Why do you need "non-standard" expansion joints in pipeline systems? — — Several common working conditions that standard parts can't handle
Anyone who has done pipeline design knows that although the standard expansion joint is cheap and delivered quickly, when it comes to high temperature, high pressure, large displacement or special media, the standard parts are just like paper. Two days ago, I met a customer who was a power plant. The temperature of the steam pipe was 650℃ and the pressure was 4.0MPa. The standard parts leaked after one month. Why? The wall thickness, number of layers and material of standard corrugated pipes are designed according to general working conditions. When encountering such extreme parameters, either the fatigue life can't be sustained or the corrosion rate exceeds expectations.
More of a headache is the space constraint. Some pipes are only 200mm away from the wall at the corner, and standard expansion joints simply can't fit in. Other pipelines need to absorb axial displacement and lateral displacement at the same time, and the standard single compensation type products can't do it at all. That's when you have to look forMetal non-standard expansion joint— — To put it bluntly, it is to redesign the structure, number of layers, end connection mode and guide tube configuration of the bellows according to the pipeline direction, displacement and medium characteristics of your site. Non-standard is not "messing around", but using customized means to solve the blind spot of standard parts.
What can non-standard metal expansion joints be made into? — — Look at common customization types from the products of this site
We stand on dozens of product series, which is actually a non-standard customized "building block library". Such asHigh temperature axial expansion jointSpecially serving hot air ducts above 600℃, the bellows are made of Inconel 625 or 321 stainless steel, with multiple layers of heat insulation in the middle, and the guide tube has heat insulation lining-if you use ordinary 304, it will crack for you in half a year.
Another exampleLarge diameter thick wall expansion jointThe inner diameter can be DN4000 or even larger, and the wall thickness can be more than 8mm, which is specially used for the inlet of desulfurization tower and air cooler. AndStraight pipe pressure balanced expansion jointThis thing can absorb axial displacement while offsetting pressure and thrust, without the need for bulky fixed brackets-often used in main steam pipes in power plants.
Not to mentionCompound hinge transverse expansion jointAndCurved tube pressure balance expansion jointThe former can make the pipeline realize a large-angle lateral displacement in a narrow space, while the latter combines two bellows and a balance ring to specially compensate the displacement of the elbow section. And guess what? Many customers didn't know that there were these ready-made structures at first, but as a result, they drew their own drawings and made a strange scheme. In the end, the process was complicated and the cost was high.
Which parameters are the most terrible in designing non-standard expansion joints? — — Pressure, temperature, displacement, fatigue life, one less is useless
DesignMetal non-standard expansion joint, there are four arguments that are "dead lines":pressureDecide the wall thickness and number of layers of the bellows;TemperatureDecide on the material and whether thermal insulation is needed;displacement amount(axial, transverse, angular) determines the wavenumber and length of the bellows;Fatigue lifeIt is directly related to the expansion energy saving and can't last until the next overhaul cycle. Underreport one parameter, the result is either a conservative design and a waste of money, or a dangerous accident.
In a petrochemical project, the pipeline pressure is 2.5MPa, the temperature is 350℃, the axial displacement is 30mm, and the lateral displacement is 10mm. The customer only gave the axial displacement. We designed an axialExternal pressure single axial expansion jointAs a result, after installation, it was found that the lateral displacement broke the bellows. Why? Because the offset of the pipe support is not considered. SoThe displacement must be clearly marked: Is it purely axial? Or combined displacement? How are directions distributed?If you can't figure it out, just provide the pipeline stress analysis report honestly. Don't let us guess.
Just put it on and you're done? The installation and maintenance of non-standard expansion joints is more particular than you think
Many people think that the expansion joint is done by screwing on the bolts, but it leaks after installation. Because of the special structure of non-standard expansion joint, there are more precautions for installation. Such asCorrect installation method of expansion joint of large tie rod: The tie rod nut is locked in the transportation state, and must be loosened after installation, otherwise the displacement all depends on the tie rod, and the bellows is equal to the display. There is also the flow direction arrow of the guide tube, which must be consistent with the flow direction of the medium-if the guide tube is installed backwards, it will be washed away, and the bellows will be directly exposed to the high-speed medium.
Don't forgetDo you need to remove the screw of the expansion joint？ The transport screw is temporarily fixed and must be removed or adjusted in place after installation, otherwise it is equivalent to welding the expansion joint to death. In addition,How to adjust the tie rod nut of expansion joint？ It should be symmetrically adjusted according to the actual displacement, and it should not be screwed to death and loosened at the same time, otherwise the bellows will be unevenly stressed. In terms of maintenance, it is recommended to check whether there are cracks and corrosion pits on the surface of the bellows every maintenance cycle. Especially under high temperature conditions, the shedding of surface oxide scale is an early warning signal.
Selection to avoid pits: How to save yourself trouble with the existing product series of this site?
Many engineers have to "non-standard customization" as soon as they come up. In fact, the existing product series on our station has covered 90% of common working conditions. For example, if you want to compensate for lateral displacement, look at it firstCompound hinge transverse expansion jointCan it be satisfied, it has simple structure and cheap price. If the axial displacement is large and the pressure and thrust need to be balanced,Straight pipe pressure balanced expansion jointMuch more reliable than getting a tie rod structure yourself. AndCurved tube pressure balance expansion jointSpecialized in treating the problem of space constraint of bend pipe section.
As for the corrosive medium, don't choose metal blindly,PTFE-lined hoseOrPTFE compensatorUse it directly, saving the need to repeatedly communicate with the material manufacturer. High temperature and dust in flue gas pipes?Non-metallic expansion joint (fabric fiber expansion joint)OrRectangular non-metallic expansion jointMore temperature-resistant, corrosion-resistant and cheaper.
So, before ordering, look through the product catalogue on our site and putUniversal corrugated expansion joint、Rotary compensator、Direct buried (fully buried) type expansion jointRead these standard series once. If you can't satisfy it, communicate with our technical team about non-standard details. Remember:The sooner you give all the four data of pressure, temperature, displacement and fatigue life, the faster the scheme will come out, and you can spend less money.