Research On The Composite Steel Pressure Vessel's Weld Interface High-temperature Creep

In high-temperature corrosive environment, composite plate are more and more widely applied in the petroleum chemical industry because it can be designed, have corrosion resistance and cost advantage. However, in the process of metallurgy, manufacturing and useing, inevitably, there were various defects in the structure of the composite steel pressure vessel. Especially, in the composite pressure vessel steel's weld, due to the special welding process and weld structure, and there is a big difference of materials, thermal physical properties, chemical composition and organization between the two kinds of combination of the composite steel plate. After welding, welding seam often appear dislocation, inclusions and voids defects. Under high temperature in a long time, these defects is easy to produce creep crack, eventually leading creep rupture failure to the container, cause a great loss and dangerous to society, so it is need of stuty the composite steel pressure vessel's weld creep.As the composite plate weld joint creep tensile specimen preparation difficult, creep test takes longer, expensive, experimental study of composite steel pressure vessel weld creep is difficult. But the finite element (FEA) method which is a comprehensive, relatively short time, inexpensive, widely used in high temperature performance of welded components.In terms of composite steel pressure vessel weld creep mechanism, composite steel pressure vessel weld different parts and different structures creep damage under high temperature, and composite steel pressure vessel safety assessment of high temperature creep crack and others, this paper completed the study about the composite steel pressure vessel weld creep.1. Useing metal viscoelastic material mechanics theory and damage mechanics theory analysis methods, studied composite steel pressure vessel weld creep mechanism, analyzed material characteristics about every layer composite steel plate,weld structure and characteristics of high temperature creep damage. Establish material differential constitutive of Generalized Kelvin model, and thus derived composite steel pressure vessel cylinder visco elastic constitutive equation.2. Adoption of international general finite element analysis software ANSYS10.0, completed numerical analysis about stainless steel composite plate (304+16MnR) pressure vessel weld high temperature creep,it is uniform with the results of similar experimental and theoretical studies. The numerical results show that: composite steel pressure vessel weld creep serious is higher than the base metal, the complex layer more serious than the primary, weld heat affected zone creep is the most serious in weld complex layer, followed by the weld interface transition layer. In addition,when t=0, the entire weld (complex, primary, intermediate layer) creep stress is common with membrane stress,enter into the first stage of creep, the complex layer creep stress is gradually increased, primary creep stress is gradually reduced and finally become stable, the maximum creep stress creep present in complex layer weld heat affected zone.3. this paper adopted the assessment of technology of the British Standard BS7910-1999 "metal structure defect evaluation method of acceptance of guidelines", combined with composite steel pressure vessel itself structural characteristics, presented a set of composite steel plate pressure vessel high-temperature integrity assessment method which assessed separately the different functions structure, that testing and evaluation methods of foot-layer is in accordance with the general pressure vessels'methods, but the main testing and assessment of complex layer is cracks whether affected its corrosion function.This subject adopted finite element numerical analysis method, studied various composite steel pressure vessel weld interfaces creep strain field and stress field distribution, intuitively reflect various weld interfaces creep damage, provided a reliable theoretical basis for optimal design, nondestructive testing and security assessment of the composite steel pressure vessel.