The phenomenon of the oilwater two phase mixed flow is often encountered in the gathering and transportation pipeline, and the study of its pressure variation is important for the gathering pipeline design and operation. Using VOF model to simulate numerically the oilwater two phase flow in bend duct of oilfield surface gathering pipe under different moisture content of crude oil and fluid velocity. Through the analysis of the calculation results, it was known that the moisture content of two phase flow and flow velocity has great influence on the pressure drop in bend duct. With the increase of moisture content, the two phase flow pressure in bend duct increases.The elbow inner wall pressure is reduced while the speed increases, the outer wall of the pressure increases while the rate decreases. While increasing the flow rate, the high moisture content of the oilwater two phase pressure drop first decreases and then increases.

The iterative formula of the cold layer economic thickness was deducted , and the formula can quickly and easily calculate the economic thickness of the layer of cold. The analyses and designs were used by examples, and in the calculation process, the economic thickness of the layer of cold drawn after comparison, so as to achieve the purpose of energy conservation. This method is not only simple and easy to understand, but also greatly improve design efficiency and quality.