Let's make it clear first: Is metal "thermal expansion and cold contraction" or "heat shrinkage and cold expansion"?
The opening chapter first solves an inevitable misunderstanding. Search "The role of heat-shrinkable and cold-expanded metal expansion joint?" on the Internet, a bunch of people think that metal pipes will shrink when the temperature is high, just like some alloys. What about the facts? Stainless steel and carbon steel used in most industrial pipelines follow thermal expansion and contraction honestly. Those very few abnormal bismuth-antimony alloys can't be used in our pipeline industry at all. So don't be literally taken off-the core mission of the expansion joint is to absorb the thermal expansion and contraction displacement of the pipe due to temperature change.
How does the expansion joint "eat" the thermal expansion and contraction?
Take this site'sUniversal corrugated expansion jointLet's use an analogy. Its bellows are like the bellows of an accordion. When the heating pipe becomes longer, the bellows are compressed; The cooling becomes shorter and the bellows is stretched. It just stretched and contracted, eating the displacement into it. The actual product will also be equipped with accessories such as guide tube, tie rod, limit bolt, etc. -the guide tube guides the flow direction of the medium to prevent high-speed airflow from directly washing the bellows; The tie rod and limit bolt control the displacement direction to avoid excessive stretching or instability of the bellows.
What about encountering high temperature conditions? For example, the temperature of steam pipes in power plants goes to five or six hundred degrees Celsius, and ordinary bellows have long been soft. This is the time to use itHigh temperature axial expansion jointHeat-resistant alloys (such as Inconel 625) and special wave patterns are designed to ensure elastic stability. And guess what? Some customers only want to be cheap when selecting models, and use ordinary bellows, which will crack and leak in a few months, which is not worth the loss.
Which expansion joint should I choose for different working conditions? Don't expect one model to conquer the world
High pressure and high temperature fluctuation of steam pipeline in power plants are the first choiceCorrugated expansion joint for power station industryAndStraight pipe pressure balanced expansion joint。 Why? Because the internal pressure will generate a huge axial thrust, ordinary expansion joints can't bear it. The pressure balance type cancels out the thrust through the internal structure, so that pipelines and equipment are safe.
What about buried pipes? Consider soil corrosion and axial thrust. At this timeDirect buried (fully buried) type expansion jointIt comes in handy-it comes with its own anti-corrosion layer and insulation layer, so you don't have to worry about it when you bury it. The flue air duct and desulfurization flue gas system in the cement industry have low temperature but large diameter.Non-metallic expansion jointOrMetal rectangular expansion jointIt is more cost-effective, can absorb multi-directional displacement, and the cost is low. If there is vibration or a location that requires frequent maintenance,rubber compensatorOrRotary compensatorIt's also a good choice.
Is that the case? With the right type, the system life difference can be ten years.
The easiest pit to step on during installation-the lesson of customer blood
Two days ago, I met a customer who tightened the tie rod nut on the expansion joint. As a result, as soon as the pipeline heated up, the bellows directly exploded, and the scene was terrible. Tsk, that's a typical mistake. Remember: the mounting bolts (those few screws) that the expansion joint is shipped with must be removed or loosened before it is officially put into operation! Tie rod nuts are meant to limit overstretching, not for you to lock up. The correct way is: adjust the tie rod nut to the designed length during installation, and the nut will naturally have a gap after the pipeline heats up.
In addition, the direction of the arrow on the expansion joint shell must point to the direction of the medium flow, and the guide tube should be directed toward the medium-if it is installed backwards, the high-speed airflow will directly flush and perforate the bellows. Also, the fixing brackets on both sides of the expansion joint must be firm, otherwise no matter how many expansion joints you install, the pipe will twist around like a snake, and it will be a matter of time before the flange interface leaks.
In one sentence: The expansion joint is the "expansion joint" of the pipeline
Just like bridges should leave joints to prevent heat expansion and damage, industrial pipelines rely on expansion joints to "breathe". Stop worrying about that "heat shrinkage and cold expansion"-choose the right type, install the right direction, leave enough space, and there will be no big problems in the pipeline system for 20 years. If you are still worried, flip through the product information of this site,Universal corrugated expansion joint、Straight pipe pressure balanced expansion joint、High temperature axial expansion joint…Each model has a clear working condition, just follow it.