Study on Fatigue Behavior and Failure Mechanisms of Full‐Scale Carbon Fiber‐Reinforced Bismaleimide Resin Composite Pipe Under Cyclic Pressure in Wellbore Environments

ABSTRACT In this study, the cyclic internal pressure‐corrosion fatigue tests were conducted on full‐scale carbon fiber‐reinforced bismaleimide resin (CF/BMI) composite pipe by simulating the combined wellbore environments involving production, acidification, and nitrogen injection, thus systematically investigating its fatigue behavior and failure mechanisms. The CF/BMI pipe exhibits outstanding initial mechanical performance, including a high‐temperature (200°C) tensile strength of 830 MPa along with superior flexural and compressive properties. Under the synergistic action of 0–16 MPa cyclic internal pressure and multistage corrosive service conditions, the pipe remains linearly elastic throughout the test program, with an accumulated elastic modulus reduction of 16% while still maintaining leak‐tight performance above 30 MPa. Microstructural characterization after fatigue tests and fluorescent tracer results reveal resin stripping, microcracking, and fiber–matrix interface debonding on the pipe inner wall, with these cracks propagating predominantly along the axial and circumferential directions and eventually coalescing, which ultimately leads to sealing failure of the pipe under cyclic internal pressure‐corrosion fatigue conditions.