Components subjected to operation at a temperature in the range of 0.4 Tm (Melting temperature of component) and above are prone to failure due to creep. The failure becomes more severe when the component is further subjected to a sequence of start-up and shutdown cycles. If the cycles are enough to induce extensive plastic strain, the failure of the component could be attributed to a combined effect of creep and fatigue known as creep-fatigue interaction. In this paper, the creep-fatigue behaviour of a straight P91 (9Cr-1Mo) martensitic stainless steel steam pipe subjected to a 24 h daily sequence of start-up and shutdown cycles under a typical operating temperature of 550° C and pressure of 18 MPa was investigated using finite element analysis code, Abaqus CAE/2019 in conjunction with fe-safe/Turbolife software. The outcome of the analysis shows that the failure of the steam pipe under the specified start-up and shutdown cycles is strictly due to creep since the operational cycle was insufficient to induce the required plastic strain capable of initiating fatigue failure. Nevertheless, the maximum creep stress developed in the pipe after an hour of operation is 126.6 MPa with a corresponding creep rate of 1.114× 10-7 h-1, while the creep stress and strain developed after 24 h operational cycle is 126.3 and 9.044× 10-7 respectively. Hence, the useful creep life and maximum creep damage for the machined-finished surface P91 steam pipe are 23.68 years and 4.823× 10-6 respectively. Lastly, a strong correlation was obtained between the analytically and numerically computed creep strain rates.