In this paper, the results of evaluations of the stress intensity factor and of natural SCC (stress corrosion cracking) growth simulations under weld residual stresses are presented. The results reveal some characteristic SCC propagation behaviors. A surface crack is assumed at the welded joint of a mock-up of a pressurized water reactor (PWR) pressurizer nozzle. SCC propagation law for the weld metal is assumed to be anisotropic. SCC propagation in the surface direction is assumed to be 10 times slower than that in the thickness direction of the welded joint. The anisotropy is caused by different solidification rates of the weld metal in these directions. The material in terms of mechanical properties is set to be homogeneous as differences in the Young’s moduli and the Poisson’s ratios are not large between the weld and the mother metal. The analytical procedures based on the finite element method with an automatic mesh generation scheme for cracked structures, the results of analyses under a various residual stress distributions and some discussions are presented in this paper.

This analysis has established a new hybrid RF/UT system for non-destructive testing of pipe walls for pipe wall thinning (PWT) in order to predict location, and enable measurement of the depth of defect by combining the group velocity method and calibration condition. A simulation of microwave (MW) behavior in a 91% brass waveguide (762mm pipe, Young’s Modulus 102KN/mm 2 ) was developed using Computer Simulation Technology (CST). The model included a frequency band of 1.283GHz for the TM nm mode (TM 01 and TM 21 ), with a sweeping frequency from 0.70GHZ to 2.00GHz. The model includes 14 instances of full-circumferential PWT, regularly spaced along the length of the waveguide with step-width of 50.8mm on center. For each we have modeled four cases of increasing PWT (5.08mm, 10.16mm, 15.24mm and 20.32mm). Considering the measurement with MW as a prediction of the location of the PWT, rather than a measurement, we can guide a straight-beam UT probe to the position predicted by MW, and use the appropriate signal velocity ultrasound to accurately measure the depth to defect from the outer surface of the pipe. The straight beam UT is found to be no better at determining the geometry of the defect than MW, but the accurate depth to defect (DD O ) measurement would allow estimation of the volume of the PWT.

This report proposes an elasto-plastic analysis method to be used for practical aseismic designing of nuclear piping systems. JSME (the Japan Society of Mechanical Engineers) initiated a task to establish an elasto-plastic analysis method for nuclear piping systems. During this task, benchmark analysis was conducted in order to examine the elastic-plasticity analytical method, in which our company decided to participate. Our policy for evaluation was that the material characteristics to be used in benchmark analysis were based on the standards for nuclear designs in Japan. As a consequence, we prepared a method to accurately simulate the vibration test on piping systems. The recommended elasto-plastic analysis method is thus specified as follows: 1) The elasto-plastic analysis method comprised of dynamic analysis on piping system modeled using beam elements and static analysis of the deforming elbow which was modeled using shell elements. 2) Bi-linear was applied as the elasto-plastic characteristics. The yield point was the standardized yield point times 1.2, and the second gradient was 1/100 the Young’s modulus. Kinematic hardening law was used as the hardening law. 3) Rain flow method and fatigue curve of an existing research were used to evaluate the fatigue life for the strain range obtained by elasto-plastic analysis.

When the ASME Code fatigue curves (S-N curves) are used in the assessment of high frequency cyclic stresses (such as those produced by flow-induced vibrations), the question arises as to the need for an E correction (i.e., multiplying the calculated cyclic stress by the ratio of the E value at the room temperature and the E value at the temperature used in the stress analysis). This question becomes significant for materials such as stainless steels when the two sets of S-N curves up to the 2007 Edition of the Code [1] are specified: i) the first curve covered the cyclic range of 10 to 10 6 cycles and specified an E value. This curve covered mostly the strain controlled fatigue data for which the correction for E is required. ii) The second curve covered the cyclic range of 10 6 to 10 11 cycles and didn’t provide a specific E value. This curve covered mostly the load controlled fatigue test data for which the correction for E is not required since the stress was independent of E (stress was either P/A for axial loading or Mc/I for bending). However the 2010 and subsequently the 2013 Editions of the Code [2] combined the two curves into a single curve with a cycle range of 10 to 10 11 cycles with E value specified at room temperature. This means that the E correction applies across the board for the entire cyclic range of 10 to 10 11 cycles including the high cycle end where the test results are independent of E. The inclusion of the E correction for the high cycle fatigue range presents a problem for the evaluation of components with vibratory loading. The present paper describes the results of a thorough review of the past technical basis papers for the ASME Code S-N curves and examines the necessity for E correction at the high cycle end of the Code S-N curves for stainless steels.

When bolted joints are subjected to thermal load, variations of the bolt clamping force are of great concern from the view point of joint safety. It is considered that titanium and titanium alloy bolts have high possibility for clamping machines and structures subjected to thermal load. Its specific characteristic of low thermal expansion expectantly works well to mitigate the reduction of bolt clamping force caused by thermal expansion. Low weight, low Young’s modulus and high resistance to corrosion of titanium and titanium alloy are also highly attractive. In this paper, the effectiveness of the numerical method proposed in the previous study is validated by experiments using bolted joints composed of titanium bolts and carbon steel plates. Then, thermal and mechanical behaviors of titanium and titanium alloy bolts are analyzed by finite element analysis in order to examine the applicability of those bolts for the joints under elevated temperature. Numerical analyses are executed as in the manner introduced in the previous paper, i.e., by incorporating the thermal contact coefficient into the finite element formulation. Numerical results suggest that titanium and titanium alloy bolts are favorably applied to the joints made of carbon steel whose clamping forces are likely to decrease under elevated temperature.

Welding is a reliable and efficient joining process in which the coalescence of metals is achieved by fusion. Welding is carried out with a very complex thermal cycle which results in irreversible elastic-plastic deformation and residual stresses in and around fusion zone and heat affected zone (HAZ). A residual stress due to welding arises from the differential heating of the plates due to the weld heat source. Residual stresses may be an advantage or disadvantage in structural components depending on their nature and magnitude. The beneficial effect of these compressive stresses have been widely used in industry as these are believed to increase fatigue strength of the component and reduce stress corrosion cracking and brittle fracture. But due to the presence of residual stresses in and around the weld zone the strength and life of the component is also reduced. To understand the behavior of residual stresses, two 10 mm thick Fe410WC mild steel plates are butt welded using the Metal Active Gas (MAG) process. An experimental method (X-ray diffraction) and numerical analysis (finite element analysis) were then carried out to calculate the residual stress values in the welded plates. Three types of V-butt weld joint — two-pass, three-pass and four-pass were considered in this study. In multi-pass welding operation the residual stress pattern developed in the material changes with each weld pass. In X-ray diffraction method, the residual stresses were derived from the elastic strain measurements using a Young’s modulus value of 210 GPa and Poisson’s ratio of 0.3. Finite element method based, SolidWorks software was used to develop coupled thermal-mechanical three dimension finite element model. The finite element model was evaluated for the transient temperatures and residual stresses during welding. Also variations of the physical and mechanical properties of material with the temperature were taken into account. The numerical results for peak transverse residual stresses attained in the welded plates for two-pass, three-pass and four-pass welded joint were 67.7 N/mm 2 , 58.6 N/mm 2 , and 48.1 N/mm 2 respectively. The peak temperature attained during welding process comes out to be 970°C for two-pass weld, 820.8°C for three-pass weld and 651.9°C for four-pass weld. It can be concluded that due to increase in the number of passes during welding process or deposition weld beads, the residual stresses and temperature distribution decrease. Also, the results obtained by finite element method agree well with those from experimental X-ray diffraction method.

Severe cyclic thermo-mechanical operating conditions during delayed coking can cause damages in the form of bulging and cracking in coke drums. As a result, the industry has to perform costly repairs and maintenance shutdowns. Therefore, it is important to understand the damage and failure mechanisms of the coke drums and to achieve more reliable coke drum design solutions. This paper explores alternative selections of clad and base material combinations for coke drum applications based on material property data provided in ASME Boiler & Pressure Vessel Code, Section II - Materials. Finite element analyses are carried out by simulating two critical loading scenarios in the coke drum operation cycle, i.e. the heating up and quenching stages. The analysis results show that the major achievement in lowering the stress level in the clad layer is due to matching of the coefficients of thermal expansion between clad and base materials. In addition, the finite element analyses indicate that the differences in Young’s modulus values play an important role in the variation of maximum stress in the coke drum shell during the quenching stage. Among eleven pairs of the clad and base material combinations studied, the combination of SA302-C as the base and nickel alloy N06625 as the cladding material is recommended.

In ASTM standard E1820, the single edge bend (SE(B)) geometry is one of those recommended for fracture toughness testing. The width to thickness ( W/B ) ratio recommended in E1820 for this specimen is 2. However, in certain cases, it is desirable to use specimens having alternative W/B ratios; the range of W/B suggested in E1820 is 1 to 4. In E1820, the crack size a may be evaluated during J -integral or CTOD resistance testing using the crack mouth opening displacement ( CMOD ) elastic unloading compliance C . The equation given to relate a to C using a dimensionless compliance BCE incorporates Young’s modulus E . For the three-dimensional (3-D) SE(B) specimens that are in neither plane stress nor plane strain condition, this parameter E may be considered as a normalizing parameter varying between extremes E (plane stress) and E /(1− ν 2 ) (plane strain) depending on crack depth (a/W) and specimen W/B ratio. In the present study, 3-D finite element analysis (FEA) was used to evaluate the CMOD compliance of B×B SE(B) specimens with shallow and deep cracks and compared with that from Tada’s plane stress equation. Crack sizes evaluated using plane stress and plane strain assumptions with the 3-D CMOD compliance obtained from FEA were compared with the actual crack size of the specimens used in FEA. It was found that the errors in crack size using plane strain or plane stress assumptions can be larger than 5%, especially for shallow-cracked specimens. In the present study, an effective modulus with values between plane stress and plane strain is proposed and evaluated by FEA for the 3-D B×B SE(B) specimens. The values were fitted to a polynomial equation as a function of u = 1/(√(BCE)+1) for use in estimating the dimensionless compliance for crack size evaluation for B×B SE(B) specimens. It is shown that the errors in crack size evaluation can be significantly reduced using this effective modulus.

Sealing of contained fluids is the primary performance required for pipe flange connections. It is well known that the leakage is likely to occur when contained fluids at high temperature are concerned. Due to the differential thermal expansion of each part, bolt preloads that tighten a pair of pipe flanges tend to decrease. Therefore, it is significantly important for the joint safety to estimate the amount of bolt preload reduction at the design stage. In this paper, a finite element approach is proposed to analyze thermal and mechanical behavior of pipe flange connections at elevated temperature, by incorporating the stress-strain curves of sheet gaskets measured in the previous paper. Then, the reduction rate of bolt preloads at elevated temperature is systematically evaluated. The analytical objects are pipe flange connections tightened with aramid sheet gaskets. When a pipe flange connection is subjected to thermal load, the gasket stress usually decreases along unloading curves. The temperature dependency of gasket stiffness is considered by defining Young’s modulus in unloading E* , which can be introduced into FE formulation using ordinary solid elements. Numerical results show that bolt preloads are decreased by as much as 30% of the initial value when using aramid sheet gaskets of 3mm thickness. The effectiveness of the proposed numerical method has been confirmed by comparing the numerical results of bolt preload reduction to experimental ones.

It is well known that an axial bolt force which tightens a gasket decreases due to a creep of non-asbestos gaskets. A bolted flange joint contains a combined condition of the creep/relaxation. A reduction behavior of a tightening pressure due to an effect of creep/relaxation is related to lifetime assessment of the non-asbestos gasket, and a leakage prevention of internal fluid. In this research, the creep/relaxation of the bolted flange joint using the non-asbestos gasket is measured. The compressed creep test is carried out using four-inch flanges and non-asbestos compressed fiber sheet gaskets. The test conditions are room temperature and 90 hours. The result of creep/relaxation is evaluated by 3-D viscoelasticity model. The creep/relaxation that was evaluated by 3-D viscoelasticity model and the Young’s modulus of the non-asbestos gaskets that was measured by the nanoindentation testing is applied to the FE analysis. FE model that include viscoelasticity is 1/16 of the test device. The stress state of the non-asbestos gasket was confirmed by the FE analysis. Then, the validity of creep/relaxation of the non-asbestos gaskets that was evaluated by the 3-D viscoelasticity model was shown by comparison with the experimental value and the analysis result.

The stability problem of a circular cylindrical shell composed of functionally graded materials with Young’s modulus varying continuously in the thickness direction under combined lateral pressure and axial compression loads is studied in this paper. The formulation is based on the first order shear deformation theory. A load interaction parameter is defined to express the combination of applied axial compression and external pressure. The stability equations are derived by the adjacent equilibrium criterion method. These equations are employed to analyze the buckling behavior and obtain the critical buckling loads. A detailed numerical study is carried out to bring out the effects of the power law index of functionally graded material, load interaction parameter, thickness ratio, and aspect ratio on the critical buckling loads. Validity of the present analysis was checked by comparing the results with those are available in the literature.

To calculate an accurate environmental fatigue life correction factor ( F en ) for evaluation of environmental fatigue, a detailed strain time history is needed. The strain history is determined by dividing the stress difference history with the Young’s modulus. ASME B&PV Code, Section III, NB-3216 has two methods of derivation of stress differences. One is NB-3216.1, “Constant Principal Stress Direction.” The other is NB-3216.2 “Varying Principal Stress Direction.” Determination methods for strain rates for two kinds of calculation methods of stress differences are proposed by applying the JSME Code for Environmental Fatigue Evaluation Method for Nuclear Power Plants. Also a sample calculation is performed for a typical nozzle to verify the proposed methods.

Reactor pressure vessels (RPV) are usually manufactured with austenitic cladding on their inner surface as a protection against corrosion from the primary circuit water environment. Thus, they are not included into the strength calculations of pressure vessels due to their lower strength properties and much smaller thickness in comparison with those of vessels as they are taken only as a corrosion layer. In the same time, due to different thermal coefficients and Young moduli, welding of austenitic cladding results in a high residual stresses in the cladding and also in the adjacent area in the base ferritic metal. These residual stresses as well as stresses resulted from the temperature field in the vessels represent necessary inputs into pressurized thermal shock calculations. WWER (Water-Water Energy Reactor = PWR type) reactor pressure vessels have relatively thick cladding — nominally 8 mm — made from two layers: first layer of 25/10 type welded by one pass while the second layer of 18/10/Ti typed is usually welded by three passes. The main part of the vessels was performed by strip welding with strips of 60 mm wide. Results of residual stresses measurements are given in the paper. Method with incremental milling of beams was used for the measurements and determination of residual stresses. Tests were performed on specimens in as-welded state and also after final heat treatment of the vessels, i.e. after several stress relieves including first hydrotest in shop. As residual stresses depends strongly also on direction of welding, beams were oriented in both directions — parallel and perpendicular to the welding direction. Results of these measurements are shown and discussed in the paper.

Buckling analysis of simply supported functionally graded cylindrical shells under mechanical loads is presented in this paper. The Young’s modulus of the shell is assumed to vary as a power form of the thickness coordinate variable. The shell is assumed to be under three types of mechanical loadings, namely, axial compression, uniform external lateral pressure, and hydrostatic pressure loading. The equilibrium and stability equations are derived based on the first order shear deformation theory. Resulting equations are employed to obtain the closed-form solution for the critical buckling load. The influences of dimension ratio, relative thickness and the functionally graded index on the critical buckling load are studied. The results are compared with the known data in the literature.

SCC (stress corrosion cracking) of low-carbon stainless steel piping has been found in Japanese BWR plants since 2002. According to JSME Fitness-for-Service Code, flaw evaluations are required to verify the life-time of piping if SCC is detected. In order to evaluate the SCC propagation behavior, it is necessary to obtain the residual stress distribution through the thickness of piping. In this study, the mock-up PLR (Primary Loop Recirculation system) piping weld joints made of L-grade Type 316 stainless steel with 300 mm and 600 mm diameter were fabricated and residual stress analyses were performed in order to obtain stress distributions. Material properties (specific heat, thermal conductivity, Young’s modulus, stress-strain curve, etc.) were obtained and temperature history during welding and weld residual stress were measured using these mock-ups. Material properties were used in the heat transfer and stress analyses. Measured temperature history and residual stress were compared with the results of heat transfer and stress analyses, respectively. Residual stress analysis of the pipe weld joint is commonly performed using axisymmetric element. In some cases of the combination of pipe diameter and thickness, residual stress obtained by the conventional method might differ from the experimental result owing to the difference of heating and constraint conditions between the axisymmetric model and the actual condition. In order to obtain more precise results, heat transfer and stress analyses were performed, taking into account the adjustment of the boundary condition in the weld passes of the last layer and the constraint condition using a spring element, respectively. On the outer and inner surfaces, almost the same residual stress distributions were obtained for the FEM analysis and the measurement. The residual stress distributions for PLR piping with different diameters, thicknesses, welding processes and groove angles were obtained by FEM analysis. Based on the results of the analyses, the influences of these parameters on residual stress were evaluated.

Currently, measurement of internal strains deep inside graphite is extremely difficult. As a consequence there is a need to assess the ability of a deep-hole drilling (DHD) method to measure internal strains in reactor core graphite and explore the potential for in-situ measurement. DHD technique is a semi-destructive method for measurement of the through thickness residual stresses. The technique previously has been applied successfully to metallic and composite materials. In this paper, the method for stress measurement in graphite is examined particularly when a significant volume fraction of porosity is present. Two types of graphite were used, PGA and PG25 filter graphite. In PGA graphite the Young’s modulus of elasticity was orientation dependent. As a consequence samples were cut from blocks in two directions. PG25 filter graphite is a surrogate for service exposed material. Known loads were applied to graphite beam samples and the DHD method was used to measure the stress/strain profile through the material. The results were compared with the strain data obtained from strain gauges bonded to the samples. Overall, there was an excellent agreement between the DHD measured stress/strain and applied stress. It is shown that deep-hole drilling technique can measure linear stress distributions in graphite.

A new method of evaluation of elastic property deterioration due to accumulated damage is suggested and experimentally verified. It is based on the explicit correlations between two groups of anisotropic properties – conductivity and elasticity, recently established for porous/microcracked materials with anisotropic microstructures. An experimental study of fatigue has been done to verify the theoretical predictions. The electrical resistance and Young’s modulus are measured as functions of the number of loading cycles in the standard fatigue tests. The agreement between the theoretical predictions and the direct experimental data is better than 10% in all cases. The results allow one to use the measurement of electric resistance to estimate the damage accumulated in metal structures and decrease in the elastic modulus.

The paper is concerned with the criterion for the instability of growth of a circumferential through-wall crack in a piping system. A simple approach involves representing the cracked section behaviour by a moment (M)–rotation (φ) relation. The criterion for unstable crack growth is then L * > EI |dφ/dM| where E is Young’s modulus and I is the second moment of area of the piping at the cracked section. L * can be viewed as a crack-system compliance length parameter or an “effective” pipe length. If the piping system, apart from the cracked system, behaves in a linear manner, L * is dependent on the system’s characteristics but most importantly, is independent of the magnitudes of any applied loadings and the characteristics of the cracked section. This paper is concerned with the effect of system non-linearity, and in particular restraint non-linearity, on the instability criterion, the considerations being based on the analyses of a simple model which contains a restraint which behaves non-linearly. In this case, we show that L * is no longer dependent only on the system’s characteristics, as is the case when the restraint behaves linearly.

Materials used in high-pressure vessels may be subjected to rapid temperature change, which may induce micro-cracks on the surface and into material. The growth of micro-cracks is detrimental to facility life. Chromium carbide (Cr 3 C 2 ) has been proved to be a potential structural material for toughening alumina in biomedical and industrial applications because of its high Young’s modulus and erosion resistance. On the other hand, TiC/Al 2 O 3 composite has been used as a magnetic head slider due to its good wear resistance and mechanical strength, and potentially could be an excellent lining material. In this study we thermally shocked ceramic material in disc shape to create different degrees of micro-cracking and use ultrasound attenuation technique to evaluate the damage. This includes narrow band tone burst at different frequency. The results showed significant dependence between ultrasonic attenuation and shock temperature. Corresponding SEM pictures show although the size of micro-crack doesn’t change, the depth of the micro-cracks increases. It is demonstrated that ultrasonic attenuation proves to be a reliable tool for evaluating micro-fractures in solids.

Organic thick coatings (epoxy, polyurethane, and acrylic-urethane) have been widely applied to high modulus substrates (e.g., steel) for anticorrosion protection. To improve performance, reinforced components (clay, bochmite, nanopaticles, etc.) are usually added to these coatings. However, the acoustic evaluation of these coatings is difficult due to their low acoustic velocities and high attenuation coefficients. In this paper, first, the scanning acoustic microscope (SAM) is used to image sub-surfaces, coating/substrate interfaces, and to measure acoustic velocities. Different phases can be observed on some coatings and defects can be found at some interfaces. Secondly, the atomic force microscope (AFM) is applied to image surfaces at high resolution (compared to SAM). These results agree with SAM images. Thirdly, a nano-indentation technique is utilized to measure the reduced Young’s modulus and absolute hardness of the coatings. The results show that epoxy has the highest Young’s modulus and acrylic-urethane has the lowest. Reinforced components can either increase or decrease Young’s modulus, and hardness depending on the coating material. Finally, results from the SAM, AFM and nano-indentation are compared and analyzed to optimize the evaluation.