The liner of reinforced thermoplastic composite pipes (RTPs) used for oil and gas gathering and transportation experienced blister failure due to gas permeation. Few reports have appeared on the problem of gas permeation in thermoplastics with absorbed crude oil. Accordingly, the permeability of CH4 in polyvinylidene fluoride (PVDF) containing crude oil was studied at the normal service conditions by molecular simulations. The results showed that the solubility coefficients of CH4 in PVDF containing crude oil were much lower than those in pure PVDF. It can be concluded that the crude oil molecules absorbed into PVDF occupied certain adsorption sites, resulting in a decrease in the adsorption capacity of CH4 molecules in PVDF. The diffusion coefficients of CH4 in oil-containing PVDF were significantly greater than in PVDF. This is because the absorption of oil molecules leads to the volume swelling of PVDF and then increases the free volume for diffusion. The permeation process showed that CH4 molecules were selective-aggregate adsorbed in the region with low potential energy in oil-containing PVDF firstly, and then they vibrated within the holes of PVDF containing oil in most cases and jumped into the neighboring holes at high temperatures and pressures.

Adding b-nucleating agents (b-NAs) has been generally considered as an effective approach to induce the formation of b-crystals in propylene-ethylene random copolymer (PPR). However, it is still difficult to obtain the expected percentage of b-crystal under normal processing conditions, due to the temperature control is always a key factor no matter with or without adding b-NAs. We assumed that simultaneously adding both a-and b-NAs to PPR in rational ratios would facilitate the growth of b-crystal. The effects of adding various amount of a-and/or b-NAs on the a-and b-crystallization behavior and morphology were investigated. More importantly, the influence of temperature control on inducing b-crystal in the presence of different NAs was parallel explored by utilizing sample bars prepared via injection molding and sample pipes produced from a typical industrial extrusion line. Different crystallization situations were carefully discussed in response to various nonisothermal crystallization processes in laboratory experiments and in actual pipes extrusion. At last, the mechanical properties of PPR samples were examined to provide new clues for further study of PPR pipes.

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