bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagating ASME PCC-1 Appendix A Compliance
Authors: Barnard Jason M.
Published: December 2016

In November 2013 the revised ASME PCC-1 “Guidelines for Pressure Boundary Bolted Joint Assembly” were published including Appendix A, “Training and Qualification of Bolted Joint Assembly Personnel.” This Appendix outlines a training, examination and qualification system for ensuring a consistent level of knowledge and experience for bolting assemblers and specialists working on bolted flange joint assemblies. The ultimate objective is a mobile workforce capable of bolting ASME plant with a minimum performance standard safely and with no subsequent leaks.

Major operators and contractors involved in oil and gas, petrochemical and power generation, or any industry that uses bolted flange joint assemblies, can benefit from PCC-1. Benefit recognition has begun with operators now specifying PCC-1 compliance in their procedures and bid packages.

However, nearly three years after the introduction of Appendix A the number of Qualifying Organizations approved to deliver the program and individuals qualified via these programs remains stubbornly small in comparison with other programs and insufficient to meet the future safety demands of the industry or the objective of PCC-1 and Appendix A.

This technical paper reviews key elements of Appendix A, compares Appendix A with other international qualifications and suggests recommendations intended to increase recognition and compliance with these guidelines. The recommendations and expected benefits follow from an extensive review of work by other organizations and published data concerned to reduce recorded leaks from bolted joints, including:

a) Implementation lessons learned from a Qualifying Organization and Review Organization.

b) Current international qualifications and the differing routes to achieve each qualification including:

1) ASME PCC-1 Appendix A Training and Qualification of Bolted Joint Assembly Personnel.

2) European standard EN1591-4 Qualification of personnel competency in the assembly of the bolted connections of critical service pressurized systems.

3) Engineering Construction Industry Training Board (ECITB) Mechanical Joint Integrity (MJI) technical training standards and Step Change in Safety Mechanical Joint Integrity Route to Competence Guidance

4) Additional country specific qualifications

c) Program effectiveness study of the Engineering Construction Industry Training Board (ECITB) Mechanical Joint Integrity (MJI) program and the Step Change in Safety Hydrocarbon Release (HCR) model set up to achieve leak reduction in the UK North Sea sector.

Finally, the paper will conclude with outlining the benefits to be gained globally through standardization of international qualification programs to enable true portability including:

a) The need to increase the number of auditable Qualifying Organizations able to deliver the program, qualify individuals and engage operator/contractors in the process.

b) Importance of effective communication and summary of the guidelines.
Validation of a Concept for Burst Pressure Prediction by Damage Mechanics
Authors: Brinnel Victoria , Schaffrath Simon , Münstermann Sebastian , Feldmann Markus
Published: December 2016

In ASME and EN pressure vessel standards the stress-based dimensioning is currently performed by either applying experience-based safety factors directly on the material’s yield or tensile strength (EN) or incorporating them in the allowable stress derivation (ASME). The current concept is penalizing modern high strength pressure vessel steels due to their yield-to-tensile ratio. The application of these steel grades is hindered despite their excellent mechanical properties. Possible benefits cannot be exploited. Probabilistic safety concepts are a suitable approach to derive adequate safety factors for high strength steels. But their application requires a large number of expensive full scale burst tests. Therefore, it is proposed to replace these by numerical simulations using damage mechanics. This paper aims at validating such a concept for the numerical prediction of burst pressures. The presented procedure uses a Gurson model to represent ductile failure behavior on the specimen scale and correlates it to an efficient strain-based failure criterion, which is more suitable for simulations on full component scale. The validation is performed on a demonstrator pressure vessel of the high strength steel P690Q. The strain-based failure criterion is derived on small scale tests and applied in simulations of the pressure vessel. The numerically predicted burst pressure only exceeds the actual burst pressure by 6% and the critical locations are correctly predicted. The approach is validated successfully. Suggestions for further improvements are made.
A Method to Characterize Residual Stresses Induced by Machining
Authors: Girinon Mathieu , Robin Vincent , Jourden Erwan , Valiorgue Frédéric , Rech Joël , Feulvarch Eric
Published: December 2016

The modeling of residual stresses induced by drilling remains an issue. Indeed, even if some models are under development, their validation is limited by the absence of universal characterization method of residual stresses inside the hole. This paper aims at presenting a procedure to characterize the residual stress profile induced by drilling. The principle is based on the preparation of a reference sample that has been pre-heat treated in order to remove bulk residual stresses without modifying the microstructure. Then the sample is instrumented with strain gauges before being cut in two parts. This enables on one hand to estimate the elastic recovery after the cut and on the other hand to provide an easy access to the investigated surface. Finally a standard X-Ray diffractometer and an electropolishing technique are combined to estimate residual stresses profiles in two directions (circumferential and axial directions). Some numerical analyses are also performed to estimate stress relaxation during thermal treatment and during sample cutting to give a better interpretation of measurements.
Cyclic Response of Enhanced Bolted Flange Joints for Piping Systems
Authors: La Salandra Vincenzo , Di Filippo Rocco , Bursi Oreste S. , Paolacci Fabrizio , Alessandri Silvia
Published: December 2016

Bolted Flange Joints (BFJs) represent the most common and critical components used nearly in all industrial piping systems, including Oil & Gas plants. Owing to their strategic importance and heavy consequences both to the environment and human lives due to both damage and leakage, BFJs are considered very important in industrial plant design. Therefore, their behaviour becomes critical also under seismic actions.

Along this line, in the first part of this paper the experimental test campaign performed on enhanced bolted flange joints subject to both monotonic and cyclic loading is presented and discussed. Then, specific values of both stiffness and strength with reference to leakage are estimated. Successively, a reliable model capable of predicting the leakage force for a generic BFJ, including the interaction between the axial and shear load, is proposed and validated; in particular, both actual and previous full scale experimental data were involved in the validation. As a result, the values predicted by the model agree well with those obtained by the experiments. This model is also adopted to predict leakage stiffness values for thick flanges. Overall, the proposed analytical model can represent a promising tool for the leakage prediction of BFJs in complex piping systems.
HRSG Header Welds Creep-Assessment Through a Procedure for the Italian Code Application and Comparison With the American Standard
Authors: Grisolia Ottaviano , Scano Lorenzo
Published: December 2016

Present work includes creep analysis of ASTM A 335-Grade P22 welds on the high-temperature-section (superheater/reheater) lower headers of bottom-supported heat-recovery steam generators (HRSG): they may be critical because of the long continued service (175000 hours or twenty years), internal reactions, stress intensification at the end-plug and finned-tube joint to the cylinder respectively. Weld life results from the Italian creep code compare to those predicted by the American standard API 579-1. Classical methods applied on the circumferential weld show consistent Von-Mises equivalent stress with both ASME and Italian pressure formulae’s (for the cylinder wall). Numerical-model stress analysis for the finned-tube tee weld shows results consistent with those on both sides of the intersection (pressure-load condition, linear); it shows instead unacceptable values for thermal-load condition, linear and nonlinear. Creep strain values are generally small for both joints, with rates in the weld metal lower than base’s for the circumferential weld. Analysis considers a strength reduction factor for the welds, disregarding possible residual stresses; it assumes a Norton-Bailey power-law for the creep, experimental data from short duration tests providing the basis for extracting coefficients. API 579-1 (Level 1 through 3) assessment results are consistent with the Italian creep code. Creep lives on the weld are consistent with those on both sides of the intersection, the circumferential weld showing lives longer than 300000 hours.
Analysis of Pressure Relief Valve Dynamics During Opening
Authors: Bossard John , Reich Alton , DiMeo Alex
Published: December 2016

In nuclear power plants power actuated pressure relief valves serve several purposes. They act as safety valves and open automatically in response to unusually high pressures in the primary system. They also act as power operated valves and are used to relieve steam in response to automatic or manually initiated control signals. These valves are required to lift completely over a short duration from the time that they receive an actuation signal, or the system pressure exceeds the set point. This short lift time results in the valve disk moving at high velocities, and can result in high impact forces on the piston and stem when the valve fully opens.

To quantitatively evaluate the dynamic performance of the Target Rocket Pressure Relief Valve, an analysis effort was undertaken which would accommodate both the fluid dynamic features of the valve operation, as well as the kinematic characteristics of the valve, during pressure relief valve operation.

To execute the analysis, the Generalized Fluid System Simulation Program (GFSSP) was used. GFSSP is a network flow solver CFD code developed by NASA that has the ability to analyze transient, multi-phase flows, and conjugate heat transfer, along with the inclusion of custom user subroutines developed by the user which can accommodate other simulation requirements.

In this paper we present the GFSSP model developed, and the computed results that could be compared with corresponding parameters as measured from experimental testing for the pressure relief valve. Adjustments to GFSSP input parameters allow the anchoring of the GFSSP valve model to test data. This makes it possible to use the GFSSP model as a predictive tool for understanding valve dynamics, as well as evaluating proposed pressure relief valve modifications for performance improvements.
An Integrated Welding and Damage Model for Practical Prediction of Creep Life in Welded P91 Alloy
Authors: Asadi Mahyar , Zhao Jun , Li Leijun
Published: December 2016

Loss of creep resistance in post-weld P91 alloy occurs mainly due to the change in microstructure particularly in the heat-affected zone under actual service operating conditions as well as residual stress from the welding process that is not often properly addressed in many damage models. In this paper, a validated deformation mechanisms map (DMM) using low temperature creep strain accommodation processes i.e. GBS, is used for the P91 alloy that predicts the creep rates over a wide range of temperature and stress including those arising under in the actual service conditions. These creep rates are further utilized into a microstructure-based creep damage model for accurate life prediction. A 3D transient computational welding mechanics (CWM) modeling of a pipe in a super-critical water loop, predicts the thermal, microstructure and stress state from welding. It also determines the coarse and fine grain heat affected zone (CGHAZ & FGHAZ). The CWM results are coupled with physics-based creep damage modeling to practically predict the creep life under the actual service conditions considering the welding residual stress and microstructure states.
A Proposed Bayesian Updating Approach to Update the Failure Probability of a Corrosion Defect After Performing Fitness for Service Based on API 579-1/ASME FFS-1
Authors: Maleki S. , Cui X.
Published: December 2016

Using Risk-Based Inspection (RBI) and Fitness for Service (FFS) approaches to manage the integrity of pressure equipment has been the industries best practice for almost a decade. However, there had never been a procedural link between these two approaches in a way that when one performed FFS analysis on a defect, one could update the risk accordingly. This paper proposes a quantitative method to refresh the risk calculated in the RBI process when FFS analysis is completed on a locally thinned area. The proposed approach applies a probabilistic technique by considering the Remaining Strength Factor (RSF) from API 579-1/ASME FFS-1 as the limit state equation and assuming the corrosion rate as a distribution variable to estimate the unconditional probability of failure. This value is then modified using a Bayesian updating method allowing for the conditional probability to represent a new failure likelihood which could be utilized in the RBI planning.
Direct Strain-Controlled Variable Strain Rate Low Cycle Fatigue Testing in Simulated PWR Water
Authors: Seppänen Tommi , Alhainen Jouni , Arilahti Esko , Solin Jussi
Published: December 2016

A tailored-for-purpose environmental fatigue testing facility was previously developed to perform direct strain-controlled tests on stainless steel in simulated PWR water. Strain in specimen mid-section is generated by the use of pneumatic bellows, and eddy current measurement is used as a feedback signal. The procedure conforms with the ASTM E 606 practice for low cycle fatigue, giving results which are directly compatible with the major NPP design codes.

Past studies were compiled in the NUREG/CR-6909 report and environmental reduction factors Fen were proposed to account for fatigue life reduction in hot water as compared to a reference value in air. This database exclusively contained non-stabilized stainless steels, mainly tested under stroke control. The applicability of the stainless steel Fen factor for stabilized alloys was already challenged in past papers (PVP2013-97500, PVP2014-28465). The results presented in this paper follow the same overall trend of lower experimental values (4.12–11.46) compared to those expected according to the NUREG report (9.49–10.37).

In this paper results of a dual strain rate test programme on niobium stabilized AISI 347 type stainless steel are presented and discussed in the context of the NUREG/CR-6909 Fen methodology. Special attention is paid to the effect of strain signal on fatigue life, which according to current prediction methods does not affect the value of Fen.
Chemical Specification and Design Factor Consideration for Creep Degradation in Grade 91 Steel
Authors: Masuyama Fujimitsu , Yamaguchi Tomiko
Published: December 2016

The power plant materials engineers are still tweaking the specification of grade 91 in order to prevent the improper production and construction. In this sense the chemistry, heat treatment conditions and design/fabrication rules for this steel should be highly optimized to achieve the safe elevated temperature properties and to avoid the abuse during the construction. This paper presents the recent findings on creep degradation behavior in grade 91 followed by the review and discussion about the effect of chemical composition and constituent on the creep strength/ductility in correlation to the chemical specification for this steel. Additionally the design factor for creep and creep-fatigue of grade 91 steels was considered to propose a new rule on the stand point of the changes in creep degradation mechanism at long-term region. As the results it was found that the martensitic lath structure in the grade 91 exposed at the creep loading significantly reduces the dislocation density to form the ferritic subgrain structure at long-term exposure which exhibits different creep mechanism from that of original martensitic structure. So that the multiplier of 0.67 applied to average stress for rupture in 100.000 h may not be used even below the temperature of 815°C. Therefore the F-factor is recommended to be applied at the temperature above 615°C for base metal and 545°C for welds considering the magnitude of the creep strength scatter band in the existing chemical specification ranges.
Design and Assessment for Creep-Fatigue and Creep-Fatigue Crack Growth
Authors: Ainsworth Robert A.
Published: December 2016

Creep-fatigue assessments require inputs for both creep damage and fatigue damage. Then these damage terms are combined using some form of interaction diagram to enable estimation of the creep-fatigue life. Similarly, creep-fatigue crack growth assessments need separate calculations of creep crack growth, fatigue crack growth and again possibly some allowance for interaction in order to obtain the total crack growth. A consequence of these approaches is that uncertainties in creep calculations, uncertainties in fatigue calculations and uncertainties in the form of interaction all lead to significant uncertainties in the overall lifetime or crack growth assessment.

This paper first briefly describes how creep-fatigue and creep-fatigue crack growth assessments are performed using the UK R5 procedure and contrasts the methods with those in other codes. Then, the paper presents the guidance in R5 on addressing the many uncertainties in these assessments and discusses the use of probabilistic methods in order to avoid over-conservative lifetime and crack growth estimates.
Seismic Response Analysis and Design for Concrete Nuclear Structures: A Comparative Study of the Time History, Response Spectrum, and Equivalent Static Load Methods
Authors: O’Leary Michael , Godfrey William
Published: December 2016

A partially buried fixed-base finite element model of a typical safety-related nuclear structure is analyzed for earthquake loads by the time history method, the response spectrum method, and the equivalent static load method. The spectra-consistent artificial time histories are generated with seed time histories in accordance with Standard Review Plan 3.7.1: Seismic Design Parameters [1] with target spectra based on Regulatory Guide 1.60: Design Response Spectra for Seismic Design of Nuclear Power Plants [2]. The response spectrum analyses are performed with the same target spectra used in generating the artificial time histories. The equivalent static loads are based on the nodal zero period accelerations from the fixed-base time history analyses. The seismic responses in a column in the structure are combined using algebraic sum, square root of the sum of the squares (SRSS), and the 100-40-40 rule in accordance with Regulatory Guide 1.92: Combining modal responses and spatial components in seismic response analysis [3]. The equivalent static load method is applied according to ASCE 4-15: Seismic Analysis of Safety-Related Nuclear Structures [4]. The resulting design forces and required reinforcement for a column in the structure are compared for each method along with the corresponding computational demand.
High Pressure 98 MPa Multifunctional Steel Layered Vessels for Stationary Hydrogen Storage
Authors: Zheng Jinyang , He Qi , Gu Chaohua , Zhao Yongzhi , Hua Zhengli , Li Keming , Zhou Chilou , Zhong Sijia , Wei Chunhua , Zhang Yimin
Published: December 2016

The storage of hydrogen in a compressed gaseous form offers the simplest solution in terms of infrastructure requirements and has become the most highly developed hydrogen storage method. Low cost and large vessels for bulk hydrogen storage are needed at central production plants, geologic storage sites, terminals and refueling stations. A multifunctional steel layered vessel (MSLV) for stationary hydrogen storage with maximum design pressure of 98 MPa has been developed. First of all, the basic structure and characteristics of the vessel were introduced. Secondly, the stress in the cylindrical shell of the MSLV was studied based on the ribbon-width-direction effective normal stress and shear stress sub-models. Besides, the stresses in the hemispherical head and reinforcing ring were obtained by combining finite element analysis with experiments in the meantime. Finally, safety of the vessel was evaluated mainly by hydrogen compatibility tests of the weld joints of austenitic stainless steel S31603 under 98MPa gaseous hydrogen according to ANSI/CSA CHMC 1-2014, as well as MSLV’s feature of burst resistant and easy for online safety monitoring. Research shows that hydrogen embrittlement of MSLV was mitigated, because the stress in the inner shell of MSLV is low, and austenitic stainless steel and its weld are well compatible with high pressure hydrogen.
On a Design Acceptability of 90° Elbow According to Pipe Length at Elevated Temperature Condition
Authors: Jeong Seong-Yun , Won Min-Gu , Choi Jae-Boong , Huh Nam-Su , Oh Young-Jin
Published: December 2016

Sodium-cooled Fast Reactor, SFR is promising candidate of Generation-IV reactor. SFR is operated at high temperature and low pressure. For reducing high thermal stress, thin-walled components and structures are employed for SFR. However, thins-walled components are vulnerable to seismic damage[1].

In this paper, the structural integrity assessment are performed to investigate the effect of piping length on creep-fatigue and seismic damage at elevated temperature. L-shaped elbow is considered for piping design and finite element analyses are conducted to calculate creep-fatigue and seismic damage. The evaluation of creep fatigue damage is carried out according to the elevated temperature design codes of ASME B&PV Sec. III Subsec. NH-3200[2]. Seismic damage are evaluated based ASME B&PV Sec. III Subsec. NB-3600[3] and ASME B&PV Sec. III Div.5 HBB-3200[4]. From the results of creep-fatigue and seismic damage, limit length of piping is determined.
Analytical Comparison Between Separate Reinforcement Nozzle and Integral Reinforcement Nozzle Behaviors Under Cyclic Loading
Authors: Mohamed Bassel Y. , Eid Tamer I.
Published: December 2016

ASME code explicitly addresses design for fatigue due to pressure or temperature cycles. Protection against fatigue failure due to cyclic external mechanical loads (e.g. piping loads) is not tackled in depth.

This paper provides a less-tedious yet fit-for-purpose approach to evaluate the effect of cyclic external mechanical loads as well as the pressure fluctuations — as a result of piping slug flow — on nozzles fatigue life. The evaluation compares between two types of nozzles construction (configuration); separate reinforcement nozzle and readily radiographed (lip type) integrally reinforced nozzle. Within the analysis, a unity fatigue damage ratio or exceeding the ratcheting allowable limits was selected as the indication for the inadequacy of the reinforcement configuration.

COMPRESS® FEA software results comprehensively predict that the separate reinforcement nozzles can’t withstand the imposed cyclic loads since the accumulated fatigue damage are greater than 1 (one) implying that the nozzle will experience fatigue failure before the end of its life time. COMPRESS® FEA results were examined at four locations, namely “shell next to nozzle”, “nozzle next to shell”, “nozzle thickness transition” and “shell away from nozzle”. The maximum stress of the four locations was always at “shell next to nozzle”.

These results have been verified against SOLIDWORKS® simulation FEA results.

The results show that the separate reinforcement nozzle construction, although adequate for static loadings, has less fatigue life compared to the integral reinforcement nozzle construction. Moreover, progressive distortion of the non-integral (separate) reinforcement connection is predicted showing that the mating members may become loose at the end of each complete operating cycle which could eventually cause disengagement. Additionally, the results support ASME 2004, VIII-2 para. 5-112 recommendations in prohibiting fillet welds in joints of category D for components subject to fatigue service.

The paper concludes the advantage of integral reinforced readily radiographed nozzle construction in protection against fatigue failure and ratcheting and also provides a roadmap for simplified fatigue analysis using commercially available software.
Study on Structure Lightweight of the Vehicle Mounted LNG Tank
Authors: Wang Yichuan , Ling Xiang
Published: December 2016

LNG vehicle tank has been widely used in transportation industry due to its high efficiency and low cost. Researchers have proved that vehicle lightweight is one of the important objectives for the development of vehicle mounted LNG tanks. The lightweight of LNG tank structure plays an important role in the weight reduction of full vehicle, and great economic benefits can be brought through the introduction of lightweight. Structure optimization is one of the most common lightweight methods and structure lightweight design is a systematical project that is involved with crashworthiness, stiffness, Eigen mode and vibration, harshness performance. The surrogate based design optimization is considered as one of the efficient approaches to dealing with complicated engineering problems. According to the force condition in the actual operation of vehicle-mounted tanks, a novel fin sandwich structure reinforcing ring had been used to replace the original angle steel stiffening ring. The fin thickness, height, width, thickness and thickness and width of upper and lower plates of the sandwich structure had been optimized using the genetic algorithm. Finite element analysis had been performed to analyze the effect of fin sandwich structure to the enhancement of the outer LNG storage tank cylinder under a variety of actual operating conditions and the stress conditions of overall and part of the tank. Results show that in comparison to the angle steel stiffening ring, fin sandwich structure with the same stiffness and strength of reinforcing ring can ensure the safe operation of tank car, and the stress distribution on the outside cylinder is also more reasonable. Through the adoption of this new type of reinforcing ring, great economic benefits can be brought which will greatly improve the operation efficiency and reduce the transportation cost.
A Statistical Approach to Estimating a 95% Confidence Lower Limit for the Design Creep Rupture Time vs. Stress Curve When the Stress Estimate Has an Error Up to 2%
Authors: Fong Jeffrey T. , Filliben James J. , Heckert N. Alan , Marcal Pedro V. , Cohn Marvin J.
Published: December 2016

Recent experimental results on creep-fracture damage with minimum time to failure (minTTF) varying as the 9th power of stress, and a theoretical consequence that the coefficient of variation (CV) of minTTF is necessarily 9 times that of the CV of the stress, created a new engineering requirement that the finite element analysis of pressure vessel and piping systems in power generation and chemical plants be more accurate with an allowable error of no more than 2% when dealing with a leak-before-break scenario. This new requirement becomes more critical, for example, when one finds a small leakage in the vicinity of a hot steam piping weldment next to an elbow. To illustrate the critical nature of this creep and creep-fatigue interaction problem in engineering design and operation decision-making, we present the analysis of a typical steam piping maintenance problem, where 10 experimental data on the creep rupture time vs. stress (83 to 131 MPa) for an API Grade 91 steel at 571.1 C (1060 F) are fitted with a straight line using the linear least squares (LLSQ) method. The LLSQ fit yields not only a two-parameter model, but also an estimate of the 95% confidence upper and lower limits of the rupture time as basis for a statistical design of creep and creep-fatigue. In addition, we will show that when an error in stress estimate is 2% or more, the 95% confidence lower limit for the rupture time will be reduced from the minimum by as much as 40%.
Localized Creep Property Estimated in the Welded Part of High-Cr Steel by an Indentation Test
Authors: Arai Masayuki , Ishikawa Takahiro
Published: December 2016

In this paper, the creep parameter involved in the constitutive equations for Norton’s law is identified for the base metal, heat affected zone (HAZ) and weld metal in the weldment of a high-Cr ferritic heat-resisting steel, which is a candidate material for the steam generating tube of the supercritical boiler, by conducting a high temperature indentation creep test. Important engineering problems, such as the welded plate and the tube subjected to a creep loading are analyzed using the estimated creep parameter by the finite element analysis.
Assessment of Welding-Induced Plasticity in Austenitic Steel Weldments
Authors: Muránsky Ondrej , Hamelin Cory J. , Tran Minh , Braham Chedly , Smith Michael C.
Published: December 2016

Historically, weld residual stresses (WRS) have been used as the primary validation parameter for welding simulations, largely due to the importance of predicting WRS for structural integrity assessments. However, the extent of welding-induced plasticity (WIP) caused by the plastic flow of near-weld material is also an important characteristic affecting weld performance. WIP has been shown to negatively affect weld integrity, since the associated accumulation of defects (dislocations) in the material will accelerate the nucleation of macro-scale defects that lead to component failure. Information on WIP is particularly important when attempting to validate the constitutive models used for weld simulation, and can assist with the proper definition of material yield strength.

The present study highlights two approaches to assess WIP in welded structures. The first approach involves the development of a micro-hardness correlation to infer the level of WIP across the near-weld region. The second approach uses electron backscatter diffraction (EBSD) data to directly calculate the average crystal misorientation in the region of interest, which is proportional to the amount of geometrically necessary dislocations present. The dissimilar approach to determine WIP between the two characterization methods allows a degree of confidence in the results obtained, therefore providing an accurate dataset for weld model validation. To exemplify this point, the two approaches are used to characterize WIP across a three-pass slot weld in AISI 316 steel (NeT TG4 specimen), and the results are compared to weld modelling predictions.
Stress Intensity Factor of an Elliptical Crack With a Wavy Crack Front
Authors: Arai Masayuki
Published: December 2016

In this paper, the stress intensity factor KI for the crack front line a − ε(1 + cosmθ), which is slightly perturbed from a complete circular line with a radius of a, is determined. The method used in this study is based upon the perturbation technique developed by Rice for solving the elastic field of a crack whose front slightly deviates from some reference geometry. It is finally shown that the solution for the stress intensity factor matches the results of a three-dimensional finite element analysis.
Predicting an Optimal Inter-Pass Temperature to Mitigate Residual Stress and Distortion in Ferritic Steel Weldments
Authors: Sun Yongle , Hamelin Cory J. , Smith Michael C. , Edwards Lyndon
Published: December 2016

The residual stress and distortion found in multi-pass welds are often influenced by the prescribed inter-pass temperature. In ferritic steel components, the severity of this influence is affected by solid-state phase transformation (SSPT) kinetics, which will depend on the overall heat input and cooling conditions. The development of an optimised welding procedure to mitigate weld residual stress (WRS) and distortion in these components can therefore necessitate an extensive test matrix, varying both preheat and inter-pass temperatures as well as the transient weld heat input.

Computational parametric studies provide an opportunity to dramatically reduce the cost and time associated with the development of welding procedure specifications. Welding procedures can be simulated using validated modelling approaches to examine parametric sensitivity and gain insights into optimal conditions for a given welding task. In the present study, a three-pass tungsten inert gas (TIG) groove weld in SA508 Gr.3 Cl.1 ferritic steel is numerically investigated using the ABAQUS finite element code with a user defined subroutine to incorporate the effect of SSPT kinetics. Parametric sensitivity is assessed whereby a representative heat input is applied to simulate weld deposition for each pass, and the inter-pass temperature is varied to examine its effect on WRS and distortion in the weldment. The implications of the overall heat input on cross-weld microstructure are also presented using this approach.
FEM Stress Analysis of Long-Term Sealing Performance for Bolted Pipe Flange Connections With PTFE Blended Gaskets Under Elevated Temperature
Authors: Sato Koji , Sawa Toshiyuki , Kobayashi Takashi
Published: December 2016

Mechanical characteristics of bolted pipe flange connections with PTFE blended gaskets under elevated temperature are examined using FEM calculations and experiments. Firstly, the basic characteristics of the PTFE blended gaskets are measured such as the stress-strain curves, the thermal expansion coefficient and the relationship between the contact gasket stress and the leak rate at room temperature and some high temperature. The leak rates of the gasket at the averaged gasket stress are measured using the rigid platen. In addition, the creep characteristics of the gaskets are measured using the rigid platen under elevated temperature. Then, using the gasket basic characteristics measured above, the FEM calculations are carried out to analyze the mechanical characteristics such as 1) changes in axial bolt forces (the load factor), 2) the contact gasket stress distributions, 3) flange hub stress. Then, the sealing performance of bolted pipe flange connections is predicted using the contact gasket stress distributions obtained from the FEM calculations and the relationship between the gasket stress and the leak rate.

In the FEM calculations, the value of the load factor due to the internal pressure is obtained as φg = 0.12. Furthermore, the sealing performance in long-term is estimated using the change in the axial bolt forces (creep) and the contact gasket stress distributions under heat cycle and internal pressure. For verification of the FEM calculations, the experiments were performed to measure the load factor (change in axial bolt forces), the leak rate of the connection at each temperature, and the hub stress. The FEM results are in a fairly good agreement with the measured results. In addition, the reduction in the contact gasket stress due to the heat cycle, internal pressure and the creep is demonstrated and the effect of the nominal diameter of pipe flanges on the sealing performance is shown.
Fatigue Crack Growth Analysis of Interacting Subsurface Cracks Using S-Version FEM
Authors: Suzuki Ayaka , Takahashi Akiyuki , Kikuchi Masanori
Published: December 2016

Fatigue crack growth simulation using the s-version finite element method (FEM) is presented. Two subsurface cracks are aligned in the depth direction of a specimen, and is subjected to a cyclic tension-tension loading. The fatigue crack growth behavior of the cracks is directly simulated using our automatic fatigue crack growth simulation system with the s-version FEM. Along with the direct simulation, proximity rules for crack combinations and surface cracks are used in the s-version FEM simulation. The numerical results with and without the application of the proximity rules are compared to make a validation of the application of the proximity rules in the evaluation of fatigue crack growth behaviors and residual fatigue life. The results clearly illustrate that the proximity rules accelerate the fatigue crack growth rate, and provide us with a substantially conservative evaluation. Finally, the proximity rules are slightly modified for making better approximation of combining and surface cracks. It can be found that the new proximity rules are able to give a fatigue crack growth evaluation closer to the direct simulation results.
Effect of Ti Additions on Microstructure and Mechanical Properties of Centrifugally Cast 25Cr-35Ni-Nb Alloy
Authors: Chen Tao , Xue-dong Chen , Lian Xiao-ming , Fan Zhi-chao
Published: December 2016

The influence of Ti element with the content from 0.018 wt.% to 0.112 wt.% on microstructure and mechanical properties of centrifugally cast 25Cr-35Ni-Nb alloy was investigated in this paper. The experiments were carried out by optical emission spectrometer, metallographic image analyzer, field emission gun scanning electron microscopy (FEG-SEM) equipped with an Oxford INCA energy dispersive X-ray spectrometer (EDS), tensile testing machine and creep testing machine. The results show that the microstructure and high temperature creep rupture properties of as-cast 25Cr-35Ni-Nb alloy are significantly affected by the addition of Ti. No precipitation of Ti carbides was observed in the alloy with the Ti content of 0.018 wt.%, whereas the skeleton (Nb, Ti) C were precipitated at grain boundaries when increasing the Ti content. Under the creep rupture condition of 1100 °C and 17 MPa, the rupture lives of 25Cr-35Ni-Nb alloy with Ti contents ranging from 0.04 wt.% to 0.112 wt.% were relatively higher. In addition, the role of Ti in ethylene pyrolysis furnace tube was also discussed in this paper.
Stress Intensity Factor Solutions for Circumferential Surface Cracks With Large Aspect Ratios in Pipes Subjected to Global Bending
Authors: Azuma Kisaburo , Li Yinsheng , Hasegawa Kunio , Shim Do Jun
Published: December 2016

In some cracks attributed to primary water stress corrosion cracking, the crack depth a was greater than half-length of the crack 0.5ℓ. This paper presents details of stress intensity factor solutions for circumferential surface cracks with large aspect ratios a/ℓ in piping system subjected to global bending. The stress intensity factor solutions for semi-elliptical surface cracks were obtained by finite element analyses with quadratic hexahedron elements. Solutions at the deepest and the surface points of the cracks with various aspect ratio (0.5 ≤ a/ℓ ≤ 4.0), crack depth ratio (0.01 ≤ a/t ≤ 0.8) and pipe sizes ( 1/80 ≤ t/Ri ≤ 1/2) were investigated, where t and Ri are wall thickness and inner radius of pipe, respectively. Proposed stress intensity factor solutions for cracks with a/ℓ = 0.5 are consistent with the values reported in the previous study. The solutions developed in this study are widely applicable to various engineering problems related to crack evaluation in piping systems.
The Research on the Effect of the Height of Free Span on Fatigue Life of Submarine Pipeline due to Vortex-Induced Vibration
Authors: Dong Jie , Xuedong Chen , Wang Bing , Guan Weihe , Fan Zhichao , Xu Ming
Published: December 2016

Free span is a risk of security of submarine pipelines. Fatigue caused by vortex-induced vibration (VIV) is a main failure mode of free spans. The height of free span which influences the VIV fatigue load is an important factor for the fatigue life assessment. In this paper, taking an in-service submarine pipeline as an example, the relation between the height and the fluctuating lift coefficient was firstly investigated by the method of computational fluid dynamics, and the critical height which can neglect its effect on the coefficient was obtained. The VIV structural response of free span with different height and length was analyzed with the finite element method. Furthermore, considering the in-service environment of the submarine pipeline, fatigue life of free span was evaluated numerically with reference to the measured data of flow velocity and its variation with time. Those results provide technical support for the maintenance of free span for the submarine pipeline.
Failure Analysis of Plastic Pipe Reinforced by Cross Helically Wound Steel Wire Subjected to Internal Pressure and Bending Load
Authors: Zhang Jie , Shi Jianfeng , Zheng Jinyang
Published: December 2016

Plastic pipe reinforced by cross helically wound steel wire (PSP) has been widely used in the transportation of petroleum, natural gas, municipal water, etc. In some serious occasions, PSP suffers from bending load caused by operating conditions such as ocean wave, pipeline laying and geological sedimentation, besides internal pressure. Thus, to understand the strength of PSP under the complex loads is crucial for ensuring safety. In this study, a finite element (FE) model of PSP was proposed by taking both internal pressure and bending load into consideration. By gradually increasing the bending load, the strength of PSP was obtained by taking the break of steel wires as the failure criterion. Then, combined loading tests were conducted to verify the proposed model. The results show that the applied bending loads bear a nonlinear relationship with the increasing deformation. By comparing experimental results and FE model calculation results, good agreement was obtained. Based on the verified FE model, the limit bending load and the effects of design parameters and internal pressure on the strength of PSP were discussed.
Assessment of Gurson-Tveergard-Needleman Model Under High Stress Triaxiality
Authors: Zhong Jiru , Xu Tong , Guan Kaishu
Published: December 2016

The Gurson-Tveergard-Needleman (GTN) model has been widely used to describe ductile fracture. In this paper, a series of tensile tests were carried out on notched specimens to assess the GTN model. The GTN model parameters were calibrated from a smooth tensile specimen by a hybrid particle swarm optimization, and the reliability of the calibrated parameters was verified by the profile of the smooth tensile specimen. The calibrated parameters were used to predict the ductile fracture of notched specimens. A comparison of fracture initiation sites between simulations and experiments indicates that the GTN model has a good performance on predicting fracture initiation site but fails at predicting fracture moment. The assessment of the transformability of the GTN model parameters was performed by comparing the load-displacement curves between simulations and experiments. It is observed that the GTN model parameters are material constant, except the critical void volume fraction fc. The influence of stress triaxiality on the critical void volume fraction fc is also discussed.
Loading Condition Evaluation for Structural Integrity Assessment of RPV due to PTS Event Based on Three-Dimensional Thermal-Hydraulics and Structural Analyses
Authors: Uno Shumpei , Katsuyama Jinya , Watanabe Tadashi , Li Yinsheng
Published: December 2016

For structural integrity assessment on a reactor pressure vessel (RPV) of pressurized water reactor during the pressurized thermal shock (PTS) events, thermal histories of coolant water and heat transfer coefficient between coolant water and RPV are important influence factors. The former is determined on the basis of thermal-hydraulics (TH) analyses simulating PTS events and the latter is derived from Jackson-Fewster correlation using TH analysis results. Using these factors, subsequently, loading conditions for structural integrity of RPVs are evaluated by structural analyses. Nowadays, three-dimensional TH and structural analyses are recognized as precise methods for assessing structural integrity of RPVs. In this study, we performed the TH and structural analyses using a three-dimensional model including cold-leg, downcomer and beltline region of RPV in order to evaluate loading conditions during a PTS event more accurately. Distributions of temperature of coolant water and heat transfer coefficient on the surface of RPV were calculated by TH analysis. Loading condition evaluation was then performed by structural analysis using these values and taking the weld residual stress due to weld-overlay cladding and post-weld heat treatment into consideration. From these analyses, we obtained histories and distributions of loading conditions at the reactor beltline region of RPV. Based on the analysis results of loading conditions, we discussed the conservativeness of current structural integrity assessment method of RPV prescribed in the current codes through the comparison of the loading conditions due to a PTS event.
Numerical Analysis of an Air Spring With Two Tanks Connected by a Long Pipe: Effect of Orifice Installed in the Pipe
Authors: Toji Masatoshi , Asami Toshihiko , Ise Tomohiko
Published: December 2016

This paper deals with the numerical analysis of an air spring that consists of two tanks connected by a long pipe. Two resonance points may appear in the frequency response of a vibratory system supported by this type of air spring despite the fact that the system has an apparent single mass. This phenomenon is caused by the presence of a secondary mass as reported in our previous paper. It was found that the secondary mass is the mass of air contained in the pipe. The magnitude of this mass is extremely small, but the acceleration of the air in the pipe — and therefore the inertia force generated from it — becomes very large. The generated force is further amplified by the Pascal’s principle and is transmitted to the supported mass. There are obvious nonlinear characteristics in this type of air spring; whereas the previous studies were based on linear assumptions. In this study, the governing equations for the air stream expressed by a nonlinear partial differential equation were solved by using the finite difference method. In particular, the pressure loss is evaluated due to air vortex being generated behind the orifice installed in the pipe. As a result of this study, it was found that the orifice is effective in suppressing the height of the secondary resonance point. Of course, it has become possible to accurately estimate the amplitude dependency of the dynamic characteristics of the air spring supported system by this non-linear analysis.
Experimental and Numerical Evaluation of Fracture Toughness on Electron Beam Welded Joint in Al6061-T6
Authors: Rekik W. , Ancelet O. , Gardin C. , Hamon F.
Published: December 2016

In order to ensure the integrity of structures, failure assessment is required. In this context, the fracture behavior of an electron beam (EB) welded joint on thick plate of aluminum alloy 6061-T6 used for structural components of experimental nuclear reactors was investigated. In the particular case of welded structures, the tearing resistance is strongly dependent on the mismatch of the welded joint and the local behavior of each metallurgical zone.

For a reliable analysis, the tensile mechanical behavior of each position of the welded joint was precisely determined by the use of a new measurement prototype. The toughness behavior under different configurations was then evaluated on CT specimens. From these experimental results a mechanical behavior contrast was highlighted. In fact, the fusion zone presents the lowest yield stress and a gradient is observed in the heat affected zone until the material behavior reaches of the base metal yield stress. On the contrary, the toughness of the welded zone is the highest and decreases strongly in the heat affected zone according to an exponential function until the base metal toughness is reached.