Confirmation work before disassembly: Is the media drained? Is the pressure released? Is the support done?
Many masters unload the bolts as soon as they come up, and as a result, the acid remaining in the pipeline is sprayed all over the face, or the expansion joint pulls and deforms the bellows by its own weight. We have seen too many such accidents. Don't be too long-winded. If you can't do these three things well before demolishing, you will be full of trouble later.
Look at the pipeline drawings first, and find out which section, model and structure the expansion joint is installed in. You thought it was a general-purpose corrugated expansion joint that was disassembled, but it turned out that a straight pipe pressure balance expansion joint was installed on site, and the disassembly sequence was completely different-if you don't read the drawings clearly, who's to blame if something went wrong?
Next, confirm that the medium is drained and the pressure is released. If it is a flue gas pipe, you have to wait for the temperature to drop, so don't dismantle it with high temperature. If it is a corrosive medium, has the line purge replacement been done? These are not the matters of the security officer alone, and the people who demolish them have to know it in their hearts.
- Drain pipeline media, confirm no residual pressure
- Check the status of pipe supports and supports and add temporary supports if necessary
- Confirm Expansion Joint Model, Construction Type and Installation Location
Understand the structure before starting: which can be dismantled and which can't be touched?
Different expansion joints of different structures have completely different disassembly sequences.
Tie rod expansion joint (such as large tie rod expansion joint) should first remove the connecting pin of the tie rod, and then remove the flange bolt. If the order is reversed, the bellows will bounce open with the pipe. The hinge device of the hinged expansion joint (like the double-hinged expansion joint of the air-cooled island vacuum pipe) bears the thrust of the pipe. If you remove the hinge first, the displacement of the pipe will be released instantly, which is no joke.
Straight pipe pressure balance type expansion joint and compound straight pipe bypass pressure balance type expansion joint have balance bellows and working bellows inside. When disassembling, be sure to confirm that the internal pressure has been completely released. The outer sleeve and bellows of the external pressure single axial expansion joint are two sets of structures. Don't take the tie rod as a load-bearing part to dismantle.
The universal corrugated expansion joint is the simplest, and it can be taken off after the flange bolts are loosened, but only if there are no tie rods or limit screws at both ends of the corrugated pipe-this will be described later.
Mark before installing: No line, put back and wait to cry
Before removing, use a marker to mark the expansion joint in three places:
First, the axial compensation amount position of the expansion joint is marked. Bellows usually have pre-deformation when they leave the factory, and this position determines whether they can normally compensate for thermal displacement after being installed back.
Second, mark the diagonal number of the flange bolts. Don't think this is redundant-there are many flange bolts. When installing them, just find two diagonal ones and screw them on. As a result, the flange is unevenly stressed, and the pipeline leaks during operation. When the time comes, it will be reworked, and the cost will more than double.
Third, mark the nut positions of the pull rod and the limit screw. Before removing, measure the length of the tie rod with a ruler, or draw a line on the tie rod with a marker, and reset it as it is when installing. Otherwise, if the tie rod is tightened and loosened by a few millimeters, the axial stiffness of the expansion joint will change, and the bellows may be directly unstable.
Sequence and method of loosening flange bolts: loosening symmetrically from the center to both sides
Symmetrically loosen from the middle to both sides, and it is strictly forbidden to dismantle it completely at once. This is done to allow the flange surface to separate evenly and avoid the bellows from bearing uneven forces.
What if the bolts rust to death? Spray rust remover first, wait for ten minutes before trying to screw. If it doesn't work, you can gently tap the head of the bolt with a hand hammer-note that it is a gentle tap, not a sledgehammer. If it is smashed hard, it will break the bolts at least, and deform the flange sealing surface at worst.
Removed bolts and spacers, check them one by one. Are the bolt threads worn? Has the gasket been crushed or aged? If the gasket has lost its elasticity, it is recommended to replace it with a new one directly. Don't let the back leak in order to save these few dollars.
Do you want to remove the tie rod or screw? Depends on the working conditions, don't one size fits all
Not all of the tie rods, limit screws, and transport fixing rods on the expansion joints can be removed.
Transport retaining bars-must be removed. This thing is used to fix the bellows when it leaves the factory, so as to prevent the bellows from deforming and displacing during transportation and hoisting. It must be removed after installation at the site, otherwise the bellows will completely lose its compensation function.
Tie rod and limit screw-depending on working condition. If the expansion joint is used to absorb thermal displacement, after the tie rod is removed, the thermal expansion force of the pipe may be applied to the equipment or bracket, causing an accident. If the bellows itself is to be overhauled, the tie rod must be dismantled, otherwise the bellows cannot be replaced.
Before removing the tie rod, record the position of the tie rod nut. This data is too important. When you install it, reset it as it is, so that the axial displacement will not deviate.
Hoisting and handling links: Bellows are afraid of smashing or touching, handle them lightly
Bellows are thin-walled pieces, which are most afraid of bumps. When hoisting, the sling is directly strung on the corrugation, leaving an indentation at the slightest, and flattening the corrugation at the worst, and the whole expansion joint will be wasted.
Use a soft sling with a backing plate so that the sling does not contact the corrugated surface directly. The lifting point should be selected at the connecting end or the reinforcing ring, and the expansion joint should not be used as a load-bearing member to lift.
Keep it level when handling and do not subject the bellows to the tensile or compressive forces created by its own weight. If it is a large-diameter thick-walled expansion joint with heavy weight and large size, you should be more careful. It is best to use a crane to cooperate with the inverted chain to keep the balance and move slowly.
Key points of inspection after removal: Don't rush to install new ones, see how dirty the old ones are first
The expansion joint is removed, so don't rush to replace it with a new one. Carefully check the old parts first. This step is done well, which can help you judge whether there are other hidden dangers in the pipeline system.
Bellows – Focus on cracks, scratches, corrosion pits. Especially the trough position of the corrugation, it is most likely to hide dirt and evil, and it is also most likely to occur stress corrosion cracking.
Deflector-See if it has been perforated by media flushing. The function of the guide tube is to protect the bellows. If it breaks first, it means that the flow rate of the medium in the pipe may exceed or contain particulate matter.
Joint End Weld – Check for fine cracks with a magnifying glass or penetration test.
Use a caliper to measure the corrugation spacing and compare it with the original data. If the corrugated spacing exceeds 10% of the original data, it means that the corrugated pipe has been overfatigued, so it should be scrapped and replaced with a new one. Don't feel bad about the money-this thing leaks after installation, and the disassembly cost is much more expensive than the expansion joint itself.
After all, the disassembly of the metal expansion joint looks simple, but it is full of details in practice. Do every step in place, and put it back before you can continue to use it. Do you have any expansion joints on hand that have been removed but not marked? Remember to get a marker before you disassemble it next time.