Compensator tie rod bent? Don't be in a hurry to change. Find out these points before you start
When you see that the compensator tie rod is bent at the scene, your first reaction is usually "it's over, you have to replace it with a new one". However, veterans who have worked in pipeline maintenance for several years know that tie rod bending is often the appearance, and the root mostly lies in installation or selection. Direct replacement treats the symptoms but not the root cause, and it may bend next time.
Why do tie rods bend? Three common "real murderers"
Inaccurate estimation of blind plate force of pipeline。 Blind plate force is the thrust generated by the medium pressure acting on the closed end of the blind plate or elbow. If this force is small, the tie rod will have to carry the axial force exceeding the design value, so it is strange that it does not bend. Especially in the steam pipeline of power station or the high-temperature air duct of cement industry, the blind plate force will soar when the pressure fluctuates, and the tie rod can't stand it at all.
Fixed bracket failure。 The fixed bracket is used to restrict the displacement of the pipe. If it is loose, slipped or directly pulled apart, the thermal displacement of the pipe will all be thrown to the compensator. At this time, the role of the tie rod is equivalent to a "temporary bracket", but when designed, it is only responsible for transmitting thrust, and does not bear transverse bending moment-one bend is permanent deformation.
Wrong selection。 For example, you useUniversal corrugated expansion jointIt mainly absorbs axial displacement. As a result, the field actually needs to absorb lateral displacement, so the tie rod becomes a "*". I have seen a cement factory install the general-purpose type on the outlet air duct of the rotary kiln. The thermal expansion of the duct is oblique, and the tie rod is bent into a bow shape after two weeks. This kind of mistake, it is useless to change the tie rod, it has to be changedCompound hinge transverse expansion jointOrCurved tube pressure balance expansion jointThat's fine.
Can it be fixed if it is bent? Look at three points
Judging whether it can be repaired, don't just rely on the naked eye. Three key points:
- Degree of bending: The bending angle is less than 5 degrees, and the deformation amount does not exceed 10% of the diameter of the tie rod. You can try to correct it. Beyond this range, the internal lattice of the tie rod has slipped, and the strength is greatly reduced.
- Whether the material is fatigued: The fatigue limits of ordinary carbon steel tie rods and 304 stainless steel tie rods are different. If the equipment runs for more than 20,000 cycles, or micro-cracks have appeared on the surface of the tie rod, don't repair it and replace it directly.
- Is there any associated damage to the compensator body: Focus on bellows. When the tie rod is bent, the bellows is often squeezed off or pressed against the guide tube. You take apart the insulation and light it with a flashlight to see if the corrugated valley floor has any scratches, bulges or penetrations. As long as the bellows is injured, fixing the tie rod is a waste of effort.
If all three points are qualified, you can try to adjust the nut fit correction. How exactly to operate? Refer to what we talked about earlierExpansion joint tie rod nut adjustment method— — First, loosen the nut to a free state, slowly push it back with hydraulic top or special correction tool, then pre-tighten the nut diagonally, and apply force to the design torque three times.
Don't do these two stupid things
"The pull rod is bent. Can I use the torch to roast it red and break it straight?" I directly advised him not to take any risks. High temperature will cause irreversible changes in the mechanical properties of steel-for example, carbon steel will decarbonize when it exceeds 650℃, and 304 stainless steel will precipitate chromium carbide when it stays in the sensitization temperature range (450-850℃) for too long, resulting in intergranular corrosion. It suddenly breaks in subsequent use, that's no joke.
Some people directly smash it with a hammer and hardtop it with a jack. This trick is the easiest to crack the bellows. The bellows wall is thin (usually 0.5-2mm), and it will crack when the local impact force is large. And guess what? The crack may be as thin as a hair at the beginning. After a few days of running, the medium flushes, and it perforates and leaks directly. If something like this happens on the steam pipeline of the power station, the loss of one day's shutdown will be enough for you to buy dozens of sets of compensators.
Change the tie rod? Don't just stare at that pole
If you decide to change it after evaluation, don't just focus on the tie rod itself. There may be other compensators in the same system-for example, you are usingCompound hinge transverse expansion jointOrCurved tube pressure balance expansion joint, their tie rod construction is completely different. The pull rod of the compound hinge type is in the form of hinge pin shaft, and two groups of hinges should be processed at the same time when disassembling and assembling; The tie rod of curved tube pressure balance type connects two bellows and the balance ring. If it is disassembled incorrectly, the bellows will become unstable. Check whether the guide tube has been displaced and the sealing surface has been worn. Many times, you don't know that the guide tube is offset. The airflow directly washes the inner wall of the bellows and wears it out in half a year.
The last heartbreaking truth
Maintenance of tie rod is only an emergency means, and the fundamental solution is to recalculate the thermal displacement and thrust of pipe system. EspeciallyCorrugated expansion joint for power plant industryAndMetal Corrugated Expansion Joints in Cement IndustryIn this kind of system with complicated working conditions, a single tie rod bending often means that the whole bracket system needs to be adjusted-it may be that the stiffness of the bracket and hanger is not enough, or it may be that the cold tightness is given wrong. At this time, it is much more useful to find a manufacturer for on-site diagnosis than to mess around with you. With 3D laser scanner and finite element analysis software, the manufacturer can give a rectification plan in half a day. If you change ten tie rods yourself, you might as well re-weld the fixing bracket once.