This case study details the determination of wall thickness for a Glass Reinforced Epoxy (GRE) tank.
Analysis
The process of defining the wall thickness was conducted in two steps. The initial step involved sizing according to the design rules specified by RTP-1 Subpart 3A “design by rules.” The subsequent step verified deviations from this code using a series of finite element analyses.
From a geometrical standpoint, the vessel was divided into three primary sections. For each of these sections and their applicable transitions, the relevant wall and laminate thicknesses were determined. The three parts included:
- The torispherical head
- The cylindrical part of the shell
- The conical head located at the bottom of the tank
Connected to these sections were four nozzles, one manhole, and the supporting ring. The highest load condition considered was the internal vacuum.
Results
The study concluded the following:
- The cylindrical shell thickness was sized for internal vacuum and required an additional stiffener to prevent buckling.
- The torispherical head was sized for internal pressure and did not require additional stiffeners.
- The conical head was sized for internal pressure and did not require additional stiffeners.
- The allowable loads for the small bore nozzles were reduced to achieve a more practical wall thickness.
- An alternative placement for the reinforcement pads of two closely spaced nozzles was proposed.
- Guidelines were provided for the thickness of the supporting structure and the size of the collar that supports the GRE by the steel.
“For GRE vessels, the buckling calculations impose the largest constraints on vessel sizing.”
