Drainage holes in non-metallic compensators, not optional

Drainage holes in non-metallic compensators, not optional

After more than ten years in this business, I have met many customers with scrapped compensators to come to me to analyze the reasons. When I took it apart, it was full of water, and the fabric layer had long been soaked. When I asked, I didn't want the drainage hole when it was too troublesome. And guess what? It saved hundreds of dollars in processing fees. As a result, it took less than a year to replace the whole non-metallic expansion joint (fabric fiber expansion joint), and the maintenance cost plus downtime loss was more than ten times. Let's make it clear today: how important is this drainage hole.

1. Why do non-metallic compensators have drainage holes? — A chain reaction triggered by condensation

Non-metallic compensators are installed in places such as flue gas pipelines and desulfurization tower outlets. The internal medium temperature is high and the external environmental temperature is low. As soon as the temperature difference is enlarged, condensation is an inevitable event. For example, the temperature of the clean flue gas after desulfurization is only 40 or 50 degrees, and it directly condenses into water when it touches the cold pipe wall. What if the water accumulates in the compensator trough and can't be drained? The fabric layer is soaked in water for a long time, and its strength decreases. Coupled with acid corrosion, leakage will soon occur. What's more troublesome is that the accumulated water will freeze, and the expansion force will directly burst the skin. Therefore, the drainage hole is not optional, but a life-saving design.

Then why do metal compensators rarely open holes? Because metal is not afraid of blisters, but the main body of non-metal expansion joint is fiber fabric and rubber, the most afraid is the erosion of water and acidic liquid. Even if you use a fluororubber composite layer, it can't handle long-term soaking.

2. How to design the drainage hole reasonably? — — Attention to position, aperture diameter and accessories

Don't think that just poking a hole in the bottom is called a drain hole. If the position is wrong and the aperture is randomly selected, it will be bad.

Location:It must be turned on at the lowest point of the compensator, and at the lowest point of drainage throughout the plumbing system. Sometimes the pipe has a slope, and the compensator is not necessarily the lowest point, so you have to set up a drainage point downstream of it. For rectangular non-metallic expansion joints, drainage holes are generally opened on the lower side plate or the flange surface at the bottom.

Aperture size:Too small is easy to block, and too large weakens the structural strength. The conventional practice is DN15~ DN25 holes, with wire plugs or ball valves. If the medium has a large dust content (such as cement industry), it is recommended to use DN25 or above, and internal threads must be brought to facilitate plugging.

Attachments:Just opening a hole without a control valve is called air leakage. The correct way is to connect a section of short pipe with a ball valve or plug at the end. Usually, open the drainage slightly, and check whether there is accumulated water flowing out during inspection. If the medium is toxic or hot, a sealed cover should be added. This site'sNon-metallic expansion joint (fabric fiber expansion joint)When leaving the factory, the drainage components can be pre-installed according to the customer's requirements. For specific parameters, you can see the product page.

3. In which scenarios must a compensator with drainage hole be selected? — — Lessons from desulfurization, cement and power stations

Three typical industries, each lesson is worse than the last.

• Desulfurization industry:The saturated humidity of flue gas after wet desulfurization is extremely high, and the dew condensation is the largest. One power plant used one without drainage holesDesulfurization flue gas baffle doorMatched with the compensator, three months later, the compensator bulged and leaked, and when it was disassembled, it was found that half a bucket of water could be poured out of it. Later, it was replaced with a drainage hole, checked regularly, and lasted four years before it was replaced.
• Cement industry:The waste heat power generation pipeline contains dust and water, and once the drainage hole is blocked by dust accumulation, there will still be problems. It is recommended to install stainless steel screens at the orifices, or use drain valves with backwash function. This siteMetal Corrugated Expansion Joints in Cement IndustryAlthough the main body is metal, non-metallic compensators are more common in cement lines.
• Power station chimney entrance:The smoke temperature is low, the acid dew point is high, and the corrosion is extremely high. If it is not drained, the acid directly attacks the flange and skin. Many power stations now clearly stipulate that non-metallic compensators must have drainage holes, otherwise they will not be accepted.

4. What is the difference between having drainage holes and not having drainage holes? -A true comparison of life and maintenance costs

Take a non-metallic expansion joint of a DN800 as an example. The ambient temperature is-10℃ ~40℃, and the smoke temperature is 60℃. Without drainage holes: We have done tracking, and on average, skin corrosion perforations occur in 1.2 years. With drainage holes and routine maintenance in place: Average life of more than 3.5 years. The difference is close to 3 times.

What about the cost of repairs? To replace a non-metallic expansion joint, the material cost is 3,000~8,000 yuan, and the labor cost is calculated separately. Tens of thousands to hundreds of thousands will be lost a day after shutdown. And opening a drainage hole, the cost is almost zero. In terms of maintenance, it takes two minutes to unscrew the valve once a quarter to drain water. This is not a difficult account, is it?

Of course, drain holes have drawbacks – increasing potential air leaks. However, as long as the accessories and seals are done correctly, this air leakage can be completely ignored.

5. Guide for selection and installation of pit avoidance: Don't let the drainage hole become a leakage hole or blockage point

Your compensator drain hole is leaking! I ran to see that the installer turned the drainage hole upward, and the water couldn't drain out at all, but smoked out of the hole. This is the typical installation error.

Pit Avoidance List:

• The drainage holes must be facing below the outside of the pipe, not to the sky, and must not be covered by insulation.
• After opening, burrs should be trimmed to prevent scratching the fabric layer. It is best to use flanging process or add reinforcing rings.
• If the medium has a large dust content (such as cement industry), it is recommended to install a deposition cavity at the front end of the drainage hole, so that the ash can settle first and then drain, so as to avoid blocking the hole.
• In northern winter: the drain pipe should be insulated, or electrified for heating. Otherwise, it freezes, the water can't drain, and the compensator is just as bad. There is a case in Inner Mongolia, where three compensators were cracked in winter without antifreezing.
• When selecting the type, if the pipe is installed horizontally and the length exceeds 10 meters, it is recommended to set a drainage point on each side of the non-metallic compensator.

6. Two things for daily maintenance: clearing blocks and antifreezing, so you can worry less if you do it

Maintenance is actually not complicated, but it is important to persist.

First thing: clear the block.Check that the drain holes are clear at least once a month. Unscrew the ball valve by hand. If it can drain water or air flow, it means that it is normal. If there is no movement, it may be blocked by dust. Prick it with a thin wire, or remove the valve to clean it. Note: If the medium is high-temperature toxic smoke, be sure to stop the machine or wear protective equipment before operation.

Second thing: freeze-proof.In areas below zero, the drainage pipe should be insulated with rock wool, and the thickness should not be less than 50mm. If conditions permit, installing self-limiting temperature heating belt costs tens of dollars per meter, which can save tens of thousands of maintenance costs. Check once a year before winter to see if the heat tape is working properly.

Do these two things, and a non-metallic compensator with drain holes will last for three or five years. If you are lazy and don't maintain it, let alone the drain hole, even bringing your own drain pump can't save you.

Don't just look at the price when selecting the model. The small detail of the drainage hole directly determines how long the compensator can last. If you are not sure of the design, go directly to the manufacturer for a mature scheme with drainage holes, such as this station'sRectangular non-metallic expansion jointAndNon-metallic expansion joint (fabric fiber expansion joint)Series, all have matching drainage components to choose from. Don't wait until you miss it to regret it.