Application Research On Two-dimensional Full Surface X-ray Inspection Of Residual Stress For Spherical Tank

Spherical storage tank is an important large pressure vessel in petrochemical plant.Most of the internal media are inflammable,explosive and toxic chemical raw materials or products.Leakage will lead to very serious impact.Crack is a common defect of spherical tank.Once the crack expands,material leakage will occur and even lead to explosion of spherical tank,which seriously endangers the safety of production and life and property of enterprises.Stress is the fundamental cause of crack formation.Spherical storage tanks are made by pressing the spherical shell plate well in the manufacturing plant,and then welding and forming on the spot.Therefore,they all have high welding residual stress,accurately measure the stress distribution characteristics of spherical storage tanks,and study how to reduce the residual stress formed in the welding process.Thus ensuring the safe operation of spherical tanks is of great significance.X-ray diffraction method for residual stress measurement is a nondestructive testing method with high accuracy and can be used to achieve industrial field inspection technology.The traditional sin~2?method has a large instrument,which requires multiple exposures to test to fit the stress value.Field inspection is difficult to operate.In this paper,the U-X360s X-ray residual stress tester,newly developed by Pulstec Company of Japan in 2016,is used.The tester is based on full two-dimensional surface exploration technology.The residual stress can be calculated by cos?method after single exposure.The tester is portable,easy to operate and has high detection accuracy.Its efficiency is at least80%higher than that of sin~2?method.This method is the first time to be used in spherical storage tanks.The welding joint of a 2000 m~3 Propylene Spherical tank used in a petrochemical enterprise in Daya Bay Petrochemical Zone is studied in this paper.Firstly,various testing techniques and principles of residual stress are introduced,and the difference between cos?method and sin~2?method is analyzed.Then a series of tests are carried out to determine the best method of surface treatment and the setting of process parameters for stress testing.The reliability of the new method is confirmed by comparing with the traditional method.Based on the periodic inspection of a 2000 m~3 Propylene Spherical Tank in use in Daya Bay Petrochemical Zone,this paper introduces the nondestructive inspection techniques for periodic inspection of spherical tanks.Selecting some cracks and welding seams with representative positions.Stress test,understand the stress distribution characteristics of the spherical tank,and analyze the measurement results.In the laboratory,Q370R welding plates were made by simulating the installation environment of spherical tanks with different welding parameters.The stress of the plates was tested and the effect of welding parameters on residual stress was studied.Finally,the test plate was annealed and the stress at the corresponding position was measured after heat treatment to study the effect of heat treatment.Through the above research,the stress distribution characteristics of spherical storage tank are understood,and the basis is provided for the determination of key inspection parts in periodic inspection;the test of welding test plate and the data comparison after heat treatment are made clear the influence of welding process parameters on welding residual stress and the effect of stress relief annealing,so as to guide inspectors in spherical storage tank.Installation works need to focus on those processes.