A rapid increase in the utilization of polymer and FRP materials over conventional metallic materials in the production of pressure vessel and piping components has become a global trend. However, factually, the design standards of ASME and its European counterpart for non-metallic materials are not material specific and as a whole vaguely follow the standards of metallic materials. Contrary to metallic PVP components, polymer components are of recent ages and this limits the statistical data available on the materials. Among polymer PVP components, polyvinylchloride (PVC) and high-density polyethylene (HDPE) constitute the majority. The inherent excellent corrosion resistance, lightweight and ease of manufacturing make these two polymer materials the ideal replacement over corrosive and heavy metallic structures. The objective of this research is to characterize the long-term creep and thermal ratcheting of soft materials.
The research revolves around the analysis of thermal ratcheting behavior of the selected PVP polymer materials including PTFE and fiber based gasket materials. The core intent of this thesis is to characterize polymer materials used in bolted flange connections. For the investigation of thermal ratcheting performance of the selected materials, meticulous experimentations were carried out using test rigs equipped with high accuracy sensors. As the operating temperature range of selected flange materials are much different from the considered gaskets, the thermal ratcheting evaluation of flanges and gaskets were performed, separately. All the selected materials were subjected to different compressive loads, various ratcheting temperature and few pre-exposure creep to evaluate the thermal ratcheting phenomenon. The characterization tests of polymers were performed with ring shaped samples. Furthermore, full-scale tests of NPS 3 Class 150 PVC and HDPE flanges were conducted to evaluate the short-term relaxation and the results are compared to the finite element counterpart.
The results provided significant insight on the vulnerability of polymer and soft materials to thermal ratcheting phenomenon. The study on the behavior of selected materials to thermal cycling highlighted the intensification of creep damage on the materials, the magnitude of which varied depending on each material. In addition, thermal ratcheting alters other fundamental properties of flange and gasket materials such as creep modulus and coefficient of thermal expansion
