On the Assessment of Through-Wall Circumferential Cracks in Steam Generator Tubes With Tube Supports

Abstract

The assessment of steam generator tubes with defects is of great importance for the life extension of steam generators. Circumferential through-wall cracks are the most severe of all tube circumferential defects, and usually require plugging of the affected tubes. The assessment of the tubes with through-wall circumferential cracks or cracks projected to become through-wall can be conducted using the failure assessment diagram (FAD) approach. This approach requires the calculation of the stress intensity factor and the limit load. The available stress intensity factor and limit load solutions for cracked tubes do not include the constraining effect of the tube supports. In the present paper, it is shown that this can be overly conservative. Solutions for stress intensity factors and limit loads are presented for tubes with circumferential through-wall cracks including the effect from the tube support plates. Different values of support spacing are considered. Based on these solutions, the assessment of a typical steam generator tube is demonstrated.

Failure Assessment Diagram in Structural Integrity Analysis of Steam Generator Tubes

“…Some models presented in the literature consider the linear elastic fracture mechanics theory, Cizelj et al (1995), Wang and Reinhardt (2003), Tonkovic et al (2005), Hu et al (2011), while other methodologies are based on the elastic-plastic fracture mechanics, Majumdar (1999a), Tonkovic et al (2005), Chang et al (2006), Huh et al (2006). These approaches can be easily generalized to different loading conditions without the need of additional experimental validation.…”

“…As a comprehensive option encompassing both limit load and fracture mechanics analyses, some authors proposed the use of the FAD as the most appropriate assessment technique, capable of predicting failures due to different mechanisms in SGTs, Lee et al (2001), Wang and Reinhardt (2003), Chang et al (2006), Tonkovic et al (2008). Thus, at present, many structural integrity assessment procedures based on the FAD methodology have been included in the most important construction codes and guides (e.g., ASME Section XI, API 579-1/ASME FFS-1, SINTAP and BS 7910).…”

“…The authors recommended a fracture toughness value of 250 kJ/m 2 for structural integrity assessments. It should be mentioned that other authors have considered alternative fracture toughness values for structural integrity assessments of cracked SGTs, but the details of their determination are not available, e.g., Wilam and Cermakova (1995), Wang and Reinhardt (2003), Tonkovic et al (2005Tonkovic et al ( o 2008, Chang et al (2006), Hu et al (2011). In most of these cases, toughness values were inferred from fracture tests performed in similar materials but using standardized specimens obtained from other product forms, e.g., plates, obtained by different fabrication routes.…”

Measuring Inaccessible Residual Stresses Using Multiple Methods and Superposition

“…One example is axial stresses in girth (circumferential) welds on piping and pressure vessels. Circumferential cracks cause the greatest concern for rupture in nuclear power plants [1,2]. To remain in service, such defected components must be demonstrated to be safe against rupture.…”

T-stress solutions for cracks at notches and in cylinders

“…In most cases the cylinder is supported, and the movement of the ends is restrained. Wang and Reinhardt (2003) provide stress intensity factor and limit load solutions taking into account end constraints. A similar analysis could be done for the T-stress.…”