External Pressure Vessel Research Articles

Strength optimization design of spherical hulls for deep-sea submersibles: A hydraulic autofrettage approach in external pressure vessels

The spherical pressure hull is the most important structure to ensure the safety of people in a deep-sea submersible. Its current main design trend is to increase the shell thickness to support greater depths and reduce overall stress. However, increased thickness greatly raises the submersible weight and the stress difference between the inner and outer surfaces. To achieve a balance between structural strength and weight, an autofrettage approach of strengthening the external pressure vessels has been studied. Firstly, an analytical solution of the autofrettage pressure of the spherical external pressure hull is derived based on elastic-plastic mechanics. Secondly, a finite element model is established to validate the analytical solutions and investigate the autofrettage process. Both theoretical and numerical results reveal that the overall stress in the spherical hull has been decreased significantly, and the stress distribution between the inner and outer surfaces becomes more even through the autofrettage approach. Additionally, a method has been developed to determine the optimum autofrettage pressure of the spherical hull for deep-sea manned submersibles which is found to be dependent on working pressure and shell size. This study could contribute to the strength optimization design of spherical hulls for deep-sea manned submersibles without increasing weight.

Review of Remaining Life Assessment of External Pressure Vessel in Creep Range

Review of Remaining Life Assessment of External Pressure Vessel in Creep Range

The Method of Tangent Modulus Factor for the Design of External Pressure Vessels

To solve the problems such as too much trial-and-error, limited material being involved in the graphs and calculation results being obviously influenced by artificial factors and errors of the graphs in the design of external pressure vessel according to current standard ASME Ⅷ-1, GB150 and EN13445, the mathematic expression of the graphic charts is examined, and a set of analytical equations and algorithms for the linear and nonlinear instability of external pressure vessel are established. The equation was applied to calculate the ultimate buckling pressure of cylinder and spherical shells. The algorithm here provided can not only avoid the shortages of current graphic analysis methods, but also be convenient for technicians to calculate, which could enrich and consummate the graphic charts in the current standards and be useful to the design of external pressure vessels to be made of new materials.

Experimental Study of Integrated Multilayer Clamping High Pressure Vessel

The hydrostatic test of integrated multilayer clamping high pressure vessel is performed from 15.7 MPa to 56.52 MPa (1.8 times of the design pressure). The measured stress values have deviation from the Lamè equation (maximum error 34%). The inner wall stress is low while the outer wall stress is high. The layered vessel mechanics model is deduced to analyze the deviation. The inner shell is an external pressure vessel and the outer shell is the internal pressure vessel. The contact of the inner shell and the outer shell generates preload stress. The multilayer structure parameter is a universal nondimensional parameter to calculate the preload stress of layered vessel, and the corrected theory values have smaller error in high pressure (less than 10%). The super hydrostatic test alters the preload stress distribution and the gaps between layers.

Stability Analysis of a Processor Unit Served in Deep-Sea

Stability is the key of designing thin-walled external-pressure Vessels. Nonlinear buckling analysis using finite element method has been carried out on a processor unit of an autonomous underwater vehicle to study the stability of the processor unit considering the screw tightening. Effects of the cylinder thickness on the critical pressure are discussed. Results show that the buckling wave number is 4 in the circumferential direction, and the critical pressure decreases with decreasing the cylinder thickness exponentially, which is in good agreement with the theoretical calculation.

Preliminary Designing Method of External Pressure Vessels for Sea Subsurface Applications

Preliminary Designing Method of External Pressure Vessels for Sea Subsurface ApplicationsThis paper describes a unique engineering method intended for the preliminary designing of marine echo-location systems. The solved designing problem consists in determining geometrical parameters and selecting structural materials for a vessel of a buoyancy necessary to contain measuring instruments of a given mass, as well as its maximum gabarites and operational submersion depth. The assumed variability range of the system's parameters determines a space of permissible applicability parameters of the method. Stress level related to permissible and critical stresses was assumed to be safety criterion for the vessel. The method may be applied also to solving converse problems consisting in determining maximum permissible submersion depth for a vessel made of assumed structural materials and having given geometrical parameters. The presented description of the method is illustrated by an example of its application.

Acoustic Microscopy Applied to Ceramic Pressure Vessels and Associated Components

Alumina ceramic is being used extensively for external pressure vessels in naval applications. The material is also used in valves and other components, where reliability, immunity from corrosion, and high temperatures are required. This report presents a technique for the nondestructive evaluation of alumina ceramic components. The cracks were produced by CO2 laser radiation. Since there is a need for the detection of very fine cracks, scanning acoustic microscopy was found to be superior to optical methods for imaging surface and subsurface cracks. We address the issue of crack initiation with the use of postirradiation analysis. This article reports our results on the evaluation of the surface and interior cracks with optical, scanning laser, scanning electron, and scanning acoustic microscopy. We present images of surface and subsurface microcracks generated at different power levels of a high power CO2 laser system. The spatial variation of the Rayleigh wave velocity is measured by the V(z) curve technique. These preliminary data suggest that, with some improvement, the V(z) technique may detect residual stress with high spatial resolution.

Proposed External Pressure Design Rules for Pressure Vessels for Human Occupancy

The safety of externally pressurized manned diving bells, submersibles and underwater work systems resides in the ability of the system to rise to the surface in case of an emergency. Use of the ASME Boiler and Pressure Vessel Code Section VIII design rules, lead to unacceptably heavy structures, and thus substantially compromise the sought-for safety in underwater manned systems. A recognition on the part of the diving industry of the inherent limitations in using the ASME Boiler and Pressure Vessel Code for design of underwater pressure vessels, motivated the formation of the ASME Safety Code Committee on Pressure Vessels for Human Occupancy (PVHO) in 1974. A subcommittee of the PVHO Safety Code Committee was formed to address the specific problems of external pressure vessel design. The mathematical development which provided the basis for the proposed rules are presented. The restrictions imposed by the External Pressure Subcommittee are also presented.