Non-Metallic Compensators with Drainage Holes: How Important Is Drainage Design?
Two days ago, I met a customer who said that their desulfurization tower was exportedNon-metallic expansion jointThe bulge tore after less than eight months of use. When I removed it, I saw that there was half a bag of condensed water inside, and the fabric layer was soaked like a rotten rag. I asked why I didn't add a drainage hole in the first place? The other party was dumbfounded. "That thing has a drainage hole?"
You see, this is the scene. Many people only focus on the non-metallic compensator, which can absorb displacement and withstand high temperatures, but ignore the most basic thing-the water can't be discharged, and no matter how good the material is, it is useless. Today, let's talk about the details of this trivial matter by 90% of people:Non-metallic compensator with drainage holesThat little hole really determines the life of a plumbing system.
Condensation, corrosion and internal fluid buildup: how dangerous is it without drainage holes?
Tell me a real case. The flue after wet desulfurization in a power plant isNon-metallic expansion joint (fabric fiber expansion joint)The design temperature is 160℃, the actual operation is about 80℃, and the humidity content of the flue gas is high. After three months of operation, the inspection found that the lower part of the compensator was bulging and water seeped on the surface. When disassembled, the inner layer of fluororubber has been layered, and the glass fiber cloth has been soaked in acidic condensed water, and it will fall off as soon as it is torn by hand.
For every 1kg of condensate accumulated in the non-metallic compensator, the local corrosion rate will increase by 3-5 times. Especially when the flue gas temperature is lower than the acid dew point after desulfurization, a mixture of sulfuric acid and sulfurous acid will be produced. You read that right-this stuff is strong acid. Accumulated at the bottom of the compensator, in less than half a year, the fluororubber layer will blister and delaminate, followed by perforation and leakage.
What happens without drainage holes? The immediate result: the compensator becomes a "water bag". When the pipeline is thermally displaced, the accumulated water cannot be discharged, the non-metallic ring belt will form local wrinkles under the action of gravity, and the stress concentration will lead to early fatigue failure. What's even more outrageous is that in some projects in the north in winter, the compensator is directly fractured after the standing water freezes-guess what? It costs tens of thousands to change another.
How to Design a Reliable Drain Hole?
The drainage hole is not just drilled. This thing is special, but it may turn into a hole that leaks air.
Location:The drain hole must be opened at the lowest point of the compensator. It sounds like bullshit, but I've seen people open the holes in the sides-the water doesn't drain out and sprays mud directly through the side holes as soon as the pressure comes up. The correct way is to install the bottom of the non-metallic expansion joint below the lowest point of the pipe, or set a water collecting trough at the bottom of the compensator, and then make a hole at the bottom of the trough. For horizontally mounted rectangular non-metallic expansion joints, holes DN15-DN25 are usually opened on the inside of the lower flange, and a section of stainless steel short pipe is connected to the trap.
Opening size:Too small is easy to block, too large affects the structural strength. The empirical value is: φ 10mm hole for pipes below DN150 and φ 20mm for pipes above DN150. If it is a medium containing particulate matter (such as wet desulfurization slurry), it is recommended to expand to Φ 25mm, and the wire plug is easy to clean.
Materials:Drainage pipes must be compatible with media. 316L stainless steel or polytetrafluoroethylene for desulfurization flue gas; Carbon steel galvanizing for ordinary steam is fine, but don't expect to last more than two years. Note: The non-metal ring band around the drain hole should be added with an additional layer of fluorine rubber reinforcement pad, otherwise the opening is most likely to tear.
- Myth 1: The more drainage holes, the better. Wrong! Too many openings can destroy the airtightness of the non-metallic layer, resulting in air leakage noise and pressure loss. Generally, 1-2 holes are sufficient for a compensator.
- Myth 2: The drainage hole opens directly downward. The condensate will flow back down the outer wall and corrode the flange bolts. The correct way is to connect a section of elbow to the collection tube.
- Myth 3: Use ordinary carbon steel as a drainage short pipe. In a humid environment, it will rust out in three months and then leak. The gain outweighs the loss.
What operating conditions must have compensators with drainage holes?
Don't take chances. In the following working conditions, without drainage holes, you dig a hole for yourself:
Desulfurization flue gas system.This is the hardest hit area. After wet desulfurization, the net flue gas temperature is 45-60℃, the relative humidity is close to saturation, the acid dew point is low, and a lot of condensed water is grasped. The power plant case mentioned earlier is typical. Do you choose this type of smoke pipeNon-metallic expansion jointIf the drainage hole is not specified, the supplier designs it according to "ordinary dry flue gas" by default, so you can wait for it to explode.
Wet steam pipe.For example, steam turbine extraction pipeline and pipeline after temperature reduction and pressure reduction. When the steam quality is not good or the degree of superheating is insufficient, a large amount of condensate water will be produced inside the pipe. If there is no drainage hole at the bottom of rubber compensator or fabric compensator, the accumulated water will quickly vaporize in hot state to produce water hammer, and instantaneous pressure impact can break the compensator.
rubber compensatorApplication Scenario. Rubber is not afraid of water, but it is afraid of long-term soaking. The rubber compensator is in the air conditioning cooling water and circulating water pipeline. If the accumulated water is not discharged during the outage, the rubber layer will swell and become sticky, and the rubber PTFE compensator is the same. I have seen a rubber compensator with two years of old water accumulated inside because the drain hole is blocked. When it is opened, it is sour and refreshing... the rubber directly turns into soft mud.
At the end of the day, as long as there is any possibility of condensation or accumulation of fluid in the pipeline medium, choose honestlyNon-metallic compensator with drainage holes。 How much is this sentence worth? Save losses from at least one accidental downtime.
Pits that are easy to step on during model selection and installation
FromJB/T 12235-2015Start with the standards and talk about the details that you thought were okay but were actually very wrong.
Article 5.2.4 of the standard clearly states: "When the medium contains condensed water or needs to discharge accumulated liquid, the compensator should be equipped with a drainage device." However, when many purchasers get the drawings, they only see the five words "non-metallic expansion joint", but don't write "with drainage hole", so the supplier does it according to the default configuration. When there is no hole found, the hole will be opened on the spot-the coating will be damaged, the fiber will be outcropped, and the subsequent corrosion will be faster.
Another pit is the drain hole direction. The standard requires that "the drainage hole should be set at the lowest point of the compensator and towards the side for easy drainage". In actual installation, if the pipe slope is wrong, the drain hole may not be at the lowest point. Therefore, it must be checked before installation: check the level of the lower flange of the compensator with a level, and the low point must be aligned with the drainage hole. Otherwise, the hole is opened for nothing.
Should the drainage hole be plugged with wire? Some projects say "screw on the wire plug after draining the water", but the inspector often forgets to screw it back, resulting in air leakage. It is safer to have an automatic drain trap, which controls the drainage by floating ball or thermostatic force. Usually, it is closed and drained only when there is water. Of course, the cost is higher, but it is worry-free.
Tips for worry-free maintenance
What if the drain hole is blocked? Don't rush to replace the compensator. First determine the cause of blockage:
- If it is fouling (such as calcium and magnesium deposits), soak in 10% citric acid solution for half an hour and rinse with water. Don't use hydrochloric acid, it will corrode the stainless steel short tube.
- If it's clutter, poke it with a thin wire. But be careful not to pierce the inner fluorine rubber.
- If it is ice blockage, heat the drain pipe with steam heating tape in winter.
Which points do you look at in daily inspection? Remember "one listen, two see and three touch":
- Listen: Is there a "fizz" air leak near the compensator. Pay special attention to the drain outlet.
- Look: drain outlet for rust or crystals (possibly acid leakage), lower flange for wet marks.
- Touch: Water accumulation will cause the temperature at the bottom of the compensator to be much lower than that at the upper part. Feel the temperature difference with the back of your hand-if the temperature difference exceeds 15℃, it means water accumulation.
To do this, letNon-metallic compensator with drainage holesYou won't be afraid of using it for 10 years. After all, a drainage design of several hundred dollars replaces the safety of the whole set of pipelines. Do you say it's worth it?