Selection of gasket coefficient

This is just one aspect to consider. When selecting gaskets, specific operating conditions such as the medium, pressure, and temperature must be taken into account; it’s not sufficient to focus only on the gasket itself

Thank you for your reply, but this is indeed a question from the certification exam. I would appreciate it if you could provide a more detailed answer. Thank you; with just your current response, I cannot gain any understanding or assistance.

If it is a single issue, it is better to choose a value of m (gasket coefficient) that is low; a lower value makes sealing easier, of course

Under the same conditions, the larger the m value, the greater the safety factor of the gasket； The smaller the y-value, the greater the safety factor.

The parameters that reflect the characteristics of the gasket are specific pressure y and gasket coefficient m, which are associated with the two sealing conditions respectively. 1. Gasket specific pressure. The gasket specific pressure is related to the pre-sealing conditions of forced sealing. The significance of pre-sealing conditions is that the sealing surfaces of the flanges are always uneven, with grooves present; these grooves can serve as pathways for leakage at the sealing surfaces. Therefore, under the force of the preload bolts, the surface of the gasket must be pressed into the uneven areas of the flange sealing surface in order to eliminate the aforementioned leakage paths. To this end, there must be sufficient compressive force on the effective sealing area of the unit gasket. The compressive force per unit area is referred to as the sealing specific pressure of the gasket, denoted by y (in MPa); different gaskets have different specific pressures. The harder the gasket material, the higher y is. 2. Gasket coefficient m: The gasket coefficient is related to the operating conditions of forced sealing. The significance of operating under sealing conditions is that the sealing surfaces, which have reached a pre-sealing condition through compression, experience a decrease in the compressive force between the gasket and these sealing surfaces due to the axial effect of internal pressure; this results in the formation of tiny gaps, through which the medium under internal pressure may leak out of the shell. To ensure its sealing, it is necessary to maintain a sufficient fluid resistance between the gasket and the sealing surface; since this fluid resistance is related to the compressive force applied to the gasket, it is essential to maintain a sufficient residual compressive force between them in order to ensure a high enough resistance. By definition: at the point just before leakage, the ratio of the remaining specific pressure on the gasket per unit area [i.e., the residual compressive force per unit area of the gasket] to the sealing pressure P is the gasket coefficient m. The gasket coefficient is obtained by dividing the gasket compression force at the critical leakage condition of the sealing test by the \"gasket area\" and the sealing pressure. In the original measurements, the gasket coefficient m takes the \"gasket area\" to be (2b)π*DG (that is, twice the effective sealing area of the gasket); therefore, the minimum compressive force required to maintain sealing of the gasket is (2b)π*DGmp. Y corresponds to the pre-tightening condition, while the m value corresponds to the operating condition. For two different gaskets that have the same shape and size and can both meet the sealing requirements, the gasket with a smaller m value results in a lower residual tightening force. The lower the tightening force, the smaller the torque generated under the same conditions, which enhances safety. Please point out any mistakes.

There are two conditions for a flange connection to be tight and leak-free: 1. During pre-tightening, the bolt force creates a specific pressure between the mating surfaces and the gasket that is not lower than value Y; 2. Under operating conditions, the bolt force is capable of resisting internal pressures, maintaining a specific pressure equal to m times the internal pressure on the surface of the gasket. So, the smaller the values of m and y, the better. A low y value makes pre-tensioning easier; a low m value results in lower bolt force during operation, thereby facilitating sealing

The M value and Y value are numbers that are used in design calculations; different gaskets have different values. For gaskets of the same type, the M values are similar to each other, and the smaller the Y value, the better! When selecting gaskets, this is also a factor to consider, but it is not a necessary one.

In fact, when the M value is large, the Y value is also large. At high pressures, gaskets with large M and Y values should be chosen

There is a question: during the initial measurement of the gasket coefficient m, the \"gasket area\" was taken as (2b)π*DG (that is, twice the effective sealing area of the gasket). Why is it necessary to use twice the effective sealing area of the gasket in the operating condition, while in the pre-tensioned state it is π*DG*b?

Realme, is there any more official explanation? I’ve gone through the design manual written by Li Shiyu as well as other books, but they all only state that \"during the initial calculations, the area of the gasket is taken as (2b)π*DG\" (that is, twice the effective sealing area of the gasket), which remains confusing.