Understanding the slow crack growth (SCG) in engineering materials is very important for the prediction of the lifetime of structures. There are many empirical and theoretical approaches to modeling of SCG. However, there are many factors controlling SCG and structural lifetime such as, as basic material properties, residual stresses, the size and location of the crack origin, the load level and rate, temperature, structure geometry, and so on. Therefore, for engineering plastics it is difficult to predict, the SCG behavior on phenomenological ground. Understanding of fracture mechanism(s), and employment of fundamental science in modeling is required in studies of SCG. In this paper, the numerical algorithm and analysis of SCG is proposed based on Crack Layer (CL) theory. In addition, the time of SCG in HDPE pipe is modeled and compared with experimental data for various stress level. The effect of the crack origin (inclusion) size and location on the lifetime of PE pipes is analyzed using the numerical technique.