Compensator deformation? Don't be in a hurry to say "broken."
Has this ever happened to you? Not long after the pipeline was running normally, the compensator was bulging, the bellows were twisted into twists, and the rubber joints were bulging like balloons. Most people's first reaction is "the quality of this compensator is not good". But I want to say that 90% of the deformation has nothing to do with the product itself, but the stress is not released. General-purpose corrugated expansion joints, rubber compensators, non-metallic expansion joints... There are all kinds of strange deformation forms, and there are only a few reasons at the root. Today, let's take a look at them one by one.
1. Working condition design deviation-the selection parameters are far from the site
High-temperature pipeline selects common general-purpose corrugated expansion joint. Once the temperature rose, the ripples crept directly-not a day or two, but slowly collapsed. There are also insufficient pressure levels, and when the medium impacts, it bulges or even bursts. And guess what? A standard expansion joint is used in the steam pipeline of a chemical plant, and the design temperature is 350℃. In actual operation, it often rushes to 420℃. After three months, the wall thickness of bellows is thinned by 40%. When selecting the model, you must keep an eye on the medium temperature, pressure, displacement, especially the applicable temperature range of high-temperature axial expansion joints and non-metallic expansion joints. Don't be too troublesome, list the media parameters clearly and check them against the product manual-this step can't be saved.
Let's talk about stress. The pressure rating should be high rather than low when selecting the model. For example, steam pipe water hammer, instantaneous pressure can soar to double the design value. Do you think choosing a 1.6MPa one is enough? It may actually rush to 3.2MPa. If the directly buried (fully buried) expansion joint is not insulated, the repeated freezing and thawing of moisture in the soil can also make the ripples crack-this is another "selection bias": the environmental conditions are ignored.
2. Improper installation and constraint setting-the number one killer of human factors
The fixed supports are not welded firmly, the guide brackets are too spaced apart, and the tie rod nuts are screwed randomly-these operations are the number one human factors of deformation. Two days ago, I met a customer. The flue gas pipeline of the power plant was equipped with a compound hinge transverse expansion joint. As a result, the guide bracket was installed inclined, the transverse displacement of the compensator was locked, and the bellows was twisted into a twist. At the scene, the installer didn't look at the drawings at all, and the bracket was crooked by five centimeters.
Always check the adjustment method of the expansion joint tie rod nut before installation. Many products leave the factory with locked rods to protect transportation and installation. After installation, it should be loosened or removed according to the instructions, otherwise the compensator will not work properly. Does the screw of the expansion joint need to be removed? The answer is: it depends on the working conditions. If it is an axial type, the transport screw is usually removed; If it is a hinge type, the tie rod nut should be adjusted to the design clearance. Don't think tightening is done.
3. Media corrosion and overtemperature and overpressure-invisible knife
Acid, alkali, salt spray or sulfide in smoke can directly chew through the bellows. Although PTFE-lined hoses and PTFE compensators are corrosion-resistant, they fail when the temperature exceeds 180℃. Tsk, many people think that "PTFE is all-powerful". As a result, the flue gas temperature rushed to 250℃, and fluoroplastics directly softened and deformed.
The water hammer in the steam pipe is more concealed. The instantaneous pressure of the water hammer can soar to twice the design value, and the bellows has no time to release, which leads to direct plastic deformation. This is not the worst-if the directly buried (fully buried) expansion joint is not insulated, the moisture in the soil will freeze and thaw repeatedly, the bellows will become brittle at low temperature, and micro-cracks will appear in a freeze-thaw cycle. You say it was wrong or not?
4. Mechanical vibration and fatigue damage-resonance is a chronic poison
The vibration frequency of the pump, fan and air-cooled island equipment matches the natural frequency of the compensator? Once it resonates, the bellows bends tens of thousands of times a day, and it will crack within three months. The double hinge expansion joint of air-cooled island vacuum pipeline is especially important for fatigue life. Many designers only consider thermal displacement and ignore vibration frequency. And the result? After the high-frequency displacement accumulates, the appearance does not change when you look at it, but in fact, the micro-cracks are already covered.
How to solve it? Manufacturers are required to provide stiffness calculation formula and fatigue life curve during model selection. When installing, add vibration damping bearings in the pipe system, or replace with rubber compensators to absorb vibration. Rubber PTFE compensator also has a certain vibration reduction effect, but attention should be paid to the medium temperature.
5. Manufacturing defects and transportation damage-no one can save it when the source is rotten
When the bellows is formed, the wall thickness is uneven, the corrugation roundness is not enough, or the stiffness test is not done before leaving the factory, and the original shape is directly revealed when installed. Also, it was flattened and bumped during transportation, and it was welded without inspection on the spot. It would be strange if there was no accident. A large number of large-diameter thick-walled expansion joints were purchased in a certain project. After the arrival, the workers didn't unpack them because they were troublesome, and directly hoisted and welded them. As a result, all three bellows had pits and all cracked after two months of operation.
When purchasing, ask for the stiffness calculation formula and material report. When receiving the goods, take a caliper to measure the wave distance and total length. Don't be too troubled. A copy of the metal hose size comparison table, expansion joint model and size must be prepared on site. If you fail the acceptance, you will return the goods directly. Don't take chances.
Prevention Guide: Three Steps
- Type selection check: The medium temperature, pressure, displacement amount and environmental conditions (freeze-thaw, corrosion) are matched one by one. High temperature axial expansion joint for high temperature, PTFE-lined or PTFE-lined compensator for corrosion, rubber compensator or damped for high frequency vibration.
- Installation Specifications: The fixed support and guide bracket shall be constructed according to the drawing. The tie rod nut is operated according to the adjustment method of the tie rod nut of the expansion joint, and the transport screw is disassembled when it is necessary.
- Periodic inspection: Is there any crack, bulge or corrosion on the surface of the bellows? Direct burial type to check whether the insulation layer is intact? The vibration frequency of air-cooled island double hinge expansion joint is measured every six months.
Causes of compensator deformation? Complicated is also complicated, and simple is also simple-it is nothing more than the five lines of type selection, installation, medium, vibration and quality. If you stomp on each of them, the probability of deformation will be reduced by 90%. Remember: compensators are not consumables, they are life-savers. Don't wait until something goes wrong to regret it.