Attempting To Establish Design Margins for Glassy Polymers In Critical Structural Service

The existing code procedures for glassy polymers are in ASME Safety Standard for Pressure Vessels for Human Occupancy (PVHO-1). The current service spans hostile conditions in the North Sea to controlled medical environments. These procedures are based on an empirical method and do not use material properties. The system is locked into specific shapes and cannot be adjusted to account for yield strength, ultimate strength, and other material considerations. An ASME task group is developing a Design By Analysis (DBA) methodology in order to allow for optimization in current service and innovation in other service. This paper presents the attempt to develop design margins as part of an overall risk assessment process that considers material properties, service conditions, and other factors not currently incorporated in the existing design method. Historical work used to develop the current system are analyzed using modern methods to attempt to quantifiably determine the existing design margins. The challenge is the empirical method implicitly relies on polymer manufacturers to greatly exceed the code. This, coupled with different modes of failure, results in no direct manner to compare PVHOs to conventional ASME pressure vessels design margins.