Two days ago, I met a buddy who was doing a power plant project. Talking about the quotation of imported non-metallic expansion joints, he shook his head: "The same caliber, imported parts are two to three times more expensive than domestic ones. Does anyone really buy them?" Yes, and there are quite a few. There is a reason why it is expensive. This thing is different from buying groceries. The bigger it is, the more expensive it is, but the material and craftsmanship have the final say.
The gap between imported non-metallic expansion joints and domestic products is really not a psychological effect
Many people think that non-metallic expansion joints are just a circle of cloth and several layers of rubber. How much technical content can they have? Thinking that is a layman.
The core competitiveness of imported non-metallic expansion joints is not in the three words "expansion joints", but in the three words "non-metallic". It is also a ring belt, with ordinary glass fiber cloth and silica gel coating for domestic production, high-purity PTFE membrane and special fiber composite structure for imported production; It is also a rubber compensator, with EPDM for domestic use and high-temperature resistant fluororubber for import. The material is a bit worse, the performance is a lot worse, and the price is three times worse. This account can be calculated.
And guess what? Many domestic manufacturers quote low prices because of the low grade of materials used. It is not that domestic production is not good, but that the positioning is different. But you have to use it on the pipeline with high sulfur content and large temperature fluctuation at the entrance of the desulfurization tower, and the bargains will give you a look in three months.
Fabric fiber loop tape, rubber compensator... Core material determines the upper limit of performance
Where are imported non-metallic expansion joints expensive? It is important that there is a clear division of labor in each layer of materials.
Take fabric fiber expansion joints, for example, its bands are usually divided into several layers: the outermost layer is a weather-resistant layer, the middle layer is a reinforcing layer, and the inner layer is a corrosion-resistant insulation layer. The imported parts use high modulus glass fiber or even aramid fiber in the reinforcement layer, and the temperature resistance grade can reach above 200°C, and the instantaneous temperature resistance is even higher. However, ordinary domestic parts use medium-alkali glass fiber, which is brittle and falls off as soon as the temperature rises.
Look at the rubber compensator and rubber PTFE compensator again. Needless to say, the corrosion resistance of PTFE materials is that the imported parts can make the composite layer of PTFE and rubber uniform and dense, and will not blister and delaminate. This thing looks simple, but it depends on the accumulation of craftsmanship to do it properly. It can't be imitated by buying a machine.
The national standard for non-metallic expansion joints is JB/T 12235-2015. When purchasing, don't just look at whether there is a test report, but also see whether the material of the sample submitted for inspection is consistent with the batch you actually got. There are a lot of things in this business.
Which working conditions are suitable for importing non-metallic expansion joints? Power plants, cement lines, desulfurization systems don't slap your head
Imported non-metallic expansion joints are not a panacea, don't use them everywhere. Let's be clear first: it is mainly used in scenes with low pressure, large displacement and corrosion resistance, such as flue duct of power plant, hot air duct of cement production line, original flue gas/clean flue gas duct of desulfurization system.
The flue gas has a high temperature, contains sulfur, and is accompanied by fan vibration. In this case, a non-metallic rectangular expansion joint can absorb multi-directional displacement and do not generate thrust on the pipe wall. The imported parts are indeed stable in temperature resistance and corrosion resistance, and can be used for an overhaul cycle without changing.
The cement line is more abrasive. Raw powder and clinker dust run with the airflow, and the ordinary circle belt wears out in a few months. The surface of the imported ring belt has Teflon coating or fluororubber protective layer, and its anti-wear performance is visible to the naked eye.
What about the desulfurization system? The flue gas of wet desulfurization has large moisture content, low acid dew point and strong corrosiveness. Polytetrafluoroethylene compensator has outstanding performance under this working condition, but it is best to import high-purity PTFE. Domestic PTFE has many impurities and poor aging resistance.
On the other hand, if your working condition is high-temperature and high-pressure steam, don't choose non-metal. Go to the corrugated expansion joint or high-temperature axial expansion joint used in the power station industry. When it comes to model selection, something will happen when you pat your head.
None of the displacement, pressure and temperature that must be clarified before selection must be missed
Do you know what the actual displacement amount of your pipe is? Don't know? Then don't rush to contact imported brands.
For the selection of non-metallic expansion joints, three parameters are laid down: displacement (axial, transverse and angular), design pressure and design temperature. Without one, the manufacturer can't calculate the number of circle layers and structural design for you. If you say "almost enough", then people can only do it according to the most conservative, and you are not happy to double the price.
The pressure of the non-metallic expansion joint itself is not high, generally not more than 0.1MPa, which is mainly borne by the ring belt and skeleton. Well, the temperature depends on the medium temperature plus the ambient temperature and then multiplied by the safety factor. For example, the original flue gas of the desulfurization system is 80°C and the net flue gas is 45°C, which doesn't look high, but what if there is a high temperature impact at the moment when the bypass is opened?
And the direction of displacement. If the horizontal displacement of the pipeline is large, it is necessary to choose a rectangular non-metallic expansion joint with a long guide tube, or increase the number of layers on the structure; The vertical displacement is large, so make sure that the self-weight will not pull the ring belt and deform it. These details, the technicians of imported brands will confirm with you item by item, while some domestic manufacturers will only ask "what caliber". This is the gap, not in the price itself, but in the thing behind the price.
Installation and routine maintenance, imported parts should still abide by the rules
Don't think that if you pay a high price for imported non-metallic expansion joints, you can install them once and for all. It's not Transformers.
Before installation, check whether there are any bruised bands during transportation, and confirm that the parameters on the product nameplate are consistent with the design. Be careful when installing: the direction of the lining cylinder should follow the flow direction of the medium, and the direction of the arrow should not be reversed. The screw of the expansion joint (that is, the transport protection rod) should be loosened after it is installed in place, but do not remove it, so that it can expand and contract freely. Many people forget this step. As a result, as soon as the system runs, the expansion joint is directly torn, and this pot manufacturer does not carry it.
For daily maintenance, the main thing is to check whether there are scratches, bulges and aging cracks on the surface of the ring belt. Especially in dusty working conditions, regularly sweep the surface ash to prevent local overheating. If you find signs of leaking in the rubber compensator, replace it early and don't delay. Non-metallic expansion joints belong to "disposable consumables". If you should change them during the maintenance period, don't feel bad about those few dollars.
Imported non-metallic expansion joints are expensive and expensive with logic. It is suitable for use in those domestic parts really can't handle the working conditions. If your project requirements are not high and domestic production is completely enough, then there is no need to spend more money. But if you want long-term stable operation and low total cost of the whole life cycle of the equipment, the extra money from imported parts should be regarded as buying insurance. Is that the case?