Hinge metal expansion joint: What is the difference between it and ordinary expansion joint?
Many people saw the metal expansion joint of the hinge at first glance, and thought that it was nothing remarkable by welding two ears and putting a pin on an ordinary bellows. If you really think so, then you will be in trouble. Although the structure of hinge expansion joint seems simple-bellows, end pipe, hinge pin and vertical plate, its design logic is completely different from that of general-purpose corrugated expansion joint. The universal expansion joint absorbs axial, transverse and angular displacements by the bellows itself, while the core ability of hinge expansion joint is to bear the blind plate force generated by internal pressure thrust. To put it bluntly, it can simplify the pipe bracket and omit the main fixing bracket, which is simply too friendly for space-constrained working conditions. This site'sDouble hinge expansion joint for air-cooled island vacuum pipelineIt's a typical example. It absorbs angular displacement and doesn't do anything else.
When do you have to use it?
The air-cooled island pipeline of the power plant turns and turns. As soon as the thermal expansion comes up, the ordinary axial expansion joint pulls and presses, and the pipe is crooked in minutes. At this time, the hinge expansion joints must be used in pairs to form a "hinge system" that allows the pipe to swing freely in the plane like a human elbow joint. This site'sCompound hinge transverse expansion jointThis is the same idea, but it uses a double hinge structure to specifically absorb lateral displacement. And guess what? Many engineers confuse these two kinds, and they make a lot of jokes when selecting the model-taking a single hinge to absorb the lateral displacement, as a result, the scene can't move at all.
Type selection is most afraid of patting the head
The amount of angular displacement compensation of hinge expansion joint depends on the hinge spacing and the effective area of bellows, and it can't be sleeved by just finding any size. I met a client two days ago.High temperature axial expansion jointThe parameters went to set the hinge, but it couldn't be installed at the scene. Remember: the hinge expansion joint only absorbs angular displacement, not axial displacement. Therefore, the layout of pipeline fixing bracket should be recalculated, and the general scheme cannot be copied. As for how to adjust the tie rod nut? Refer to the article "How to adjust the tie rod nut of the expansion joint" in our Q&A. The adjustment logic of the hinge is similar, but it depends more on the positioning accuracy of the hinge pin-if the adjustment is not good, the pin will be crooked, and the whole compensation amount will be wasted.
Installation is the real test
The vertical plate of the hinge expansion joint must be perpendicular to the pipe axis, and the hinge pin must be lubricated, otherwise it will be directly stuck during thermal expansion. Many people find a "bang" sound after installing it. In fact, the hinge gap is not enough, or the pin material is not selected correctly. The pre-stretching skill was mentioned in the Q&A of "Correct Installation Method of Large Tie Rod Expansion Joint" on this site, but the hinge expansion joint does not need to be pre-stretched-it depends on angular displacement, not axial stretching. However, the cold tightness angle must be calculated accurately, otherwise the hinge will not die directly when the temperature rises when it is started. This job looks rough, but it is actually very delicate.
It's not a panacea, don't use it indiscriminately
In the final analysis, hinged metal expansion joints are most suitable for large-diameter, low-pressure circulation pipelines, such as flue gas pipelines in power stations and cement industries. But if you encounter high-pressure, small-caliber working conditions, why not take a lookExternal pressure single axial expansion jointOrCurved tube pressure balance expansion joint。 There are specializations in the industry, so don't be greedy for more selection. Understanding the displacement form and pipeline direction is better than anything else. We still have one in our stationUniversal corrugated expansion joint、Straight pipe pressure balanced expansion joint, each has its own strengths for different scenarios. Don't expect a single hinge to take over the world.