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In the first two episodes, we analyzed how to select gaskets by looking at aspects related to gaskets, flanges, and fasteners. Today’s episode serves as a supplement and summary of the content from the previous two episodes. 1. Gaskets – Flanges – Fasteners: To ensure that bolted flange joints perform satisfactorily, all components must be suitable for the design conditions (chemical compatibility, temperature, pressure, etc.). These identical components must be highly suitable as an assembly to maintain sealing. More specifically, the fasteners (size, quantity, material, etc.) must be capable of applying sufficient load to the gasket under the designed operating conditions to achieve the desired sealability. The washer must be able to operate under the designed operating conditions and provide sealing under the given available bolt load. The flange ratings must correspond to the design operating conditions, and it must have sufficient stiffness to ensure that the load on the gasket remains at the expected level. II. Stress characterization: The minimum gasket seat stress (ASME = Sgmin – S, EN = Qmin) essentially corresponds to the absolute minimum stress required by the flange; this is under the assumption that the internal pressure is very low or non-existent. Most washer manufacturers can provide these values for washer materials. Typically, these values are determined by conducting low-pressure leak tests on each gasket material; this minimum stress value is usually used solely for flange design calculations. The minimum working stress of the gasket (Sgmin-O) generally depends on the design pressure of the component. It will be higher than the valve seat stress or Sya value of the gasket. Most gasket suppliers can provide the minimum working stress while taking pressure into account. It is not uncommon for these values to increase as the gasket thickness increases. The minimum operating stress is always lower than the minimum seat stress, but manufacturers recommend that the installation stress be higher than both of these values. The maximum gasket stress (Sgmax) is the stress level that can damage the integrity of the gasket and negatively affect its ability to maintain a seal. Many gasket manufacturers will conduct laboratory tests to determine the maximum stress on the gasket. When considering the maximum stress or compressive strength of a material, many variables come into play, including surface finish, gasket width, thickness, material type, and temperature. Most manufacturers will use smooth surfaces as well as standard ASME/EN serrated flange surfaces for testing. Thicker gaskets generally are less resistant to over-compression and crushing. Furthermore, serrated flanges tend to handle higher compressive loads, as the rough surface provides better grip or retention of the gasket. The smooth surface allows the gasket to slide laterally and to crack under lower stresses. The Target Gasket Stress (SgT) is the load that permits the gasket and the entire joint to operate with optimal performance and sealing. Furthermore, the installation stress generates a pre-tightening force in the joint to compensate for the relaxation of the entire bolted joint after installation and during operation over its service life (taking joint integrity into account). III. How to select the gasket installation stress: For equipment such as pumps, valves, drivers, and sight glass assemblies, it is necessary to consult the manufacturers of these components. Pipeline designers for standard installations or plant engineers typically determine the maximum bolt stress based on the bolt grade, operating temperature, and flange design stress. Once the maximum bolt installation stress is known, gasket suppliers can provide recommended gasket stresses. They need to know the operating conditions of the components in order to select the correct gasket stress. If the system will operate at very low pressures, the minimum allowable gasket working stress can be used. For example, components using pipe and flange materials with low compressive strength may require the use of as low a gasket stress as possible to achieve sealing while avoiding damage to the flanges. Flanges operating at higher pressures and temperatures will experience stresses above the minimum working stress. The simplest way to select the target gasket stress for installation is to calculate the available compressive stress at the maximum bolt stress. This maximum bolt stress is usually determined by plant engineers; in some plants, it may range from 40% of the bolt’s yield strength to over 75%. As long as the allowable gasket stress under the maximum bolt stress is lower than the maximum gasket stress (or the compressive strength of the gasket), and higher than the minimum recommended gasket stress under operating conditions (which can be used as a target stress), this concludes the discussion on \"how to select sealing gaskets\". See you next time!