The safety factor of a pressure vessel is related to both the tensile stress and yield strength for material allowance. ASME code section VIII has fully covered these two on the construction code for pressure vessel. This code section addressed mandatory and non-mandatory appendixes requirement, specific prohibition, vessel materials, design, fabrication, examination, inspection, testing, certification, and pressure relief. Mechanical design of a horizontal pressure vessel based on this standard had been done incorporating PV ELITE software. Analyses were carried out on head, shell, nozzle and saddle. The input parameters are type of material, pressure, temperature, diameter, and corrosion allowance. Analysis performed the calculations of internal and external pressure, weight of the element, allowable stresses, vessel longitudinal stress check, nozzle check and saddle check.