Understanding the basic parameters of gaskets and their selection
Thread Content
This post was last edited by Final Fantasy on 2010-4-18 13:47 Flange gasket is a simple yet very professional issue. It’s simple because we see it every day, and there are people getting gaskets at the warehouse every day. ； It is said to be very professional because even if a professional engineer explains the basic parameters and some selection principles of the gasket, he may not be able to explain it clearly. The following is a brief introduction to "Understanding and Selection of Basic Gasket Parameters". The most basic parameters of the gasket are the gasket coefficient m value and the minimum design specific pressure y value. The minimum design specific pressure y value (the name of ASME as Minimum Design Seating Stress y) is also called the preload seal specific pressure in domestic textbooks. The m value is the ratio (dimensionless) of the working seal specific pressure (σg) and the medium working pressure (Pc) at critical leakage. Generally speaking, the difference between σg and y values is not very big (they are in the same order of magnitude unit). Based on the y value of the gasket, we can confirm the approximate applicable working pressure range of the gasket. When calculating the flange, we directly use m * The product of Pc and the working area of the gasket is used to calculate the required bolt force. The larger the m value of the gasket, the corresponding flange bolt diameter must be thicker or larger. The minimum design specific pressure y value reflects the bolt force required by the flange in the pretightened state. The smaller the m value of the gasket, the smaller the flange bolt diameter required or the fewer bolts required. The preceding comparison must be based on the same type of gasket specifications and dimensions. The y value and m value of the gasket can be obtained through corresponding standard tests to obtain specific data. Let’s now look back at the issue of gasket substitution. Let’s first look at the basic parameters of several sets of gaskets.: Ø Metal pad: m=3.75, y=62.1MPa; Ø Metal wound pad: m=3.0, y=69.0MPa; Ø Metal toothed pad: m=4.25, y=69.6MPa; Ø Corrugated tooth composite pad: m=3.0, y=50.0MPa; From the above data (the base metal is 304SS), it can be seen that under the same working pressure, the corrugated tooth composite gasket requires the minimum bolt load to ensure sealing! This is why the corrugated tooth composite gasket can replace the above three gaskets. There is no need to calculate the strength of the flange again, that is to say, it can be directly replaced. Wound gaskets can generally be replaced by metal-wrapped gaskets. However, when metal toothed gaskets are used instead of spiral gaskets, it is generally necessary to calculate the strength of the flange. This is because the pretightening force or working load of the bolts may not meet the sealing requirements, and sometimes the stiffness of the flange cannot meet the requirements of use. For more knowledge, you can consult relevant textbooks on chemical engineering. It is recommended that everyone use "Petrochemical Pressure Vessel Design" compiled by Professor Zhao Zhengxiu of the University of Petroleum. Corrugated tooth composite pads already have special * * Standard, see GB/T 19066-2003, new * * The standard is being revised. This post was last edited by Wu Qianli on 2008-5-18 17:14 ]
Corrugated tooth composite pad is* * A display of human intelligence. I wonder if there is international patent protection? If anyone knows about patent protection, please reply.
The gaskets of our heat exchange equipment here all use corrugated tooth composite pads. This standard is difficult to find. You need to enter GB/T 19066.1 (or2, 3) 2003 to search. http://bbs.hcbbs.com/viewthread.php?tid=157268
Corrugated gaskets are indeed effective, but they are more expensive. We only use it on high-temperature equipment pipelines, and we still use Barkin pads and winding pads in other parts.
The price of the gasket is compared with the loss caused by a leak of the device. The following data is for your reference.: The price of a corrugated gasket of 1500lb DN450 is about 800RMB, and the price of a spiral wound gasket is about 600RMB. The cost of sealing a leak under pressure is at least 60,000RMB. Pressure plugging is basically 10 times the input price. The price ratio of plugging and gasket input for small pipelines is even higher, the ratio is about 30,000 RMB to 30 RMB, which is more than 1,000 times. Generally speaking, gaskets are wearing and consumable parts. The price of gaskets should not be considered in relation to the smooth operation of the device, shutdown for repairs, etc. This is also the reason why gaskets are generally not allowed to be reused during device overhaul (except for metal gaskets and toothed gaskets).
The sealing effect of the corrugated gasket is better, but I personally think it has disadvantages compared to the wound gasket. If a leak occurs when used on gas media, the graphite on the surface of the corrugated gasket will be easily washed away, and the tightening will not work, but the wound gasket can be tightened.
The author may not understand the sealing principle of the corrugated gasket, or the corrugated gasket selected is not a product of a regular manufacturer. The resilience performance of the corrugated tooth pad and the expanded graphite between the tooth grooves are the key to sealing technology. You can view the dedicated technical introduction. The tooth top must be strictly located at the upper part of the arc, and the filling amount of graphite must be strictly calculated. General manufacturing companies just imitate without understanding the core technology and related technology accumulation. The performance of the product may be very different!
The basic parameters of the gasket are only represented by y and m, which cannot fully reflect the sealing performance of the material. Internationally, research in this area has been carried out, and the concept of sealing tightness has been introduced. The American Pressure Vessel Council, PVRC, and the Alliance have proposed new gasket coefficients for selection to ensure sealing, but the technology is not yet fully mature, but eliminating old gaskets is the trend of technological development.
study* , it turned out that I didn’t really understand the gasket, and thought it didn’t have much effect. It turns out that the theory is quite deep.
Thank you to the original poster. I hope you can send more detailed information. Gaskets are very important for the installation.
I would like to ask the original poster. It seems that this gasket standard can only be used on pipe flanges. What should I do with equipment flanges?