Semi-probabilistic fracture mechanics approach for a quality assurance system for welds of a containment for a 1000 MW nuclear power unit Original Research Article

The paper deals with a quality control system based on: (1) limit stage design for a given level of failure probability (Pf≤10−6), and (2) fracture mechanics requirements for welds, the heat-affected zone (HAZ), and parent material (St 355 E). This quality control system was carried out under on-site-conditions when building a steel-sheet/reinforced concrete composite construction of a containment for a nuclear power station. The basic element of the quality assurance system are the control welds produced simultaneously with the welds on site (manual electrode welding). The materials testing program of such control welds and statistical evaluation of test results are described. The results show a fairly good reproducibility of measured J-integral values of welds gained from on-site-specimens (control welds) and those obtained from pre-tested welding technologies. The objective of this paper is to encourage the application of the proposed semi-probabilistic fracture mechanics approach for cases, when the area of proven experience for designing and fabricating welded metallic constructions must be left. Some conclusions of practical interest are discussed, for instance: (1) restrictions for high-strength steels, resulting from the limitation of yield to ultimate tensile strength ratio (Rp0,2/Rm≤0.75) in the standards and regulations; (2) importance of demand for a portion of plastic component of the J-integral to exclude brittle fracture of welds; and (3) derivation of a fracture toughness criterion for application to high strength steels.