Comparison of ASME B31.1 Sustained Load Stresses to Corresponding Tresca Stresses

2012 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Circumferential Stress ◽  
Elastic Beam ◽  
Beam Theory ◽  
High Energy ◽  
Parent Material ◽  
Sustained Load ◽  
Piping System ◽  
Longitudinal Stress ◽  
Analytical Methodology ◽  
Sustained Loads

Conventional United States designs of high energy piping (HEP) systems use the American Society of Mechanical Engineers (ASME) B31.1 Power Piping Code. The analytical methodology in this code is based on linear elastic beam theory. The ASME B31.1-2010 Power Piping Code (Code) [1] recommends Equation 15 to calculate the piping stress due to sustained loads. Many practitioners believe that the sustained load stress (SL) results using Equation 15 are not significantly less than using a Tresca methodology for the same set of forces and moments. This paper provides a comparison of the ASME B31.1 SL stresses to the corresponding Tresca stresses in parent material, based on empirical HEP system stress analyses. The results of three piping system evaluations are considered, including examples of longitudinal stress lower than the circumferential stress and examples where the longitudinal stress is greater than the circumferential stress. This study considers the elastic primary stresses on the outside surface of the pipe, prior to any creep redistribution. At locations where the longitudinal stress is greater than the circumferential stress, the SL stress is nearly the same as the elastic Tresca stress. At locations where the longitudinal stress is considerably less than the circumferential stress, the SL stress is considerably less than the elastic Tresca stress. This conclusion is due to the fact that the SL stress is primarily governed by longitudinal loading. The paper also considers inelastic primary stresses, after complete creep redistribution. For piping materials operating in the creep regime, the axial and circumferential pressure stresses are eventually redistributed and are maximum at the outer surface of the pipe. After several years of operation, the Code SL stresses and elastic Tresca stresses are significantly less than the inelastic Tresca stresses. Consequently, the use of SL stresses and elastic Tresca stresses for estimating component inelastic primary stresses would be nonconservative.

Ranking of Creep Damage in Main Steam Piping System Girth Welds Considering Multiaxial Stress Ranges

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Marvin J. Cohn ◽  
Fatma G. Faham ◽  
Dipak Patel
Keyword(s):  
Creep Damage ◽  
High Energy ◽  
Sustained Load ◽  
Piping System ◽  
Multiaxial Stress ◽  
Analysis Model ◽  
Principal Stresses ◽  
Piping Systems ◽  
Girth Welds ◽  
Main Steam

A high-energy piping (HEP) asset integrity management program is important for the safety of plant personnel and reliability of the fossil plant 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 the most critical girth welds of MS piping systems have creep failures which can be successfully ranked by a multiaxial stress parameter, such as maximum principal stress. Inelastic (redistributed) stresses at the piping outside diameter (OD) surface were evaluated for the base metal of three MS piping systems at the piping analysis model nodes. The range of piping system stresses at the piping nodes for each piping system was determined for the redistributed creep stress condition. The range of piping stresses was subsequently included on a Larson–Miller parameter (LMP) plot for the grade P22 material, revealing the few critical (lead-the-fleet) girth welds selected for nondestructive examination (NDE). In the three MS piping systems, the stress ranges varied from 55% to 80%, with only a few locations at stresses beyond the 65 percentile of the range. By including evaluations of significant field anomalies and the redistributed multiaxial stresses on the outside surface, it was shown that there is a good correlation of the ranked redistributed multiaxial stresses to the observed creep damage. This process also revealed that a large number of MS piping girth welds have insufficient applied stresses to develop substantial creep damage within the expected unit lifetime (assuming no major fabrication defects). This study also provided 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 in the as-found (current) condition for a complete set of MS piping system nodes. The evaluations of redistributed maximum principal stresses in the as-found condition were useful in selecting high priority ranked girth weldment creep damage locations. The evaluations of B31.1 Code as-designed sustained load stresses were not useful in selecting high priority creep damage locations.

The TransAlta High-Energy Piping Program—A Five-Year History

2000 ◽  
Vol 123 (1) ◽  
pp. 65-69 ◽  
Author(s):  
Marvin J. Cohn,
Keyword(s):  
Creep Damage ◽  
Analytical Techniques ◽  
High Energy ◽  
Management Plan ◽  
Piping System ◽  
Engineering Consulting ◽  
Piping Systems ◽  
Creep Fatigue ◽  
Sustained Loads ◽  
Selection Of

In 1995, the High-Energy Piping Strategic Management Plan (HEPSMP) was initiated at TransAlta Utilities Corporation (TAU) for the three generating facilities. At that time, it was recognized that several of the piping systems were exhibiting signs of creep relaxation, with some hangers bottomed or topped out online and/or offline. Previous hanger adjustment attempts were not always adequate. The program workscope included: 1) hot and cold piping system walkdowns, 2) selection of high-priority girth weld inspection locations, 3) examination of critical weldments, 4) weld repairs where necessary, 5) adjustments or modifications of malfunctioning steam line hangers, and 6) recommended work for future scheduled outages. Prior to 1996, examination locations were limited to the traditional locations of the terminal points at the boiler and turbine, with reexaminations occurring at arbitrary intervals. Since the terminal points are not necessarily the most highly stressed welds causing service-related creep damage, service damage may not occur first at the pre-1996 examined locations. There was a need to maximize the safety and integrity of these lines by ensuring that the highest risk welds were identified and given the highest priority for examination. An engineering consulting company was selected to prioritize the highest risk weldments for each piping system. This risk-based methodology included the prediction and evaluation of actual sustained loads, thermal expansion loads, operating loads, multiaxial stresses, creep relaxation, and cumulative creep life exhaustion. The technical process included detailed piping system walkdowns and application of advanced analytical techniques to predict and rank creep/fatigue damage for each piping system. TAU has concluded that the program has met its objective of successfully prioritizing inspection locations. The approach has also resulted in reducing the scope and cost of reexaminations. Phases 1 and 2 evaluations and examinations have been completed for all units. Results of some of the important aspects of this program are provided as case history studies.

Formula for Estimation of Effective Applied Load at Cracked Section Considering Compliance Change and its Application Under Dynamic Loading Conditions

2018 ◽  
Author(s):  
Yeji Kim ◽  
Young-Jin Oh ◽  
Yun-Jae Kim ◽  
Il-Soon Hwang
Keyword(s):  
Dynamic Loading ◽  
Time History ◽  
Elastic Beam ◽  
Beam Theory ◽  
Piping System ◽  
Fe Model ◽  
Loading Conditions ◽  
Formula One ◽  
Integrity Assessment ◽  
Dynamic Loading Conditions

The refinement of the piping integrity assessment methods has emerged as a priority issue, in response to heightened concerns about the beyond design basis accident following several events. The compliance change in structures may have a significant influence on the fracture estimation. For instance, the deformation of a crack in the piping system may result in a decrease of the applied moment at the cracked section. To consider these effects, the authors have developed the general formula for prediction of the effective applied moment at circumferential cracked section based on the elastic beam theory. Using the developed formula, one can evaluate the extent of the load reduction at a crack position due to the change in compliance. This paper aims to expand the applicability of the formula for dynamic loading conditions. By conducting the time history analysis using FE model accompanying the comparisons with the piping system experiment results, it was confirmed that the formula is also available for dynamic loading conditions. It is expected that the proposed formula can be implemented in sthe piping integrity assessment to consider the restraint effect.

scholarly journals Design and Analysis of a Novel Flexure-Based Dynamically Tunable Nanopositioner

Micromachines ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 212
Author(s):  
Zeying Li ◽  
Pengbo Liu ◽  
Peng Yan
Keyword(s):  
Magnetic Field ◽  
High Performance ◽  
Dynamic Models ◽  
Elastic Beam ◽  
Beam Theory ◽  
Variable Stiffness ◽  
Sustained Load ◽  
Element Analysis ◽  
Dynamic Tuning ◽  
Trade Offs

Various tools, such as biomedical manipulators, optical aligners, and ultraprecision manufacturing tools, implement nanopositioners that must be dynamically tunable to satisfy the requirements of different working conditions. In this paper, we present the design and analysis of a flexure-based nanopositioner with dynamically tunable characteristics for the implementation of a high-performance servomechanism. The nanopositioner is composed of four flexure beams that are positioned in parallel and symmetric configurations sandwiched between magnetorheological elastomers (MREs). The properties of MREs impart dynamicity to the nanopositioner, allowing the workspace, stiffness, and damping characteristics in particular to be tuned under the action of an external magnetic field. By utilizing elastic beam theory and electromagnetic field coupling analysis, kinetostatic and dynamic models of the proposed nanopositioner were established to predict the variable stiffness property and dynamically tunable characteristics. The models were validated by performing a finite element analysis. Herein, it is shown that the proposed nanopositioner model can actively adjust the trade-offs between the working range, speed, and sustained load capability by changing the magnetic field. The proposed dynamic tuning method offers new insight into the design of flexure-based nanopositioners for real applications.

scholarly journals Nonlinear ferro-electro-elastic beam theory

2009 ◽  
Vol 46 (11-12) ◽  
pp. 2397-2406 ◽  
Author(s):  
Uri Kushnir ◽  
Oded Rabinovitch
Keyword(s):  
Elastic Beam ◽  
Beam Theory

scholarly journals Mechanical Behaviour of Inconel 718 Thin-Walled Laser Welded Components for Aircraft Engines

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Enrico Lertora ◽  
Chiara Mandolfino ◽  
Carla Gambaro
Keyword(s):  
Inconel 718 ◽  
Gas Turbines ◽  
Shape Control ◽  
Postweld Heat Treatment ◽  
Fatigue Behaviour ◽  
High Energy ◽  
Parent Material ◽  
High Energy Density ◽  
Welding Parameters ◽  
Technical Specifications

Nickel alloys are very important in many aerospace applications, especially to manufacture gas turbines and aero engine components, where high strength and temperature resistance are necessary. These kinds of alloys have to be welded with high energy density processes, in order to preserve their high mechanical properties. In this work, CO2laser overlap joints between Inconel 718 sheets of limited thickness in the absence of postweld heat treatment were made. The main application of this kind of joint is the manufacturing of a helicopter engine component. In particular the aim was to obtain a specific cross section geometry, necessary to overcome the mechanical stresses found in these working conditions without failure. Static and dynamic tests were performed to assess the welds and the parent material fatigue life behaviour. Furthermore, the life trend was identified. This research pointed out that a full joint shape control is possible by choosing proper welding parameters and that the laser beam process allows the maintenance of high tensile strength and ductility of Inconel 718 but caused many liquation microcracks in the heat affected zone (HAZ). In spite of these microcracks, the fatigue behaviour of the overlap welds complies with the technical specifications required by the application.

scholarly journals Comparison of 1D and 2D solutions for a beam under transverse impact

2018 ◽  
Vol 148 ◽  
pp. 05005 ◽  
Author(s):  
Vítězslav Adámek
Keyword(s):  
Analytical Solution ◽  
Timoshenko Beam ◽  
Elastic Beam ◽  
Beam Theory ◽  
Two Dimensional ◽  
Transverse Impact ◽  
Dimensional Theory ◽  
Beam Geometry ◽  
Stationary Vibration ◽  
Main Factors

The problem of non-stationary vibration of an elastic beam caused by a transverse impact loading is studied in this work. In particular, two different approaches to the derivation of analytical solution of the problem are compared. The first one is based on the Timoshenko beam theory, the latter one follows the exact two-dimensional theory. Both mentioned methods are used for finding the response of an infinite homogeneous isotropic beam. The obtained analytical results are then compared and their agreement is discussed in relation to main factors, i.e. the beam geometry, the character of loading and times and points at which the beams responses are studied.

Developing and Implementing Ch. VII O&M Programs at CCGT Plants: Case Studies

2021 ◽  
Author(s):  
Peter Jackson ◽  
Robert Rosario ◽  
Andreas Fabricius ◽  
Anita Johny ◽  
Alexandria Wholey
Keyword(s):  
High Temperature ◽  
High Energy ◽  
Piping System ◽  
Inspection Planning ◽  
Accelerated Corrosion ◽  
Advantages And Disadvantages ◽  
Effective Implementation ◽  
Creep Fatigue ◽  
The Usa ◽  
High Temperature Steam

Abstract We will present the results from several projects from the USA and other jurisdictions where ASME B31.1 Ch. VII O&M Covered Piping System (CPS) Programs have been implemented at several types of natural gas-fired CCGT plants. Common elements of programs for different plants will be summarized as well as plant-specific considerations for high energy piping condition assessment for newer plants. Pros and cons between a common program for a thermal fleet and plant-specific programs will be discussed including advantages and disadvantages of each approach. Effective implementation of parts of the Nonmandatory Appendix V guidance within the CPS Program will be described and recommendations for best practices. A brief overview of degradation-specific mechanisms for high energy piping and approaches for planninng/scheduling NDE inspections will be described. This overview will include: creep, fatigue, corrosion (erosion-corrosion - E/C and flow accelerated corrosion - FAC) as well as mechanisms that are commonly responsible for high energy piping leaks, failures and repairs including thermal quench cracking of HRSG interstage, terminal desuperheaters and turbine bypass attemperators. A brief summary of Gr. 91 inspection planning in Ch. VII O&M Programs will also be included as well as corrosion under insulation (CUI) and common inspection scopes for high temperature steam drains. Resolution of constant force and variable spring pipe supports on high pressure/high temperature piping that are not accommodating thermal expansion as per their engineering design can be evaluated using pre-outage pipe stress models and data obtained from field walkdowns to support rapid decisions for repair/replacement in the field. Finally, experiences with long term scheduling the need for adaptive management of the CPS Programs will be summarized with typical management oversight actions described for effective implementation.

Investigation of bond between fibre-reinforced polymer bars and concrete under sustained loads

2006 ◽  
Vol 33 (11) ◽  
pp. 1426-1437 ◽  
Author(s):  
F Shahidi ◽  
L D Wegner ◽  
B F Sparling
Keyword(s):  
Reinforced Concrete ◽  
Sustained Load ◽  
Reinforcing Bars ◽  
Bond Slip ◽  
Reinforced Polymer ◽  
Sustained Loads ◽  
Fibre Reinforced Polymer ◽  
Term Performance ◽  
Frp Bars

Although the use of fibre-reinforced polymer (FRP) bars to replace steel in reinforced concrete is becoming more common, uncertainty remains concerning the long-term performance of FRP, including the effect of a sustained load on the bond between the FRP bars and the concrete. An experimental study was therefore undertaken to investigate the long-term durability of the bond for various types of bars embedded in concrete: one type of glass FRP, two types of carbon FRP, and conventional steel reinforcing bars. Pullout specimens were tested both statically to failure and under sustained loads for periods of up to 1 year while free-end slip was monitored. Results revealed lower short-term bond strengths for FRP bars relative to steel and significant variability in long-term bond-slip performance among FRP bars of different types. Post-testing investigations revealed damage to bar surfaces at the macroscopic level, as well as broken longitudinal fibres and damage to the surface coatings at the microscopic level.Key words: reinforced concrete, fibre-reinforced polymer (FRP), bond, creep, pullout, sustained loads.

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