Developing “Design by Analysis” Methods for Glassy Polymers for Pressure Vessels

Commercial diving systems, medical hyperbaric systems, and submersibles were the driving applications for the development of using glassy polymers such as poly methyl methacrylate (PMMA), also known as acrylic, and polycarbonate (PC) materials for pressure vessels for human occupancy (PVHO).  PVHOs have heightened safety concerns beyond conventional pressure vessel hazards because a rapid decompression may not damage the pressure vessel but can kill the occupants.  PVHOs require windows in order to observe the occupants and assess their health or to allow the occupants to look outwards to operate equipment.  The current methods for designing acrylic structures are constrained to specific shapes, are empirically based, do not calculate stresses or deflections, and are essentially unchanged since the 1970s.  Conversely, the methods for designing pressure vessels using metallic or nonmetallic materials has advanced considerably, to include methods for design and in-service evaluations using modern methods such as Finite Element Analysis.   The current PVHO methods have been proven to be reliable but are constrained to the limited range of shapes and conditions tested over 45 years ago.  This limits the ability to innovate the use of PMMA and PC.  This has become more critical with the pending adoptions of acrylic material in conventional pressure vessel applications in Section VIII of the Boiler and Pressure Vessel Code.  While conventional pressure vessels have range of material definitions, the PVHO code has a minimum material properties that do not reflect the range of PMMA and PC that could be used.  Conventional  pressure vessel calculations incorporate material properties into their calculations, whereas the PVHO code uses empirical design tables.  New methods are needed to incorporate classic design principles into using glassy polymers into pressure vessel designs beyond the parameters of the ASME PVHO code.  Given the strength of the glassy polymers are more than an order of magnitude less than the metallic portions, the thickness of the polymer sections generally exceeds the thin wall “membrane” theory used in Section VIII, Divisions 1 and 2.  This creates multiple challenge in developing new methods which have the same safety and reliability of current methods. This poster summarizes the approach presented in “Developing ‘Design By Analysis’ methodology for PVHOs using V&V and Stochastic FEA” to be published in ASCE/ASME Journal of Risk and Uncertainty in Engineering Systems, Part B: Mechanical Engineering  in September, 2020 and presents how the risk and uncertainty of the new methodology is mitigated through Verification and Validation (V&V).   The design methodology has potential applications beyond pressure vessels including aerospace and architectural uses.