How long does induced draft fan non-metallic expansion energy saving last? 5 Key Factors That Affect Lifespan
The design life of non-metallic expansion joints of induced draft fans is usually 8-10 years, but how long it can actually be used depends on the working conditions. Two days ago, I met a power plant customer. The rectangular non-metallic expansion joint exported by their induced draft fan leaked after 6 years, while another similar unit was fine after 12 years. What's the difference? Temperature, medium corrosivity, installation stress and selection matching degree determine the upper limit of life. Let's talk about this thoroughly today.
First Pit: Temperature Over Limit
The skin material of non-metallic expansion joint (also called fabric fiber expansion joint) has a limited temperature resistance range-silicone cloth can withstand 200℃, fluororubber cloth can withstand 250℃, and ceramic fiber cloth can withstand 1000℃, but it has to be matched with heat insulation layer. The inlet temperature of induced draft fan is generally 100-150℃, and the outlet may be heated by flue gas to above 180℃. If you choose a bargain (regular rubber cloth), it will age and embrittle 2-3 times faster. According to JB/T 12235-2015 standard, the working temperature must be lower than the continuous use temperature of materials by more than 15%, which is ignored by many projects. Think about it, every time the temperature exceeds 10℃, the skin life may be directly cut in half. In actual selection, I suggest redundancy according to "working temperature +30℃"-for example, the outlet is up to 180℃, and at least fluororubber cloth or composite ceramic fiber layer with resistance to 250℃ is selected.
Second Pit: Media Corrosion
The desulfurization flue gas contains SO₂, HCl, HF, high humidity and fly ash. Ordinary non-metallic expansion joints are coated with glass fiber cloth + silicone rubber, and delamination begins in the second half of the year in acidic environment. Our experience is that the upstream and downstream of the desulfurization flue gas baffle door should use PTFE compensator or PTFE hose-lined corrosion-resistant scheme, and at least the inner layer of the skin should be added with PTFE film. Every pH unit increase in the corrosion rate may shorten life by 40%. Alas, in order to save hundreds of dollars, many factories leaked in half a year, and they lost tens of thousands once they shut down the furnace, which was not worth it.
Pit 3: Mechanical damage and installation issues
The induced draft fan vibrates greatly, especially in the start-up and shutdown stages, and the displacement of the pipeline may exceed the design value. If the rectangular non-metallic expansion joint is not properly installed, the airflow directly washes the skin, and it can be worn out in a few weeks. There is also improper adjustment of the tie rod nut-the role of the expansion joint tie rod is to restrain the pressure thrust but allow displacement. If it is adjusted too tightly, it will tear the skin, and if it is too loose, it will lead to over-stretching. The standard installation process is: first pre-stretch 50% of the displacement, and then lock the nut. And guess what? I have seen a scene where the installer screwed the tie rod to death directly, and the skin collapsed as soon as the unit started. Therefore, the adjustment of the guide tube and the pull rod must be according to the instructions, and don't rely on the feel.
The fourth pit: insufficient matching degree of type selection
Many people only stare at the price, not the actual working conditions. For example, the outlet of the induced draft fan needs to compensate for large displacement, so the general corrugated expansion joint is selected, and the stiffness is wrong, resulting in the stress concentration of the pipeline. Or the number of layers of non-metallic expansion joints is not enough-at least 3 layers are required in normal working conditions (the outer layer is weather-resistant, the middle is insulated, and the inner layer is corrosion-resistant), and some cheap products only give 2 layers, which will blister in a few months. According to JB/T 12235-2015, the fatigue life is not less than 1000 cycles, but cheap products may not last even 500 cycles. Calculate an account: the labor + shutdown loss of replacing an expansion joint may exceed 10 times the price of the product itself-spending 3,000 yuan to buy an inferior part will not save enough money to make up the electricity bill for an air leak.
Pit 5: Inadequate maintenance
Non-metallic expansion joints are not as solid as metal pieces, and they need to be checked regularly. Once the skin surface is blistered, hardened and delaminated, it should be changed. Don't wait for leakage before stopping the furnace. We have a customer who measures the skin thickness once a year when shutting down for maintenance, and gives an early warning when grinding from 8mm to 5mm, so that non-metallic expansion and energy saving can last for 10 years. In addition, pay attention to check whether the deflector is loose and the tie rod nut is corroded-these details directly affect the life.
How to extend life? Two practical suggestions
First, redundant design according to actual working conditions during model selection-for example, the working temperature is 180℃, and materials resistant to 250℃ are selected; If the medium is corroded, add PTFE film to the inner layer or directly put on PTFE compensator. Second, establish a regular inspection system, and take a look at the skin condition every time the machine is shut down. Don't wait until the flue leak is alerted to deal with it, by then the damage has been done.
Don't just look at the price. In the final analysis, the service life of non-metal expansion joint of induced draft fan is determined by the selection, installation and maintenance. It is better to choose the right one time and use it for ten years instead of changing it once half a year. If you have any questions, welcome to chat. We have a complete set of schemes such as rectangular non-metallic expansion joints, desulfurization flue gas baffle doors, PTFE-lined hoses, etc. to help you settle this account.