearance and non-destructive inspection of the weld, and there are no over-standard defects such as cracks near the weld and the welding seam of the socket.

6.4 For steam headers with a long operating time and a temperature above 450C, it should be inspected for abnormalities such as graphitization, creep, deformation, cracks, etc.

3.6.5 Normal expansion. Check that the expansion indicator should return to the zero position when cold, and the reserved expansion gap is free of debris.

1 The boom should have anti-loosening device.

2 Each hanger is evenly stressed, without rust.

3 There is no crack in the welding seam of header and lifting lugs.

4 Use a small hammer to check that the comb-shaped plate of the support and hanger is not burned or damaged. If it is replaced, the expansion gap should be adjusted.

5 There is no debris on the support, which does not affect the expansion.

6 Check that the gap between the anti-vibration bracket stopper device and the body meets the requirements.

a. Spot check the recirculation pipe and steam pipe. The key spot check is the ellipticity of the pipe elbow, the wall thickness of the outer arc surface and the appearance inspection. The ovality and wall thickness of the outer arc should not exceed the standard, and the outer wall should be free of cracks and other defects.

b. Pipes at higher temperature locations and pipes exposed to rain in semi-open weather should be inspected for corrosion cracks on their outer walls.

3.8.2 Pipe tee and support hanger a. Check the surface of the tee and the high stress area near the welding seam for cracks.

b The support and hangers suspected of external inspection should be thoroughly inspected, and those with defects should be repaired.

8.3 Valve disassembly inspection and repair requirements a. Check the valve stem bending and corrosion should not exceed 0. d. The corrosion pit depth of the valve head and valve seat sealing surface can be eliminated by grinding method under 0.

3.9 Boiler safety valve, water level gauge, thermal instrument and protection device 3.9.1 Check the water level gauge, water level alarm, pressure gauge and related pressure transmission pipes for no leakage, pay special attention to whether the pressure transmission pipes in the furnace top cover are overheated, Bulging phenomenon.

9.2 The safety valve is disassembled and inspected, and it is installed in the boiler after passing the cold verification.

3 The main instrument, automatic device and protection device are qualified.

9.4 Whether the temperature measuring elements installed on the soda pipes and headers have erosion and no cracks on the surface.

10 The 3.10.1 furnace wall inside the combustion chamber and the flue shall be complete and tight without serious burnout.

3.10.2 The nozzles of the burner are intact, without scorch flooding, severe burnout, abrasion and deformation, the position is correct, and the fuel gun and secondary door casing are firmly fixed.

10.3 The furnace door, peep hole, scorch door and manhole door are complete and can be closed tightly. There are no scars, cracks and perforated sand holes on the inner and outer surfaces, and the switch is flexible.

10.4 The location of the accessories of each measuring instrument and control device is correct, complete, tight and smooth.

10.5 The weight and opening angle of the door cover of the explosion-proof door shall be checked according to the drawings. The explosion-proof door shall be complete, tight and free of debris.

10.6 There is no coke in the furnace and ash bucket of the slag fishing machine, and there is no ash blocking in the heated surface of the tail and the flue.

11 Load-bearing components 3.11.1 The load-bearing beams are not bent and deformed, and there is no corrosion on the surface. If necessary, measure the deflection of the load-bearing beams.

3.11.2 The boom is evenly stressed, and there is no overheating or oxidative corrosion on the surface. If necessary, measure its working temperature and check the insulation measures. If it is over temperature during operation, the mechanical performance should be checked.

3.12 Inspection requirements for special pressure vessels such as high-pressure, low-pressure, continuous row, fixed row, hydrophobic expansion vessels, etc. b. Manholes, inspection holes and the surroundings of their reinforcement; h. Locations with cracks or corrosion marks on the surface.

3.12.2 Pressure vessel safety valve, pressure gauge and protective device a. The opening pressure of the safety valve shall not exceed the design pressure of the pressure vessel, check the setting value (P vent b, spring-type safety valve shall prevent the adjustment screw from being turned casually Lead seal device, lever type safety valve should have a device to prevent the free movement of the weight and a guide frame that restricts the lever from going out.

c. The accuracy of the pressure gauge of the low-pressure container should not be lower than 2.5, and the accuracy of the pressure gauge of the medium-pressure and high-pressure container should not be lower than 1.5.

d. The safety mark of the protection device should be obvious, intact and clear.

The over-temperature or over-pressure safety protection device passed the verification.

4 Welding quality construction process requirements 4.1 General requirements for welding of pressure components 1 Welding components and pressure vessels must have welding records and inspection reports for welding pressure components. Welding joints should have repair records when they are repaired. Spectral inspection must be performed when replacing alloy tubes.

2 Welding of pressure components of boilers and pressure vessels must be performed by a welder who has been trained and has passed the examination corresponding to the item being welded, and the welder's code stamp is stamped near the weld.

3 The welding quality of boiler pressure components must be inspected in accordance with relevant regulations.

4 The quality of welding materials shall comply with the provisions of national standards and power industry standards. The welding rod and welding wire shall have the quality certificate of the manufacturer, and shall be used only after being qualified according to relevant regulations.

5 The selection of welding materials should be considered in accordance with the chemical composition and mechanical properties of the base metal, the process performance of the welding materials, and the design requirements and performance of the welding joints.

1 Except for the specified cold drawn welds, strong alignment is not allowed during the assembly of the weldment. During welding and post-weld heat treatment, the weldment should be cushioned and suspended or subject to external forces. The cold-drawn tool used in the cold-drawn welded joint shall not be removed until the entire welded joint is welded and heat-treated.

4.2.2 Drums, distribution headers, secondary desuperheaters, superheaters, headers, headers and pressure vessels, low-carbon steel containers with thickness greater than 30mm, and pipes and fittings shall be heat treated after welding.

3 Pearlite, bainite and martensite heat-resistant alloy steel pipes and fittings and weldment joints to be heat-treated are determined by the welding procedure qualification test, and heat treatment shall be carried out after welding.

4 High temperature section superheater tubes, screen superheater tubes and 12CrMoV steel pipes with a wall thickness not greater than 6mm, when using arc welding or argon arc welding, preheating before welding, and slow cooling measures after welding, the welding joints can be exempted Heat treatment.

3 Post-weld heat treatment specifications and requirements 3.1 Overall heat treatment should be used. If section heat treatment is adopted, the overlap heat treatment length should not be less than 150mm, and heat insulation measures should be taken outside the heat treatment furnace.

3.2 Girth welds and repaired welds are allowed to adopt local heat treatment. The welds with local heat treatment shall include the entire weld. The heating width of each side of the welding seam shall not be less than 3 times of the whole strip, and heat preservation measures shall be taken for the shell near the heating part.

3.3 In the heat treatment process, the rising and cooling speed V should generally meet: the rising and falling temperature below 300V can generally not be controlled.

4.3.4 The temperature difference between any two points within the heating range should not exceed 50V during the process of temperature rise, cooling, and constant temperature. 3.5 The temperature measuring device and meter should be accurate and reliable, and the measuring point should be no less than two points. The post-heat and post-weld heat treatment should be Make technical records and signs.

3.6 For steel materials that have a tendency to produce delayed cracks after welding, post-heating or post-weld heat treatment should be carried out in time according to the process determined by the welding procedure qualification test. The heating range of post-heat treatment is the same as the post-weld heat treatment requirements.

4 Welding repair of pressure component defects 4.1 Welding repair of pressure component defects should be careful, and important pressure components (such as steam drums) should undergo a strict welding repair process evaluation test before welding repair, and the welding repair technical program should be reported to the superior power company Approved.

4.2 The repaired parts of parent metal surfacing must be smoothed, and the repaired length after the weld defect is removed should not be less than 100mm. 4.4.3 Pressure components shall not be repaired by patch repair.

4.4 The technical requirements for the repair and repair of local defects in the weld are the same as those for repairing the defects of pressure components. The excavation and repair of the same part shall not exceed three times. For the welds that are still unqualified after the second rework, the re-repair should be approved by the chief engineer. â–¡

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