The study presents a numerical analysis of the impact of creep in thermoplastic stub ends on the flange clamping force of a thermoplastic pipe flange connection. The analysis uses available creep modulus values that depend on the stress level, temperature and time. A method that takes the creep modulus into account is proposed and applied to four different detailed variants with the aid of the finite element method. The calculations were performed for selected times at a constant temperature and with static load. The obtained results show that the influence of creep in thermoplastic stub ends causes a substantial reduction in flange clamping force in less than one year.