Where are metal expansion joints fixed? — — Detailed explanation of installation position and fixation method
Two days ago, I received a call from a power station customer, saying that the corrugated expansion joint they installed in the power station industry leaked after only half a year of operation. I asked him: How do you arrange the fixed brackets? The other party was stunned. Fixed? Isn't it just welded to the pipe?Tsk, this is the typical use of expansion joints as rigid parts.Today, let's break this matter apart and explain it clearly-where and how to fix the metal expansion joint.
1. The expansion joint is not something you can fix if you want to: first understand why it needs to be "positioned"
Absorbs thermal displacement, absorbs vibration, absorbs installation errors.But it does not carry the self-weight of the pipeline, nor does it carry the pressure thrust.Therefore, the so-called "fixing" is not to lock it to the pipe with bolts, but to draw a range of motion for it with brackets, tie rods or restraints-let the bellows only move where it should move, and stay honestly where it shouldn't move. To put it bluntly, fixing is to draw a working area for the expansion joint, not to weld it to death. What's the difference between welding it to death and using a steel pipe? The bellows are either pulled and cracked or compressed to permanent deformation.
Many manufacturers' installation manuals state that "guide brackets must be set at both ends of the expansion joint", but the on-site construction team saves trouble and directly lets the expansion joint support itself on the pipeline. And the result?Corrugated pipes are fatigued and cracked in a few months, and the repair cost is dozens of times more expensive than the bracket money.This account has to be clearly settled.
2. Fixed bracket and guide bracket: The two brothers have different division of labor
Fixation bracket (main fixation point)It is the anchoring point of the pipeline, which should carry the thrust generated by the pressure of the pipeline, the thermal expansion thrust, and the self-weight of the pipeline. Whileguide bracketJust one thing: limit the lateral displacement of the pipe and allow it to slide freely along the axis. Expansion energy saving is mounted between two fixed brackets, or one end can be fixed and the other end free. Take the general-purpose corrugated expansion joint and high-temperature axial expansion joint in our station for example. When installing, guide brackets must be set at both ends, otherwise the pipe will twist like a snake, and the corrugated pipe will soon yaw and fail.
Let's talk about the straight pipe pressure balance expansion joint-it comes with its own tie rod or hinge, and the fixed point design must strictly follow the drawings, so it can't be taken for granted.
3. The "fixation" posture of different expansion joints is very different
Different types of expansion joints, the fixing methods are very different, don't take the same set of schemes everywhere.
- Axial expansion joint(For example, external pressure single axial type and general type): The fixed bracket must be welded to the main fixed points at both ends of the bellows, and guide brackets must be added at every other section in the middle. The spacing is calculated according to the stiffness and thermal displacement of the pipe.
- hinged expansion joint(For example, double hinge of double hinge and double hinge of air-cooled island vacuum pipeline): It itself restricts the angular displacement through the hinge structure, and the fixed bracket only needs to resist the thrust, and the distance between the guide brackets can be appropriately relaxed.
- Pressure balanced expansion joint(Straight pipe pressure balance type, curved pipe pressure balance type): There is a balanced bellows or tie rod inside, and the thrust of the fixed bracket is very small, and even a small bracket can be used, but the guide bracket must be in place, so that the pipe cannot deviate laterally.
- Sleeve expansion joint: The fixed point is set at the outer tube end of the sleeve, and the inner tube slides freely. At this time, special attention should be paid to whether the sealing packing is pressed and biased.
- Treatment of tie rods/screws: Many customers ask "Do you want to dismantle the screw of the expansion joint". Let me say the conclusion directly: the transport screw is for protection, and it should be adjusted according to the pre-tension or pre-compression requirements after installation. For the specific torque value, refer to the product manual, and it is not just twisted for a few turns.
4. The most common pit stepped on the site: Take the expansion joint as a pipeline support
They used the corrugated expansion joint in the power station industry as a pipe support, and the corrugated pipe directly pressed against the weight of the pipe, and it leaked in half a year. The right thing to do is simply —The expansion joint itself does not bear any vertical loadAll pipe weights must be carried by brackets or hangers. For large-diameter thick-walled expansion joints, they must be fixed with temporary supports during installation, and then remove the temporary parts after the pipeline is welded and the bracket is adjusted in place. Otherwise, the bellows will be compressed and deformed before it even works.
When the expansion joint is installed near the elbow, the fixed bracket cannot be directly welded to the elbow, but should be set on the straight pipe section behind the elbow, otherwise the stress at the elbow will be concentrated and the bellows will soon be torn.
5. Where exactly is it fixed? A table to state the recommended location
No more forms, just talk about dry goods:
- Straight pipe section: The fixed brackets are arranged at both ends of the expansion joint, and the distance is generally no more than 6 meters (specifically adjusted according to the pipe diameter and medium temperature).
- Near elbow: The fixed bracket is arranged on the straight pipe section behind the elbow to avoid stress concentration at the elbow.
- Close to equipment entrance and exit: For example, pumps, valves, cooling towers, the equipment itself can be used as a fixed point, but the thrust allowed by the nozzle of the equipment must be checked. Some equipment nozzles are fragile and deform with a slight top.
- buried pipelineFor example, for directly buried fully buried expansion joints, reinforced concrete fixed piers are usually poured at both ends to prevent the compensator from being torn by soil displacement.
- High temperature region: Referring to the application of metal corrugated expansion joint in kiln head pipeline in cement industry, the fixed bracket should avoid the high-temperature section, otherwise the steel of the bracket will soften and fail first.
6. To summarize a hard truth: the fixation of the expansion joint is not "locking", but "guiding"
Without proper guidance and fixing, there is a high probability that the bellows will be scrapped within a few months.When designing and selecting, it is best to send the pipeline layout drawing to the manufacturer, so that they can help check the force of the fixed bracket. There are various installation guides and technical parameters of expansion joints in our station, such as the adjustment method of expansion joint tie rod, the function of guide tube, etc. How much maintenance cost can you save by turning it over before installation? Do the math for yourself.
So, the next time someone asks, "Where is the metal expansion joint fixed," you can tell him:Fixed to brackets, fixed to drawings, fixed to your heart – not locked with brute force, but guided by knowledge.