Which part do you think is most prone to problems with an expansion joint costing tens of thousands or even hundreds of thousands? A lot of people would say bellows, or flanges. Actually, the biggest headache is often an obscure little thing-the expansion joint metal spacer. The cost is only a few cents to a few dollars, but once the wrong choice or installation is wrong, leakage, shutdown and equipment scrapping will all come. Two days ago, I met the maintenance supervisor of a chemical plant, and complained to me that one of their high-temperature axial expansion joints began to leak after less than half a year, and the gasket was changed three times, but it was not solved. As a result, when I removed it, I saw that the gasket material was not high-temperature resistant at all, and the flange surface was scratched. Alas, this is typically a small loss.
First, what exactly is the expansion joint metal gasket? What is the relationship between it and bellows and flanges?
Simply put, the expansion joint metal gasket is a seal sandwiched between the flange connecting surfaces. Expansion energy saving absorbs the thermal displacement and vibration of the pipeline, relying on bellows-such as this station'sUniversal corrugated expansion jointOrHigh temperature axial expansion joint, they have a bellows structure inside. But no matter how powerful the bellows is, it has to be connected to the pipe through a flange, right? If there is a gap between the flanges, the medium will leak. Metal spacers are what fill in these microscopic gaps.
Metal gaskets are not the same as regular rubber gaskets. Rubber gaskets have low temperature resistance and are easy to age, while metal gaskets (such as stainless steel wound pads, metal toothed pads and metal coated pads) can withstand high temperature and pressure. Its relationship with bellows is "each performs its own duty": the bellows is responsible for compensating for displacement, and the gasket is responsible for sealing the interface. The flange is the connecting carrier. All three are indispensable, but gaskets are often the least valued link.
Second, the cost of choosing the wrong gasket: from leakage to equipment scrapping, real cases tell you why you can't make do
Tell me the truth. Last year, a power plant was overhauled and replacedCorrugated expansion joint for power station industryWhen, in order to save a few dollars, ordinary asbestos rubber gaskets were used. The pipeline medium is high-temperature steam with a temperature of 420℃ and a pressure of 4.0MPa. Less than 48 hours after turning on, the gasket was flushed open, steam leaked, and the whole production line was stopped emergency. Maintenance cost plus shutdown loss, 300,000 wasted. And the purchase price of that qualified metal wound gasket is only 8 yuan.
There are more serious ones. Another chemical plant deals with corrosive media (containing chloride ions) and uses 304 stainless steel gaskets. If the material is wrong, it will soon be pitted and perforated, and the medium will leak into the environment, which will not only result in environmental fines, but also almost lead to safety accidents. Then they switched toPTFE-lined hoseThe matching polytetrafluoroethylene coated gasket can completely solve the problem.
So don't underestimate the difference of a few cents. If the wrong gasket is selected, the leakage may be slight, the bellows will be cracked, the flange will be deformed, and the whole expansion joint will be scrapped. Are you willing to gamble to save a few bucks?
3. Key points of metal gasket selection under different working conditions: temperature, pressure and medium are indispensable
- TemperatureWhen it exceeds 400℃, the filler of ordinary graphite winding pad will oxidize and fail, so it must be filled with pure metal gasket or ceramic fiber. This site'sHigh temperature axial expansion jointThe matching is the high-temperature-resistant alloy winding pad.
- pressure: Metal toothed pad or octagonal pad is recommended for high-pressure working conditions (such as above 10MPa), and sealing is achieved by tooth surface embedding. Just use metal covering pads for low-pressure applications, which is cost-effective.
- Medium: Corrosive media (acid, alkali, chloride ion) must be made of corrosion-resistant materials. Such asPTFE-lined hoseThe gasket is made of PTFE; The oxidizing medium cannot be filled with graphite, and polytetrafluoroethylene must be used.
Also don't forget the flange face form. Protruding flanges are suitable for winding pads, and concave and convex flanges are suitable for metal ring pads. If there are scratches on the flange surface, no matter how good the gasket is, it will be useless. So it is common sense to check the flange face before installation, but many people ignore it.
Fourth, the three most common mistakes when installing metal gaskets, how many have you been recruited?
Uneven bolt tightening torque. Some people are used to tightening a bolt first and then the opposite one. As a result, the gasket is unevenly stressed and the seal fails. The correct way is to pre-tighten diagonally, gradually apply torque in 2-3 times, and finally beat it to a uniform value with a torque wrench. Do you usually just tighten the wrench casually?
Reuse old spacers. Once the metal gasket is compacted, the surface has been permanently deformed, and it will basically leak when used again. Don't feel bad about that little money, you must replace new gaskets every time you disassemble and assemble. Especiallydirectly buried expansion jointThis kind of buried equipment, if it leaks and then digs out, the cost is enough to buy a thousand gaskets.
Ignore the installation direction of the gasket. For example, the inner ring and outer ring of the metal winding pad have a specific orientation, which will lead to lax seal if installed backwards. There are also spacers with locating bosses that must be aligned with flange grooves. Read the product manual carefully before installation, don't install blindly by experience.
5. How to judge whether the metal gasket should be replaced in routine maintenance? Don't wait until you leak to remember
Many equipment managers are "don't worry about anything". But waiting until the leak is replaced is often passive. Pay attention to these tricks during daily inspection:
- Visual inspection: There are rust, salt out and oil stains at the flange connection, indicating that there has been a trace leak and the gasket is beginning to age.
- listening to sound: If there is a hissing sound in high-temperature and high-pressure pipelines, don't think it is normal noise, which is probably a sign of gasket erosion.
- Torque measurement: Regularly check the flange bolts with a torque wrench. If the torque drops significantly, it means that the gasket creeps and the sealing force is insufficient.
- When the equipment is shut down for maintenance: Open the flange to check the surface of the gasket. If there are cracks, crushing, scratches and corrosion pits, change them directly. Don't hesitate.
Although the expansion joint metal gasket is small, it directly determines the sealing life of the whole system. Products on this site-fromMetal rectangular expansion jointToCompound hinge transverse expansion joint, each with a corresponding metal spacer recommendation. Don't just stare at the bellows during installation. Spend an extra two minutes checking the gaskets, and you can save a lot of maintenance costs.