Hoisting scheme of boiler flue expansion joint: hoisting point arrangement, in-place alignment and key points of safety control
To be honest, over the years of boiler installation in dry power stations, I have seen more hoisting and rollover scenes than I have eaten box lunches. The most common thing is that when the expansion joint is hoisted, it is found that the direction is reversed, or the weld cracks when it is hoisted in mid-air, or the non-metallic ring belt is strangled by the steel wire rope. Today, let's make it clear how to hoist the expansion joint of the boiler flue.
Find out what kind of expansion joint you have in your hand before lifting
When you get the equipment, don't hurry to hang the hook. First, ask: Is this a metal rectangle, a non-metallic fabric or a high-temperature axial type? Different materials and structures of expansion joints, hoisting stress points and protection requirements are completely different. Rectangular non-metallic expansion joints and metal rectangular expansion joints are commonly used in the flue of power station boilers-the former is small in weight but afraid of sharp scratches, while the latter is bulky and needs to be deformation-proof. During acceptance, focus on checking the size, flatness of flange and direction of guide tube. The arrow of guide tube must point to the medium flow direction. If the flue gas flow is installed backwards, it will directly impact the bellows, and its life will be directly cut in half. By the way, check whether the tie rod nut is in the factory preload state-this should be adjusted later, and don't remember when you can't twist it.
A few days ago, at a construction site, the technician brought the ring of the non-metallic expansion joint to the wire rope to strangle a hole, and insisted that it was okay. As a result, the trial operation leaked. When I took it down, 30% of the fabric fibers were broken. You say it was wrong or not?
Hanging point calculation is not a matter of slapping the head
Get the net weight of equipment first. Each expansion joint in the product information of this site has a weight reference. For example, large-diameter thick-walled expansion joints are much heavier than general-purpose types of the same size, so don't rely on experience to estimate. Then distribute the load by four-point crane or six-point crane. The center of gravity of metal rectangular expansion joints is usually on the side of the deflector tube in the geometric center. For non-metal expansion joints, attention should be paid to the deformation of flexible bodies, and hoisting belts or widening slings must be used. It is strictly forbidden to strangle steel wire ropes directly on fabric fibers. The welding position of the lifting lug should avoid the bellows or non-metallic ring belt, and do coloring flaw detection after welding-don't wait until the weld cracks in mid-air, that's no joke.
If there is no position map of lifting lugs provided by the manufacturer at the site, then weld temporary lifting lugs on the outside of the reinforcing rib or flange of the expansion joint. The welding current should be well controlled, and the base metal should not be burned through. For large-tonnage equipment such as corrugated expansion joints used in power station industry, it is recommended to use suspension beams to prevent flange deformation, and to save trouble, directly use a single wire rope to stay by cable.
Positioning and centering is a fine job
The boiler flue interface often has installation errors, and the expansion joint must be installed in a free state. It is strictly forbidden to forcibly pull it in place. First, lift the expansion joint to the interface position, fine-adjust the height and left-right offset with the inverted chain, align the bolt hole and then penetrate 1/3 of the number of bolts, loosen the hook and then install the rest of the bolts. For expansion joints with tie rods, such as double hinge transverse type or straight pipe pressure balance type, at this time, loosen the tie rod nut to release the preload force, so that the bellows is in a natural expansion and contraction state. If it is a non-metallic expansion joint, you have to check whether the loop belt is twisted or discounted-once the loop belt is tightly twisted, it will tear in minutes when running.
When is the tie rod nut adjusted? The answer is that the preload force required by the design must be adjusted during installation, but the temporary preload should be loosened before it is in place to allow the bellows to be free. How exactly to adjust? Refer to the FAQ on this siteHow to adjust the tie rod nut of expansion jointThat one has detailed moment values in it.
Fastening and final inspection make or break
The bolts are pre-tightened diagonally in 3 times, and the torque value is according to the design requirements-you can check the parameters in the expansion joint model. Don't underestimate this step. If the torque is not enough, the flange will leak smoke. If the torque is too large, the ring belt or bellows will be crushed. After completion, check whether the flange clearance is uniform and whether the clearance between the guide tube and the inner wall of the pipe is consistent. For the high-temperature axial expansion joint, it is necessary to confirm whether the insulation layer has reserved expansion space-if the insulation layer is thick, the expansion joint will be stuck, the thermal expansion will not come out, and the pipeline stress will all be eaten on the equipment.
Push and pull the pipe manually to observe whether the expansion joint can expand and contract freely. Don't forget to remove the transport fixings before trial operation-some expansion joints come out of the factory with limit screws, such as straight pipe pressure balanced expansion joints, which must be removed after installation or they will get stuck. Two days ago, there was a project that did not dismantle the limit screw. As soon as the system heated up, the expansion joint directly cracked, and it would be necessary to shut down the furnace for three days.
The most common rollover in the hoisting process are these points
One is to directly hook the flange hole of the non-metal expansion joint with a hook, causing the loop band to tear-do you think the edge of the flange hole is so sharp that the fabric fiber can stand it? Second, when the large-diameter expansion joint is hoisted, the suspension beam is not used, which leads to flange deformation, and the bolt hole is misaligned and hard smashed in, which will definitely leak air in the later period. Third, forget to adjust the tie rod before it is in place, and wait for the bolts to be fully tightened to find that the tie rod is installed backwards-the direction of the tie rod is reversed, and the expansion joint shrinks when it should be stretched, and it stretches when it should be shrunk, so it is directly scrapped.
Compare the installation instructions in the product information of this station in advance, especially for special models such as corrugated expansion joints and high-temperature axial expansion joints for power station industry, and there are clear hoisting specifications. Spend an extra 10 minutes looking at the drawings, saving half a day's rework-this account, can you figure it out?