Issue 41

G. G. Cunto et alii, Frattura ed Integrità Strutturale, 41 (2017) 332-338; DOI: 10.3221/IGF-ESIS.41.44 335 morphology and material properties (obtained by hot tensile test), PICEP return as output the size of a critical crack and a curve of leakage flow rate versus crack size. For the tearing collapse verification, the elastic-plastic J-Integral analysis is, in general, applied with the aid of finite element methods. For usual engineering cases, such as piping with a through-wall crack, solutions listed in manuals that are derived from numerical solutions are available. One of the most well-known and valid reference is the Ductile Fracture Handbook developed by Zahoor [4], that provides solutions for applied J and T, where each solution corresponds to a system of geometry, crack orientation, applied loading, and material properties. The applied J-Integral equation, proposed by Zahoor, for a circumferential through-wall crack present in a piping, considering bending moment loads, is the following:   Elastic Plastic J J J (3)                        1 2 2 0 0 1 3 2 0 1 n b J Elastic J Plastic f M M J R H M R t E (4) where: M = Is the applied bending moment; 0  and  b f M = Are parameters that depend on pipe dimensions, load conditions, crack size and orientation and material properties; H 1 = Is based on finite element analyses, and can be found in reference [4]; R, t e θ = Are the pipe mean radius, wall thickness and crack half-angle, respectively; and E, α, σ 0 , ε 0 and n = Are constants in the RO stress-strain relation as showed in Eq. 1. Determination of LBB viability It shall be determinate the size of through-wall cracks that will result in a detectable leakage with a margin of 10 applied between the predicted leakage and the detectable leak, to cover various uncertainties associated with leakage prediction and leakage detection. Historically, a leakage detection capability of 1 gallon per minute (gpm) that presents 3.78 liters per minute in a PWR plant has been used for leakage detection capability [5]. Consequently, a 10 gpm leakage crack is considered in the LBB analysis. LBB viability for an analyzing pipe system is demonstrated if a margin of at least two exists between the leakage crack size and the critical through-wall crack size. R ESULTS Mechanical tests results ot tensile test results show a well-defined behavior among the three zones, where the base material has a high toughness behavior with relative low yield strength and high uniform elongation, the weld show a low toughness behavior with relative high yield strength and low uniform elongation, and the HAZ showed intermediate mechanical properties between the base material and the weld. Fig. 1 present typical stress x strain curves for the three different zones of the welded pipe. Ramberg-Osgood analyses according Eq. 1 were performed for all specimen data, tested according to Tab. 1 for hot tensile test. The results of yield strength (σ 0 ) tensile strength (σ R ), flow stress (σ f ), elongation, Ramberg-Osgood parameter (α) and strain-hardening exponent (n) are presented in Tab. 2. Fig. 2 present typical J-R curves obtained for the three different zones in the welded pipe. The results of all base material and HAZ are not valid according to ASTM E1820-13 because J Q is much larger than the J limit value. All J Q results for the weld zone have met the criteria of validity of the standard and can be considered valid JIC values. For the power law analyses, according Eq. 2, only one weld specimen, CT2 of Tab. 3, fulfilled all the requirements to be validate. Even though the results for the base material and HAZ did not present valid J IC values, the tests demonstrated the high toughness of these zones of the welded pipe. Thus, for the elastic-plastic J-Integral analysis, only the weld zone will be considered, once that the analysis of the weld will bring the most conservative results. The results of J IC and power law material constant (C) and exponent (m) obtained from the weld J-R curves and Eq. 2 are presented in Tab. 3. H