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

摘要：

环氧乙烷（EO）是重要的石化产品，该产品易燃易爆，同时也是一种有毒的致癌物质。山东某化工厂EO生产装置T形三通管件材料与焊缝质量合格、管内介质无腐蚀性，但是频繁出现裂纹故障导致介质泄漏。T形三通裂纹故障原因不明导致该厂几乎半年更换一次T形三通管件，造成了严重的经济损失。为了解决该厂T形三通频繁失效问题，必须准确查明T形三通故障原因，分析T形三通故障机理成为解决问题的关键。本文运用流场分析软件，结合T形三通管线现场故障情况，分析该厂T形三通内部流场特性及故障机理：T形三通管件内部流场存在两个对称的漩涡，导致T形三通流场速度、压力分布不稳定，形成了大范围低于汽化压力的低压区，液体汽化形成了大量气泡，气泡在三通内壁破裂产生巨大的压力冲击，导致汽蚀破坏，使贫水管线T形三通产生裂纹。基于T形三通故障机理，本文提出了3种改进建议，使用Y形三通、圆弧形三通和球形三通3种三通结构代替T形三通结构，并分析这3种三通结构流场特性。数值计算结果表明：提出的3种三通结构能减小三通管件汽蚀破坏，其中Y形三通有微弱的流体漩涡产生，产生低压区体积最小，但管道入口方向需要改变；圆弧形三通结构不改变原来入口方向，流场压力、速度分布更稳定；球形三通流场绝对压力高于Y形和圆弧形，其结构出口及下游流场压力最稳定。本文为解决T形三通裂纹故障提供了新思路，为保障化工厂三通管件的安全提供了技术支撑。

关键词: 裂纹, 三通管件, 计算流体力学, 汽化, 汽蚀