Why stare at the compensator? — You may not be able to bear the cost of not monitoring
Two days ago, I met a guy who was doing power plant maintenance, and told me that their factory burst three pipes in a month. In the end, it was found that the compensator (oh, that is, the expansion joint) couldn't bear the thermal expansion and contraction and was torn apart. Not to mention the maintenance cost of tens of thousands, but the loss of one day after shutting down production is enough to buy dozens of sets of monitoring equipment. Think about it, aOn-line monitoring of compensatorHow much is the system? After this account is calculated, whoever doesn't pretend will lose.
The compensator, whether it is a general-purpose corrugated expansion joint, a non-metallic expansion joint (fabric fiber expansion joint) or a rotary compensator, carries displacement and stress at the weakest link of the pipeline. Once something goes wrong, it will leak at least, and the pipeline will fly out and hurt people at worst. Manual inspection? Watch it once a week, and the day lilies are cold when something goes wrong. Only by staring at it in real time can the accident be pressed to death in the bud.
Step 1: Figure out what parameters your compensator needs to monitor – displacement, temperature, or pressure?
Don't buy sensors as soon as you get up. Ask yourself three questions first: Is your pipeline steam, smoke or corrosive medium? Is your compensator metallic or non-metallic? What displacement does it mainly bear?
- High temperature pipeline(For example, corrugated expansion joints and high-temperature axial expansion joints used in power station industry) -Temperature is the first threat, so priority is given to temperature measurement. If the temperature exceeds, the life of the bellows is directly discounted in half.
- Large diameter or long pipeline(Like directly buried (fully buried) expansion joint and sleeve pipe expansion joint) -displacement is the protagonist, and axial, transverse and angular displacements have to be watched.
- With corrosive media or dust(Desulfurization flue gas baffle door, metal corrugated expansion joint in cement industry) -Pressure fluctuation and leakage should not be careless, and pressure sensor plus vibration sensor is more reliable.
If you're not sure? Then it's a two-pronged approach of temperature + displacement, and the cost is not much more, but you feel at ease. Remember: Every penny you spend is to save ten times the money you spend repairing your pipes later.
Step 2: How to choose the sensor? -Don't waste your money, take your seat according to the type of compensator
And guess what? Many customers bought expensive laser displacement sensors, and as a result, they were installed on non-metallic expansion joints (fabric fiber expansion joints), and they were pasted to death by dust in less than two months. Choosing a sensor is the same as marrying a wife-the more expensive the better, the better.
- Metal bellows(Universal type, double hinge transverse type, straight tube pressure balance type, etc.) -Magnetostrictive displacement sensor or pull-wire encoder is recommended, with high accuracy and anti-interference. If you just need to see if there is an overlimit, the cheap proximity switch will work as well.
- Non-metal(Rubber compensator, rubber PTFE compensator, rectangular non-metallic expansion joint) -the non-metallic itself will creep, and the displacement is too large. Use ultrasonic sensors or lidar (pay attention to the protective cover). Afraid of dust? Choose ultrasound, not afraid of getting dirty.
- Rotary compensator, sleeve type pipe expansion joint— — This type mainly monitors the rotation angle and axial slip, and the angular displacement sensor or encoder does it.
- Flue gas baffle door, electric plug-in insulation door— — The key point is that the switch is in place. Micro switch or magnetic switch is enough. Don't spend tens of thousands of dollars on lasers. Waste of money.
When purchasing, ask the manufacturer "What is the protection level of this sensor?" If it is lower than IP65, it is a disposable consumable in outdoor or dusty environments.
Step 3: What are the pits for installing wiring? -Step-by-step teaches you to avoid 90% of common mistakes
This pit is the most installed. I'll list a few of them and you can compare them to see if you have stepped on them:
Pit 1: The sensor is welded directly to the bellows.One of our customers welded the displacement sensor bracket to the corrugation of the general corrugated expansion joint. As a result, the sensor was not broken, but the local stress concentration of the corrugated pipe cracked first. Correct practice: The bracket is fixed to the flange surface of the pipe body or expansion joint, away from corrugations.
Pit 2: The cable is not thermally protected.The temperature sensor cable next to the high-temperature pipe was not wrapped with a heat-resistant sleeve, and it was baked after two days of operation. Especially near the corrugated expansion joints and high-temperature axial expansion joints used in the power station industry, the temperature is hundreds at any rate, and the cables must be sheathed with silicone gel or metal braided pipes.
Pit 3: The signal line and the power line go through the same trough.The interference is so big that you doubt your life, and the data received by the acquisition module jumps and jumps. Walk apart, at least 20cm apart.
Pit 4: No redundancy length reserved.The compensator itself moves, and the cable is so tight that it breaks when it is stretched. Allow at least 10% allowance for each sensor cable and attach it to the pipe bracket without shaking.
First fix the bracket → install the sensor body → route the wiring → upper acquisition module → power-on test. Shake the sensor with your hand at each step to confirm that it is secure.
Step 4: The data is in hand, what do you think? — — How much is the alarm value set so that you don't call blindly
The data keeps coming back, but when you turn on the monitor screen, the alarm lights crackling into a disco-that means your threshold is too dead. How to set the alarm value?
Alarm threshold =70% of design allowable value。 For example, the design of a high-temperature axial expansion joint allows an axial displacement of 50mm, so a pre-alarm will be sent at 35mm and an emergency alarm will be sent at 45mm. Why leave an allowance? Because the actual bearing capacity of the compensator will decrease after aging, don't wait until it is really broken before calling, early reminder and early maintenance.
Early warning is set at 80% of the upper limit of working temperature, and shutdown is set at 90%. The same goes for pressure. Don't engage in "calling the police after exceeding the design value", which is equivalent to hindsight.
Just install the system. Don't rush to set the dead threshold. Run for a week first and collect baseline data. Under different working conditions (cold start, steady state, shutdown), the values are different. After figuring out the normal fluctuation range and resetting it, the alarm will not shout blindly.
Step 5: Don't be done with it-a small doorway for regular calibration and routine maintenance
You think you can sit back and relax after installing the sensors? Alas, there is no such cheap thing in the world. The sensor will also drift after long use, especially in harsh environments. It is recommended to do on-site secondary calibration every six months: measure the displacement of the compensator with a micrometer or caliper, and compare it with the system reading. If the deviation exceeds 2%, it should be adjusted.
- Take a look at the surface of the sensor every week to see if there is any dust and scale, especially near the non-metallic expansion joint (fabric fiber expansion joint) and rubber compensator. When the wind blows, it is all dust, so blow it with compressed air.
- Check whether the cable joints are loose and oxidized every month, especially in the area near the flue gas baffle door and desulfurization flue gas baffle door. Acid gas is very corrosive.
- Do a simulated trigger test every quarter, and artificially give an over-limit signal to see whether the alarm mechanism responds normally. Don't really find out that the system has gone offline when something happens.
On-line monitoring of compensatorNot a one-time investment, but a continuous closed loop of maintenance. If you spend half a day maintaining it, what you might save is the safety of the entire pipe gallery. Tsk, this is a good deal no matter how you calculate it.