Piping & Tank Applications

Not all of the work performed by Metis Design involves plastic and composite design. Our engineers have worked on projects in several industrial fields, including various tank and pipe analyses. One of the earlier projects that MDC consulted on was the structural analysis of a large horizontal fluid tank for Russell Engineering. Although the product had functioned well for a number of years, they wanted to quantify the structural integrity of the tank. From blueprints provided by Russell, Metis Design created a Finite Element Analysis (FEA) model to determine the stress in various locations on the tank. As a result, suggestions were made for adding supports to eliminate any stress-related problems. These supports could either be retrofit into existing tanks or integrated into new designs. The work performed by MDC ensured that the tanks were operating under safe conditions as well as reducing future maintenance requirements.

Soon after, Russell again relied on MDC, this time to perform the structural analysis for a new product they were developing. In this case, the tank was a complex shape and sat at an angle rather than horizontally. The problem was how to quantify the volume of the liquid in the tank based on the reading from a single pressure transducer at the end of the tank. MDC developed a mathematic model of the tank to provide a closed form solution. This allowed them to publish charts correlating the pressure and the type of liquid to the volume left in the tank.

There can be several factors involved in the failure of a cryogenic pipe, including internal pressure, thermal loading, displacement of the support structure due to thermal changes, and dynamic fatigue. Metis Design was employed to ascertain which of these factors caused the failure of a particular pipe, and to determine how to prevent a reoccurrence. In this case, MDC utilized both static and dynamic FEA to determine exactly what was causing the pipe to fail. Our work showed that there were two problems underlying the failure. First, the thermal load on the pipe was causing excessive stress at some of the piping joints. Second, the natural frequency of the pipe was close to the vibration frequency to which the overall structure was being exposed. This meant that the stresses on the pipe were being amplified by as much as a factor of four. By changing the geometry and structure of the pipe design, MDC was able to reduce the stresses and increase the natural frequency to avoid resonant amplification, eliminating the root causes of the pipe failure.

One of the more recent of Metis Design's projects involved modeling weld fatigue. Our client was experiencing failure consistently at one support on a larger structure. MDC was hired to analyze the stresses on the support and the dynamic loading on the structure. The welded region was governed by ASME's Pressure Vessel and Boiler code so the requirements of the code were used as the load conditions for the FEA model created by Metis Design. The design guidelines for the weld were based on S-N curves from the American Association of State Highway and Transportation Officials (AASHTO), which show the fatigue life in number of cycles for a particular stress level, given the weld geometry category. Because the load on the weld for this application was different than those used to create the S-N curves, the plots were adjusted using material and fatigue theory. These modified S-N curves were then used in conjunction with the stress results from the FE model to estimate the fatigue life of the design. Modifications to the design were suggested to reduce the static stresses in the weld and to increase the fatigue life for the assembly.

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