Study On Fracture And Fatigue Behavior Of The 15MnVR Plate Used In Urea Reactors

Urea reactors are the key equipments of urea synthesis devices. However, cracking of layers was induced because of residual welding stress, manufacturing defect and stress corrosion. Series cracking may lead to serious urea reactor blasting accidents. Urea reactors are equipments with security risks definitely. It's necessary to test and study the mechanics behavior of the urea reactor layers.The author took samples in a disabled urea reactor from a factory of Shandong Province. Tensile tests were carried out under room temperature and medium temperature, as well as impact test under room temperature. The material properties are compared with other urea reactors. The results indicate that, the material properties including tensile strength and toughness still satisfy the standard after service. They are quite close to the value of urea reactor from Qilu. The tensile strength is higher than urea reactor from Pingyin, but the toughness is lower.Fatigue crack propagation test under 180℃was carried out by using compact tension specimens. The crack length was caculated by compliance measurement method. The test data are described by Paris formula, Forman formula and Wang's formula separately. The parameters of Paris formula and Forman formula are got from the test. The results reveal that the data are described quite well by Paris formula. The fatigue crack propagation rate hasn't increased obviously after srevice. And it is independent of the position where the specimens taken. The average stress doesn't affect the crack propagation rate much in the stable crack growth area. But data estimated by Wang's formula are marked different from the test results.CTOD test was carried out according to resistance curve method by using SE(B) specimens. The resistance curves of the material are obtained by the test, as well as CTOD characteristic value. The results validate the conclusion that steadyδ_c can be obtained when the thickness of specimens is bigger than 5mm. Referring to the relationship between fracture toughness and temperature of 20Cr3MoWV steel, the fracture toughness of 15MnVR under 180℃is also discussed in the paper. The fatigue crack propagation data of urea reator material are supplied by the test. The fracture toughness data are accumulated at the same time. Basic data for estimating the residual life of urea reators are also provided here.