bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simplified Methodology for Analysis of Reflected Detonation and DDT: Part 1 — Elastic Analysis
Authors: Ligon Thomas C. , Gross David J. , Ahnert Stephen D. , Minichiello John C. 
Published: November 2014

This paper introduces a simplified approach for analyzing local elastic hoop response of piping to reflected gaseous detonations and deflagration-to-detonation transitions (DDT). A consequence associated with gaseous explosions is the potential for DDT to occur near the end of a closed pipe or gas pocket. As an accelerating deflagration flame approaches a closed end, the unburned fuel ahead of the flame front is compressed to an elevated initial pressure. This process is often referred to as pressure piling or pre-compression, and the combination of detonation reflection with the elevated initial pressure, can produce extremely high peak pressures and large values of impulse. In this paper, the event where DDT occurs immediately ahead of the reflecting surface is referred to as a reflected-DDT (R-DDT).
In addition to gas mixture and initial conditions, the peak pressure and shape of the pressure time-history associated with a reflected detonation or DDT is a function of the detonation propagation distance prior to reflection and the relative distance between the ignition location, the DDT location, and the reflecting surface. An empirical pressure time-history has been developed using pressure data from approximately 190 explosion tests using hydrogen and nitrous oxide mixtures in 2-inch and 4-inch pipe to describe events ranging from fully-developed reflected detonations to R-DDTs. The empirical model of the pressure time-history was validated by comparing measured elastic hoop strains to finite-element model predictions using the pressure time-history model. Part 2 of this paper compares the methodology to plastic response data.
Frequency Distribution Curves for Main Steam Piping Multiaxial Stresses
Authors: Cohn Marvin J. , Faham Fatma G. , Patel Dipak 
Published: November 2014

A high energy piping (HEP) asset integrity management program is important for the safety of plant personnel and reliability of the generating unit. HEP weldment failures have resulted in serious injuries, fatalities, extensive damage of components, and significant lost generation. The main steam (MS) piping system is one of the most critical HEP systems. Creep damage assessment in MS piping systems should include the evaluation of multiaxial stresses associated with field conditions and significant anomalies, such as malfunctioning supports and significant displacement interferences.
This paper presents empirical data illustrating that lead-the-fleet girth welds of MS piping systems have creep failures which can be successfully ranked by a multiaxial stress parameter, such as maximum principal stress. Both the as-found elastic (initial) stress and inelastic (redistributed) stress at the piping outside diameter surface are evaluated for the base metal of three MS piping systems. Frequency distribution curves are then developed for the initial and redistributed piping stresses. The frequency distribution curves are subsequently included on a Larson Miller Parameter (LMP) plot for the applicable material, revealing the few critical (lead-the-fleet) girth welds selected for nondestructive examination (NDE).
By including an evaluation of significant field anomalies, multiaxial operating stress on the outside surface, and weldment performance, it is shown that there is a good correlation of calculated creep stress versus the operating time of observed creep damage. This process also reveals the large number of MS piping girth welds that have insufficient applied stress to have substantial creep damage within the expected unit life time (assuming no major fabrication defects).
API 579 recommends an effective stress to compute the creep rupture life using the LMP. This constitutive stress equation includes a combination of the maximum principal, von Mises, and hydrostatic stresses. Considering the stresses in these three MS piping systems, this paper reveals that when the axial and hoop stresses are nearly the same values, the API 579 effective stress may be 10% greater than the maximum principal stress. However, the maximum principal stresses are greater than the API 579 effective stresses at the maximum stress locations in the three MS piping systems, because the axial stresses are significantly greater than the hoop stresses.
This study also provides a comparison of the results of a conventional American Society of Mechanical Engineers (ASME) B31.1 Code as-designed sustained stress analysis versus the redistributed maximum principal stresses for a complete set of MS piping system nodes. A comparison of Code-sustained load versus redistributed maximum principal stress results are illustrated on frequency distribution curves.
Study on the Deflection of Gaskets and its Effects on Residual Bolt Forces and Tightness of Bolted Flanged Connections
Authors: Kobayashi Takashi 
Published: November 2014

The deflections of gaskets after initial tightening largely affect the residual bolt forces and the tightness of bolted flanged connections. The bolt forces decrease significantly due to the deflections of gaskets after initial tightening in the cases where expanded PTFE gaskets are used. The visco-elastic characteristic of the gaskets is the main cause for the phenomenon. It was shown in the paper PVP2012-78694 that the tightness improved even if the bolt forces reduced in the long term. This is because the gasket becomes packed under a high gasket stress. It is important to estimate the thickness change of gaskets to evaluate the tightness of bolted flanged connections.
In this paper, an analytical model of a bolted flanged connection, in which the flanges, the bolts and the gasket are represented by spring constants, is proposed. Experiments were carried out to measure the creep characteristic of the expanded PTFE gasket. The residual bolt forces and the deflection of the gasket were estimated based on the analytical model of the bolted flanged connection and the creep characteristic of the gasket. Thus, the relationship between gasket deflection and the tightness of the bolted flanged connection are clarified.
Analysis of Stresses and Strains in Packed Stuffing-Boxes
Authors: Kazeminia Mehdi , Bouzid Abdel-Hakim 
Published: November 2014

Packed stuffing-boxes are mechanical sealing systems that are extensively used in pressurized valves and pumps. Yet there is no standard design procedure that could be used to verify their mechanical integrity and leak tightness. It is only recently that standard test procedures to qualify the packing material have been suggested for adoption in both North America and Europe. While the packing contact stress with the side walls is predictable using existing models there is no analytical methodology to verify the stresses and strains in the stuffing-box housing.
This paper presents an analytical model that analyzes the stresses and strains of all the stuffing box components including the packing rings. The developed model will be validated both numerically using FEM and experimentally on an instrumented packed stuffing box rig that is specially designed to test the mechanical and leakage performance of different packing materials.
Fatigue Evaluation Under Continuous Strain Rate Changing Condition of Carbon Steel in BWR Environment
Authors: Hirano Akihiko , Mizuta Satoko 
Published: November 2014

Fatigue evaluation methods have been proposed based on environmental fatigue test results regarding parameters selected for simulating Boiling Water Reactor (BWR) and Pressurized Water Reactor (PWR) conditions. The effects of strain wave form have been discussed by comparing experimental fatigue life with predicted fatigue life evaluated by modified rate approach (MRA) method. The applicability of the MRA method has been verified extensively by the environmental fatigue tests with strain rate changing conditions consisting of combined constant strain rates. However, different results have been obtained for a sine strain wave in simulated BWR and PWR conditions. More study for evaluating the applicability of MRA method was required by evaluating with continuous strain rate conditions such as a sine wave. For the purpose of verification, two approaches were applied. One is performing the environmental fatigue tests with the sine strain wave in simulated BWR condition. The other is to evaluate the low cycle thermal fatigue test performed in simulated BWR condition because the wave form of this test contains continuous strain rate changing condition. MRA method was indicated to be applicable to predict fatigue lives under these kinds of continuous strain rate changing conditions.
All of the studies including this study verifying the applicability of the MRA method were performed with small specimens having the well polished surfaces in the gage length. These results indicate that the evaluation by the MRA method includes the synergistic effect between the water environment and the transient. However, the synergistic effects with the surface roughness and the component size are not known. Design margin derived by the multiplication of the sub-factors of environment, surface roughness and component size may be conservative. The evaluation of the conservatism is considered to be beneficial.
The Analysis of Hydrogen Diffusion Behaviors Coupled With the Analysis of Heat Transfer Around the Heat Affected Zone of Welding
Authors: Ohmi Toshihito , Yokobori Toshimitsu , Takei Kenichi , Konishi Yuki 
Published: November 2014

Hydrogen penetrates into the metal and causes Hydrogen embrittlement due to the increase in hydrogen concentration. This is caused by the local stress fields such as residual stress field at the site of welding or local stress field around a crack tip. It accompanied with incubation time of several hours since the components were exposed to hydrogen atmospheric condition. This incubation time is time lag of hydrogen diffusion and concentration at the site where the hydrogen embrittlement occurs. Therefore, clarification of the hydrogen diffusion behavior is important to prevent from fracture of hydrogen embrittlement.
In this paper, the numerical analyses of hydrogen diffusion around weld part including HAZ (Heat Affected Zone) under residual stress coupled with that of heat transfer during the cooling process before and after weld were conducted and the behaviors of hydrogen concentration were analyzed. On the basis of these analyses, the method of heat treatment to prevent from hydrogen concentration at the weld part was investigated. Results obtained by these analyses showed that pre weld heat treatment is effective in the prevention of hydrogen concentration and combined pre weld heat treatment with post weld heat treatment was found to be the most effective treatment.
The Effect of Inspection on Maintenance Planning for Fossil Fuel Fired Power Plant
Authors: Takahashi Jun , Sakai Shinsuke 
Published: November 2014

Periodical inspection is necessary for stable operation of the plant. But usually, inspection cost and inspection period are limited, and it is difficult to inspect all of the objective location of the plant in allowed cost and period. Therefore, for maintenance planning, probability of failure is presumes by the obtained sample size inspection data. In that case, presumed probability of failure includes uncertainty, and the one-side tolerance limit of the probability is changed by the sample size of the inspection.
For maintenance on boiler tubes of fossil fuel fired power plants, only limited sample size inspection data can be used for maintenance planning. On the other hand, the conditions of the tubes for maintenance are different because environmental conditions of the tubes like actual temperature are different. Then the inspection results don’t demand enough information to presume probability of failure because the standard deviation is not known. But usually to presume probability of failure for maintenance, the standard deviation is not considered only the average is used.
Therefore, considering mainly uncertainties depend on sample size of the inspection data, presumed probability of failure is related to rational maintenance planning.
Proposal of Surface Finish Factor on Fatigue Strength in Design Fatigue Curve
Authors: Fukuta Yuichi , Kanasaki Hiroshi , Asada Seiji , Sera Takehiko 
Published: November 2014

The published papers related to the effects of surface finish on fatigue strength are reviewed in order to formulate its factor in the design fatigue curve in air environment.
Firstly, some of regulations and literatures were examined to verify the surface finish effect on fatigue strength and formulation of that in design fatigue curve.
The fatigue strength of carbon and low alloy steels is decreased with an increase of its surface roughness and tensile strength but that of stainless steel is not decreased except for special conditions.
After screening the data of carbon and low alloy steels, a surface finish factor is formulated with these data which is a function of tensile strength, surface roughness and mean stress.
Study on Simplified Prediction Method of Thermal Ratchet Deformation Based on Parallel Bar Model
Authors: Kokufuda Toshiaki , Kasahara Naoto 
Published: November 2014

For elevated temperature structures such as fast breeder reactor components, inelastic deformation is likely to occur because of reduction of yield stress and occurrence of creep deformation. The typical failure modes for elevated temperature structures are excessive deformation caused by the accumulation of inelastic deformation and creep fatigue caused by inelastic strain concentration at structure discontinuities. In order to prevent such failures, it is necessary to evaluate inelastic deformation adequately.
Thermal ratchet deformation, namely the progressive plastic deformation induced by cyclic thermal stress with uniform primary stress, has some possibility resulting in excessive deformation. ASME boiler & pressure vessel code provides elastic evaluation methods for thermal ratchet. However, these methods are so focused on preventing thermal ratchet deformation, that it could be too conservative under some conditions. Therefore, a simplified elastic evaluation method to quantify thermal ratchet deformation is desired.
In this paper, the simplified prediction method for thermal ratchet deformation is proposed using parallel bar model, which represents stress redistribution mechanism of cylindrical vessels. The solution of thermal ratchet deformation of parallel bar model was derived and compared with FEM calculation results of cylindrical vessels. This theoretical solution is proposed as a prediction method for thermal ratchet deformation of cylindrical vessels. The applicable area of the proposed prediction method is the cylindrical vessel under linear and parabolic temperature distribution through the wall thickness.
Large Openings in Cylindrical Pressure Vessels: An Assessment Based on Absolute Size
Authors: Chandiramani Dipak K. , Gopalakrishnan Shyam , Mathkar Ameya 
Published: November 2014

Clauses UG-36 through UG-43 of ASME Section VIII Division 1 [1], describe the method of calculating the adequacy of compensation of openings in shells, using an area-replacement method. The method is based on determining and suitably replacing the missing metal area along any section, with metal available or provided, within the limits of reinforcement on the shell and nozzle.
Clause UG-36 (b) of ASME Section VIII Division 1 provides limits on the size of the opening for applicability of Clauses UG-36 through UG-43. If these limits are exceeded, supplemental rules of Clause 1-7 of Appendix 1 need to be complied with or alternatively the rules of Clause 1-10 of Appendix 1 may be applied.
The rules for large openings as stated in the Code are not dependent upon the absolute size of the nozzle and shell. For example, same calculations would be required to be carried out whether a nozzle of NPS 1 is attached to a shell of NPS 1.5 or a nozzle of NPS 16 is attached to a shell of NPS 24.
The work presented in this paper is an attempt to determine whether the additional calculations in Clause 1-7 need to be carried out for finished openings exceeding the limits of UG-36(b) irrespective of the absolute size of the nozzle and shell. This has been done by carrying out calculations for a wide range of nozzle-shell combinations and comparing the results so obtained with the results of a Finite Element Analysis.
Through-Wall Bending Stress Equations for the Design of Safety-Related Buried Piping
Authors: Marohl Michael P. H. , Moenssens Mark A. 
Published: November 2014

In the design of buried piping, resistance of the pipe-soil system to the applied vertical load is a significant design consideration. Application of a resultant vertical load perpendicular to the longitudinal pipe axis results in ovalization of the pipe, with resulting vertical pressures in the soil bedding and horizontal pressures in the soil backfill adjacent to the pipe, as well as internal forces and moments in the pipe wall. For pipes that are relatively rigid compared to the soil backfill, the developed internal forces in the pipe hoop and resulting internal moments in the wall tend to be higher than a more flexible pipe with a stiffer soil backfill. For many buried pipes, design to consider through-wall bending stress is not included and consideration of a buckling allowable is considered adequate. However, for safety-related pipes, investigation to include the through-wall bending stress is considered important.
Although estimation of the internal hoop stresses in a buried pipe is relatively straight forward, several different methodologies are presented in various industry documents for calculating the through-wall bending stress due to the resulting internal moments. Recommended approaches for calculating the through-wall bending stress vary depending on the pipe material, wall thickness, wall type, deflection, burial condition and other factors. A sensitivity study comparing various theories estimating the through-wall bending stress in a buried pipe subject to external loads with a vertical resultant force is performed. The range of variables is assessed to determine the applicability of the results to typical safety-related piping. This study presents the results of the sensitivity study and provides recommendations for the calculation and incorporation of through-wall bending stress in the design of buried safety related piping.
A Non-Isotropic Approach to Predict Fatigue Crack Growth of Embedded Flaw in Engineering Criticality Assessment
Authors: Carlucci Antonio , Li Jun , Mcirdi Kamel , Auvret Pierre-Louis 
Published: November 2014

An analytical method to predict the fatigue crack growth of embedded flaw in metallic structure has been established by using a non-isotropic approach. Within Engineering Criticality Assessment, the embedded flaw is considered as planar elliptical defect located inside of structure wall thickness. In the analytical standard assessment procedure [1], since only the minor ligament (the shortest distance between material surface and embedded crack tip) is applied to calculate the stress intensity factor, the fatigue crack propagation prediction in height direction is symmetrical for each side. Therefore, the crack growth is overestimated when, as it usually is the case, the embedded flaw is not centered and/or submitted to non-uniform stress range in the wall thickness of the structure.
The proposed method allows to predict the fatigue crack propagation rate in asymmetrical way, by taking into account respectively the minor and major ligament, in order to remove the above conservatism and consequently to improve the ECA results for embedded defects.
Proposal of the Screening Method for Prevention of the Accumulation of the Ratcheting Strain Derived From the Movement of the Temperature Distribution
Authors: Okajima Satoshi , Wakai Takashi , Ando Masanori , Inoue Yasuhiro , Watanabe Sota 
Published: November 2014

The prevention of excessive deformation by thermal ratcheting is important in the design of high-temperature components of fast breeder reactors (FBR). This includes evaluation methods for a new type of thermal ratcheting caused by a traveling temperature distribution. Igari et al. [1] proposed a mechanism-based evaluation method to evaluate thermal ratcheting caused by temperature distributions traveling long and short distances.
In this paper, we simplify the existing method and propose a screening method to prevent thermal ratcheting strain in the design of practical components. The proposed method consists of two steps to prevent the continuous accumulation of ratcheting strain.
The first step is to determine whether all points through the wall thickness are in the plastic state. This is based on an equivalent stress, which comprises the primary stress, the thermal membrane stress, and the thermal bending stress. When the equivalent stress is less than the yield strength of the cylinder material, overall plastic deformation through the wall thickness does not occur. When the equivalent stress exceeds the yield strength in some regions of the cylinder, the ranges of these regions are measured for the second step. To prevent the acceleration of the plastic deformation due to creep, we define the upper limit of the equivalent stress based on the relaxation strength, Sr.
The second step is to determine whether the accumulation of the plastic strain saturates (i.e. if shakedown occurs). For this purpose, we define the screening criteria for the range of the plastic region. When the range of the plastic region is sufficiently small, residual stress is generated in the direction opposite to the plastic deformation direction. As a result of residual stress, further accumulation of the plastic deformation is suppressed, and finally shakedown occurs. If the range of the plastic region exceeds the defined criteria, a more detailed evaluation method (e.g. inelastic finite element analysis) may be used for the component design.
To validate the proposed method, we performed a set of elasto-plastic finite element method (FEM) analyses, with the assumption of elastic perfectly plastic material.
Comparison Between Cyclic Testing and Analysis of Piping Bends With Local Thinning
Authors: Reinhardt Wolf , Duan Xinjian 
Published: November 2014

A series of tests on small-bore Carbon steel piping specimens with bends has been performed within the Feeder Bend Testing Program. The objective of the tests was to explore the effect of global and local wall thinning on the structural behaviour of feeder pipes in CANDU® reactors. Tests involved both cyclic and monotonic bending loading together with static pressure in order to obtain information about both the ultimate load carrying capacity and the fatigue life.
The specimens were thinned locally to below the NB-3600 pressure based wall thickness within or near the bend. Results of cyclic tests are reported and discussed. For one of the tests, a fatigue crack initiation and a fatigue crack growth analysis were performed. The results have relevance as an evaluation of the conservatism of traditional piping design methods, as well as a benchmark for fitness-for-service approaches, such as flaw tolerance evaluation.
Case Study: Failure Analysis of a BFJ in Cyclic Service
Authors: Seipp Trevor G. 
Published: November 2014

A bolted flange joint was in cyclic temperature and pressure service in a natural gas dehydrator (mole sieve) vessel. The flange joint suffered from multiple failures on a frequent (9 month) basis.
This paper details the investigation into the failure and highlights the most probable cause of failure. A finite element analysis of the pressure and temperature transients in the bolted flange joint pointed to the temperature cycle as tending to unload the joint. Then, a parametric study was undertaken to evaluate the effectiveness of potential solutions.
The bolted flange joint was placed back into service and has been operating for more than three times the prior mean time between failures.