Introduction of chimney construction method and detailed steps

Speaking of chimneys, I don't think everyone will feel strange. Chimney is a very important thing in our life, ranging from the daily smoke emission of every household to the exhaust emission of many factories, which plays a very key role. The installation of chimney should not be underestimated. Its installation directly affects the use, but many inexperienced people often don't understand it. Because of IC, this article will introduce the installation of chimney for your reference when necessary.

Construction technology of chimney combined installation

Basic marking → equipment inventory inspection → socket combination welding → socket acceptance → socket climbing acceptance → socket installation → phased acceptance → overall installation acceptance → installation completion.

Chimney combination

Combined platform installation

Before chimney assembly, according to the radiation range of crane hoisting radius, set up a steel-concrete composite platform at the selected position. According to the space of the site, the platform area should meet the requirements of simultaneous assembly of at least four pipe sections, and the clear distance between the pipe sections should be more than 2m, so as to facilitate the ground installation of the chimney platform. In order to facilitate the construction workers to enter the chimney barrel from the bottom, the elevation of the steel support top of the combined platform is set to 800 mm, and a platform is set at the top of the steel support according to the diameter of the barrel joint. The flatness of the top platform shall be 1 mm. Draw the outline of the outer circle of the chimney on the horizontal frame of the top platform, and weld the limit blocks on the ribs of the top platform to prepare the assembly of the chimney segments.

Selection of combined hoisting machinery

7650 crawler crane and 7 100 crawler crane are selected according to the site machinery configuration and project progress. 7650 crawler crane is mainly responsible for the lifting and positioning of socket, and 7 100 crawler crane is responsible for the ground assembly of socket. 7650 crawler crane adopts tower working condition and is arranged at the rear of waste heat boiler. The main arm is 72m, the auxiliary arm is 36m, the turning radius is 50m, the rated load is 44.5t, the actual lifting weight is 35t, and the load rate is 78.65%.

Welding process flow and correction

Welding construction process flow

Construction disclosure → welding material distribution → groove inspection → butt joint fixation → welding → welder self-inspection → joint inspection → repair → quality acceptance evaluation.

The longitudinal weld should be welded first, and then the circumferential weld. All longitudinal welds are assembled on the ground and welded symmetrically by three people; During the construction process, at least three longitudinal welds of a single tubular joint shall be welded simultaneously by the method of sectional withdrawal welding. Circumferential weld shall be symmetrically welded by two people; During the construction process, it shall be ensured that two welders who are symmetrically welded shall perform segmental jump welding at the same time. All circumferential and longitudinal seams of the chimney are full penetration welds. After backing weld is completed, the back of the groove shall be repaired with grinding wheel. After the welding of longitudinal seam and circumferential seam is completed, the corresponding inspection shall be carried out, and the construction can be continued only after passing the inspection.

During the welding process, all welders use the same welding specification. During the welding process, use theodolite to monitor the deformation of each column at any time. And monitor the distance between two side-by-side beams and the diagonal of each span. If the difference is too large, immediately notify to stop welding.

Welding of other welds

When welding other welds, such as platforms, ladders, railings, etc. , to ensure the welding is firm, the weld size must meet the requirements of the drawings, so that the weld shape is beautiful; The appearance of fillet weld is concave.

In case of wind, rain and snow, a shelter against wind, rain and snow should be built with tarpaulins in the joint area. When the ambient temperature is lower than the minimum allowable welding temperature, all welds must be preheated before welding. The preheating temperature of carbon steel should be selected according to the following contents, and the heating mode is flame heating or electric heating:

δ δ = 16 ~ 24 mm, preheated to below -5℃ 100℃ ~ 150℃.

24 mm δ > 30mm, when the ambient temperature is lower than 5℃, a higher preheating temperature should be adopted.

Correction of welding deformation

In order to reduce stress and prevent deformation, it is necessary to ensure that the longitudinal and transverse shrinkage of the weld is relatively free and not subject to great constraints. When welding butt joints, the welding direction should point to the free end. For thin plates, try to use covered electrode with small specification (diameter) and small welding specification when welding; Welds with large shrinkage should be welded first. If there are butt welds and fillet welds at the same time, the butt weld should be welded first, and then the fillet weld should be welded. When welding cross-welded joints, the welding sequence must be adopted to ensure that cracks are not easy to occur at the intersection; After welding, if the weldment is deformed greatly, mechanical correction should be considered first, and special fixtures and correction tools can be made according to the actual shape of the site. When mechanical correction cannot be used, local heating method can be used for correction. The heating mode can be flame, and the temperature in the heating area should be below 650℃.

Skirt seat combination

First, combine the skirt of the chimney. The skirt seat is fixed on the concrete foundation by bolts, so the skirt seat combination is directly carried out on the chimney foundation. Firstly, according to the size of the skirt, configure the shim to the design bottom elevation of the skirt, with a deviation of 1 mm, and the number of shims should meet the requirements of drawings and technical specifications. When welding, first weld the vertical seam of the cylinder, and pay attention to the fact that the upper part of the vertical seam is not welded for 200 ~ 300 mm, so as to adjust the flat-fell seam when combined with the upper seam of the cylinder. Weld the skirt bottom plate again. Because the welding groove of the chimney skirt bottom plate is downward, it is necessary to weld the top of the skirt bottom plate first, and then weld the bottom plate. It is necessary to lift the skirt by about 500mm to facilitate the welder's operation. After welding, the bottom plate should be heat treated to release thermal stress. Put the skirt on the prepared pad iron, adjust the position of the skirt with the chain, and then set out the cross center line of the foundation, and then measure the size from the inner wall of the cylinder to the midpoint. The verticality of skirt should meet the requirements of drawings and technical acceptance specifications.

Barrel joint combination

Except for the chimney skirt, the barrel section assembly can be carried out after the skirt assembly is completed, or at the same time with the skirt assembly. Each socket is divided into three pieces. Re-measure the size of each socket according to the drawing size, and then assemble the socket. Put three pipe joints on the combined platform, adjust the pipe joints for butt spot welding, and then measure the upper and lower perimeters of the pipe joints. The upper and lower deviation should be less than 5mm, which is 5 ~ 8 mm longer than the theoretical week. Then divide the upper circle into eight equal parts, measure the verticality at the equal parts, control the verticality within 7mm, and adjust the diameter of the socket with four inverted chains to meet the requirements of the drawing specification. When there is no problem, carry out vertical seam welding of the cylinder joint. When welding, pay attention to reserve 200 ~ 300 mm from top to bottom without welding, so as to adjust flat-fell seam when the upper and lower barrels are combined. After each barrel section is assembled, mark the quarter points of the barrel section on the upper and lower circles of the barrel section, and draw obvious marks for proofing. This mark is the basis for assembling the socket up and down and lifting the socket in place.

Combination between cylinder joint and cylinder joint

In order to reduce the overhead operation of the chimney, according to the hoisting capacity of the crane, two or more pipe joints are combined and welded on the ground combined platform, and then hoisted in place. Principle of combination: when the lower bucket section is heavy, two sections are combined; When the upper barrel joint is light, it can be combined in multiple sections, but the combined weight shall not exceed 35t. When assembling multiple sections, the combined scaffold should be erected on the combined platform, with internal and external scaffolding erected, the inner side is convenient for root cleaning, and the outer side is convenient for assembly and welding between pipe sections. In order to facilitate hoisting, scaffolding should be 200 ~ 300 mm away from the wall. After the combined cylinder joint is lifted and dismantled, other cylinder joints can be assembled and welded on the original basis.

Installation of ladders and platforms

In order to facilitate the installation and welding of the upper barrel joint assembly, after the acceptance of the barrel joint assembly, a formal ladder and platform should be installed on the barrel wall. After the butt joint of the ladder and other tubular joints is completed, pay close attention to welding. The ladder will gradually improve with the rise of the tubular joints, so there will be traces passing through the top of the chimney. When the platform is installed, determine the direction of the barrel joint, determine the platform position according to the drawings, weld the platform support first, then install the platform frame, then lay the platform grid, and then install the railing and skirting board on the platform. So is the ladder. Set the direction of the barrel joint on the ground, find out the position of the ladder, and weld the ladder in place.

Temporary platform for barrel assembly

In order to weld the coupling assembly and the formal platform, it is necessary to set a temporary platform at the elevation 1m below the coupling interface. In order to reduce the amount of welding on the chimney, a special temporary platform was built on the bracket directly welded on the chimney. The whole temporary platform is divided into three sections to avoid installing high-altitude pipe joints with spiral plates. The temporary platform shall be welded at a position 1m away from the upper part of the assembly, and a safety fence with a height of 1.2m shall be set, and a high-density net shall be used for protection. The temporary platform can be reused. After aligning the barrels, use the crane to cut off the temporary platform and install it on the next barrel for further use. It should be noted that after the overall installation of the chimney is completed, the cage needs to be hoisted by a crane to cut off the temporary platform.

Installation of barrel joint spiral plate

Before installing the socket spiral plate, mark the socket with Mo Dou according to the drawing calculation. In order to ensure that the spiral plate is perpendicular to the barrel joint, angle steel is welded on the barrel joint along the black line and perpendicular to the barrel joint, and the distance of the angle steel can allow three angle steels to support a spiral plate. Then the gap between the spiral plate and the barrel joint is corrected and welded. When welding, anti-deformation measures should be taken, and spot welding and sectional welding should be carried out at both sides of the spiral plate, and finally full welding should be carried out.

Integral hoisting of chimney

The assembly of the socket should be combined according to the lifting capacity of the hoisting machinery, and the assembly height on the ground should not be too high. According to the actual situation at the site, there are generally at most 3 tubular joints. Anti-deformation measures should be taken when lifting the socket assembly, such as lifting with a cross bar or reinforcing the support in the socket. When lifting the socket, it is necessary to use theodolite to measure whether the verticality of the socket meets the installation requirements on the ground, otherwise, correct the socket size, and the theodolite measurement shall be subject to the punching of four equally divided templates on each socket. Because the girth joints of the barrel joints need RT spot check, and the spot check length of each girth joint is not less than 280mm, after the barrel joints are hoisted, aligned and welded, a platform should be built in the chimney for inspection.

After the chimney is installed to 36m, install the reinforcement of the barrel joint. The reinforcing ribs are arranged at the opening where the flue gas enters the chimney, and the five reinforcing ribs are evenly and vertically arranged to prevent stress and deformation. Attention should be paid to anti-deformation welding measures when welding reinforcing ribs: first, double-sided cross-section welding should be carried out, and then two welders should carry out double-sided welding at the same time. After the welding of reinforcing ribs is completed, continue to hoist the upper barrel joint.

Through the above introduction, we have a general understanding of the installation method of chimney, from which we can see that the installation method of chimney is very complicated, involving foundation marking, barrel assembly, welding, barrel acceptance and so on. Every step requires extra care. The installation method introduced in this paper is mainly suitable for the installation of large chimneys. If you install small chimneys at home, you can refer to the previous part. In short, everyone should consider their own actual situation, such as budget and terrain.