Find out what displacement you want to compensate for first-the core types and applicable scenarios of metal expansion joints
And guess what? Many problems in engineering are not rooted in the product itself, but in the fact that we didn't understand what the pipeline had to compensate at the beginning. The right choice of metal expansion joint tool can keep you stable for ten years; If you choose the wrong one, it will leak in half a year. So the first step, don't rush to turn over the sample, look at the displacement type first.
Axial, transverse, angular. Axial expansion and contraction are the most common, and high-temperature steam pipes expand and contract by heat, so you have to go upUniversal corrugated expansion jointOrHigh temperature axial type expansion joint. What about lateral displacement? For example, there is an offset at the corner of the pipeline or the interface of the equipment, at this timeCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointMore appropriate. Angular displacement is generally solved by hinge or tie rod structure.
Two days ago, I met a customer who was a power plant, and I had to use the axial expansion joint to compensate for the lateral displacement. As a result, the bellows twisted and cracked after three months. You say it was wrong or not?
Let's talk about the flapper door. In the flue gas system,Flue gas baffle doorAndRound Flap Door (Double Seal)It is used to cut off the airflow and isolate the pipeline, and is used in conjunction with the expansion joint. But don't get confused: the expansion joint absorbs displacement, and the baffle door is responsible for sealing and switching. If you need zero leak isolation,Double-sealed single-axis circular baffle doorOrElectric plug-in insulation doorThat's the right answer.
Type selection is not as simple as looking up a table: How pressure, temperature, and media affect the selection of bellows and baffle doors
Many engineers like to directly turn the manufacturer's sample, and look at the nominal diameter and working pressure. Tsk, that's naive. There are three hard parameters in the selection of metal expansion joints that must be calculated by yourself.
First, temperature.Under high temperature conditions, the permissible stress of corrugated pipe material will drop sharply. For example: the allowable stress of austenitic stainless steel 304 is 137MPa at room temperature, and it is cut in half directly at 500℃. That's when you have to chooseHigh temperature axial expansion jointOr use heat-resistant alloys. Don't expect the GM to carry it.
Second, the medium.Corrosive media, such as desulfurization flue gas, contain a large amount of SO₂ and chloride ions, and ordinary stainless steel bellows will perforate in one or two years. Must be onDesulfurization flue gas baffle doorMatch with corrosion resistant lining, or choosePTFE-lined hose,PTFE compensator。 If there are particulate matter in the medium, the design of the guide tube is particularly critical-the role of the guide tube is specifically mentioned in the Q&A of this site, which is to prevent scour and reduce the flow rate.
Third, pressure and safety factor.Don't just look at the design pressure, but also consider the hydraulic test pressure and fatigue life. Used in power station industryCorrugated expansion joint for power station industryUsually requires a cycle life of more than 100,000 times, while the cement industryMetal Corrugated Expansion Joints in Cement IndustryMore attention to wear resistance and high temperature. If you choose a low-pressure general-purpose type for high-pressure steam pipelines, it is no different from laying mines.
When the medium temperature exceeds 600℃, the internal seals of ordinary electric baffle doors will burn out.Manual plug-in insulation doorOr with a water cooling structure. When the medium pressure exceeds 0.1MPa, the single shaft baffle door may not be closed tightly,Single-axis double-flapper doorIt's reliable.
The selection tool is not an Excel sheet, but your understanding of the working conditions. The three dimensions of pressure, temperature and medium are cross-considered, and all are indispensable.
Don't wait for a leak-a practical tool for routine inspection and life management of metal expansion joints
Many factories are the idea of "replacing after breaking", but as a result, they are shut down for emergency repair, resulting in heavy losses. If the metal expansion joint tool is used correctly, it can completely eliminate the failure in the bud.
- Bellows appearance.Are there any noticeable distortions, scratches, corrosion pits? EspeciallyDirect buried (fully buried) type expansion jointThis kind of underground, regular excavation and inspection is unrealistic, so you have to at least judge by ground signage and pressure monitoring. Under high-frequency vibration conditions, pay attention to inspectionSpecial hose for vacuumAndDouble hinge expansion joint for air-cooled island vacuum pipelineJoint welds of.
- Tie rod and nut.Look at the "How to adjust the tie rod nut of the expansion joint" mentioned in the question and answer of this site-the loosening of the tie rod will cause the bellows to be subjected to extra torque, and in severe cases, it will burst directly. Tightening once a month? No, you have to calculate the preload moment based on the displacement, not the feel.
- Deflector worn.If the medium contains particulate matter, the bellows will be directly exposed after the guide tube is worn through, and the life will drop sharply. ForLarge diameter thick wall expansion jointYou can install a thickness gauge to record wear data regularly and establish a replacement threshold.
In terms of life management, don't be superstitious about the so-called "design life of 10 years". The actual life depends on the number of times you start and stop, the amplitude of temperature fluctuation, and the corrosiveness of the medium. There is a practical tool called "equivalent number of cycles" calculation method, which converts each temperature change into the standard number of cycles, and gives an early warning if it exceeds the design value. The specific formula can be found online, but it is recommended to ask the manufacturer directly for the fatigue curve.
Non-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion jointThe fabric layer should be checked for tearing or aging. If you find it, you have to change it. Don't repair it and use it again-the patch won't last long. Rubber products such asrubber compensatorAndRubber PTFE compensatorPay attention to the aging and hardening of the rubber, and it has to be replaced as a whole after 3-5 years of normal use.
In the final analysis, the metal expansion joint tool is not bought and installed, it needs a set of closed-loop management of inspection-recording-early warning. Do you have this kit on hand? If not, build a ledger from today, and record the model, installation date and inspection data, which is more useful than anything else.