Research on Key Factors of Sealing Performance of Combined Sealing Ring

In this study, the mechanical properties of a combined seal ring under different loads were numerically calculated using ANSYS. The effect of the working pressure and pre-compression ratio of a rubber O-ring on the contact stress of the combined seal ring was studied. The influence of the wear ring’s chamfer, thickness, and width on the contact stress and contact force of the combined seal ring was analyzed. Studies have shown that it is particularly important to select a compression ratio that is suitable for the working conditions. Under the same conditions of working pressure and compression ratio, upon increasing the wear ring chamfer, the contact pressure is decreased due to the decreasing contact bandwidth between the wear ring and the cylinder wall. This has little effect on the contact stress of the combined seal ring as well as the contact force, while the width of the wear ring is proportional to the latter.

Dynamic failure analysis of static seals under pressure fluctuation in an ultrahigh-pressure water piston pump

For ultrahigh-pressure piston pumps, in the reciprocating action of the piston, the fretting between the static face seal and the mating surface occurs with the change of the pressure in the piston chamber. This phenomenon will seriously affect the service life of the seal ring and lead to the failure of the pump. However, the failure of static seals used to seal ultrahigh-pressures is usually studied from the directions of shear, stress, or rubber material. These studies cannot explain the failure phenomenon of the sealing ring found in our experiment. This paper analyzed the failure of the face seal ring in a piston pump with a maximum pressure of 120 MPa. A two-dimensional axisymmetric finite element model was established based on the Mooney-Rivlin constitutive relation of the rubber material, and the fretting conditions of the sealing ring were analyzed. Combined with the wear scars observed by the scanning electron microscope the face seal ring’s dynamic failure mechanism on the ultrahigh-pressure piston pump was determined. A better sealing scheme was proposed and verified by the duration test of the pump, which provided a basis for the design of the sealing of the ultrahigh-pressure fluid with high-frequency fluctuations.

Designing and Optimising Duplex/Superduplex Compact Flanges to Negate HISC in Subsea Applications

Hydrogen Induced Stress Cracking (HISC) is a phenomena related with metals, with potentially severe consequences when utilizing Duplex / Super Duplex stainless steels in subsea equipment exposed to Cathodic Protection (CP). In general, the three conditions need to be present: hydrogen source (CP), susceptible material (Duplex/Super Duplex stainless steel) and high stresses/strains. The third one can be related with loads, calculation promises and parts design in general (for example risers). The designing rules to minimize the risk of HISC failure are still in development and the latest state of art is presented in DNVGL-RP-F112 June 2018 edition. The Compact Flange (CF) is much lighter and more robust connection than standard ASME or API types as the CF design methodology is based on plastic capacity which is presented in the ISO-27509 code. However, ISO standardization covers only topside applications (with IX seal ring type), pressure class range up to CL2500 and simplified face angles methodology. The ISO-27509 flanges are not HISC proven. Therefore, to deal with HISC requirements and subsea conditions the SPO-S (Subsea) flange series with HX seal ring type was defined and type approved by DNVGL based on extensive FEA documentation, testing and field experience. The SPO-S range has, currently, only HISC compliant designs for the 5K, 7.5K, 10K and 15K flange ranges. For the projects where the Duplex / Super Duplex flanges are used subsea with CP, consideration for HISC still must be addressed. For such cases, the process is not straight forward and often many FEA rounds are needed depending on the engineer’s experience and project related restrictions. The process is time consuming and every decision reflects many aspects to finalize the design. Genetic Algorithms (GA) are a good optimization tools to use in such situations, because at the end, the engineer will only get few design propositions to choose from, and the process itself, is highly automated. In the following paper the results for HISC optimized CF flange connection will be presented and compared with standard ISO-27509 flange design. The GA optimization steps and designing process will also be presented in the same example. Commercial FEA code ANSYS will be used for calculations based on parametrical model and GA implemented by APDL scripting. The following optimization method is already in use for HISC related projects.

3D-gedrucktes Siliciumcarbid als Gleitringwerkstoff

Reaction bonded silicon carbide is well known for use as axial seal faces. The properties have been optimized in order to improve the performance of dynamic seals. 3D-printed silicon carbide will be introduced. The new material allows forming much more complicated shapes and seal ring designs. The new material shows a different structure compared to compression molded reaction bonded silicon carbide due to the special manufacturing process. Therefore, first comparative tests of seal-rings under marginal lubricated conditions have been performed. The results are presented and the possible use of 3D-printed silicon carbide in the sealing technology is discussed. A first fundamental design study implies the potential of producing seal rings with an additional functionality. A simplified model of a seal ring with internal structures is shown and some ideas will be shared whether additional benefit could be achieved.