Installation of flue expansion joint, if you don't pay attention to these points, it is equivalent to white installation
Alas, after working in the pipeline compensation industry for more than ten years, the sentence that I am most afraid of hearing is: "Our expansion joint leaked after only half a year of use." When asking about the installation process, nine times out of ten, the specifications were not thoroughly understood. The flue expansion joint can last for ten or eight years if it is installed, but it will be scrapped if it is installed wrongly for three months-and the flue is filled with high-temperature smoke and corrosive gas. Once something goes wrong, the loss of shutdown for maintenance is not small. Today, let's break it up and talk about the installation specifications of flue expansion joints. All of them are solid dry goods, which can help you avoid many detours.
Start by figuring out which expansion joint you use for your flue – non-metal, metal rectangle, or flapper door? The installation of different structures is far different
Many customers ask "How to install expansion joints" as soon as they come up. I usually ask: What type do you use? Because the flue expansion joint is not a universal part, different structures and installation requirements vary greatly.
Such asNon-metallic expansion joints (fabric fiber expansion joints)It relies on flexible fabric to absorb displacement, and is most afraid of being scratched by sharp objects or burned through by high temperature open flame. When installing, leave enough room for movement, and do not adhere to the insulation layer. WhileMetal rectangular expansion jointIt is different. The bellows is part of metal and rigid, but it is afraid of twisting and lateral forces. When installing, it must ensure that the pipe axis is centered. AndFlue gas baffle doorAlthough it is a valve equipment, it is often used in series with expansion joints, and the installation tolerance of baffle doors directly affects the force of expansion joints. Think about it, if the baffle door is not closed tightly and air leaks, the expansion joint will have to bear additional thermal shock-after this calculation, shouldn't it be clearly distinguished before starting?
Before installation, you must keep an eye on the size and direction: the direction of the guide tube, the direction of the arrow, the pre-tightening force of the pull rod, and the whole mess after one wrong step
Get the expansion joint and don't rush to the flange. The first step is to check the size. The installation length of the pipeline, the compensation amount of the expansion joint, and the hole spacing of the flange bolts. A difference of 1 mm in these data may cause the installation stiffness. I have seen a project in which the metal rectangular expansion joint was 10mm long, and it was pulled up with a hoist. As a result, cracks appeared in the bellows after three months of operation-do you think it was wrong?
Step 2, look at the direction.guide tubeThe orientation of the medium must follow the flow direction of the medium, which is to prevent the medium from directly washing the bellows. There is usually an arrow on the body of the expansion joint, which refers to the flow direction of the medium. Don't install it backwards. Many metal corrugated expansion joints (such asUniversal corrugated expansion joint) There is also the tie rod, the tie rod nut will be pre-tightened a little when leaving the factory, the purpose is to protect the bellows from being stretched during transportation and hoisting. This preloading force cannot be loosened or adjusted casually before installation, and it should be loosened in place according to the design requirements after the pipeline system is completely fixed. You remember a saying: Where the arrow is pointing, the deflector is pointing; Tie rod nut, don't move until the pipe is welded.
Three "minefields" in the installation process: Is pre-stretching done or not? How to place the fixed bracket and the guide bracket? Don't reverse the welding sequence
Pre-stretched. Not all metal expansion joints need to be pre-stretched, only those that absorb large thermal displacementHigh temperature axial expansion jointOrLarge diameter thick wall expansion jointWill do cold drawing during installation. The purpose of pre-stretching is to allow the expansion joint to pre-stretch a section at low temperature, so that when the pipe heats up and expands, the expansion joint can work in a compressed state. The specific stretching amount is according to the design drawing, usually 50% ~70% of the compensation amount. You must use a special stretching tool to do this step, and it is strictly forbidden to use a chain hoist to hard pull, otherwise the bellows will be unstable.
Bracket Arrangement. Both sides of flue expansion joint must be designedFixed bracket and guide bracket。 The fixing bracket can only be arranged on one side of the expansion joint (usually the main fixing point) to withstand the pressure thrust; The guide bracket is arranged on the other side to ensure that the pipe can only move axially. Many on-site diagrams save trouble, weld both sides to death, or simply don't set up guide brackets-as a result, the expansion joint is twisted into a twist when the pipeline is thermally expanded. Do you think it's irritating?
Welding sequence. If the expansion joint is welded at both ends, remember one mantra: first weld the fixed end, then the free end. Why? Because welding both ends at the same time will generate welding stress, which will pull the bellows and deform it. The specific operation is: first, spot weld the expansion node on the pipeline, check the centering, weld the annular seam on one side of the fixed end, wait for the weld to cool to room temperature, and then weld the free end. ForCorrect installation method of expansion joint of large tie rodIn particular, Li emphasized that the tie rod nut must be loosened during welding (if the design requires), otherwise the welding thermal expansion will break the bellows.
Don't go in a hurry after installation. Three-step debugging and inspection: see if there is any stiffness, whether the sealing surface leaks or not, and whether the tie rod nut should be loose
You think it's over after you weld it? Don't worry, there are three more key checks.
First, check the holding. Use a gauge to check whether the clearance between the flange surface of the expansion joint and the pipe flange is uniform. If the clearance on one side is large and the clearance on the other side is small, it means that the pipe is deflected during installation and must be readjusted. Forced operation in the state of holding up, the life of the bellows is discounted in half.
Second, sealing surface detection. Special attention should be paid to non-metallic expansion joints. Its fabric layer is usually fixed on the flange with beading. Check whether the beading bolts are tightened and whether the sealing gasket of rubber PTFE compensator is intact. If you find a leakage point, don't rush to glue, most of them are because the strips are not flattened. ForDesulfurization flue gas baffle doorFor this kind of equipment with sealed air system, it is also necessary to check whether the sealed air duct is unblocked.
Third, the adjustment of the tie rod nut. Many expansion joints are fitted with tie rods or limit screws, such asStraight pipe pressure balanced expansion joint。 The tie rod nut is pre-tightened during installation, but after the pipeline system and heat insulation are completed, the nut must be loosened to the clearance required by the design (usually 2~5mm), otherwise the expansion joint cannot expand and contract normally. There is a common misconception here: Some people think that the tighter the nut is, the safer it is. In fact, it is the opposite-locking the expansion joint is equivalent to not installing it. How to tune it? refer toHow to adjust the tie rod nut of expansion jointFollow the steps.
Pits that customers stepped on: deformation of expansion joint caused by backward installation, forgetting to disassemble the transport screw, and falling off the guide tube-how to remedy it
Finally, let's talk about a few real cases to save you from falling into the pit again.
Pit 1: Installation of expansion joint backwards。 A customer of a cement factory installed the guide tube of the metal rectangular expansion joint backwards. As a result, the high-temperature flue gas directly washed the bellows, and it was perforated in two months. Remedy: It can only be removed and reinstalled, and there is no other way. Therefore, be sure to check the direction of the arrow before installation, and don't focus on catching up with the construction deadline.
Pit 2: Forgot to remove the transport screw。 In order to prevent deformation when the general-purpose corrugated expansion joint leaves the factory, it usually screws several more transport screws on the tie rod (some are called transport fixings). Many people directly welded the pipeline to death, and when the pipeline heated up, the expansion joint didn't move at all, forcibly cracking the bellows. Solution: All transport screws must be removed prior to operation. If you are not sure, you can tap the screw on the spot. The one that can turn is adjustable, and the one that does not move at all may be the one that should be dismantled.
Pit 3: The guide tube falls off。 This problem mostly lies in the non-metallic expansion joint, where the guide tube and the flange are welded or riveted. If the welding is not firm or the vibration is too great during operation, the guide tube will fall off and directly block in the pipeline. The remedy is troublesome-stop the furnace and reach through the manhole to salvage it. Therefore, be sure to check the fixed point of the guide tube when installing, and it is best to add welding anti-shedding rib plates on both sides of the guide tube.
To say a thousand words, the core of the installation specification of flue expansion joint is one sentence: construction according to the drawing, confirmation item by item, and no luck. Don't think it is a waste of time to spend an extra half hour checking. If something goes wrong, the loss of a day's downtime is enough for you to buy dozens of expansion joints. If you are still unsure, take a look at the product information or Q&A on this site, or call the manufacturer's designer directly-it is better than installing the wrong thing and reworking it.