Compensator inspection content, follow these 5 steps to not work in vain
Two days ago, I met a customer and called to say that the corrugated expansion joint that had just been installed for half a year was leaking. As a result, I went to the scene to see that the tie rod nut was loose and the guide tube was worn out. Alas, it should have been inspected long ago. To be honest, the content of the compensator inspection looks simple, but when it really arrives at the scene, many people just go through the motions, don't see what they should see, and don't measure what they should see. Today, we will break it up and crumble it, and explain these five steps clearly. You can use it directly after reading it, and your work will not be in vain.
1. Prepare everything before the inspection. Don't go to the scene empty-handed
Think about it, when you arrive at the scene and find that you don't have a wrench or vernier caliper, what else are you playing? As embarrassing as the cook not bringing a knife. So before you go, go through this list:
- Tool Class: Live wrench, torque wrench, vernier caliper or special displacement gauge. Don't rely on your eyes to measure the displacement. A difference of one millimeter may be a hidden danger.
- Detection class: Flashlight (look at the dead corner), reflector (check the back weld), soapy water or leak detector (check the seal). If you are inspecting steam or gas pipelines, it is recommended to bring an infrared thermometer gun to feel the abnormal temperature.
- Safety class: Hard helmets, protective gloves, overalls. Don't bother. Last week, there was a master who didn't wear gloves and had a cut on his hand from the bellows burr.
- Record Class: A paper notebook or tablet, preferably a template with a form-date, device bit number, appearance, displacement data, handling measures. Don't rely on your brain to remember, it's easy to forget.
Tips: If there is high-temperature medium on site, remember to wait for the pipeline to cool to room temperature before starting. It's not worth it if it's hot.
2. Appearance inspection Don't just look at the surface, these details are very critical
Many people took a flashlight and shone it, hey, there was no oil leak or deformation, and it passed. Tsk, what's the difference between this and just looking at photos on a blind date? You have to put your eyes on it and zoom in.
Let's startMetal corrugated expansion joint(For example, corrugated expansion joints and general-purpose corrugated expansion joints for power station industry). Focus on the corrugated surface: are there any cracks, corrosion pits, and dents visible to the naked eye? Especially the trough position is most prone to dust accumulation and stress concentration. Touch it with your hand, do you feel any burrs or local bulging? And guess what? A lot of early failures start with a small pitting corrosion.
Look againNon-metallic expansion joint(fabric fiber or rubber compensator). Don't just look at the outer layer of cloth, but see if it has aged, hardened, delaminated or partially ablated. Especially the rubber PTFE compensator, if close to the high-temperature heat source, the rubber is easy to become brittle. Gently press with your hand, it should be elastic normally, but if it doesn't bounce back when pressed, it is basically wasted.
Don't leave the flange bolts alone. Twist it with a wrench to see if it is loose. Loose directly tight, tight to the torque value. But be warned-some bolts are rusty and may break if you screw them hard, so you have to replace them with new ones.
And welds. The circumferential welds at both ends of the expansion joint and the connecting welds with the pipe, look at the back with a reflector to see if there are any holes, cracks or bitten edges. Don't tell me that "the manufacturer checked it when welding", the vibration and temperature difference will also crack in the later period.
3. Displacement and seal inspection, hands-on measurement counts
This section is the key of the key. In the compensator inspection content, the most easily fooled is the displacement measurement. Many people make a random gesture with a ruler and write "normal". How can that work?
Before measuring the displacement, confirm what state the pipeline is in-is it cold or at operating temperature? If it is cold, compare that displacement value with the initial value when you installed it, and you can see whether the compensator has been biased or crushed to death.
- Axial displacement: Select two fixed points on the bellows (such as the flange surfaces at both ends) and measure the distance with a vernier caliper. Then compare the initial length of the installation record. If the difference is within the design range, it will be fine, otherwise it may be that the pipeline stress is too large or the compensator is not selected correctly (for example, the straight pipe pressure balance expansion joint should be used but the ordinary axial type is used).
- Lateral displacement: Use a plumb line or a horizontal ruler to see if the flange surface is skewed. Usually, for sleeve-type pipe expansion joints, the allowable lateral displacement is very small, and crooked is a problem.
First see if there are any obvious leakage marks (oil stains, water stains). No traces don't mean no leakage-for gaseous media, brush soapy water on bellows welds and flange sealing surfaces to see if there are bubbles. If there are bubbles, it means it is leaking. You may ask: What if I leak it? Don't worry, Step 5 will say.
By the way, some masters feel that they are experienced enough to know if they leak at a glance. Don't brag, the real micro-leak can't be seen by the naked eye, so soapy water is reliable.
4. Special inspection of pull rods, guide tubes and baffle doors, where problems are prone
These three are the "Achilles heel" of the compensator system. A lot of the accidents are due to these parts.
tie rod(Especially on large tie rod expansion joints and double hinge transverse expansion joints). See if the nut is loose first. If loose, re-tighten according to the torque value given by the manufacturer. Note: The tighter the tie rod nut is not tightened, the better. Tightening too tightly will limit the normal displacement of the bellows, but increase the stress instead. Refer to the common question and answer "How to adjust the tie rod nut of the expansion joint" in our station-generally, it is screwed to the initial set value first, and then fine-tuned according to the actual displacement.
Let's see if the tie rod is bent and deformed? If it is bent, it means that the thrust of the pipe is too large and the tie rod bears a force that should not be beared. At this time, it is necessary to check whether the fixing bracket is displaced.
guide tubeIt is the sleeve inside the expansion joint that directs the flow of the medium. It is particularly prone to wear, especially if the medium contains particles (such as flue gas, cement dust). Inspection method: Shine with a flashlight from the entrance or exit to see whether the inner wall of the guide tube is worn out or fallen off. If it is worn out and the medium flushes the bellows directly, then the bellows will soon hang too. The function of the guide tube is to protect the bellows (see the specific function of the expansion joint guide tube for details).
baffle door(Flue gas baffle door, circular baffle door, desulfurization flue gas baffle door, etc.). Check if the switch is flexible? Turn it by hand or operate it electrically to see if there is any stuck. Then check the sealing surface-after the baffle door is closed, use a gauge or visually to see if the gap is even. If the gap is large, the flue gas will leak, and the environmental protection will not meet the standard. And is the graphite packing or elastic sealing piece on the sealing surface aged? Change when you need to.
If you're inspectingManual plug-in insulation doorOrElectric plug-in insulation doorIt also depends on whether the plug-in board track has dust accumulation and deformation. Clean it up, or it won't be tight.
5. Don't be fooled when recording data, and how to deal with problems found
The last step is also one that many people tend to be lazy. Think about it, after a hard inspection, if you don't record it, how will you compare it with the historical data in the next inspection?
Equipment number, ambient temperature, medium temperature, measured displacement value, appearance (with or without cracks, corrosion, leakage), baffle door opening, tie rod nut status, bolt tightening. Don't fake every piece of data. Two days ago, on a project, the inspection records were all "normal". As a result, the expansion joint exploded half a year later. Before the inspection, it was found that the displacement exceeded the standard, but it was written as "normal". It is still yourself who takes the blame.
How to deal with problems found?
- Bolt loosening: Tighten directly to the torque value, and the torque value refers to the original factory manual. If the threads slip, replace the bolts with new ones.
- Minor leakage: Judge the leak point first. If it is a flange sealing surface, you can try to tighten the bolts; If it still leaks, it may be that the gasket is damaged and needs to be replaced or the compensator replaced (such as a rubber compensator or a PTFE compensator).
- Displacement exceeds standard: Check whether the nearby pipe support is loose or deformed. If the pipe thrust is excessive, it may be necessary to recalculate the stress or replace it with a model that can absorb greater displacement (such as a double straight pipe bypass pressure balanced expansion joint).
- Guide tube wear: Light wear can continue to be used, but the interval between the next inspection should be shortened; Heavy wear (wear out or fall off) must be replaced with the guide tube or the entire compensator.
- Baffle door stuck: Clean the track and sealing surface, add grease (pay attention to temperature resistance grade). If the sealing surface is severely worn, replace the sealing assembly.
- Significant crack or bulge in bellows: Don't hesitate to stop and replace it directly. This can explode at any time.
For high-temperature, high-pressure or hazardous chemical pipelines, after serious problems are found, they should be reported as soon as possible and stopped for treatment. Don't run with illness.
Well, to sum up: the content of compensator inspection is actually not complicated, but you need to do it with your brain. Bring all tools, look carefully at the appearance, measure the displacement by hand, can't leak special items, and record is really complete. Before your next inspection, go through these five steps, and you'll know what it means to spend money wisely.