The proposed concept relates to the flange design of removable coupling connections of H2 pipes. Such a connection typically requires a very low leak rate, which is of high importance for H2 applications due to safety and operational reasons. In order to maintain the leak rate requirements, a seal or multiple seals are needed and they must provide good performance, reliability and are fail-safe. In this concept, flange designs and sealing arrangements are proposed to address these challenges. In the H2 distribution system, a doubled walled pipe is typically used in which liquid hydrogen (LH2) or gaseous hydrogen (GH2) is transported in the inner pipe and the outer pipe is maintained in a vacuum condition for leak containment and heat insulation, see Figure 1. At the coupling connection, a single flange can be used with an inner seal and an outer seal as also illustrated in Figure 1. The flanges from the opposing pipe sections are typically kept together by a V-clamp or a bofted flange as shown in Figure 2. The performance of the seals in the flange depends on many factors such as the pressure differential, the temperature, the seal seating load and the seal surface roughness. In order to minimize the leakage rate, it is common to have more than one seal in the flange, which reduces the pressure differential across the seals and therefore, reduces the leak rate. However, each seal requires a certain seating load and there is a limitation on how much total seating load can be applied on the flange due to installation reasons. Furthermore, in case the V-clamp or the bolted flange fails, there may be a sudden reduction of seating load on all seals leading to a strong performance deterioration.
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