How to make expansion joint insulation layer? Think clearly why you should do it
Insulation is not a panacea, but it is not a small trouble without it. The expansion joint is responsible for absorbing heat displacement in the pipeline system. If the heat insulation is not done well, not only will the heat be lost in vain, but also may cause condensation to corrode the bellows, and even discount the overall compensation amount. Let's first find out the purpose of heat insulation-not just wrap a layer, but minimize the heat loss on the premise of ensuring free expansion and energy saving. You may ask: Wouldn't it be good to pack it thicker? Alas, it really isn't. The bag is too thick and too dead, and the bellows can't move, which is equivalent to turning the compensator into a rigid connection. Therefore, the core is one sentence: the insulation layer can't jam the bellows.
Before you start, take a look at what kind of expansion joint you are using
The thermal insulation methods of metal corrugated expansion joints and non-metal expansion joints (fabric fiber expansion joints) are very different. The bellows part of the metal must leave enough space to not be filled; The non-metallic expansion joint itself has a heat insulation layer, which in many cases only needs external protection or local reinforcement. If you have a high-temperature axial expansion joint or a directly buried (fully buried) expansion joint in your hand, the thermal insulation requirements are different-aluminum silicate fiber cotton for high-temperature working conditions and polyurethane for low-temperature antifreeze scenes. Don't get confused. Two days ago, I met a customer who stuffed rock wool directly into the ripples of the directly buried expansion joint. As a result, it stuck as soon as it ran, and the compensation amount was directly returned to zero.
Core Principle: The insulation layer cannot jam the bellows
Some construction sites save trouble, and the rock wool is directly tied to the corrugations with iron wire. As a result, the insulation layer is torn as soon as the expansion joint is stretched, or the wire strangles the corrugations. The correct way is to make a detachable thermal insulation sleeve, which is divided into two layers: the inner layer is filled with flexible thermal insulation material (such as aluminum silicate needle blanket), and the outer layer is made of stainless steel skin or aluminum skin as a shell, leaving a gap of 15-20mm between the shell and the bellows. If it is a large-diameter thick-wall expansion joint or a compound hinge transverse expansion joint, the influence of transverse displacement must be considered, and the shell should be designed as an overlapping sliding structure. And guess what? Many expansion joints that leak in the later stage are not treated properly at the junction, and water flows into the corrugated root along the insulation layer, resulting in stress corrosion cracking.
Specific construction process: four steps, bypassing three pits
The first step is to clean the surface of the expansion joint to remove oil and rust. Don't be lazy in this step, otherwise the insulation layer will not be stuck firmly, and it will be more troublesome to fall off later. The second step is to apply a waterproof layer on the inner insulation material (especially for outdoor open-air conditions). The third step is to install the removable jacket and fix it with stainless steel hoops. Be careful not to tighten the bolts too tightly to leave a margin for thermal expansion. The fourth step is to seal the junction between the insulation layer and the pipeline insulation to prevent moisture from penetrating. You have to remember these three pits: first, don't tie it with wire, second, don't wrap the bellows to death, and third, the junction must be sealed with silicone rubber. Last year, there was a power plant project, and the junction of the insulation layer was not treated properly. Half a year later, the root of the bellows was corroded and perforated. Changing an expansion joint and the loss of production shutdown was enough to buy several sets of insulation jackets.
Material selection: temperature has the final say
For conventional steam pipelines with temperatures below 200℃, rock wool felt is enough; However, in the case of flue gas pipeline or power station boiler, the temperature often rushes above 400℃, so aluminum silicate fiber or ceramic fiber must be used. If you are equipped with desulfurized flue gas baffle door or round baffle door (double seal), the insulation layer has to be extra considered for acid corrosion resistance, and a layer of PTFE film or anti-corrosion paint should be added to the outside. Another reminder, never use glass wool-the fiber is too brittle and will be powdered after a few vibrations. By the way, if it is a rubber compensator or rubber PTFE compensator, there is no need to insulate at all. Rubber itself is an insulation material, and if you wrap it hard, it will affect its displacement.
Practical case: Negative textbooks are more valuable than positive textbooks
Two years ago, there was a cement plant project, which used metal corrugated expansion joints in the cement industry, and the insulation layer was made into a whole wrapped type. As a result, the bellows leaked after half a year's operation. When I disassembled it, I found that the insulation cotton was full of water, and the bellows was pitted like a honeycomb. Later, it was replaced with a segmented detachable insulation sleeve, and each section was sealed with silicone rubber. So far, there has been no problem for three years. Another negative example is the general-purpose corrugated expansion joint used on gas pipelines. The thickness of the insulation layer is not enough, and the outer shell is rusted through due to condensation in winter. Therefore, don't be too troubled. The thickness should be calculated clearly, and the gap should be left enough, so that the insulation layer can really work. If you use air-cooled island vacuum pipe double-hinged expansion joint or sleeve-type pipe expansion joint, the insulation design has to be confirmed with the manufacturer-this structure with hinges and sleeves has complicated displacement direction, and the insulation jacket must be specially customized.
How to make expansion joint insulation layer? There are three cores-select the right material, leave enough gaps, and seal well. Don't think about the one-time package. Make it detachable, and it will be convenient for future maintenance. If you are not sure, ask the expansion joint manufacturer directly for the insulation scheme, and don't think about it yourself. After all, an expansion joint is tens of thousands of thousands, and it is scrapped in advance because of improper insulation. Is it distressing?