Study On Failure Behavior And Mechanism Of Jacket In Ultra-high Pressure Reactor

In a petrochemical plant, the jacket pipe of ultra-high pressure reactor was thinning andperforated during the operating period, which caused a lot of demineralised water leakage andaffected the normal operation of the reactor. Based on the mechanical material damage modeltheory, this dissertation carried out the failure analysis on the jacket pipe. By the use of thephysical and chemical test and CFD numerical simulation method, studying on the thinningmechanism systematacially combining failure mode, wear surface morphology characteristics,operating condition, mechanical properties and related fluid dynamics factors.By physical and chemical tests, it is found that the hardness gradually reduces fromoutside to inside along with the wall thickness direction. In the inside wall, the roughness andmetallographic grain degrees deteriorated, the banded and Widmannstatten structure areabnormal. The results of internal pipe impurities phase analysis and demineralised waterquality properties test show that flow environment exists oxide in large amount, dissolvedoxygen in desalted water was up to7.31mg/L.Through the flow distribution for desalted water in the jacket pipe, velocity, stress,temperature, pressure and the turbulent coefficient distribution are obtained. The water flowimpacts on both sides of the pipe wall in the jacket straight pipe inlet area, to produce themaximum shear stress. In jumper pipe inlet, the direction of flow suddenly turned90°,making the impactness concentrated on the inside wall, also forms local shear stressextremum area. As the water also carried solid particles, the wall shear stress increasedsignificantly, and by gravity, the shear stress focus on one side along the gravity direction, andthe area acting force enlarged. With the particle size and volume concentration increasing, theshear stress level increased significantly.In addition, a flow stagnant zone was formed in the area between jacket straight pipeinlet and shrinkage ring, where the desalted water temperature rised significantly, reaching theboiling point and evaporation condition. The jumper section changed because of theconnection for straight pipe and the cross pipe, which causes turbulence intensity andturbulent kinetic energy increase, up to maximum value, and caused the second eddy currentoccurrence. In these areas, partial static pressure reduced largely, which resulted in cavitationalso.Finally, complex failure mechanism of jacket system is summarized comprehensively.The results show that the jacket system suffered multiple impact combining of erosion, cavitation and oxygen and chlorine corrosion. Under the mechanical and electrochemicalinteractions, pipe material was continuously peeling off, leading to thinning and perforation inthe surrounding area of connection for straight pipe and cross pipe, and fanally causeddemineralised water leakage.