The Effect of Testing Direction on DHC Growth Rate Using Zr-2.5Nb Plate

Abstract

Delayed Hydride Cracking (DHC) is a fracture mechanism responsible for several failures of zirconium alloy components. The Zr-2.5Nb alloy is used to manufacture CANDU pressure tubes, which are the primary pressure boundary in CANDU reactors.The rate of crack propagation in these tubes depends on direction. CANDU pressure tubes have anisotropic grain structure and texture due to extrusion and heat treatment.Disk-shaped hydrides preferentially form on certain crystallographic planes that are hypothesized to be responsible for the difference in DHC growth rates in certain directions. If bulk hydrides slow crack growth, then no directional difference in crack velocity will be observed when no bulk hydrides are present; i.e, where the DHC test temperature is reached by cooling to temperatures above the terminal solid solubility of precipitation (TSSP). Furthermore, below TSSP, where bulk hydrides are present, the crack velocities should begin to diverge as temperature is decreased, as oriented hydrides impede the crack growth to different extents in different directions. In this study, DHC crack velocities are determined using cantilever beam specimens with cracks propagating in both the longitudinal and through-thickness directions with and without bulk hydrides present, i.e., below and above TSSP. The DHC crack velocities in the longitudinal direction were observed to be higher than the corresponding through-thickness crack velocities with or without bulk hydrides present. Thus, the hypothesis is disproved; the orientation of bulk hydrides relative to the direction of DHC cracking does not explain the direction difference in crack velocities. Alternative hypotheses are presented.ii

On the Development of a Novel Technique for Hydriding Using Zirconium Hydride Powder

“…Differences in peak breadth and height will also be qualitatively discussed. For further detail, see Hanlon [20] and von Zeppelin et al [21]. The hydrogen concentration of each sample was found to be approximately 5 ppm, as is shown in Table 2.…”

THEORETICAL AND NUMERICAL STUDY OF HYDROGEN DIFFUSION IN Zr-Nb ALLOYS

“…La curva (a) corresponde a Zr-α [8], (b) y (c) corresponden a Zr-2.5wt %Nb con tratamientos térmicos de 565 ºC y 400 ºC respectivamente [1], (d) es la medición de [4] también para Zr-2.5wt %Nb, (e) es la predicción de [4], (f) la de [1] y (g) la del presente trabajo. Para esta última, las variables 1 y 2 de la Tabla 1 se fijaron en 0.08, lo que resulta en una fracción de volumen de 9 % para la fase β , por debajo del máximo permitido de 10 % [11]. El rango de temperaturas de 453 a 543 K es el que en general se utiliza para los ensayos de DHC [11].…”

“…Las variables 1 y 2 se fijan buscando el mejor ajuste con las mediciones de cociente de velocidades de propagación de fisuras (V P ) en sentido longitudinal vs. radial; según Dutton et al [10] V P es proporcional a las difusividades. Además imponemos la condición que el volumen de las láminas rodeando al grano α no debe exceder el 10 % del total [11].…”

A Novel Technique for Addition of Hydrogen to Zirconium Alloys: Mechanical Hydrogen Ingress and Its Applications

“…As the DHC crack grows, the pressure tube approaches failure. The crack grows in the through-thickness, and longitudinal directions of the pressure tube at different rates [7] [11]. If the crack reaches a critical length in the longitudinal direction, the pressure tube will undergo unstable crack growth characterized by the rapid splitting of the tube in the longitudinal direction [7].…”

“…The horizontal axis is the temperature of the specimen, and reference. Figure 22: DSC heating curve #1 for sample F08-20-4T 11 The value for concentration on some of the DSC curves from CNL Chalk River using the DSC Q20 from TA Instruments was incorrect. The lab technician mistakenly used the wrong TSSD equation, and the data was subsequently corrected for in the concentrations reported in Table 6.…”