The durability and serviceability of composite pipes under thermal and power influences (loads, strains) determine the safety factor for their calculation. Determination of the safety factor is reduced to the decision of deformations from thermal and force effects, at which the probability of failure will be maximum. This paper proposes determining the safety factor of composite pipes subjected to thermal and power loads. The safety factor serves as a measure of the mechanical reliability of composite pipes. It is a statistical value determined by probabilistic calculation methods, particularly the ratio of the mathematical expectation of the strength criterion to the mathematical expectation of the destructive factor’s value. The technique has been successfully tested (proved) for composite pipes for hot and cold-water supplies using various polymers.