Experimental and analytical evaluation of the performance of hybrid steel-CFRP pipelines at high external pressures

Behavior of hybrid steel-CFRP pipe systems under external pressures is studied herein using a combination of experimental, analytical, and finite element (FE) methods. Hyperbaric chamber tests are conducted on steel tubes and those wrapped with CFRP of different thicknesses and winding orientations to evaluate their performances. Based on the experimental observations and using analytical methods, new equations are proposed that can predict the collapse and propagation pressures of the hybrid steel-CFRP pipelines. The results revealed a significant enhancement in the collapse and buckle propagation capacities of the hybrid steel-CFRP pipes, with average increases of 60% and 200% respectively, compared to bare steel pipes. The failure mode observed in the hybrid steel-CFRP pipe was characterized by a U-shaped pattern, which occurred at higher pressures than the dog-bone shape mode observed in bare steel pipes. As evidenced in the FE results, the presence of CFRP in the hybrid steel-CFRP pipe system led to improved stress distribution, enhanced buckle propagation capacity, and reduced ovality. These findings demonstrate the effectiveness of CFRP in reinforcing steel pipes and highlight the potential for the hybrid steel-CFRP pipe system to offer superior performance in deep-waters.