Experiments of water-assisted injection molded polypropylene curved pipe were carried out on newly developed equipment in this lab. First, four processing parameters, including short-shot size, melt temperature, water injection delay time, and water pressure, were investigated in terms of their effects on the water penetration length and residual wall thickness of curved pipe. Second, an orthogonal array of Taguchi, the SIN ratio, and ANOVA were utilized to find the optimal processing parameters resulting in maximum water penetration length. Finally, the crystallization behavior difference between the beginning and the end of the water channel of the curved pipe was analyzed using differential scanning calorimetry. It was interesting to find that the crystallinity of sample from the middle is higher than those from both outer and inner layers at position near the water inlet. The samples taken from the outer layer, middle, and inner layer show similar melting peak and crystallinity at position near the end of water channel. (c) 2007 Wiley Periodicals, Inc.