Why insulate flue expansion joints? Think clearly before you do it
Think about it, the flue is full of high-temperature smoke, at least three to four hundred degrees, and even seven to eight hundred degrees on some occasions. The expansion joint itself-no matter what your home is fitted toMetal rectangular expansion joint、Corrugated expansion joint for power station industryStillNon-metallic expansion joints (fabric fiber expansion joints)— — To put it bluntly, it is a flexible "joint", which is specially used to absorb the displacement of thermal expansion and contraction of pipelines. But what happens if you don't do insulation?
First, the heat spreads out, which is a waste of energy. The energy consumption report is ugly, and it is easy to burn people. Second, the flue gas condenses when it is cold, and the acidic condensate seeps into the expansion joint ripples, and the corrosion rate is much faster than you think. A while ago, a buddy from a cement factory told me that their factoryMetal Corrugated Expansion Joints in Cement IndustryIt leaked after less than a year of use. When I took it apart, I found that the insulation was not done well at all, and the condensed water soaked the corrugated roots.
Therefore, insulation is not optional, it is a must. But thermal insulation can't be fooled around-the following three things are not clearly confirmed, so don't do it.
3 Things You Must Confirm Before Insulation: Material, Temperature, Gap
1. Confirm the material of the expansion joint
Are your expansion joints metallic or nonmetallic?Metal rectangular expansion jointAnd stainless steel bellows (such asHigh temperature axial expansion joint) The surface is smooth, and the insulation material is directly made of rock wool and aluminum silicate fiber blanket. But if it isNon-metallic expansion joints (fabric fiber expansion joints)Orrubber compensatorThe outer layer has flexible fabric, and the insulation layer cannot be pressed too tightly, otherwise the fabric will be squeezed and deformed, affecting the displacement amount. When encountering such products, it is recommended to first pad a thin layer of temperature-resistant rubber and then wrap insulation cotton.
2. Find out the flue gas temperature
The temperature determines what grade of insulation you use. The temperature resistance of ordinary rock wool is about 600℃, and the aluminum silicate fiber can reach over 1000℃. If the flue gas temperature exceeds 800℃, such as the outlet of some power plant boilers, ceramic fiber modules are needed. By the way, you have to pay attention to the temperature resistance of the expansion joint itself-likePTFE-lined hoseFor this kind of product, the PTFE layer can only carry more than 200 degrees, and the insulation design must ensure that the external surface temperature is lower than this value.
3. Leave good expansion clearance
This is the easiest place to roll over. The expansion joint is called an expansion joint because it has to move. You wrap it tightly, crushing the insulation and even pulling the bellows with a move. How to stay? Look at the displacement data given by the manufacturer-such asUniversal corrugated expansion jointThe axial compensation amount is ±50mm, and a gap of at least 10~15mm is left between the inner side of the insulation layer and the outer wall of the expansion joint to keep the air layer. If you useCompound hinge transverse expansion jointThe lateral displacement is larger, and the gap has to be widened.
Teach you the construction steps of insulation layer step by step: from cutting to fixing
Okay, confirmation is over, it's time to get started. I'll just say the steps, and you just follow them.
- Step 1: Clean up the surface.First, wipe the dust, oil and rust on the outer wall of the expansion joint. It is best to brush a layer of anti-rust paint on the metal surface, and wait until it is dry before drying the next step.
- Step 2: Measure the blanking.Use a tape measure to measure the total length and circumference of the expansion joint, and be careful not to include the gap. When cutting insulation cotton (aluminum silicate fiber blanket or rock wool felt is recommended), reserve an overlap amount of 50mm per piece.
- Step 3: Wrap.Wrap the insulation cotton along the axial direction of the expansion joint, wrap it in a circle, and compact it by hand while wrapping it. encounterRound Flap Door (Double Seal)OrFlue gas baffle doorNearby expansion joints, which may have stepped shapes, require local cutting and feeding.
- Step 4: Fix.Use galvanized iron wire with a diameter of 1.2mm or special stainless steel cable ties, and tie them every 200~300mm. Don't use plastic cable ties, which will break when baked at high heat. Note that the wire should not be hooped too tightly, and flattening the insulation layer will affect the insulation effect.
Tips:If it isNon-metallic expansion jointYou can also wrap a layer of glass fiber cloth outside the insulation layer, which is both heat insulating and corrosion resistant. In addition,Large tie rod expansion jointDon't pack the pull rod part too thick, otherwise the insulation layer will be worn when the pull rod moves.
Sealing and protection, don't let the insulation layer be made in vain
The insulation layer is wrapped and it is over? Not even close! If you don't do external protection, rain, moisture and corrosive gases will directly penetrate into the thermal insulation cotton, and the thermal conductivity will soar once it is damp, which is equal to being dry for nothing. To make matters worse, acidic condensate will flow along the insulation cotton to the metal surface of the expansion joint, accelerating corrosion.
The standard practice is to use 0.5~0.8mm thick aluminum sheet or galvanized iron sheet as the outer shell. Note when blanking:
- The overlapping length of each shell is not less than 100mm;
- The lap seam should be below the side of the expansion joint to avoid rainwater backflow;
- Both ends of the shell are fixed with self-tapping screws, but the screws cannot penetrate the insulation layer and contact the expansion joint body;
- Use high-temperature-resistant sealant (silicone sealant recommended, temperature resistance above 260℃) to make a circle at the joints.
The heat insulation must be in place at the pipe flanges or butt welds at both ends of the expansion joint-otherwise it will become a thermal bridge and still dissipate heat. Can be usedRotary compensatorOrSleeve type pipe expansion jointThe matching insulation sleeve (many manufacturers have prefabricated parts) can be stuck directly.
Common Rollover Sites and Pit Avoidance Guide
I've been in this business for more than ten years, and I've seen a rollover scene that can write a book. Pick a few of the most common ones, and you just avoid them.
Rollover 1: The insulation layer is too thick and the expansion joint is squeezed to death.There's a case of a thermal power plant where they gaveStraight pipe pressure balanced expansion jointIt was wrapped with 200mm thick rock wool + iron sheet, and as a result, the bellows couldn't stretch at all in the hot state, which directly led to the tearing of the welding seam of the joint. The correct way is to control the insulation thickness between 80~120mm (calculated by temperature), and leave a good air gap.
Rollover 2: Forgot to leave room for tie rod and deflector.Have a masterexpansion joint tie rodIt is also wrapped in the insulation layer, and the insulation cotton is torn as soon as the pull rod moves. Andexpansion joint guide tubeThe guide tube itself extends into the pipeline. Don't block the outlet of the guide tube during heat preservation, otherwise the airflow will be turbulent and the noise will increase.
Rollover 3: The non-metallic expansion joint used the wrong insulation material.Rubber PTFE compensatorFor this kind, the outer layer is PTFE or rubber, which can't be rubbed directly with hard thermal insulation cotton, otherwise it will wear out quickly. Solution: Wrap a layer of alkali-free glass fiber cloth first, and then wrap a soft aluminum silicate blanket.
Material matching, accurate temperature, enough gaps, and sealed in place. If you press this, the construction master will have to praise you for your professionalism.