Boiler Separator Outlet Expansion Joint Leaking? Three-step troubleshooting method, teach you how to deal with it step by step
Once the expansion joint at the outlet of the boiler separator leaks, the steam carries water, the system vibrates, and even stops for maintenance, which is enough for you to have a headache. Two days ago, a friend from a power plant called me in the middle of the night, saying that there was a white steam at the scene, and the pressure dropped badly, and asked me if I could block it first. Don't worry, let's find out where the leak is first, and it's not too late to start.
1. Don't rush to replace the parts yet-find out where the leak is
Many people directly place an order to buy a new one as soon as they see a leak. However, at the outlet of the boiler separator, the working temperature is high and the medium flow rate is fast, so there is often more than one possibility of leakage point:
- Damaged bellows: Most common. High-temperature steam washing + long-term fatigue, thinning of bellows wall thickness, pinholes or cracks appear. Use a flashlight from one side, and see if there are any light-transmitting spots on the other side.
- Weld cracking: Especially for circumferential and longitudinal welds, if the welding quality is poor or the thermal stress is concentrated, the cracks will extend along the fusion line. You can use colored penetration inspection, and there are generally reddish-brown marks at the leakage point.
- The guide tube is worn out: The function of the guide tube is to guide the medium and protect the bellows from direct scouring. Once the guide tube is worn out, the high-speed steam directly hits the bellows and quickly perforates. Disassemble and look at the end of the guide tube for any penetrating wear marks. Many old factories have encountered this problem, thinking that the bellows was broken. After changing it twice, it was found that the deflector tube had a problem first.
Judge which one first, then decide on the scheme. Don't come up and change something, that's a problem with the money in your pocket.
2. Temporary emergency treatment on the spot: How long can leak plugging last? Which circumstances require immediate shutdown?
After discovering a leak, if it is only a small amount of leak, you can useMetal wound gasketAddHuff FestivalTemporary hoops. But note: this will only last a few shifts, and leakage changes must be monitored continuously.
Situations where immediate shutdown is necessary:
-The leakage medium temperature exceeds 400°C, the pressure exceeds the design value by 80%, and the amount of leakage continues to increase.
-The bellows is obviously bulging or twisted, indicating that it has become unstable and may burst at any time.
-The leakage point is close to the weld or the fixed end of the guide tube, and once the weld cracks, the whole may fall off.
Temporary plugging is just to buy time for maintenance. Don't think of "waiting for overhaul for a few more days". Boiler Separator Outlet This high pressure and high temperature working condition, you can't afford to gamble.
3. Professional maintenance plan: replace metal or non-metal? How to choose a model without stepping on a pit
For what? That's the core issue. Boiler separator outlet, preferredCorrugated expansion joint for power station industry。 Specially designed for power station boilers, these products are resistant to high temperatures and fatigue, and generally use austenitic stainless steel (such as 316L or Incoloy 825).
But-if your pipe has a particularly large axial displacement because of space constraints, or needs to absorb multi-directional displacement, consider High temperature axial expansion joint。 There is a big difference between the two: the former mainly deals with the outlet of large-diameter and low-pressure boilers, while the latter is better at absorbing the axial expansion and contraction of long-distance pipes. Choose the wrong model, and it leaks after less than a year of installation.
In addition, some working conditions (such as desulfurization flue gas with low temperature but strong corrosion) can be consideredNon-metallic expansion joints (fabric fiber expansion joints)However, it is generally not recommended to use non-metal at the outlet of the boiler separator, because the temperature often exceeds 400℃, and the non-metal layer is easy to age and brittle. Remember: The more expensive the selection is not the better, it is the matching working conditions. Refer to the pages of "Corrugated Expansion Joints for Power Station Industry" and "High Temperature Axial Expansion Joints" of this site, and compare your parameter table: displacement, pressure grade, temperature, medium composition, and don't miss one item.
4. Installation details determine life: how to adjust the tie rod nut? Is the guide tube oriented correctly?
With new expansion joints installed, don't think everything will be fine. If the installation details step on a pit, they will have to be changed after three months.
Tie Rod Nut Adjustment:Many installers screw the tie rod nut to death, feeling that the tighter it is, the safer it is. Wrong! The tie rod of the expansion joint is used to withstand the internal pressure thrust of the pipe, and the nut should be adjusted to the position designed to be pre-tensioned or pre-compressed. Generally, the manufacturer will mark the installation length when leaving the factory, measure the actual distance between the two ends of the bellows on the spot, adjust the tie rod nut to the free state, and then fine-tune it according to the requirements of cold tightening or hot tightening. How to adjust the tie rod nut? For details, please refer to the question and answer of "How to adjust the tie rod nut of the expansion joint" on this site, which has a detailed step diagram.
Guide tube orientation:The direction of the arrow of the guide tube must coincide with the direction of the medium flow. In some factories, it is installed backwards. As a result, the opening of the guide tube faces downstream, and the medium directly impacts the root of the bellows, which will wear out in a few months. After installation, be sure to check the direction, don't wait for it to leak before disassembling it.
There is also the grounding jumper. Don't forget-the steam flow rate at the outlet of the boiler separator is high, which is easy to generate static electricity. If it is not jumped, it may cause electric sparks. How many of these pits have you stepped on?
5. What indicators should we focus on in daily inspection? Two years or five years? Don't wait until you miss it before you regret it
- Displacement indicator scale: There is generally a scale on the outer wall of the expansion joint to record the initial position. If the deviation of the scale value exceeds 20% of the design displacement, it means that the pipeline stress is abnormal, and the bracket and guide need to be checked.
- Bellows surface temperature: Sweep the infrared temperature measuring gun once regularly. If the temperature difference on the same section exceeds 50℃, it may be fouling on the inner wall of the bellows or bias flow of the medium.
- Deflector outlet sound: Listen to it with an auscultation stick. If there is an abnormal "hissing" sound, it means that the guide tube may have been perforated and the airflow is howling inside.
- Tie rod nuts and bolts: Check for looseness and rust. The bolts are prone to slack at high temperatures, and it is recommended to re-tighten the torque every time the machine is stopped for maintenance.
As for the replacement cycle, don't stick to "every two years" or "every five years". If the working conditions are stable and the inspection data are normal, many power station industries will use corrugated expansion joints for 8-10 years without any problem. However, if there is a leakage or an overtemperature or overpressure event, it must be replaced regardless of how long it has been used. Remember: Do it regularlyLife Assessment of Bellows (S-N Curve)It is much more reliable than patting your head to set the cycle.
After all, what if the boiler separator outlet expansion joint leaks? Step 3: First locate the fault point, then choose the right product to replace it, and finally make it use for a few more years by installation and inspection. Don't wait until there is white steam at the scene to flip through the manual, when every second is money.