关键词: 裂纹, 三通管件, 计算流体力学, 汽化, 汽蚀

Abstract:

Ethylene oxide (EO) is an important petrochemical product. This product is flammable and explosive, and it is also a toxic carcinogen. In Shandong province, a chemical plant's EO production equipment has qualified T-shaped piping materials and welds, and the medium in the pipe is non-corrosive, but frequent cracks cause the medium to leak. The reason for the failure of the T-shaped tee crack is unknown, causing the plant to replace the T-shaped tee almost every six months pipe fittings caused serious economic losses to the plant. In order to solve the frequently failure of the T-shaped tee at the plant, the cause of the T-shaped tee failure must be accurately identified. Therefore, identifying the failure mechanism of the T-shaped tee becomes the key to solving the problem. This paper uses flow field analysis software, combined with the on-site fault condition of the three-way pipeline, to analyze the internal flow field characteristics and the failure mechanism of the T-shaped three-way device. There are two symmetrical vortices in the internal flow field of the T-shaped three-way device, which results in unstable flow velocity and pressure distribution of the T-shaped three-way flow field. A low-pressure zone with a large range below the vaporization pressure is formed. The liquid vaporizes to form a large number of bubbles, and the bubbles rupture on the inner wall of the tee creates a huge pressure shock, causing cavitation corrosion and damage, and causing the T-shaped tee of the lean water pipeline to crack. Therefore, three improvement schemes are proposed, use Y-shaped tee, arc tee and arc-shaped shaped tee structure instead of T-shaped tee structure, and analyze the flow field characteristics of three tee structures. Numerical calculation results show that the proposed three-way structure can greatly reduce the cavitation damage of the three-way pipe. Among them, the Y-shaped tee has a weak fluid vortex, which produces the smallest volume in the low pressure zone, but the inlet direction changes, not easy to transform; The arc-shaped three-way structure does not change the original inlet direction, the flow field pressure and velocity distribution are more stable, and the flow field characteristics are better than the Y-shaped three-way; Although the absolute pressure of the spherical three-way flow field is higher than that of the Y-shaped and the arc-shaped shaped, the structural outlet and the downstream flow field pressure are the most stable. This article provides a new idea for solving T-shaped tee crack failure and provides guarantee for the safe and effective operation of tee fittings in chemical plants.

Key words: crack, tee-fitting, computational fluid dynamics(CFD), vaporization, cavitation