If There Is a Leak In the Gasket, You Can Start By Checking With the Torque Wrench First
There are three types of gasket leakage, and the first case is the most common one.
Interface leakage - The medium escapes from the contact interface between the gasket and the flange, accounting for 80% to 90% of the total leakage. This is the most common form of leakage, usually due to insufficient pre tightening force, rough flange surface, or insufficient gasket rebound ability.
Penetration leakage - The medium passes through the micro pores of the gasket material itself, accounting for 10% to 20% of the total leakage. This requires the gasket material itself to be sufficiently dense, especially when facing small molecule media.
Blowing out leaks - this is the most dangerous situation and often occurs in accident scenarios. When the pressure borne by the sealing system exceeds the bearing limit of the gasket, the gasket may be blown out of the sealing surface as a whole, causing a large amount of medium to leak instantly.
Why is the installation phase the biggest variable?
Taking the commonly used DN200 flange in refrigeration compressors as an example: the process requires a bolt torque of 270NM, which is not arbitrarily set, but is accurately calculated based on the sealing load of the gaskets, bolt specifications, and flange size. If 270NM is considered as the "passing line", in actual installation, if a torque wrench is not used and only tightened by the worker's hand, the torque deviation may reach 30% or even higher.
The direct consequence of insufficient torque is that the compression stress on the gasket does not reach the minimum value required for sealing. Especially in high demand scenarios such as compressors that require a leakage rate of 10 ⁻⁵ (with an annual leakage of no more than 2 grams of refrigerant), a torque difference of several tens of Newton meters may be the world's difference between "qualified" and "alarm".
If it is found that the gasket leaks and does not meet the requirements, there are usually three ways to go.
Firstly, ensure the torque is in place. The most direct solution is to lubricate the bolts to reduce friction loss and install them according to the standard value with a torque wrench.
Secondly, optimize the gasket design. By reducing the force area of the gasket without changing the installation torque, the compressive stress per unit area can be increased, resulting in better sealing effect with the same bolt force.
Thirdly, choose low load sealing materials. The required sealing load varies greatly among different grades of gasket materials. Similarly, for a refrigerant medium with a sealing capacity of 2.0MPa, a certain material may require a sealing load of 75MPa, while another material may only require 25MPa - selecting the right material can easily meet the standard under existing installation conditions.
Sealing is one kind of system engineering. The gasket quality is the foundation. Installation torque is the key, and selection and matching are wise. Next time your compressor leaks, you can start by checking with a torque wrench.
