[en] Studies have been carried out on carbon steel pipes to demonstrate the leak before break design criterion and validate the analytical procedures. Fatigue crack initiation, fatigue crack growth rate and fracture resistance behaviour of the pipes have been experimentally and analytically evaluated. The tests have been carried out on pipes of outer diameter 219 and 15.1 mm wall thickness having a part through notch in the circumferential direction. The aspect ratios (2c/a) of the notches were 56, 28 and 18. Comparing the analytical and experimental results has validated analytical procedures. It has been observed that the analytical and experimental results compare well. The fatigue crack growth curve (da/dN∼ΔK) obtained from three point bend specimens and pipe tests have been compared with the fatigue crack growth curve in ASME Section XI. The comparison shows that use of the ASME curve in analysis of components will give a conservative result in comparison to the curves obtained from the actual pipe tests. Fracture resistance behaviour of the pipe has been observed to be strongly dependent on the load histories to which the pipe has been subjected

[en] Fracture behaviour of piping components used in pressurised heavy water reactors of nuclear power plants are of great importance to ensure safety and integrity against the extreme load conditions. Fracture mechanics approach predicts crack growth behaviour under normal operating conditions and failure load under accidental conditions. Leak-Before-Break concept is used to investigate the structural integrity of the piping components. Experimental investigations were carried out on straight pipes to study their fatigue and fracture behaviour under bending. Fatigue tests were conducted on 406 mm outer diameter straight pipes to study the crack growth with various notch configurations. Fracture tests were also conducted on the pipes, which were tested in fatigue, under monotonic loading for their fracture resistance. A new database on fatigue life of large size carbon steel pipes has been created which will be very useful for integrity assessment of power plant structures. The details of the studies are presented in this paper. (author)

[en] Earthquake load, which is cyclic in nature and of short duration, is the main design basis accident load for designing the Primary Heat Transport (PHT) piping components of Indian Nuclear Power Plants. Adequate protection of piping components from the effects of earthquake requires detailed knowledge of strength and deformation characteristics of the components and assemblies making up the piping system. Experimental investigations were conducted to understand the fracture behaviour of pipes under cyclic loading. Fracture tests were conducted on 10 carbon steel (SA333 grade 6) of 219 mm OD and 8 stainless steel (AISI type 304LN) pipes of 168 mm OD with through-wall circumferential crack. The influence of various parameters such as cyclic load ratio, range, amplitude and initial crack size on crack growth and number of cycles for failure was investigated. Out of 18 pipes tested, 14 were tested under load control and 4 were tested under displacement control. The studies showed significant reduction in the fracture resistance under cyclic loading conditions. (author)

[en] In order to demonstrate Leak Before Break (LBB) design criterion and also have better understanding of the fatigue and fracture behaviour of piping components, detailed experimental investigations were carried out on straight pipes made of SA312 Type 304LN steel and elbows made of SA403 Type 304LN steel. Fatigue tests were carried out under constant amplitude cyclic loading on five pipes of 168 mm outer diameter having part through notch. The notch angle varied from 4.7° to 29.7° and notch depth varied from 3.4 mm to 3.6 mm. The notch length to depth ratio varied from 2.05 to 12.15. Four pipes had notch in the weld metal and one pipe had notch in the base metal. Fatigue crack growth during the tests was continuously monitored. It was observed that the number of cycles required for the crack to grow through thickness was significantly large compared to the cycles expected during the lifetime of the reactor. Fracture tests were subsequently conducted on the through wall cracked pipes under monotonic loading. Seven elbows were tested under cyclic loading out of which four elbows were of 168 mm OD and three elbows were of 324 mm OD. One elbow of 324 mm OD did not have any notch (healthy elbow) while the other elbows had a machined part-through notch on the outer surface at different locations namely crown, extrados and intrados. The notch was in the axial direction for crown while it was in the circumferential direction at extrados and intrados. The ratio of notch depth to thickness (a/t) varied from 0.20 to 0.28. The crack aspect ratio (a/2C) varied from 0.11 to 0.67 for the notched elbows. The notch angle varied from 1.6° to 17.7°. Fracture tests were subsequently conducted on the through-wall cracked elbows under monotonic loading. These studies provide valuable inputs which are essential to ensure structural safety and carry out life assessment and life extension studies of power plants. (author)

[en] Fail-safe design criteria like Leak-Before-Break (LBB) based on fracture mechanics methods are being used to ensure the safety and integrity of components under operational and extreme loading conditions. This paper deals with Level II of LBB evaluation. Detailed experimental studies were conducted on 15 circumferentially cracked carbon steel pipes of SA 333 Grade 6 material used in Indian PHWRs. The results of the studies are discussed in this paper. (author)