Acrylic plastic as structural material for underwater vehicles

Underwater manned vehicles and remotely operated unmanned vehicles require for their construction materials that do not corrode in the marine environment, and do not contribute significantly to the weight of the structures. One of such materials is acrylic (polymethyl methacrylate) that, in addition to the above attributes is also transparent. It allows the occupants of the submersible or underwater observatories to observe and study hydrospace, in the same manner as it allows the visitors to the aquaria to study the denizens of the sea in safety and comfort enveloped by acrylic barriers. Historically, the primary application of acrylic was in the construction of viewports in opaque pressure hulls of submersibles, ROV's and hyperbaric chambers. However, its application does not end with viewports. Whole pressure hulls of acrylic for submersibles, underwater observatories, ROV's and hyperbaric chambers have been fabricated and successfully operated. Today acrylic submersibles operate to depths of 1000 meters (10 MPa). Depths of up to 2438 meters (24.5 MPa) can be achieved economically by acrylic submersibles with proper hull design, and there is no depth limit for designs of viewports with acrylic windows. Acrylic has been found, also, to be an ideal structural material for construction of transparent walls and tunnels in land-based aquaria and shore-based underwater walkways, hotels, and laboratories where the occupants can, in comfort, observe sea life beyond the acrylic walls of the structure. Acrylic has also successfully replaced metals as construction materials for medical hyperbaric chambers utilized for pressurization of patients with oxygen. The acrylic enclosures prevent attacks of claustrophobia in patients and allow unobstructed observation of the patients by the doctor while undergoing oxygen pressurization treatments. This paper summarizes the proven approaches to the design of acrylic viewports and acrylic pressure vessels utilizing the empirical procedures of ASME PVHO-1 Safety Standard for Pressure Vessels for Human Occupancy (hereafter referred to as the Standard). It also presents for the first time the recommended analytical procedures for design of acrylic structural components and whole acrylic structures outside the scope of the standard which currently is limited to components of enclosed pressure vessels for human occupancy under differential pressure loading