bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Reliability Assessment Method for Piping Containing Local Metal Loss at Structure Discontinuity
Authors: Qu Qiang , Izumi Satoshi , Sakai Shinsuke
Published: December 2016

In chemical plants, Corrosion Under Insulation (CUI) is a typical maintenance issue of internal pressed pipes. This form of localized corrosion leads to metal loss at the outside surface of pipes, reduces the pipe’s resistance to internal pressure [1]. Once the local metal loss is inspected, it is important to apply a Fitness-For-Service (FFS) assessment to evaluate the remaining safety margin against working internal pressure. However, if the local metal loss occurs at the piping discontinuity, it is impossible to calculate the critical collapsing pressure without any existing theoretical expression. Moreover, evaluation based upon standards may produce too much conservative evaluation and lead to unnecessary repairing-replacement cost. In this study, both deterministic analysis and probabilistic reliability analysis are performed to evaluate the safety margin of piping containing local metal loss at piping branch connection, and the obtained results are compared with those evaluated based upon API579-1/ASME FFS-1 standard. In addition, sensitivity analysis is conducted to show the dependence of metal loss geometries regarding both width and depth, material strength and working internal pressure on the safety margin. Finally, a proper reliability assessment procedure by using advanced Response Surface Method (RSM) is proposed. In the deterministic analysis part, a FEM structural analysis is performed to calculate the critical collapsing internal pressures (CIP) for several cases of various metal loss geometries regarding width and depth and material tensile strength. These results are compared with maximum allowable working internal pressure (MAWP) calculated by the procedures which are provided in API579-1/ASME FFS-1 standard. (The safety margin is defined as CIP/ MAWP). It is shown that the safety margins are greater than 6 in most of the cases. Since there are uncertainties in the geometrical dimensions of local metal loss, material tensile strength and working internal pressure, it is necessary to perform a reliability analysis to quantify the probability of failure (Pf) caused by these uncertainties. In the probabilistic analysis part, the metal loss geometries, material strength and internal pressure are considered as random variable with distributions. The reliability index of each group of geometries-strength-pressure combinations is calculated by first order reliability method (FORM). The reliability index of the case working under MAWP is also investigated. In order to define the limit state function, response surface method is used to predict the response which relates the critical collapsing internal pressure to the metal loss geometries and material strength. Finally, the sensitivity analysis is performed to clarify the dependence of metal loss geometries, material strength, and internal pressure on the Pf, and to specify the dominant variables and negligible variables.
Finite Element Simulation of Creep Deformation for Gr. 91 Steel at 600 °C Using Garofalo Model
Authors: Won Min-Gu , Choi Jae-Boong , Huh Nam-Su , Lee Hyeong-Yeon , Kim Woo-Gon
Published: December 2016

The present paper provides predictive creep deformation model for Gr. 91 steel at 600 °C. To cover primary-secondary creep regions, two types of creep models, i.e. Garofalo’s and RCC-MRx models were considered in the present study, where the parameters of Garofalo’s model were characterized based on experiment results, and the parameters of RCC-MRx model were determined by the values given in the RCC-MRx code. Furthermore, each creep model were developed based on CREEP (user creep subroutine invoked in ABAQUS) codes for applying to finite element (FE) simulations using commercial code. Then, FE analyses for creep deformation were performed by using the developed CREEP codes (for Garofalo’s and RCC-MRx models), and the results were compared with experiment data. As results, Garofalo’s model provides more accurate results than RCC-MRx model.
Irradiation Embrittlement Behavior of SA508 Gr.4N RPV Steel Model Alloy
Authors: Kim Min-Chul , Lee Bong-Sang
Published: December 2016

The mechanical properties and irradiation embrittlement behavior of SA508 Gr.4N low alloy steel have been characterized systematically using SA508 Gr.4N model alloys. For an evaluation of neutron irradiation embrittlement behavior of model alloy, several irradiation tests were carried out at the research reactors, HANARO and HBWR, up to a fluence level of 1.5 × 1020n/cm2 (E>1MeV) at 290 ± 10°C. The master curve method according to ASTM E1921 was adopted to evaluate the fracture toughness in the transition region. Ni and Cr additions resulted in increasing the martensite fraction in low alloy steel by enhancing the hardenability of the steel. Thus, the predominant microstructure of SA508 Gr.4N model alloy is a mixture of tempered martensite and bainite, while SA508 Gr.3 steel shows a typical tempered upper bainitic structure. SA508 Gr. 4N model alloy shows excellent strength and transition behavior compared to commercial SA508 Gr.3 steel. After neutron irradiation, the yield strength and tensile strength of model alloy were increased with an increase in the neutron fluence level. The transition temperature shifts of SA508 Gr.4N model alloy obtained by both Charpy impact and fracture toughness tests were not significantly larger than those of commercial SA508 Gr.3 low alloy steel. It seems that the increased Ni content in the SA508 Gr.4N model alloy did not show significant effects on the irradiation embrittlement behavior owing to the controlled low Mn content. In addition, good fracture toughness of the SA508 Gr.4N model alloy was maintained even after neutron irradiation up to a level of ∼1020n/cm2.
Comparison of Fracture Toughness Properties of Advanced Ferritic ODS-Alloys Based on 0.2T C(T) Specimen Tests
Authors: Eiselt Charles C. , Hoelzer David T. , de Carlan Yann , Hein Hieronymus , Serrano Marta , Diano Pascal , Schendzielorz Herbert , Seubert Andreas
Published: December 2016

Based on the good experiences gained by using small specimens made of ferritic RPV materials, the Master Curve fracture toughness approach was applied to determine the fracture mechanical properties of oxide dispersion strengthened (ODS-) materials. A ferritic ODS-alloy (Fe-14Cr-1W-Ti-Y2O3) has been produced through the powder metallurgical production path via hot extrusion and hot isostatic pressing (HIP). Optimized oxide dispersion strengthened (ODS)-alloys have a promising potential to meet the foreseen requirements of components in future Gen IV power plants due to their high creep strength and swelling resistance under irradiation at elevated operational temperatures. The fracture toughness was characterized with mini 0.2T C(T) specimens in different material orientations (R-L / L-R) in the ductile-brittle and upper shelf region in the un-irradiated state, accounting especially for the ODS-material’s anisotropy as one key effect of manufacturing. Despite all tests were performed in orientation required by ASTM standards E 1921 and E 1820 not all validity criteria (e.g. height of yield strength, evenness of the crack, admissible K during testing or admissible stable crack growth) were met by the ODS-material: consequently, a valid T0 value and a standard-compliant Master Curve could not be determined for the ODS-material in the transition region especially in the respective R-L orientation, also due to a comparably low fracture toughness over the whole evaluated temperature range. Promising fracture toughness properties were obtained in the crack growth direction perpendicular to the prior main deformation (extrusion) direction, where a KJQ value of 196 MPa√m at T = 22°C was measured. Within the ductile regime, only a JQ = J0.2BL technical initiation toughness value could be calculated and at T = 22°C, a comparably large JQ of 137kJ/m2 is obtained for specimens with crack growth direction perpendicular to the extrusion direction, while in extrusion direction the toughness is again low.

In addition two further ODS-materials (14YWT and PM2000) were tested and compared to the alloys above. Non-conformances of ODS relating to the material requirements in ASTM standards E1921 and E1820 were finally detected and explained.
Creep Behavior and Defect Interference of Volume Defect Under High Temperature
Authors: Tang Ping , Wang Min , Ling Zhangwei , Jin Nanhui , Guo Weican
Published: December 2016

Volume defect is the common defect in high temperature pressure pipeline. Those defects have a great influence on stress redistribution of the pipes in high temperature, and affect the integrity and safety operation of high temperature components. In this paper, the defects were regularized, and a high temperature creep model was established. Based on this model, creep behavior of high temperature pressure pipeline with volume defect was studied, and the stress concentration of the main feature points in the defect was researched. Then, defects interference effect was discussed, and the critical interference distance was given. The results provide theoretical support to the safety assessment of high temperature structure with defects.
Numerical Investigation of Nozzle Aspect Ratio Effects on Hydrogen Jet Release Characteristics
Authors: Bie Haiyan , Hao Zongrui , Ye Jianjun
Published: December 2016

As one of the carbon-free energies, hydrogen is considered as an important energy carrier in the 21st century. The minimum ignition energy of hydrogen is the lowest among flammable gases, hence, hydrogen leaking from pinholes, narrow gaps, or broken pipes can be ignited by ignition sources such as static electricity. Understanding of the characteristics of the hydrogen jet release is crucial for the better design and the applications. In this paper, the hydrogen under-expanded jet and flammable envelope were studied by simulation method. The effects of the nozzle shape and release pressure on the under-expanded jet, the downstream shock structure and flammable envelope were investigated. The simulation results showed that the nozzle geometry had great influence hydrogen under-expanded jet. And the maximum flammable length increased with the increasing of aspect ratio. For the split nozzle, with the increasing of pressure the hydrogen diffusion region of minor axes in the near-to-nozzle field increased but decreased of major axes.
Development of Guidance for the Assessment of Non-Sharp Defects Using the Notch Failure Assessment Diagram
Authors: Horn Anthony J. , Cicero Sergio , Bannister Adam , Budden Peter J.
Published: December 2016

Structural integrity assessment codes such as R6 [1] and BS7910 [2] provide guidance on the assessment of flaws that are assumed to be infinitely sharp using the Failure Assessment Diagram (FAD). In many cases, such as fatigue cracks, this assumption is appropriate, however it can be pessimistic for flaws that do not have sharp tips such as lack of fusion, porosity or mechanical damage. Several Notch Failure Assessment Diagram (NFAD) methods have been proposed in the literature to quantify the additional margins that may be present for non-sharp defects compared to the margins that would be calculated if the defect were assumed to be a sharp crack. This paper presents the first stage of on-going work to validate an NFAD method and to develop guidance for its application in safety assessments. The work uses 3D Finite Element (FE) Analysis in conjunction with a wide range of test data on non-sharp defects as a basis for validation. The paper also develops some practical guidance on the treatment of Lüders strain in the FE analysis of specimens containing notches instead of fatigue pre-cracks.
Accurate Prediction of Large Ductile Tearing in Dissimilar Material Welds Using a Non-Local Gurson Model
Authors: Lacroix Rémi , Drouet Julie , Gallée Sébastien , Chapuliot Stéphane , Gilles Philippe
Published: December 2016

The experimental assessment of ductile failure of Dissimilar Materials Welds (DMW) of NPP components can be challenging. For instance, the European project ADIMEW [1] has shown the technical complexity of the bending set-up on a DMW join at 300°C.

Such experiments are so scarce that their analysis is highly valuable to quantify the validity of alternative methods for assessing the ductile failure. This paper presents the application of the numerical simulation of ductile failure with a local approach in the case of the ADIMEW mock-up and discusses its validity.
New Edition of the NORSOK U-001 for Subsea Production Systems
Authors: Kirkemo Finn , Osen Per , Katla Erling , Muff Anthony , Tvitekkja Arve , Hashemizadeh Hussain
Published: December 2016

NORSOK U-001 4th edition was released October 1st, 2015. It replaces edition 3 from 2002. The 4th edition is based on industry experience and use of the previous version. With focus on Norwegian Continental Shelf (NCS) operations and experience, NORSOK U-001 provides normative reference and amendments to selected parts of ISO 13628 (equivalent to API 17 series). The focus areas of this paper are the informative annexes to NORSOK U-001: The revised Annex A (informative), and the new Annex B (informative). These annexes provide NCS related amendments to Part 4 (API 17D), Part 7 (API 17G), and Part 15 (API 17P) of ISO 13628. Annex A (informative) provides loads for design and selection of subsea trees, wellheads and templates and has been completely revised with new standard design loads. Annex B (informative) gives recommendations for structural design, manufacture and testing of subsea wellhead and tree equipment (ISO 13628-4/API 17D) and completion/workover riser systems (ISO 13628-7/API 17G). This paper provides a brief introduction and background to Annex A and Annex B. Some differences between NORSOK U-001 Annex B, ISO 13628-7 (API 17G), ISO 10423 (API 6A), API 6X, ISO 13628-4 (API 17D), ASME VIII Div. 3 and ASME VIII Div.2 are also highlighted.
Research on Forming Temperature of Metastable Austenitic Stainless Steel Head Based on Strain-Induced Martensitic Transformation
Authors: Lu Qunjie , Zheng Jinyang , Zhang Xiao
Published: December 2016

Formation of strain-induced martensite (SIM) is found in metastable austenitic stainless steel (m-ASS) during cold forming. The presence of SIM may cause reductions in toughness, ductility and corrosion resistance of the m-ASS. Although these mechanical properties can be restored and improved after cold forming by using proper heat treatment, the manufacturing cost rises greatly. However, the cost of warm forming is cheaper and the SIM reduces with forming temperature increasing. Thus, the main purpose of this research is to investigate a suitable forming temperature, at which the strain-induced martensitic transformation (SIM-Tr) of m-ASS head in forming will reduce. Primarily, a series of static tensile tests were conducted based on several batches of S30408 plates. The tests were carried out at different temperatures varying from 20 °C to 180 °C, with the effect of deformation temperature on SIM evaluated. Moreover, according to the stacking fault energy (SFE) calculation method, the m-ASS’s chemical composition was taken into further consideration to investigate its effect on SIM. Eventually, a formula was established that related to SIM and chemical composition for optimizing the forming temperature. The results obtained by this formula were compared to the experimental results of 304 ASS head stamping tests, and satisfactory matching is found for the proposed forming temperatures and the predicted FN values (readings of the Ferritescope measurement, as a representation of the amount of martensite in this study). Additionally, an enhancement of the cryogenic impact properties and a fewer quantity of delta-ferrite in the microstructure are observed when stamping temperature is higher than 90 °C.
Variations in Measured Fatigue Life in LWR Coolant Environments due to Different Small Specimen Geometries
Authors: Twite Marius , Platts Norman , McLennan Alec , Meldrum James , McMinn Andrew
Published: December 2016

Small specimen fatigue testing is challenging in simulated LWR coolant environments at elevated temperatures and pressures. Two approaches to isothermal uniaxial testing in such environments have been developed: use of an autoclave to contain the environment around the specimen, which is conventionally of a solid design (e.g. circular cross-section, parallel sided gauge length); and use of a thin-walled hollow or tubular specimen, where the coolant environment passes through the bore of the specimen.

It is often assumed that fatigue lives measured using these two specimen designs are equivalent. However, recent isothermal strain-controlled fatigue endurance tests on a single heat of Type 304L stainless steel at Amec Foster Wheeler — on behalf of Rolls-Royce — have indicated a significant difference in life from testing of these different specimen designs in high temperature PWR coolant, with hollow specimens consistently giving shorter lives.

This paper presents those test results, and identifies a range of possible reasons for the differences in fatigue life through consideration of relevant literature and laboratory examination of failed specimens.

These new test results have potentially significant implications for test programmes in which solid specimen test results in air are compared to hollow specimen results in LWR environments, and for fatigue databases that include results from testing of both specimen types.

The use of a conversion factor, to be applied to fatigue lives from hollow specimens tests to allow comparison to solid specimen test results, is discussed. Further work to investigate the relevance of findings to further heats of material and to a wider range of loading conditions is identified.
Analysis of Water Hammer due to Sudden Rupture of Reactor Coolant System
Authors: Dubyk Iaroslav , Orynyak Igor
Published: December 2016

In this article we have analyzed the most severe design accident for the reactor facility — sudden rupture of the primary cooling loop. This rupture causes a water hammer event for the reactor core barrel, which is a significant but short term load. Assuming that core barrel is a thin shell, we have performed dynamic stress and strain calculations in the frequency domain. The Duhamel integral was used to calculate the transient response of a shell to an impulse load caused by the water hammer event. The results obtained were used to estimate structural stability of the core barrel.
The Application of Long and Short Cylindrical Shell Solutions for Stress and Flexibility Determination in a Single Mitred Bend
Authors: Orynyak Igor , Bogdan Andrii , Selivestrova Iryna
Published: December 2016

The continuous pipe bend behavior is well elaborated in literature. It is characterized by local ovalization of each cross section during bending which results in enhanced flexibility of it as compared to straight pipe. When pipe bend approaches some other structural elements of a piping system the end effect take place which can be described by so called long shell solution. This long solution is, in fact, a semi-membrane Vlasov’s solution when the derivative of any geometrical or force function in axial direction is much smaller than in the circumferential one [1].

Mitred bend is formed by conjunction by welding of two oblique sections of initially straight pipes. Its behavior during loading by pressure or bending moment is not evident and poorly described in standards. The goal of this paper is to give a set of general functions within a thin cylindrical shell theory which will give the opportunity to consider the mitred bend as an element of a piping system. Here we additionally introduce the so called short solution when the derivative of any parameter in axial direction is much bigger than that in circumferential one. Its main goal is to give the local behavior of stress in the vicinity of the oblique weld. Each of these two solutions satisfy by differential equations of forth order.

The complete theoretical solution for a particular mitred bend is compared with

a) existing analytical solutions and formulas;

b) numerical results obtained by FEM with distinction of the zones of influence of a long as well as short shell solution;

c) experimental data on real mitred bends given in the literature.
A Study of Axial Compression in the ASME B&PV Code for Pipe Supports and Restraints
Authors: Wiseman Phillip E. , Hoch Zara Z.
Published: December 2016

Axial compression allowable stress for pipe supports and restraints based on linear elastic analysis is detailed in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section III, Division 1, Subsection NF. The axial compression design by analysis equations within NF-3300 is replicated from the American Institute of Steel Construction (AISC) using the Allowable Stress Design (ASD) Method which was first published in the ASME Code in 1973. Although the ASME Boiler and Pressure Vessel Code is an international code, these equations are not familiar to many users outside the American Industry. For those unfamiliar with the allowable stress equations, the equations do not simply address the elastic buckling of a support or restraint which may occur when the slenderness ratio of the pipe support or restraint is relatively large, however, the allowable stress equations address each aspect of stability which encompasses the phenomena of elastic buckling and yielding of a pipe support or restraint. As a result, discussion of the axial compression allowable stresses provides much insight of how the equations have evolved over the last forty years and how they could be refined.
Fatigue Crack Initiation and Propagation in Cr-Mo Steel Hydrogen Storage Vessels: Research on Design for Safe Life
Authors: Solin Jussi , Briottet Laurent , Acosta Beatriz , Bortot Paolo , Furtado Jader , Mecozzi Elisabetta , Dey Randy
Published: December 2016

International standards and codes dedicated to design of pressure vessels are still unable to competitively ensure safe design and fitness for service of steel vessels for high pressure gaseous hydrogen. Emptying and shallow pressure cycles subject the material to hydrogen enhanced fatigue. A pre-normative project, MATHRYCE under the EU joint research program focused in this subject through material and component testing, analytical work, review of design methodologies and international collaboration.

An easy to implement, safe and economically competitive vessel design methodology is targeted. Steps towards this goal were taken by deepening our understanding on hydrogen enhanced fatigue in different kinds of laboratory specimens and real vessels designed for hydrogen service at maximum 45 MPa pressure. This included cyclic pressure testing of artificially notched vessels both in hydrogen and inert environment.

The effect of hydrogen pressure, frequency and mechanical loading parameters (ΔK, Sa) on fatigue crack initiation and propagation was analyzed. Attention was paid on the definition of “initiation” and influence of hydrogen on the relative parts of initiation and propagation on the fatigue life of a component. A good correlation between results with various test types was found. Particularly promising was the match between the measured — and estimated — crack growth rates in laboratory specimens and vessels. This supports our proposal for a safe design procedure based on crack growth and defect tolerant approach. Recommendations for implementation in a new international standard, on how to properly address hydrogen enhanced fatigue based on laboratory tests, were given and will be summarized in this presentation.

Our results indicate that crack initiation from inclusions or other small microstructural features is not necessarily affected by hydrogen to a similar extent as crack growth, but when initiated, the remaining life may be short due to fast growth. This is challenging for design and inspection rules to allow economically competitive construction of hydrogen equipment without compromising safety.
Computation of the Welding Process: The Engineering Practice Consolidated Thanks to R&D Tools
Authors: Rossillon Frédérique , Albrecht David
Published: December 2016

The integrity of structures in nuclear power plants has to be assessed to meet given safety criteria. For a better understanding of the in-service loads in welded areas of PWRs components, the residual stresses resulting from the welding process have to be evaluated. For that purpose, numerical simulation of welding has proved efficient. However, in an industrial context, simple models have to be used to stay reliable, brief and easy to use.

Among all the steps required to run a suitable computation of the welding, this paper focuses on the calibration of the heat source. Two complementary approaches are applied to define an equivalent heat input, which coarsely include complex phenomena in the weld pool. The engineering practice is driven by a know-how: simplified method are used to get an efficient result in short modelling time. On the other hand, EDF R&D develops tools which quantify the difference between models and lead to an objective choice. The mix of both approaches enables to consolidate the engineering practice.
Estimation of Head Loss due to Flow Intrusion With Inner Ring Spiral Wound Gaskets
Authors: Rice Dale A. , Waterland Jerry , Chandler David G.
Published: December 2016

The spiral wound gasket, developed after the turn of the 20th century, has been a popular gasket choice in the chemical, petrochemical, power and other industries. Since that time, metal gasket manufacturers have developed various designs for this popular type of gasket, using different metals and fillers in the windings. As a result, some subsequent spiral wound designs have included a metal inner ring inserted inboard of the windings, with the primary objective of preventing inward radial buckling of this gasket as well as to cover more of the flange face and minimize erosion between flange faces. However, the cost of fabricating the spiral wound increases in accordance with the metallurgy of the inner ring, as does the assembly bolt force required to fully compress this now captured spiral winding. Additionally, another recently identified drawback of the inner ring is the head loss due to the contraction of the flow area caused by the inner ring intrusion into the flow for certain nominal pipe sizes (NPS) and pipe schedules. For example, standard ASME B16.20 spiral wound gaskets with inner rings designed for ASME B16.5 Class 150 raised face flanges extend inside the flange and pipe wall to varying degrees for most Schedule 10 pipe between NPS ½” and 6”. Such intrusions can impact the flow in the form of minor head loss resulting from intrusion of the inner ring. Flow equations for an orifice can be used to estimate head loss; such an empirical equation has been applied to estimate head loss associated with an inner ring style spiral wound gasket in various pipe schedules and NPSs. Total head loss for multiple flanges in a pipe network has also been calculated as the head losses from individual “inner ring orifices” are accumulated. Several scenarios were identified to indicate where spiral wound gaskets with an inner ring can not only lead to pipe network head loss but substantial hidden energy costs.
Effects of Multiple Parallel Flaws on Crack Opening Area
Authors: Walter Matthew , Sommerville Daniel
Published: December 2016

Cracking in boiling water reactor (BWR) core shroud welds has been identified in operating nuclear plants worldwide. The Boiling Water Reactor Vessel and Internals Project (BWRVIP) has published several reports providing inspection and evaluation (I&E) guidance for intergranular stress corrosion cracking (IGSCC) in the core shroud of BWRs. This guidance is predominately focused on evaluating crack stability. Calculating through-wall leakage was not previously a focus of the existing BWRVIP I&E guidelines for the core shroud; however, there is some guidance in the current documentation. In recent years there has been some evidence of through-wall indications in the core shroud where the through-wall indications were aligned in an array of parallel, short, flaws.

BWRVIP-158-A contains rules for treating parallel flaws with respect to calculation of structural margin for both net section collapse (limit load) and brittle fracture (linear elastic fracture mechanics (LEFM)) failure modes. There is currently no BWRVIP document or other open literature, to the authors’ knowledge, that provides insight into whether the crack opening displacements (CODs) for an array of parallel through-wall cracks are larger than that calculated for a single through-wall crack. Developing an understanding of the effect of parallel cracks on the CODs and subsequent crack opening areas (COAs) of each crack is important in augmenting the existing guidance on how to appropriately disposition through-wall cracking in reactor internal components. Specifically, it is important to know if multiple parallel cracks can lead to individual COAs that are larger than for a single crack of the same length, in order to perform accurate leakage rate calculations.

This paper documents linear-elastic finite element analyses (FEA) performed to study the effect of a parallel crack configuration on the resulting COA for the set of cracks compared to the COA calculated if each crack was treated as an individual crack, without adjacent cracking present. Various separation distances, number of crack cases and crack lengths are considered. While the object of this work is to provide criteria for the evaluation of reactor internals, the results can be applied to evaluate COD and COA in any component for which the cracking configuration and inherent assumptions of LEFM are applicable.
FFS Assessment of Pressurized Equipment Utilizing a Thickness Mapping Tool
Authors: Hantz Benjamin , Akula Venkata M. K. , Leroux John
Published: December 2016

For pressure vessels, loss of thickness detected during scheduled maintenance utilizing UT scans can be assessed based on Level 1 or 2 analyses as per API 579 guidelines. However, Level 1 and 2 analyses can point to excessively conservative assessments. Level – 3 assessments utilizing the finite element method can be performed for a more accurate estimate of the load carrying capacity of the corroded structure. However, for a high fidelity structural response prediction using the finite element method, the characteristics of the model must be accurately represented. Although the three nonlinearities, namely, the geometric, material, and contact nonlinearities can be adequately included in a finite element analysis, procedures to accurately include the thickness measurements are not readily available.

In this paper, a tool to map thicknesses obtained from UT scans onto a shell based finite element models, to perform Level – 3 analyses is discussed. The tool works in conjunction with Abaqus/CAE and is illustrated for two different structures following the elastic-plastic analysis procedure outlined in the API 579 document. The tool is intended only as a means to reduce the modeling time associated with mapping thicknesses. The results of the analyses and insights gained are presented.
Suggested Modifications to API RP 934 Reactor Requirements for Thinner Wall Equipment
Authors: Shargay Cathleen , Cuevas Alex , Antalffy Leslie
Published: December 2016

Cr-Mo steel reactors being purchased for the oil refineries, gasification, and other industries have excellent standards for achieving fit for service designs, material specifications, and fabrication requirements. These standards include the ASME Pressure Vessel Code and API Recommended Practice (RP) 934-A for the 2¼Cr-1Mo alloy family and RP 934-C for 1¼Cr-½Mo. The RPs’ scopes indicate that they were developed for the most severe, high pressure refinery services, which typically require thick wall reactors. However, these standards are also widely used by industry as guidance for thinner Cr-Mo equipment. This paper aims to identify and present the appropriate requirements derived from the RPs that can be justified for less severe services and/or thin wall equipment falling outside the intended scope of API RP 934-A and 934-C.
Small Punch Testing on High Chromium Steels
Authors: Tonti Andrea , Holmström Stefan , Lega Daniela , Augugliaro Giuseppe , Delle Site Corrado , Antonini Alessandra , Alvino Antonello
Published: December 2016

The Small Punch test is a miniaturized non-intrusive methodology that allows performing creep tests using very small specimens. It can be used for the residual lifetime assessment of in service components.

In the last years, numerous applications of Small Punch Testing as well as related pre-normative work and Round Robin exercises have led to new insights which motivate a revision of the current Code of Practice for Small Punch Testing (CWA 15627, Dec. 2007) and/or its transfer in an EN norm.

In this paper we present the state-of-art of the small punch technique: its performances, usefulness and critical aspects have been discussed and some examples have been reported. Some measurements carried out during the round-robin exercises have been reported: several testing laboratories are cooperating in a round-robin on a virgin P92 material. The tests are still in progress, so only preliminary data will be shown in this paper.

A series of measurements performed during the pre-normative time will also be shown: a serviced (116,000 hours) ASME A213 T91 tube, installed in a petrochemical plant has been investigated. Small punch tests were performed and the residual life was then estimated by Omega Method. A microstructure characterization has been also reported.

The results obtained encourage new efforts for material testing by SPT; sampling, however, was found as a critical step if the analyzed material may suffer from localized damage.
A Probabilistic Approach to the Thermo-Mechanical Analysis of Coke Drums
Authors: Gassama Edrissa , Spring Daniel W. , Stenta Aaron , Cochran Jeffrey , Panzarella Charles
Published: December 2016

A coke drum experiences operating conditions that are severe and unrelenting, and their lifespans reflect this. In this paper, a coupled thermal-mechanical model of an operating coke drum is presented. The impacts of important operating parameters, such as the cycle time and quench rate, on an ideal operating cycle and a cycle that produces hotspots are discussed. The model is constructed in three stages: (i) the through-wall temperature distribution is probabilistically determined using a Bayesian inverse approach that calculates the heat flux profile on the inside of the drum wall from a temperature reading on the outside of the wall; (ii) a thermal-mechanical finite element analysis of the drum wall is conducted using the heat flux profile as a spatially and temporally varying boundary condition — to obtain the stress and strain behavior at a critical location (weld seam) on the drum; and (iii) hotspots are introduced in the vicinity of the weld through a novel approach, and their impact on the plastic behavior of the drum wall is examined. The influence of the operating conditions on the behavior of the coke drum is to be incorporated into a financial analysis of the entire coke drum’s life cycle — in a companion paper — to determine an optimal operating strategy.
Fitness-for-Service Assessment of Piping Subject to Random Vibration
Authors: Breaux Lyle , McNeill Scot , Szasz Gyorgy
Published: December 2016

A methodology is presented for Level 1 and 2 Fitness-for-Service (FFS) assessments of process and power piping subject to random vibration loading. The intent is to provide a basis for random vibration assessment based on concepts from spectral fatigue, which is simplified to the degree that a non-specialist can conduct the FFS assessment with little prior knowledge of the subject matter. The proposed Level 1 FFS assessment is based on extension and generalization of established industry screening curves for piping vibration. The measured (overall) RMS vibration level is compared against allowable values given by the curves evaluated at the average crossing frequency of the measured vibration. The proposed Level 2 FFS assessment utilizes an allowable cyclic stress. The allowable stress is a function of the target design life as well as the average crossing frequency and kurtosis of the measured vibration. Both approaches are illustrated by example.
Experimental and Numerical Analysis of Structures With Bolted Joints Subjected to Low Impact Load: Part 1
Authors: Karpanan Kumarswamy , O’Toole Brendan
Published: December 2016

Bolted joints are the most common type of fastener in army vehicles and play a very important role in maintaining the structural integrity of combat vehicles. In combat, these vehicles may be subjected to various kinds of shock loading, such as initiated by a mine blast, projectile impact, or frontal crash.

This study analyzes the transient behavior of structures with bolted joints subjected to impact or shock loads using experimental methods and Finite Element Analysis (FEA). Factors such as damping that affect the bolted joint structures for shock loading are studied. Only a limited amount of published literature describes the proper method for analyzing transient shock propagation across bolted connections for high-impact loading. The initial case study focused on a simple cantilever beam with a bolted lap joint subjected to relatively low levels of impact force. The second case study used a flat plate bolted to a hat-section. These simple configurations are representative of structures found in many military ground vehicles that can be subjected to transient impact and blast loads. These structures were subjected to low-impact loading (non-destructive) using impact hammers and high-impact loading (destructive) using an air gun. The responses were measured using accelerometers. LS-DYNA FE solver was used to simulate the shock propagation in the bolted structures.

For all the bolted structures, the modal analysis was performed both experimentally and numerically. The results are in excellent agreement for the lower modes and exhibit a small deviation in the higher modes. Secondly, the time history responses of experimental and FE analysis are compared. This is a two-part paper. In this first paper, a simplified bolted connection (bolted cantilever beam) is used for studying the low-impact shock propagation.
Evaluation of the Anchor-Bolt Chair Design Considering Localized Stresses in the Shell of Anchored Storage Tanks
Authors: Rondon Andres , Guzey Sukru
Published: December 2016

Anchor bolt chairs are structural attachments used to control the overturning stability of aboveground storage tanks subjected to external and internal forces. Throughout this investigation three different design procedures were evaluated in order to determine the localized stresses occurring in the shell above the chairs due to wind load. The implemented methods are based on mathematical equations, stress linearization and stress extrapolation. Moreover, 3D finite element models were built to estimate the effect of tank height, diameter, shell thickness and anchor chair height. The results of the three methods are compared in terms of the localized stresses obtained from each one as well as in terms of the utilization ratio of the shell material.
A High-Accuracy Approach to Finite Element Analysis Using the Hexa 27-Node Element
Authors: Marcal Pedro V. , Fong Jeffrey T. , Rainsberger Robert , Ma Li
Published: December 2016

In most finite-element-analysis codes, accuracy is achieved through the use of the hexahedron hexa-20 elements (a node at each of the 8 corners and 12 edges of a brick element). Unfortunately, without an additional node in the center of each of the element’s 6 faces, nor in the center of the hexa, the hexa-20 elements are not fully quadratic such that its truncation error remains at h2(0), the same as the error of a hexa-8 element formulation.

To achieve an accuracy with a truncation error of h3(0), we need the fully-quadratic hexa-27 formulation. A competitor of the hexa-27 element in the early days was the so-called serendipity cubic hexa-32 solid elements (see Ahmad, Irons, and Zienkiewicz, Int. J. Numer. Methods in Eng., 2:419–451 (1970) [1]). The hexa-32 elements, unfortunately, also suffer from the same lack of accuracy syndrome as the hexa20’s.

In this paper, we investigate the accuracy of various elements described in the literature including the fully quadratic hexa-27 elements to a shell problem of interest to the pressure vessels and piping community, viz. the shell-element-based analysis of a barrel vault. Significance of the highly accurate hexa-27 formulation and a comparison of its results with similar solutions using ABAQUS hexa-8, and hexa-20 elements, are presented and discussed. Guidelines are proposed for selection of better elements.
Parametric Study on Pressure-Temperature Limit Curve
Authors: Choi Shin-Beom , Surh Han-Bum , Kim Jong-Wook
Published: December 2016

The final goal of this study is to solve the round-robin problem for the safety of a reactor pressure vessel by adopting a finite element analysis and probabilistic fracture mechanics. To do so, a sensitivity analysis and a deterministic analysis should be conducted. This paper contains the results of the sensitivity analysis as intermediate results of a round-robin problem. Key parameters such as the initial Reference Temperature for Nil Ductility Transition, Ni contents, Cu contents, fluence, and input transient were chosen to conduct the sensitivity analysis. In addition, different values of crack depth to the thickness ratio are considered to develop FE models. Moreover, a series of FE analyses are carried out. As a result, each key parameter has an influence on RTNDT and KIc. This means that the P-T limit curve is shifted. If the value of each key parameter is increased, the P-T limit curve is moved to the right side. Therefore, the operating area of the P-T limit curve should be reduced. The results of this paper will be very helpful in enhancing our understanding of the P-T limit curve. In addition, it will be used to adjust the probabilistic fracture mechanics and solve the round-robin problem.
Study of Bolt Tightening Methods Using Load Indicating Bolts
Authors: Jung Gong H. , Flocken Russell R.
Published: December 2016

Alternative bolting patterns have been studied and received with wide acceptance for their performance, and are presented in ASME PCC1. However, it seems that the use of the alternative methods has been limited. Users may not have enough confidence to be motivated to use the alternatives. This paper summarizes results of tests on 24” Class 300 flanges tightened by hydraulic torque wrench and pneumatic torque multiplier. The flanges were assembled with two bolting patterns, Legacy pattern and Alternative #3, and their bolt loads were measured using ASTM F2482 load indicating studs. The results may provide validation and supporting information for users who have looked for more time-saving bolting method.
Introduction of Warm Pre-Stress Concept in French RPV Structural Integrity Assessment: Part II — RSE-M Appendix
Authors: Marie Stéphane , Chapuliot Stéphane , Moinereau Dominique , Ait-Bachir Malik , Jacquemoud Clémentine , Tanguy Benoit
Published: December 2016

A new appendix is introduced in the RSE-M code, devoted to in-service operation on PWRs, dealing with the assessment of a defect in the Reactor Pressure Vessel. This new appendix reflects the current French practice and introduces a second criterion to consider the Warm Pre-Stress (WPS) effect.

This appendix is applicable to under clad defects and defects partially in the cladding, and covers nominal, incidental and accidental conditions. The main criterion is the classical comparison between the stress intensity factor (amplified to account for the plasticity of the cladding) and the material toughness (taking into account the irradiation induced ageing). For incidental and accidental situations, if the conventional criterion is not verified, an alternative criterion is proposed to take into account the WPS effect. The criterion corresponds to the ACE criterion developed by AREVA, CEA and EDF taking into account the effective material toughness depending on the loading history.

The present paper presents this new RSE-M appendix and provides some basic elements of justification and validation on the ACE criterion.
Seismic Performance of Piping Anchored to Concrete in Case of Nonlinear Load-Bearing Behavior of Post-Installed Anchors
Authors: Dwenger Fabian , Kerkhof Klaus
Published: December 2016

In nuclear power plants, post-installed anchors are used for connections between concrete structure and non-structural components such as piping systems. Piping is usually connected to concrete fastenings by pipe hangers. Dynamic loading during an earthquake leads to dynamic interactions between concrete structure and non-structural component. These dynamic interactions result in dynamic loads which have to be transferred by fastenings such as anchor plates with post-installed anchors. Besides the vibrational behavior of the subsystems, the dynamic behavior of the coupled system concrete-fastening-piping is also influenced by the load-bearing behavior of the anchors. At anchor loads close to ultimate load, the load-bearing behavior of anchors is highly nonlinear due to plastic deformation of the anchor bolt and cracking of the concrete. Additionally, permanent displacement of anchors which already occurs at smaller loads can lead to change of pipe hanger stiffness characteristics and nonlinear vibrations of the component.

For an ongoing research project, various numerical design calculations are carried out for a test set-up. The test set-up is designed to study the dynamic interactions and effects mentioned above.

In order to investigate the necessity for a coupled analysis of the structural and non-structural part of the test set-up, one study in this paper deals with the effect of coupling/decoupling on calculated natural frequencies and pipe hanger loads.

For simulating the nonlinear behavior of the fastening during seismic loading, anchor models with different levels of complexity were developed which were then implemented in a large-scale finite element model of the test set-up. Comparative seismic analyses in the time domain with different anchor models are presented which are carried out as preliminary simulations for the design of the test set-up.