MMM Characteristics Of Welded Joint Stress Concentration Zones

Welded joint of pressure vessel are often affected by high temperature, high pressure, corrosion and fatigue. Meanwhile, the sites of weld are often located in area of stress concentration, and there are weld defect. In these situation, weld are easily to become invalid. Magnetic memory testing technology, a new nondestructive testing method, can not only discover the plastic deformation and the macroscopic of material, but also can assess the stress concentration districts and the microcosmic weld defects of metal endangered state before the injury to early diagnosis.This article through weld metal magnetic memory testing, respectively from the gradient, extremum, difference value, zero, zero frequency etc makes a comparative analysis of tension, compression load condition, weld unfully and solid add slag two defects types, static tensile and pull - pull fatigue load, stress corrosion and corrosion fatigue weld-line of metal magnetic memory signal features in multi-angle.By weld metal magnetic memory testing, this thesis analyzed respectively the elasticity and yield loads stage of the weld on the analysis of the magnetic memory signal features with tension, and found the conclusion that the variation of lack of penetration magnetic memory signal wave is lager, while it is mores sensitive presenting the solid slag inclusion by signal gradient. After the experiment of weld lacking of penetration and weld slag inclusion two typical of weld defect of magnetic memory testing, by comparing the regular pattern of variation, we found that the magnetic memory characteristic signal's feasible and effectiveness in determining weld defect and the drawback degree , made the magnetic memory testing technology could be used in the filed of quality evaluation qualitatively and quantificationally.Meanwhile, this theme found that slope of magnetic memory signals under the static tensile load increase gradually and increase more obviously in the elastic stage; the curve of magnetic memory signals under the fatigue loads fluctuate more before break but the trend is stable. In the study of stress corrosion and corrosion fatigue under the magnetic memory signal features, we analyzed the difference of minimum and maximum value of magnetic memory signals, discover that magnetic memory signals bouncing up and down fitfully in the corrosion and may be appear two kinds of curve morphology alternately. This theme provided data and experimental base for the use of magnetic memory testing technology in estimating destroying styles.