ABSTRACT
This chapter discusses an easier and more accurate analytical tool than those failure envelopes. The general equation computes the mechanical global strains on composite circular cylinders under the simultaneous action of pressure, torque, hoop and axial loads. The chapter illustrates the computation protocol for oil and sanitation pipes. The failure envelopes proposed by ISO 14692 for the long-term analysis of composite oil pipes are cumbersome, artificial and inaccurate. The analysis of composite pipes is best done in terms of strains, instead of average stresses. The reasons for the use of strains in place of stresses are: the failure strains are ply properties not affected by Poisson effects. Unlike the stresses, which change from ply to ply, the global strains have the same value for all plies of circular pipes. The load-dependent durability analysis readily follows from the unified equation and the total ply strains.
