<p>Reinforced Thermoplastic Pipe (RTP) has been widely adopted in offshore oil and gas transportation because of its excellent corrosion resistance, ease of installation, and design flexibility. However, its reliability can be compromised during the laying process, where the pipe is subjected to torsion and external pressure. This study examines the evolution patterns of RTP failure modes under typical operational conditions during installation, analyzing the influence of structural parameters and torsion direction on failure modes and loads. The findings indicate that RTP exhibits strength failure under torsion, with torsion direction significantly affecting failure torque. As winding angle increases and diameter-thickness ratio decreases, the RTP failure mode transitions from buckling failure to strength failure under external pressure. The loading sequence influences the failure mode under combined action. Reinforced thermoplastic pipes (RTPs) with small diameter-thickness ratios and large winding angles demonstrate superior performance under combined external pressure and torsion in deep sea environments. An evaluation method for rapid safety state prediction is proposed based on the failure load envelope curve under combined action.</p>