Two days ago, I met a customer who was bidding for heating pipelines. When I came up, I threw over a drawing that said "directly buried compensator" and asked me whether to quote. When I looked at the drawings, wasn't this oursDirect buried (fully buried) type expansion jointYeah. This kind of thing happens almost every day-the same thing, compensator is written on the drawing, expansion joint is called in the design institute, and another name is marked in the manufacturer's product catalog. Let's break this up today.
Difference between expansion joint and compensator, the standard answer is no distinction
According to national standards and industry norms, Expansion Joint and compensator are two names of the same thing, and they are both called Expansion Joint in English. There is no difference in function-all are flexible connections used to absorb thermal displacement of the pipe and reduce vibration of the equipment.Difference between Expansion Joints and CompensatorsAt the standard level, it is a false proposition, and there is no technical difference.
But if you go to the production workshop and listen to the old engineers chatting, you will find that the "difference" in their hearts is clear: metal bellows are called expansion joints; Non-metallic, rubber, called compensator. This habit does not come out of thin air. Behind it are objective differences in materials, structures and applicable working conditions.
Why metal bellows are called "expansion joints"
Universal corrugated expansion joint、Straight pipe pressure balanced expansion joint、High temperature axial expansion joint、Corrugated expansion joint for power plant industryThe core components are all stainless steel bellows. This kind of equipment depends on the elastic deformation of corrugations to absorb thermal displacement, and has to bear high temperature and pressure, so the requirements for corrugated material, wall thickness and fatigue life are extremely strict.
For example, the corrugated expansion joint on the main steam pipeline of the power station has a working temperature of above 550℃ and a pressure of more than ten MPa. The corrugated pipe has to be made of heat-resistant alloy steel, and if one layer is not enough, it has to be double and three layers. Under this working condition, the fatigue life calculation, instability check and stiffness matching of bellows should not be careless. Therefore, the default "expansion joint" in the industry refers to metal bellows, because its technical content and manufacturing threshold are indeed higher.
Why are non-metals and rubbers called "compensators"
Non-metallic expansion joint (fabric fiber expansion joint)、rubber compensator、PTFE compensator、Rubber PTFE compensator。 These things are mainly made of flexible fabrics, rubber or fluoroplastics, which have a particularly large compensation displacement and good vibration and noise reduction effect, but their pressure-bearing capacity is low. Generally, they can carry a flue pressure of tens of kilopascals or a water pressure of several kilograms.
When the workers on the spot looked at it, this thing was soft, and it deformed when they pressed it with their hands. Naturally, they called it "compensator"-compensation, it sounded like soft adjustment. The drawings may say "non-metallic expansion joint" straight on the end, but no one calls it that when they get to the scene. An old engineer who has worked for decades, you ask him, "Where is the non-metallic expansion joint?" He has to be stunned for a moment before he realizes that you are talking about the cloth bag.
The real technical difference lies in the selection logic
Then how do you choose? Look at the medium, the temperature, the pressure, not the name.
Flue gas, dust, corrosive media, preferredNon-metallic expansion jointOrRubber PTFE compensator。 This kind of working condition has low pressure, but may be corrosive, corrosion resistance with non-metallic material, large compensation amount, and fabric fiber structure can absorb multi-directional displacement, so it is convenient to install.
High-temperature steam and high-pressure pipelines can only use metal corrugated expansion joints, such asExternal pressure single axial expansion joint、Compound hinge transverse expansion joint。 The selection of corrugated pipe material is a technical job-304, 316L and Inconel, which is used at which level of pressure and temperature.
There is also a confusing category —Rotary compensatorAndSleeve type pipe expansion joint。 These two are completely different from bellows. They absorb displacement by sliding or rotation. There is no corrugated structure, and the compression amount may not be as good as that of bellows, but they are better than high pressure resistance and long life, so they are used a lot in thermal pipe networks. They are different from the question of "the difference between the expansion joint and the compensator". They are another type of structure.
The easiest pits to step on when purchasing
Tell me a real case. There is a chemical plant project. The design institute drawings are marked with "corrugated expansion joint" and the purchase list is written with "compensator". As a result, the supplier quoted a certain brand of "expansion joint" series. Fortunately, it was checked according to the parameters in the end. Otherwise, there was more than twice the price difference in the middle, which was due to different names, resulting in inconsistent quotation caliber.
So don't dwell on the term "the difference between expansion joint and compensator". The medium, temperature, pressure, displacement and connection method are clearly reported-the nominal diameter, the temperature, the pressure, and the axial displacement, which are a hundred times more important than the name of the entanglement. The clearer you report, the less likely the manufacturer will fool you with the wrong model.
According to the national standard, the expansion joint and the compensator are the same kind of equipment; According to industry custom, metal ones are called expansion joints, and non-metal and rubber ones are called compensators. If you really want to talk about the difference, it is the difference of material, pressure bearing capacity and applicable working conditions-if you choose the right type, you can call it whatever.