Hydrostatic and Cyclic Pressure Testing of Small-Scale Composite Pipes and Vessels

Abstract

In this study, overlapped biaxial and seamless twill carbon fiber pipes and vessels were manufactured. Steel pressure vessels were repaired with flexible twill and biaxial fabric. The pipes and vessels were subjected to hydrostatic pressure, internal cyclic pressure, postfatigue functional failure (FF) and burst pressure. Overlapped tubes with composite and metallic end caps experience premature FF at less than 50% of the theoretical pressure due to delamination. However, seamless tubes almost reached the theoretical pressure. Fatigue tests were applied to the tubes at stress levels of 45% and 75% FF pressure up to 9,000 cycles. Thin seamless tubes sustained the cyclic hydrostatic pressure at 45% of FF up to 9,000 cycles, while at 75% of FF some slight damage occurred. The overlapped tubes showed little damage at 45% FF after 9,000 cycles, but severe damage at 75% FF with an explosion. The fatigued seamless and overlapped composite tubes showed a maximum of 30% and 50% reduction of FF pressures. The reorientation of the flexible fiber tows in seamless vessels is the primary energy dissipation mechanism and avoids failure. The repaired pressure vessels experienced FF at 40% of the theoretical FF. The ASME boiler and pressure vessel equations safely predict the load-carrying capacity of the seamless tubes.