Experimental Investigation Of Stress Corrosion For Sa543Steel For Ethylene Oxide (EO) Reactor In High Temperature Boiler Feed Water

To solve the stress corrosion crack (SCC) problem of Ethylene Oxide (EO) reactors in the boiler feed water containing Na3PO4of a company, the stress corrosion cracking of SA543steel in the boiler feed water containing Na3PO4and improved boiler feed water containing (NH4)3PO4are investigated by using stress corrosion tests with pre-cracked wedge-open loading (WOL) specimens and slow strain rate tests (SSRT), the experimental results provide some technical supports for safety assessment of Ethylene Oxide reactors. The proposal of WOL tests in high temperature is studyed, an test device of WOL tests in high temperature environment is developed. Safety assessment of defect of Ethylene Oxide reactors is made according to experimental results.The main research works and findings in this paper are summrized as follows:(1) The tests of sensitivities of SA543steel to stress corrosion in the boiler feed water containing Na3PO4and improved boiler feed water containing (NH4)3PO4are investigated, which show that sensitivities of SA543steel to stress corrosion in the260℃boiler feed water containing Na3PO4is comparatively high, which has certain stress corrosion tendency, and that sensitivities of SA543steel to stress corrosion in the100℃and260℃boiler feed water containing (NH4)3PO4are almost same, both of the susceptibility indexes are slightly lower than25%without stress corrosion tendency, the extended features should also almost same, and that the sensitivity of welded joints of SA543steel to stress corrosion in the250℃boiler feed water containing Na3PO4is much higher than that in the250℃boiler feed water containing (NH4)3PO4, indicating that stress corrosion tendency is remakble, which implies the resistance to SCC initiation and propagation of SA543steel significantly increases in the improved boiler feed water.(2) The testing tests of KISCC and da/dt of S A543steel to stress corrosion in the100℃boiler feed water which containing (NH4)3PO4is investigated, which show that the stress corrosion crack growth rate of SA543steel is nearly zero in the100℃boiler feed water which containing (NH4)3PO4,the critical stress intensity factor (KISCC) is not less than160.91MPα√m.(3) In order to improve the accurancy and reliability of stress corrosion tests for pre-cracked wedge-open loading (WOL) specimens in high temperature environment, the test method of WOL tests in250℃envirenment and the major work to be done are investigated in detail, including calibration of thermal strain measurement, design and reconstruction of test equipment, and test of lead seal, an test equipment of WOL tests in high temperature environment is developed, the device is capable of WOL tests which maximum temperature is250℃and maximum pressure is4.0MPa.(4) The results of tests of sensitivities and testing tests of KISCC and da/dt of SA543steel to stress corrosion in the boiler feed water are combined to make safety assessment analysis of defect of EO reactor, which show that EO reactor with defects can continue to use in the improved boiler feed water environment. The experimental results provide some technical supports for safety assessment of Ethylene Oxide reactors.