High-density polyethylene (HDPE) is one of the most widely used materials in fluid transport networks due to its good resistance to wear and corrosion, ease of installation, and low cost. However, HDPE is a flexible material and therefore more vulnerable to scratches and other types of damage during transport and installation. Therefore, accurate prediction of crack initiation pressure in damaged pipes is a very important point in the safety analysis of HDPE piping systems. In this study, a new semi-empirical formulae, which predicts this critical pressure, is developed. The cracking pressure depends on the mechanical characteristics of the material and the geometric parameters (pipe geometry and defect size). A parametric study based on numerical simulations was established in order to quantify the influence of each parameter on the cracking pressure. The pressures calculated by the proposed formulae in a HDPE pipe having a superficial defect are in good agreement with the burst pressure determined experimentally for the same geometry.