[en] Stress intensity factors for semi-elliptical surface cracks in internally pressurised thick-walled cylinders of radius ratio 3 are presented for a wide range of crack sizes. These solutions were obtained using the boundary integral equation method for three-dimensional stress analysis. Only one crack shape is considered - a semi-ellipse with the length of its semi-minor axis equal to 0.6 times the length of its semi-major axis - but the ratio of crack depth to wall thickness ranged from 0.2 to 0.8. Hoop strain distributions at the outer circumference of the cylinder are also presented for the different crack sizes analysed; the results are useful for experimentally monitoring crack growth. (author)

[en] The results of an elastic-plastic three-dimensional finite element analysis for a nozzle corner crack in a pressurised reactor test vessel are presented. The calculations were performed by the finite element program ADINA incorporating von Mise's yield condition and isotropic hardening. The crack plane was taken parallel to the axis of the vessel and the crack front straight and perpendicular to the symmetry line of the nozzle corner in order to obtain the worst position for a nozzle corner crack. The calculations were performed up to that pressure level where general yield of the ligament in the nozzle corner section takes place. For the chosen crack length, which is relatively small in comparison to the ligament, the crack opening stress as well as the crack opening displacement have a maximum in the centre of the crack. The differences between the maximum and minimum values along the crack front increase rapidly in the plastic range when the pressure load is raised above half of the general yield pressure. The results of the finite element analysis are compared with figures obtained from analytical procedures of elastic-plastic fracture mechanics. (author)

[en] This work summarises the results obtained from a failure analysis of a pipe crack in a BWR water clean-up system. The cracking occurred in an AISI 304 steel pipe section area where mixing of the water streams at two different temperatures (280⁰ and 130⁰C) took place. The temperature difference and turbulence induced a cyclic thermal loading which, together with the environment, caused cracking. Cracking propagated as transgranular brittle cleavage-like fracture, probably on a stress level below yield stress. Cracking was still observed in areas where the cyclic temperature differences caused by turbulence were markedly lower. The AISI 304 steel was in fully solution annealed as-received condition. (author)

[en] An attempt is made to assess the susceptibility of stress-relief cracking (SRC) of simulated heat-affected zone microstructures in heated specimens of SA508 Class 2 steel, using a notched bend relaxation test. The ability of this test to reproduce service conditions is explored by comparing cracking behaviour and the fractographic details of the cracks produced with observations made on stress-relief cracks in actual weldments of SA508 Class 2 obtained from the same manufacturer. It is shown that SRC in the relaxation test and in the weldments exhibited similar fractographic features and micromechanisms of cracking. From the test specimens, it was found that a critical value of stress-intensity factor was necessary to produce 'severe' cracking and applications of this value to the cracking observed in the weldments appears to be fully consistent with the details of weldment manufacture. It is proposed that a stress-intensity approach of this sort can provide a general method for the assessment of possible SRC in welded components. (author)

[en] In order to assess the structural integrity of pressure vessel steels in the nuclear and chemical industries a need has arisen to measure fracture toughness using Charpy V-notch surveillance specimens. A procedure for determining the initiation fracture resistance of a material using pre-cracked Charpy specimens loaded in three-point bend is described. The size restrictions imposed by the geometry of a Charpy specimen on the measurement of the plane strain fracture toughness, and the elastic-plastic toughness parameter are discussed for typical low- and medium-strength steels. Consideration is given to the measurement of crack growth, side-grooving and the use of exclusion lines to interpret the fracture resistance versus crack growth curves. (author)

[en] Charpy shelf data and lower bound estimates of Ksub(IC) shelf data for the same steels and test temperatures are given. Included are some typical reactor pressure vessel steels as well as some less tough or degraded steels. The data were evaluated with shelf estimates of Ksub(IC) up to and exceeding 550 MPa√m. It is shown that the high shelf fracture toughness representative of tough reactor pressure vessel steels may be obtained from a knowledge of the Charpy shelf energies. The toughness transition may be obtained either by testing small fracture toughness specimens or by Charpy energy indexing. (U.K.)

[en] A report is given of a survey of defects in pressure vessels from conventional plant in the UK. The relevance of these data to nuclear circuit component assessments is commented upon. A design equivalence criterion has been adopted to identify and compare events. Data have been obtained from surveyors' reports in which detected faults are appraised and analysed and fitness for continued service considered. Two categories of failure are defined. These are potential and catastrophic (disruptive) failures. Results of the survey are given in detail and these indicate that, from more than 3 x 10₅ vessel years service accumulated by some 20,000 vessels, the potential failure rate is 6.9 x 10^-₄ per vessel year averaged over the survey period and the catastrophic failure rate for the same period is 4.2 x 10^-₅ per vessel year. Information on defect causes, mechanisms, locations and materials involved is listed. Published American and German data are also referred to and commented on. Operating experience with nuclear reactor vessels and their associated heat exchangers in the UK and the USA amounts to approximately 4 x 10₃ vessel years. It is concluded that this is insufficient to provide a significant body of data from which to establish meaningful failure probabilities for reactor vessels. The problem of transferring data obtained from conventional plant to nuclear plant is discussed. (U.K.)

[en] The study of cyclic strain embrittlement during the growth of fatigue cracks in a pressure vessel steel used in Swedish boiling water reactors, A533B, emanated from observations made in Germany of stepwise crack growth fatigue. It was demonstrated that stepwise crack growth does not occur in the investigated batch of A533B. No indication of embrittlement was found. (author)

[en] Metal components in LMFBR's are subjected to random temperature fluctuations. These are caused by the turbulence in the liquid sodium coolant, and the existence of jets at differing inlet temperatures. The mean square stresses, and the mean square equivalent strain range are calculated for tubes and beams subjected to spatially incoherent temperature fluctuations. This may be used as a measure of crack initiation likelihood. The results depend on the thermal and mechanical boundary conditions, and on the integral scale of the spatial coherence. The mean square equivalent strain range is not necessarily reduced by the reduced spatial coherent. (author)

[en] An accurate assessment of the influence of defects on structural component integrity is needed. Generally accepted analytical techniques are not available for the very ductile materials used in many nuclear reactor components. Some results are presented from a test programme to obtain data by which to evaluate proposed models. Plate and pipe specimens containing surface flaws were fabricated from annealed Type 304 stainless steel and tested at room temperature. An evaluation of an empirical equation based on flow stress is presented. In essentially all instances the flow stress is not a constant but varies as a function of the size of the surface flaw. (author)