CFRP strengthening and rehabilitation of corroded steel pipelines under direct indentation and bending

Objectives/Scope: This paper develops a technique to rehabilitate damaged or sub-standard steel pipelines, which utilizes the lightweight, high strength and corrosion resistance characteristics of carbon fibres reinforced polymers (CFRP) composites have been proposed. Methods, procedures, and process: The study conducted experimental tests for two series of CFRP strengthened and rehabilitated pipes under quasi-static large deformation 3-point bending. The main parameters examined in this paper were (a) the corrosion penetration in the wall thickness; (b) its extent along the pipe; and (c) the type and number of the CFRP sheets. The corrosion was artificially induced 360° around the circumference and in the wall thickness by machining, where four different severity of corrosion were examined of 20% (mild), 40% (moderate), 60% (sever), and 80% (very sever). Results, observations, conclusions: The first series was for rehabilitation of 31 artificially degraded pipes with limited corrosion, which were repaired using externally wrapped sheets. The extent of corrosion along the pipe was in the range of L_c/D_n=1.0 to 8.0, where L_c=length of corrosion and D_n is the nominal diameter of the pipe. The second series represents rehabilitation of 12 degraded pipes with full corrosion along the length of the pipe. The extent of corrosion along the pipe in this series was L_c/D_n= 8.0. The section slenderness examined in this paper was in the range of D₀/t =20.32 to 93.6. The CFRP sheets were wrapped around the section in the longitudinal and transverse direction with a sufficient overlap. The results show that the combined flexural and bearing strength of the pipe can be significantly increased by adhesively bonding CFRP. Novel/Additive information: This research and experiments developed an appropriate technique using CFRP, which significantly improved the repair and rehabilitation of corrosion in steel pipes. The percent increase in strength was mostly affected by the corrosion level where the maximum gain was 434% which was obtained for the most severe 80% corrosion in the wall thickness. The average increase in the load carrying capacity was 97% and 169% for the rehabilitation and strengthening series respectively.