High-density polyethylene (HDPE) pipes can typically withstand continuous operating temperatures up to approximately 60 degrees Celsius to 80 degrees Celsius (140 degrees Fahrenheit to 176 degrees Fahrenheit), depending strictly on the specific material grade, wall thickness, and internal working pressure. Exceeding these thermal thresholds for extended periods compromises the structural integrity, tensile strength, and pressure rating of the piping system, meaning they are primarily restricted to cold water and specialized industrial applications.