Accepted Manuscripts

Alireda Aljaroudi, Premkumar Thodi, Ayhan Akinturk, Faisal Khan and Mike Paulin
J. Pressure Vessel Technol   doi: 10.1115/1.4036217
When offshore pipelines approach the end of their design life, their condition could threaten oil flow continuity as well as become a potential safety or environmental hazard. Hence, there is a need to assess the remaining life of pipelines to ensure that they can cope with current and future operational demand and integrity challenges. This paper presents a methodology for assessing the condition of aging pipelines and determining the remaining life that can support extended operation without compromising safety and reliability. Applying this methodology would facilitate a well-informed decision that enables decision makers to determine the best strategy for maintaining the integrity of aging pipelines.
TOPICS: Underwater pipelines, Pipelines, Safety, Reliability, Design, Hazards, Flow (Dynamics)
Kay Langschwager, Jürgen Rudolph, Alfred Scholz and Matthias Oechsner
J. Pressure Vessel Technol   doi: 10.1115/1.4036140
Austenitic stainless steel of type X6CrNiNb18-10 exhibits advantageous mechanical and chemical properties and is a common material for numerous applications in the nuclear power plant and chemical industries. Besides the mechanical strain induced by high pressure, the fatigue life in welded pipelines is affected by additional thermomechanical strains due to thermal loading. The welding process mainly determines the geometry and metallurgical constitution of the welded joint. Therefore, the butt welds additionally influence the strain gradient along the component and reduce its lifetime. While the base and weld material are similar, they show different softening and hardening behavior, especially at ambient temperature. Cyclic hardening occurs in the base material, whereas cyclic softening can be observed in the weld material. The hardness distribution along the welded joint reveals no clear differentiation of base material, the heat affected zone and weld material. The attributes of the individual materials cannot be transferred to the welded joint automatically. Thus, the analysis of the interaction between the materials along the welded joint is a main topic of this research. To this end, digital image correlation is used for different kinds of specimens and load conditions. The position along the testing area at which fatigue failure occurs depends on the specimen type and the load condition but not on the temperature. Further, isothermal and anisothermal fatigue tests on welded cruciform specimens are presented. The common practice of the effective strain is discussed for the analyzed conditions.
TOPICS: Welded joints, Fatigue, High temperature, Temperature, Stress, Hardening, High pressure (Physics), Welding, Heat, Fatigue failure, Chemical industry, Strain gradient, Chemical properties, Pipelines, Testing, Fatigue life, Fatigue testing, Geometry, Nuclear power stations, Stainless steel
Krishna Sampath, Thomas Drube and Mahendra D. Rana
J. Pressure Vessel Technol   doi: 10.1115/1.4036138
To assure adequate fracture resistance of cryogenic pressure vessels designed to operate at a minimum design metal temperature (MDMT) colder than 77K, current ASME VIII-1, UHA-51 rule requires that the weld metal (WM) meet or exceed 21 mils lateral expansion (LE) at 77K as determined using Charpy V-Notch (CVN) impact test. To the credit of this rule, cryogenic pressure vessels fabricated to date meeting the WM CVN 21 mils LE requirement had continued to serve well - without any adverse incident - in numerous applications across the world, at cryogenic temperatures colder than 77K. However, a critical examination of the underlying research revealed that the technical basis used for establishing the above requirement can be further improved. The present research used an insightful data analysis approach to provide a rational basis for describing a fracture resistance parameter that also reaffirmed the WM CVN 21 mils LE at 77K toughness requirement for cryogenic service colder than 77K. While the fracture resistance parameter remains applicable to both 77K and 4K service, its use offers a tremendous benefit to the cryogenic equipment manufacturers as the fracture resistance parameter for both 77K and 4K service can be evaluated using LE, KIc and YS values measured at 77K.
TOPICS: Temperature, Metals, Design, Fracture toughness, Vessels, Fracture (Materials), Fracture (Process), Pressure vessels, Impact testing
Hongsong Zhu
J. Pressure Vessel Technol   doi: 10.1115/1.4036139
e stress analysis method for fixed tubesheet (TS) in pressure vessel codes such as ASME VIII-1, EN13445 and GB151 are based on the classical theory of thin plate on elastic foundation. In addition, these codes all assume a geometric and loading plane of symmetry at the midway between the two TSs so that only half of the unit or one TS need be considered. In this study, based on Ambartsumyan's theory of transversely isotropic thick plate, a refined theory of stress analysis for TS is presented which also considers unequal thickness for two TSs, different edge conditions, pressure drop and dead weight on two TSs, the anisotropic behavior of the TS in thickness direction and transverse shear deformation in TS. Analysis shows floating and U-tube heat exchangers are the two special cases of the proposed theory. Theoretical comparison shows that ASME method can be obtained from the special case of the simplified mechanical model of the proposed method. Numerical Comparison results indicate that predictions given by the refined theory agree well with finite element analysis (FEA) for both thin and thick TS heat exchangers, while ASME results are not correct or not accurate.
TOPICS: Stress analysis (Engineering), Finite element analysis, Heat exchangers, Pressure drop, Shear deformation, Weight (Mass), Pressure vessels, Anisotropy
Masayuki Kamaya
J. Pressure Vessel Technol   doi: 10.1115/1.4036141
According to Appendix L of the Boiler and Pressure Vessel Code Section XI, flaw tolerance assessment is performed using the stress intensity factor even for low-cycle fatigue. On the other hand, in Section III, the fatigue damage is assessed using the design fatigue curve, which has been determined from strain-based fatigue tests. Namely, the stress is used for the flaw tolerance assessment. In order to resolve this inconsistency, in the present study, the strain intensity factor was used for crack growth prediction. First, it was shown that the strain range was the key parameter for predicting the fatigue life and crack growth. The crack growth rates correlated well with the strain intensity factor even for the low-cycle fatigue. Then, the strain intensity factor was applied to predict the crack growth under uniform and thermal cyclic loading conditions. The estimated fatigue life for the uniform cyclic loading condition agreed well with that obtained by the low-cycle fatigue tests, while the fatigue life estimated for the cyclic thermal loading condition was longer. It was shown that the inspection result of “no crack” can be reflected to determining the future inspection time by applying the flaw tolerance analysis. It was concluded that the flaw tolerance concept is applicable not only to the plant maintenance but also to plant design. The fatigue damage assessment using the design fatigue curve can be replaced with the crack growth prediction.
TOPICS: Low cycle fatigue, Stainless steel, Fracture (Materials), Fatigue life, Fatigue, Inspection, Stress, Design, Fatigue damage, Tolerance analysis, Plant design, Plant maintenance, ASME Boiler and Pressure Vessel Code, Fatigue testing
Mohammad Shafinul Haque and Calvin M. Stewart
J. Pressure Vessel Technol   doi: 10.1115/1.4036142
The classic Kachanov-Rabotnov (KR) creep damage model is a popular model for the design against failure due to creep deformation. However, the KR model is a local approach that can exhibit numerically unstable damage with mesh refinement. These problems have led to modified critical damage parameters and alternative constitutive models. In this study, an alternative Sine hyperbolic (Sinh) creep damage model is shown to (i) predict unity damage irrespective of stress and temperature conditions such that life prediction and creep cracking are easy to perform, (ii) develop a continuous and well-distributed damage field in the presence of stress concentrations, and (iii) is less stress-sensitive, is less mesh-dependent, exhibits better convergence than the KR model. The limitations of the KR model are discussed in detail. The KR and Sinh models are calibrated to three isotherms of 304 stainless steel creep test data. Mathematical exercises, smooth specimen simulations, and crack growth simulations are performed to produce a quantitative comparison of the numerical performance of the models.
TOPICS: Creep, Fracture (Materials), Stainless steel, Damage mechanics, Damage, Stress, Engineering simulation, Simulation, Fracture (Process), Failure, Constitutive equations, Design, Cracking (Materials), Temperature
Technical Brief  
Kleio Avrithi and Harrison Hyung Min Kim
J. Pressure Vessel Technol   doi: 10.1115/1.4036144
Optimization of piping supports is a well-known problem. The paper considers the optimization of piping supports with respect to cost and the loads transmitted to the supporting structural elements, when the orientation of the supporting structure is to be determined. This is the case, when new structural elements need to be added to the existing building structure to support components and piping systems that come as a new addition to a nuclear plant. The Analytical Target Cascading (ATC) method is used for the optimization, combining the support loads from different piping analyses in a hierarchical framework. It is shown that the ATC method can be used for an optimized location of structural elements simultaneously supporting complex piping systems and implemented in a structural analysis software.
TOPICS: Optimization, Pipes, Structural elements (Construction), Stress, Piping systems, Structural analysis, Computer software, Nuclear power stations
Uday S. Dixit and Rajkumar Shufen
J. Pressure Vessel Technol   doi: 10.1115/1.4036143
Autofrettage is a metal working process of inducing compressive residual stresses in the vicinity of the inner surface of a thick-walled cylindrical or spherical pressure vessel for increasing its pressure capacity, fatigue life and stress-corrosion resistance. The hydraulic autofrettage is a class of autofrettage processes, in which the vessel is pressurized using high hydraulic pressure to cause the partial plastic deformation followed by unloading. Despite its popularity, the requirement of high pressure makes this process costly. On the other hand, the thermal autofrettage is a simple method, in which the residual stresses are set up by first maintaining a temperature difference across the thickness of the vessel and then cooling it to uniform temperature. However, the increase in the pressure carrying capacity in thermal autofrettage process is lesser than that in the hydraulic autofrettage. In the present work, a combined hydraulic and thermal autofrettage process of a thick-walled cylinder is studied using finite element method package ABAQUS® for aluminum and SS304 steel. The strain hardening and Bauschinger effects are considered and found to play significant roles. The results show that the combined autofrettage can achieve desired increase in the pressure capacity of thick-walled cylinders with relatively small autofrettage pressure. For example, in a SS304 cylinder of wall-thickness ratio of 3, an autofrettage pressure of 150 MPa enhances the pressure capacity by 41%, but the same pressure with a 36 ?C higher inner surface temperature than outer surface temperature can enhance the pressure capacity by 60%.
TOPICS: Finite element methods, Autofrettage, Pressure, Temperature, Cylinders, Vessels, Residual stresses, Stress corrosion cracking, High pressure (Physics), Deformation, Cooling, Aluminum, Metalworking, Steel, Pressure vessels, Wall thickness, Work hardening, Fatigue life
S. Ali Faghidian
J. Pressure Vessel Technol   doi: 10.1115/1.4035980
The stress function approach is revisited for the inverse determination of residual stresses and eigenstrains from limited point-wise data in spherically symmetric stress state. The robust least squares technique is utilized to minimize the deviation of measurement data from the model predictions while a full range of continuum mechanics requirements are satisfied. The application of the newly proposed spherical stress function is effectively demonstrated for two cases of analytical solutions considering different material models. Also the eigenstrains are inversely determined satisfying the equations of strain compatibility and a closed form analytical solution is presented.
TOPICS: Pressure vessels, Residual stresses, Stress, Continuum mechanics
Ji-Soo Kim, Hyun-Suk Nam, Yun-Jae Kim and Ju-Hee Kim
J. Pressure Vessel Technol   doi: 10.1115/1.4035977
This paper investigates the effect of initial residual stress and pre-strain on residual stresses due to laser shock peening for Alloy 600 using numerical simulation. For simulation, the strain rate dependent Johnson-Cook hardening model with a Mie-Grüneisen equation of state is used. Simulation results are compared with published experimental data, showing good agreement. It is found that the LSP process is more effective for higher initial tensile residual stress and for larger initial pre-strain in terms of compressive stress at the near surface. However, the effective depth decreases with increasing initial tensile residual stress and initial pre-strain.
TOPICS: Alloys, Residual stresses, Nozzles, Laser hardening, Stress, Hardening, Compressive stress, Equations of state, Simulation, Computer simulation, Simulation results
Review Article  
Omesh K. Chopra, Gary L. Stevens, Robert Tregoning and A. S. Rao
J. Pressure Vessel Technol   doi: 10.1115/1.4035885
The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code) provides rules for the design of Class 1 components of nuclear power plants. However, the Code design curves do not address the effects of light water reactor (LWR) water environments. Existing fatigue strain-vs.-life (e-N) data illustrate significant effects of LWR water environments on the fatigue resistance of pressure vessel and piping steels. Extensive studies have been conducted at Argonne National Laboratory and elsewhere to investigate the effects of LWR environments on the fatigue life. This article summarizes the results of these studies. Existing fatigue e-N data were evaluated to identify the various material, environmental, and loading conditions that influence fatigue crack initiation; a methodology for estimating fatigue lives as a function of these parameters was developed. The effects were incorporated into the ASME Code Section III fatigue evaluations in terms of an environmental correction factor, Fen, which is the ratio of fatigue life in air at room temperature to the life in the LWR water environment at reactor operating temperatures. Available fatigue data were used to develop fatigue design curves for carbon and low-alloy steels, austenitic stainless steels, and nickel-chromium-iron (Ni-Cr-Fe) alloys and their weld metals. A review of the Code Section III fatigue adjustment factors of 2 and 20 is also presented and the possible conservatism inherent in the choice is evaluated. A brief description of potential effects of neutron irradiation on fatigue crack initiation is presented.
TOPICS: Fatigue life, Water, Light water reactors, Fatigue, Alloys, Steel, Design, Fatigue cracks, Fatigue design, Pipes, ASME Boiler and Pressure Vessel Code, Iron, Nuclear power stations, Stainless steel, Pressure vessels, Irradiation (Radiation exposure), ASME, Carbon, Temperature, Neutrons, Metals, Nickel, ASME Standards, Operating temperature
Prof. Amro Zaki, Sayed Nassar, Serge Kruk and Meir Shillor
J. Pressure Vessel Technol   doi: 10.1115/1.4035695
In this paper, an inverse bi-harmonic axisymmetric elasticity problem is solved by invoking measured out-of-plane surface deformation values at discrete locations around a preloaded bolt head, in order to calculate the underhead contact stress and joint clamp load that would have caused that out-of-plane surface deformation. Solution of this type of inverse problem promises to improve the automation process of bolted joint system assembly, especially in critical and safety related applications. For example, a real-time optically measured joint surface deformation can be utilized for automating process control of bolted joint assembly in a reliable fashion. This would be a significant reliability improvement as compared to the commonly used method in mass production using torque-only control method in which there is wide scatter in the torque-tension correlation due to the normal scatter in frictional variables. Finite Element Analysis (FEA) method is used to validate the inverse problem solution provided in this paper.
TOPICS: Surface deformation, Stress, Manufacturing, Torque, Electromagnetic scattering, Finite element analysis, Inverse problems, Tension, Elasticity, Mass production, Process control, Safety, Reliability, Clamps (Tools)

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