Evolution of microstructure during fabrication of Zr-2.5 Wt pct Nb alloy pressure tubes

Stress-reorientation of hydrides and hydride embrittlement of Zr–2.5 wt% Nb pressure tube alloy

“…A section of pressure tube illustrating the orientation of circumferential and radial hydrides [6] is shown schematically. Typical a phase grain dimensions [24] observed in cold worked and stress-relieved Zr-2.5 wt% Nb pressure tube alloy. A -axial, C -circumferential and R -radial directions.…”

“…2(a) and (b) that the trace on radial-axial plane is straight (with minimum irregularity or serrations) and longer than that on radial-circumferential plane. This is expected because the longer a phase grain dimension along axial direction of the pressure tube [24] provides uninterrupted growth along axial direction. The branching of the trace of the hydride on the radial-circumferential plane is due to shorter grain dimension along the circumferential direction [24] of the pressure tube (Fig.…”

“…Also an understanding of the stressreorientation behavior of hydrides will help in understanding the hydride precipitation and its preferred orientation during delayed hydride cracking [22] and hydride blister formation [23]. Moreover, no information is available in open literature on the stress-reorientation behavior of the Zr-2.5 wt% Nb pressure tubes of Indian 500 MWe PHWRs, which are manufactured by a fabrication route similar to the modified route II followed by AECL [24][25][26]. Studies on the stress-reorientation behavior of hydrides in CWSR Zr-2.5 wt% Nb alloy, the temperature dependence of the threshold stress for reorientation of hydrides in this alloy and the influence of reoriented hydrides on the tensile properties of this alloy in the temperature range of ambient to reactor operating temperature (573 K) will generate useful data and understanding for assessing service life of the pressure tubes of PHWR.…”

Stress field estimation around a semi-constrained inclusion and its validation by interpreting hydride platelet orientation around a blister in a Zr–2.5Nb alloy

“…The hydride platelet dimension along axial direction is comparatively straighter when compared to that of its dimension along circumferential direction. This elongated a-grains [24] along the axial direction of the PT allows uninterrupted growth of hydride platelets. As the hydrogen concentration increases, the hydride platelets become longer and thicker.…”

Effect of process variables on texture and creep of pressurised heavy water reactor pressure tubes

“…In general, pressure tubes having grains that are thinner in the radial direction show higher diametral creep and vice versa [9]. because the microstructure and texture established during extrusion does not undergo any appreciable change in the subsequent process steps [14,15]. Thus extrusion effectively decides the final metallurgical condition of the pressure tubes and hence their performance in the reactor.…”