First, are you really adjusting the expansion joint, or are you using the compensator as a fixed bracket?
Why is the construction and pre-stretching according to the drawing also done, and the system leaks as soon as it heats up? When disassembled, the bellows were either crushed to death or cracked. What's the problem? Many people understand "metal expansion joint adjustment" as "screwing and adjusting the length".
Actually, you're not adjusting the expansion joint itself at all — you're adjusting the displacement space the system leaves for it. The core task of an expansion joint (also called a compensator) is only one: to absorb thermal displacement. Its bellows is born to move, and if you use it as a fixed bracket, it will strike in minutes. To put it bluntly, 90% of installation accidents are because the compensator is regarded as a force point, not a displacement absorption point.
A steam pipe was installedHigh temperature axial expansion jointThe manufacturer's nominal compensation amount is 100mm. As a result, you screwed the tie rod nut tightly when you installed it, and it felt "tighter and not leaking". After the test run is heated, the pipe is elongated, and the bellows has nowhere to go, and it bulges and bursts directly. What exactly are you adjusting? You're adjusting that nut, but missing out on the thermal expansion needs of the pipe.
What about that? Think clearly before adjusting: This device isUniversal corrugated expansion jointStillStraight pipe pressure balanced expansion joint？ The way it is constrained determines which part you should move. Don't twist as soon as you come up, first understand the design intention.
Second, three things before adjustment: understand the model, find the positioning, and confirm the medium temperature
Once I went to the site of a power plant, and the worker was holding aCompound hinge transverse expansion jointAsked me, "How to adjust this?" I asked him what the medium temperature was, and he said he didn't know. Asked him where to install it, he pointed to a section of elbow. I said, your model is subject to lateral displacement, and it is true that it is installed near the elbow, but you have to know the temperature to calculate the cold tightness.
Before adjusting, you must find out three things, and don't do anything less:
- Understand the model: likeExternal pressure single axial expansion jointAndCurved tube pressure balance expansion jointThe adjustment method is completely different. The former relies on the tie rod to limit the position, and the latter relies on the internal pressure balance, so accidents will happen.
- Find and locate: See if there are directional arrows on the device (Arrow direction of expansion jointPointing to the direction of media flow). The arrow is not drawn for fun. If it is installed backwards, the bellows will be eroded directly.
- Confirm Media Temperature: Temperature determines the amount of thermal expansion. For example, in steam pipelines, the cold tightness difference between 300℃ and 100℃ is three times. Without temperature data, pre-stretching is blind.
Only after these three things are done will you have the basic qualifications for "adjustment".
III. Core action: How to do pre-stretching/pre-compression? When is the tie rod nut removed?
The pipeline is installed at normal temperature, and the medium heats up and expands after operation. Because the bellows has been fixed at both ends of the pipeline, it is necessary to leave compression space for it in advance. For axial expansion joints, if the pipe is elongated by heat, you need toPre-stretching； If the pipe shrinks when exposed to cold (e.g. cryogenic media), you need toPre-compression。 What is the specific stretch amount? Look at the installation length table given by the manufacturer. Such asUniversal corrugated expansion joint"Installation length L0" will be written on the sample of, and the actual installation length on site L1= L0-amount of pre-stretch. Don't smack your head.
thattie rod nutWhat? This is a protective piece when the equipment is transported, and it is also a limiting piece when adjusting. When will it be dismantled? And the answer is:Wait until the pipeline system is completely installed, the pressure test is qualified, and the temperature is ready to rise before disassembly。 If you dismantle it in advance, the bellows will deform when hoisted; If you don't dismantle it, the pipe won't move. Two days ago, I met a client.Large tie rod expansion jointThe nut was screwed until the test run, and as a result, the thermal expansion of the pipe made the bracket crooked. You say it was wrong or not?
First, loosen the nut to the preset position with a wrench (for example, stretch 20mm). After the system heats up and stabilizes, loosen the nut completely to allow the bellows to expand and contract freely. If you are usingDirect buried (fully buried) type expansion jointThis step has to be adjusted in advance on the ground, and it can't move if it is buried.
Fourth, the pits planted in those years-the spacing of guide brackets, the amount of cold tightness is miscalculated, and the bolts are screwed to death
After ten years in the industry, there are three pits that I have seen the most, one by one.
Pit 1: The spacing between the guide brackets is too large.loadedCompound straight pipe bypass pressure balanced expansion jointAs a result, the pipe shook like noodles near the bellows. The reason is simple – the boards are too far apart, the pipe loses its lateral restraint, and the bellows bear bending moments that they shouldn't. Specification requirements: The distance between the first guide bracket and the end of the expansion joint should not exceed 4 times the pipe diameter. Many people save trouble and are directly separated by 10 meters, so it is weird that there are no problems.
Pit 2: The amount of cold tightness is miscalculated.Once a cement plant project,Metal Corrugated Expansion Joints in Cement IndustryThe cold tightness is calculated according to the ambient temperature of 30℃, and as a result, the construction just caught up with minus 10℃ in winter. The worker made pre-stretching according to the drawing, and after heating up, it was found that the compensation was not enough, and the bellows was pulled to the limit. Why? Because the cold tightness is calculated based on the temperature difference between the installation temperature and the working temperature, you can't take the design temperature directly. Correct practice: Measure the ambient temperature during installation, and recalculate the actual required pre-stretching amount.
Pit 3: The bolts are screwed to death.That's the lowest level of mistake. Some workers habitually putMetal expansion joint adjustmentThe tie rod bolt used is tightened to the tightest, which is considered "firm". In fact, the function of bolts is to limit, not lock. The correct way to do this is: use double nuts to lock, leaving the clearance required by the design. Such asSleeve type pipe expansion jointAfter tightening, the sleeve must be ensured to slide, otherwise there will be no compensation effect at all.
5. How to accept after adjustment? It doesn't count until you run a thermal cycle
Just call it a day after the adjustment? Don't worry, the acceptance criteria are just one sentence:After running a full thermal cycle。 What's the meaning? It is to let the pipeline rise from normal temperature to working temperature, then cool it to normal temperature, and observe whether the displacement of the expansion joint is within the design range.
First, the bellows has no plastic deformation (such as bulging and wrinkling); Second, the pull rod and the guide bracket are not abnormally displaced or stuck; Third,Non-metallic expansion jointOrrubber compensatorTo check for leaks. By the way, if it isDesulfurization flue gas baffle doorIn this high-temperature smoke environment, don't forget to see if the sealing surface is damaged.
Can you replace it with a cold press? No way. Cold compression can only check the strength, but not the thermal displacement. Only by raising the temperature to the working temperature can you confirm whether the cold tightness is correct and the spacing between the guide brackets is reasonable. A few years ago, there was a petrochemical project that did not do heat cycle during acceptance. As a result, it was put into production three months laterMetal rectangular expansion jointAll four corners are cracked because of the stress concentration at the corners caused by thermal expansion. The rework cost is enough to buy ten new pieces of equipment.