After more than ten years of pipeline installation, I have seen more expansion joint accidents than I have repaired. Every time the manufacturer calls to say that the expansion joint is leaking, cracked, and the bellows is pulled off, I run over and have a look-80% is not a product quality problem, but the installation is not held. If the metal expansion joint installers only installed it as an ordinary pipe fitting, the thunder would have been buried long ago, waiting for it to explode one day.
First, don't rush to get started before installation: medium, temperature and displacement, all these three parameters are useless if you make a mistake
You get an expansion joint, don't hurry to call someone to hoist it. Have you checked the model number written on the box and the parameters on the nameplate item by item? Especially these three things: medium, temperature, and displacement.
The media determines the bellows material. The corrosive flue gas containing chloride ions in flue gas desulfurization pipeline, if you install ordinary stainless steel bellows, it will pitting and perforating in less than a year. In this case, special materials resistant to chloride ions should be used, or they should be applied directlyNon-metallic expansion joint (fabric fiber expansion joint)。 Two days ago, I met a customer who said that the expansion joint used at the entrance of their desulfurization tower had been changed three times a year. When I went to the scene, I saw that the bellows were full of numb spots, which were buried during typical selection.
Temperature is directly related to the calculation of compensation amount. The thermal elongation difference of normal temperature pipeline and 350℃ steam pipeline is several times the same length. If you choose the compensation amount according to normal temperature, it will exceed the limit as soon as the machine is started at high temperature, the bellows will be directly crushed to death, and the tie rod will be bent for you.
The amount of displacement is another pit that can be easily rounded into. Is the displacement given by the design institute axial or transverse? Angular displacement or combined displacement? The structures of the expansion joints corresponding to different displacement forms are completely different.Compound hinge transverse expansion jointIt can only absorb lateral displacement. If you hold it hard to carry axial compression, it is not that it can't do it, but that you are not particular.
Second, the core steps of on-site installation: hoisting, centering and welding, each step is particularly specific, don't take the general type as the universal type
The lifting matter looks simple, but the most overturns. What the expansion joint is most afraid of is the force of the bellows-the sling is directly tied to the corrugation, and I have seen the weld of the bellows joint cracking when it is hoisted to the half-air. The correct way is to fix the hoisting belt on both ends of the connecting pipe or reinforcing ring, and the bellows does not bear weight.
Alignment is the mounted vital gate.Universal corrugated expansion jointWhen designing the default pipeline is ideally aligned, do you have a hard deviation of two or three millimeters on site by pulling the bolts to align? Dreaming. The cold alignment deviation will directly superimpose on the thermal displacement, and the fatigue life of bellows will fall exponentially. After accurate alignment, the expansion joint is fixed with temporary support, so that it cannot sink with the pipe.
In the welding process, remember that welding splash is strictly prohibited near the bellows. Many installers try to save trouble. They don't wrap the bellows before welding, and a grain of welding slag splashed on it is a hole. Also, the welding process evaluation and welder qualification must meet the requirements. Don't let an unlicensed electrician come here-if something happens, you don't even dare to write a report.
3. Tie rods, nuts and guide tubes, these accessories are not decorations: they should be disassembled and adjusted. If they are reversed, they will be scrapped directly
When many metal expansion joint installers get the expansion joint with a tie rod, their first reaction is "Should this tie rod be pulled all the time". Not. The function of the tie rod is to transport protection or restrain the reaction force. After installation in place, what should be disassembled must be disassembled, and what should be loosened must be loosened. If you don't dismantle it, the tie rod and nut lock the expansion joint tightly, the bellows can't move, and the thermal expansion and contraction of the pipe are all poured into the equipment and bracket. What is the plan of installing the expansion joint?
Some expansion joints have adjustment screws, which are used for adjusting pre-deformation, not for you to hard open the installation gap. The instructions say that the number of turns to adjust is as many turns. If you twist two more turns, the bellows will be in a biased state, and the fatigue life design at the time of leaving the factory will be directly voided. After adjustment, the temporary positioning part should be disassembled, otherwise it will become a "permanent support part". At that time, the place that should be expanded will be held up, and the place that should not be deformed will be hard deformed.
The direction of the guide tube is also often installed in reverse direction. The guide tube is used to guide the flow and protect the bellows, and the direction of the arrow points to the flow direction of the medium. Install backwards, the medium directly washes the root of the bellows, and you can't find the reason if you wear it out. What does the arrow mean, you ask? The arrow on the expansion joint is the flow direction of the medium, which is consistent with the flow direction arrow on the pipe, which is more true.
4. Differences in installation under different working conditions: power stations, cement and desulfurization flue gas have different environments and different techniques
On the steam pipeline of the power station boiler, the temperature is high, the pressure is high, and the steam pipeline is generally usedHigh temperature axial expansion jointOrCorrugated expansion joint for power station industry。 When installing this kind of expansion joint, special attention should be paid to the cold tightness-when the pipeline is cold, a part of the expansion joint should be pre-stretched, which is equivalent to leaving compression space for the hot state. The amount of cold tightening is calculated according to the design temperature. If you are afraid of trouble, do not do cold tightening, and the expansion joint will quickly reach the limit when it is hot.
The flue gas pipelines at the head and tail of the kiln in the cement industry, with large temperature difference and heavy dust, mostly useMetal Corrugated Expansion Joints in Cement IndustryOrNon-metallic expansion joint。 Here, the installation should pay special attention to the smooth cleaning channel, and the heat insulation and skin splicing should be tightly joined. Otherwise, the dust will go in and jam the bellows, and the compensation function will directly fail.
Desulfurization flue gas systems are even worse. The flue gas temperature repeatedly jumps up and down the acid dew point, and corrosiveness and condensation problems force you to useDesulfurization flue gas baffle doorInstall with corrosion-resistant expansion joints. Under this working condition, the expansion joint should be arranged to avoid the low point liquid accumulation section, and the kerosene leakage inspection should be done after the welding is completed. The installation techniques of various working conditions vary a hundred and eighty thousand miles. If you use the casing method of the power station to install the desulfurization system, it is equivalent to wearing a suit and going to the paddy field. You can walk but feel bad all over.
5. Is it done after installation? Pressure testing, inspection, maintenance, these finishing tasks are more testing than the installation itself
Before pressure test, confirm that the temporary support and positioning screw on the bellows are disassembled; Pressure is slowly increased during pressure test, without impact; The test pressure is usually 1.5 times the design pressure, but must never exceed the test pressure value on the expansion joint nameplate. Some installers are quick, holding back the pipeline test pressure directly, and the expansion joint bellows is permanently deformed-that thing is not the container you use to pump air pressure.
During the pressure test, you should keep your ears up to listen to any abnormal noises, and stare at the bellows to see if there are any bulges or depressions. During the pressure holding period, brush the weld and bellows ring weld with soapy water, and bubbling is leakage. This step is in place, and it will be practical to put into operation later.
You can't let go at the beginning of operation. Check the displacement change of the expansion joint once a day in the first week, record the actual displacement of cold and hot states, and compare it with the design value of the equipment. When the tube is hot and cold, the expansion joint should move how to move. If it doesn't move, it shows that there is a jam. If it moves too much, it shows that the selection is small. After running and maintaining the record for one year, you will know the true performance of this expansion joint under actual working conditions, and the next selection will be more spectral.
To put it bluntly, the position of metal expansion joint installer is stuck between design and operation and maintenance. No one will praise you if you do it well. See you on the wall of the accident. But if you understand all the above points thoroughly, ask a few more questions when selecting a model, have more thoughts when installing it, and do a few more checks at the end, then you will really understand this job.