Hydrostatic test chambers are a significant part of test and simulation efforts in the Ocean Simulation Laboratories (OSL). These test chambers are designed to safely and reliably contain extreme pressures that simulate ocean and oilfield conditions. With a lifespan of decades, they require significant engineering efforts for not only initial design, but also for long term maintenance and monitoring. With mankind continually reaching deeper depths in both the ocean and in the oilfield, it is necessary to expand the OSL capabilities to perform condition simulation testing in higher pressures and larger form factors. To address this need, the Marine Structures & Engineering (MS&E) Section has teamed with the OSL to develop a new chamber design with a large bore and full ocean depth pressure rating. A key feature of this design is the development of a closure system that operates easily and quickly. Overall chamber design will focus on easy operation, safety, and long fatigue life. This chamber design will increase existing capabilities while reducing the load on aging test infrastructure.
The 30-inch chamber design will be performed in accordance with ASME Section VIII, Division 3 Code Requirements, SwRI internal operating procedures, and general engineering ‘best practices.’ Specific attention will be given to ease of chamber closure operation. Since 2010, SwRI has supplied various oil & gas industry clients with custom test chambers purpose-built to test individual products. Many of these customers focus on efficiency, especially concerning the ease and speed of an open/close cycle. SwRI will consider design aspects of these recent projects to develop a quick-acting closure system rated for higher pressure than previous designs.
The chamber will operate vertically, have a 30-inch minimum internal working diameter with an approximate 15-foot internal working length. The vessel will have a planned maximum allowable working pressure (MAWP) rating near 16,500 psig (considered full ocean depth) and the current design for the main body will use SA-508, Grade 4N Class 2 forgings.
The target service life of the pressure vessel will be 25+ years with a pressurization profile that includes many cycles to maximum pressure per year. Design considerations will be taken to increase fatigue cycles as much as possible to reduce associated maintenance and inspection costs across the life of the chamber.
The team has explored several closure options and has chosen a design dubbed the ‘rook’ (Figure 1) that allows for a minimal number of operator actions and only requires one piece to be lifted via crane for chamber access. Detailed design for major components is near completion. Specifically, shape optimization of the load bearing structures is complete. Fatigue life predictions for postulated critical crack locations are promising as shown in Figure 2 and were obtained using models in SwRI’s NASGRO® fracture mechanics software (www.nasgro.swri.org) as shown in Figure 3.