What are the expansion joint insulation liner structures? One article clarifies three mainstream schemes
The temperature of the medium in the high-temperature pipeline is always five to six hundred degrees, or even thousands of degrees. When the bellows is directly exposed to this environment, the material strength will drop by a cliff, and the fatigue life will not be sustained. The insulation lining is like putting an insulation suit on the expansion joint, separating the heat source from the bellows. Common scenes: smoke duct of power plant, cement kiln tail, blast furnace gas pipeline of iron and steel plant-if bare bellows are used in these places, they will have to be scrapped in a few months.
What are the expansion joint insulation lining structures? Don't worry, break up the three mainstream schemes and break them into pieces to explain them clearly, with real cases and product benchmarking.
Scheme 1: Lined Castable Structure
This stuff is most common in the cement industry and power station industry. To put it bluntly, a layer of high-temperature resistant concrete is poured on the spot inside the expansion joint, with a thickness of generally 50-150mm. The advantages are high temperature resistance (up to more than 1200 ℃), wear resistance and good integrity. The disadvantages are also obvious-heavy, and the curing cycle of castables is long, so it is anxious to die during emergency repair.
The "Metal Corrugated Expansion Joint for Cement Industry" and "Corrugated Expansion Joint for Power Station Industry" of our station are equipped with this structure as standard, and with the guide tube, it can effectively prevent the medium from directly washing the bellows. However, it should be noted that castable cracking is an old problem, which must be controlled by the design and construction quality of anchors. Two days ago, I met a customer of a cement plant. During the maintenance, I found that the castable was partially peeling off. It was found that the spacing between the anchors was too large. Later, the cloth welding was re-welded at a spacing of 150mm, and there was no accident again.
Option 2: Ceramic fiber/non-metallic insulation
This solution is much lighter, and is mainly used in high temperatures but non-abrasive media. For example, flue gas pipelines and desulfurization systems. The structure is simple: fill ceramic fiber felt or aluminum silicate wool between the bellows and the guide tube, and wrap a layer of stainless steel wire mesh on the outside.
Our "non-metallic expansion joint (fabric fiber expansion joint)" and "rectangular non-metallic expansion joint" use this idea. The advantages are fast installation, low cost and good thermal insulation effect (thermal conductivity below 0.1W/m·K). However, there is a pit-fiber materials are afraid of water vapor, and the performance of flue gas will decay when the moisture content is high, so it has to be matched with waterproof layer. How to prevent it? Usually a layer of PTFE film or stainless steel foil is added on the outside. If the budget allows, go directly to the "PTFE-lined hose" scheme, and you won't be afraid of sour gas.
By the way, don't think that you can choose just because the temperature and pressure are low. There was once a desulfurization project with a temperature of only 150℃, but the condensed water of wet flue gas soaked the ceramic fiber into mud, and it collapsed in three months. Later, it was replaced with aluminum silicate cotton + PTFE cladding, which has not been changed for three years now.
Option 3: Composite thermal insulation lining
This is a combination of the first two schemes, specializing in the treatment of various difficult and complicated diseases. For example, the medium is high temperature and dusty, or the temperature fluctuates violently periodically. Structurally, the innermost layer is castable anti-scour, the middle layer is ceramic fiber insulation, and the outer layer is guide tube to protect bellows.
Two days ago, a customer asked, saying that their pipeline temperature circulated from normal temperature to 800℃, and it cracked in the first week if only castables were used. Later, it was replaced with a composite structure and used it for three years without any problems. Well, the cost is 30% more expensive, but the life span has doubled by 5 times, which is cost-effective.
Composite structures are not simply stacked and done. The difference of expansion coefficient between the layers must be calculated well, otherwise it will be peeled off in layers after several cold and hot cycles. Solution? A layer of stainless steel expansion mesh is added between the castable and the fibers, and the elasticity of the mesh absorbs the displacement.
Don't just look at the temperature when selecting a model
Pressure, media corrosiveness, installation space and maintenance frequency must be considered. For example, desulfurization flue gas pipeline, the temperature is not high but the acid corrosion is strong, so it is better to choose non-metallic insulation layer with PTFE lining. Our "desulfurization flue gas baffle door" and "PTFE-lined metal hose" are for this working condition.
In addition, the thickness and material of the guide tube also directly determine the heat insulation effect-if the guide tube is too thin, it will easily be burned through, and if it is too thick, it will increase the cost. It is recommended that it be determined according to the medium flow rate and particle hardness, generally 304 or 316L, with a thickness of 3-6mm. If the medium contains hard particles (such as coal powder and slag), it is best to add a layer of wear-resistant lining plate, such as high chromium cast iron or ceramic patch, to the inner wall of the guide tube.
Don't forget to reserve access
Access port reserved for insulation liner. Many projects have installed expansion joints, but when they are broken, they find that the lining can't be changed. In the design stage, space should be allowed, or split structure should be used. Our Round Flap Doors (Double Seal) and Manual Insulated Doors have a quick-service design-bolted end caps that remove the liner module.
All in all, thermal insulation lining has no universal solution, it has to be tailored to the working conditions. If you are not sure, directly take the parameters to find the manufacturer to come up with a plan, and don't make it yourself. After all, if the bellows is burned through, it is not as simple as changing a piece-the loss of the whole pipeline may be hundreds of thousands.