Fitness for Service of Dents Associated With Metal Loss due to Corrosion

2014 ◽  
Author(s):  
Hans Olav Heggen ◽  
Joe Bratton ◽  
David Kemp ◽  
Jun Liu ◽  
Jason Austin
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Maximum Stress ◽  
Dynamic Pressure ◽  
Equivalent Stress ◽  
Metal Loss ◽  
General Effect ◽  
Element Analysis ◽  
Pressure Cycling ◽  
Pressure Cycle

Current federal regulations in the U.S. require excavation of all dents associated with metal loss due to corrosion identified through in line inspection surveys. Once a dent has been found to be associated with metal loss through excavation, there is little guidance to determine the serviceability of the anomaly. Past research has provided methodologies to assess the fatigue life of plain dents, considering the shape of the dent, but there are no widely accepted assessment methodologies to predict the effect of associated metal loss due to corrosion on the fatigue life of dents. This paper focuses on the fitness for service of dents associated with metal loss, particularly corrosion in dents. Currently, fitness for service assessments of plain dents provide an estimated remaining life of a dent based on the geometry of the dent and current pressure cycling of the pipeline. Dynamic pressure cycling at each dent location is estimated using the upstream and downstream pressure cycle data, elevation, and distance along the pipe. The dynamic pressure cycle data at each dent is then converted into equivalent stress cycles based on the results of rainflow cycle counting. Finite element analysis (FEA) of a dent without metal loss and with metal loss is performed to compare the maximum stress concentration areas. The FEA program Abaqus is used with solid elements to model the dents. The differences between maximum stress concentration areas is compared for a matrix of extent of metal loss, and orientation of metal loss to analyze the general effect of metal loss and the interaction of metal loss in a dent. The stress concentration areas of dents without metal loss and with metal loss are then applied to current fatigue assessment methodologies provided in API 579 to analyze the effect of metal loss on the fatigue life of dents.

An Approach for Evaluating the Integrity of Plain Dents Reported by In-Line Inspection Tools

2012 ◽  
Author(s):  
Joseph P. Bratton ◽  
Tom Alexander ◽  
Thomas A. Bubenik ◽  
Shane Finneran ◽  
Hans Olav Heggen
Keyword(s):  
Dynamic Pressure ◽  
Equivalent Stress ◽  
The United States ◽  
Peak Strain ◽  
Maximum Strain ◽  
Element Analysis ◽  
Pressure Cycling ◽  
Pressure Cycle ◽  
Integrity Management ◽  
Rainflow Cycle Counting

Current federal regulations in the U.S. require excavation of plain dents identified through in-line inspection surveys based primarily on depth. Industry experience, and previous research, has shown that the depth of the dent, alone, is not sufficient to assess dent severity and that releases could occur at dents below the excavation threshold (Dawson, 2006). Canada’s National Energy Board released a safety advisory on June 18, 2010, to all companies under their jurisdiction regarding two incidents involving shallow dents. The safety advisory stated that all integrity management programs should be reviewed and updated where appropriate to address the threat posed by shallow dents. Similar incidents have raised awareness in the United States and elsewhere around the world. This paper focuses on the fitness for service of dents identified by in-line inspection surveys. The fitness for service assessment provides an estimated remaining life of a dent based on the geometry of the dent and current pressure cycling of the pipeline. Dynamic pressure cycling at each dent location is estimated using the upstream and downstream pressure cycle data, elevation, and distance along the pipe. The dynamic pressure cycle data at each dent is then converted into equivalent stress cycles based on the results of rainflow cycle counting. Maximum strain levels of the dents are calculated based on the geometry of the dent as determined by radial sensor measurements from the in-line inspection survey. The combination of assessment methods provides estimates of remaining fatigue life and peak strain which can be used for prioritizing the investigation and remediation of plain dents in pipelines. Finite element analysis (FEA) is performed for one dent to calculate the maximum strain levels and identify stress concentration areas. These results are compared with the values applied during the fitness for service assessment to validate the accuracy and conservatism of the calculation methods used. An idealized dent will be analyzed to investigate the strain calculations in ASME B31.8 and localize maximum strain values.

scholarly journals Elastic stress concentration at radial crossholes in pressurized thick cylinders

2007 ◽  
Vol 42 (6) ◽  
pp. 461-468 ◽  
Author(s):  
T Comlekci ◽  
D Mackenzie ◽  
R Hamilton ◽  
J Wood
Keyword(s):  
Stress Concentration ◽  
Maximum Stress ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
Maximum Principal Stress ◽  
Radius Ratio ◽  
Graphical Form ◽  
Element Analysis ◽  
Parametric Finite Element Analysis ◽  
Von Mises

Results of a parametric finite element analysis investigation of stress concentration at radial crossholes in pressurized cylinders are presented in numerical and graphical form. The analysis shows that the location of maximum stress does not generally occur at the junction between the bores, as is commonly supposed, but at some small distance up the crosshole from the junction. Maximum stress concentration factors (SCFs) are defined on the basis of the maximum principal stress, von Mises equivalent stress, and stress intensity. Three-dimensional plots of the SCF against the cylinder radius ratio b/a and the crosshole-to-main-bore-radius ratio c/a are presented. The SCFs were found to vary across the range of geometries considered with local minima identified within the parameter range in most cases. The results therefore allow designers to select optimum b/a and c/a ratios to minimize stress concentration in real problems.

Pressure Cycling Monitoring Helps Ensure the Integrity of Energy Pipelines

2010 ◽  
Author(s):  
Peter Song ◽  
Doug Lawrence ◽  
Sean Keane ◽  
Scott Ironside ◽  
Aaron Sutton
Keyword(s):  
Fatigue Life ◽  
Pipeline System ◽  
Outer Diameter ◽  
Operating Pressure ◽  
Potential Growth ◽  
Integrity Assessment ◽  
Pressure Cycling ◽  
Pressure Cycle ◽  
Primary Focus ◽  
Pump Stations

Liquids pipelines undergo pressure cycling as part of normal operations. The source of these fluctuations can be complex, but can include line start-stop during normal pipeline operations, batch pigs by-passing pump stations, product injection or delivery, and unexpected line shut-down events. One of the factors that govern potential growth of flaws by pressure cycle induced fatigue is operational pressure cycles. The severity of these pressure cycles can affect both the need and timing for an integrity assessment. A Pressure Cycling Monitoring (PCM) program was initiated at Enbridge Pipelines Inc. (Enbridge) to monitor the Pressure Cycling Severity (PCS) change with time during line operations. The PCM program has many purposes, but primary focus is to ensure the continued validity of the integrity assessment interval and for early identification of notable changes in operations resulting in fatigue damage. In conducting the PCM program, an estimated fatigue life based on one month or one quarter period of operations is plotted on the PCM graph. The estimated fatigue life is obtained by conducting fatigue analysis using Paris Law equation, a flaw with dimensions proportional to the pipe wall thickness and the outer diameter, and the operating pressure data queried from Enbridge SCADA system. This standardized estimated fatigue life calculation is a measure of the PCS. Trends in PCS overtime can potentially indicate the crack threat susceptibility the integrity assessment interval should be updated. Two examples observed on pipeline segments within Enbridge pipeline system are provided that show the PCS change over time. Conclusions are drawn for the PCM program thereafter.

Determination of Stress Concentration Around an Oblique Hole by a Finite-Element Technique

1983 ◽  
Vol 105 (2) ◽  
pp. 206-212 ◽  
Author(s):  
Hua-Ping Li ◽  
F. Ellyin
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Maximum Stress ◽  
Plate Thickness ◽  
Two Dimensional ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Parametric Studies ◽  
Element Technique

A plate weakened by an oblique penetration of a circular cylindrical hole has been investigated. The stress concentration around the hole is determined by a finite-element method. The results are compared with experimental data and other analytical works. Parametric studies of effects of angle of inclination, plate thickness, and width are performed. The maximum stress concentration factor (SCF) obtained from the finite-element analysis is higher than experimental results, and this deviation increases with the increase of angle of skewness. The major reason for this difference is attributed to the shear-action between layers parallel to the plate surface which cannot be directly included in the two-dimensional elements. An empirical formula is derived which accounts for the shear-action and renders the finite-element predictions in line with experimentally observed data.

scholarly journals Stress concentration and optimal design of pinned connections

2019 ◽  
Vol 54 (2) ◽  
pp. 95-104 ◽  
Author(s):  
Niels Leergaard Pedersen
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Mechanical Engineering ◽  
Maximum Stress ◽  
Civil Engineering ◽  
Three Dimension ◽  
Element Analysis ◽  
Standard Design ◽  
Connection Type

A pinned connection or lug joint is a common connection type used both in civil engineering and mechanical engineering. In civil engineering, this connection is used for assembling truss members, and in mechanical engineering, this connection type is widely used in machine elements. The standard design is with a circular pin. The stress concentration factor size depends on the tolerances between pin and assembled parts and also by the three-dimensional design. Relatively different maximum stress values are seen depending on the modelling being done in two dimension (with assumptions) or in full three dimension. The focus in the present article is on the two-dimensional design and minimizing the maximum stress. It is shown that not only the contact geometry is important for reducing the stress, the external design is equally important. By finite element analysis including contact modelling, it is shown that reduction in the stress concentration factor of up to 18% is possible.

scholarly journals Force Transfer and Stress Distribution in an Implant-Supported Overdenture Retained with a Hader Bar Attachment: A Finite Element Analysis

2013 ◽  
Vol 2013 ◽  
pp. 1-12 ◽  
Author(s):  
Preeti Satheesh Kumar ◽  
Kumar K. S. Satheesh ◽  
Jins John ◽  
Geetha Patil ◽  
Ruchi Patel
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Stress Distribution ◽  
Maximum Stress ◽  
Alveolar Bone ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Finite Element Software ◽  
Force Transfer ◽  
Edentulous Mandible

Background and Objectives. A key factor for the long-term function of a dental implant is the manner in which stresses are transferred to the surrounding bone. The effect of adding a stiffener to the tissue side of the Hader bar helps to reduce the transmission of the stresses to the alveolar bone. But the ideal thickness of the stiffener to be attached to the bar is a subject of much debate. This study aims to analyze the force transfer and stress distribution of an implant-supported overdenture with a Hader bar attachment. The stiffener of the bar attachments was varied and the stress distribution to the bone around the implant was studied. Methods. A CT scan of edentulous mandible was used and three models with 1, 2, and 3 mm thick stiffeners were created and subjected to loads of emulating the masticatory forces. These different models were analyzed by the Finite Element Software (Ansys, Version 8.0) using von Mises stress analysis. Results. The results showed that the maximum stress concentration was seen in the neck of the implant for models A and B. In model C the maximum stress concentration was in the bar attachment making it the model with the best stress distribution, as far as implant failures are concerned. Conclusion. The implant with Hader bar attachment with a 3 mm stiffener is the best in terms of stress distribution, where the stress is concentrated at the bar and stiffener regions.

The Analysis of Mutual Authentication between Finite Element Analysis and Qi Erxi Answer

2011 ◽  
Vol 396-398 ◽  
pp. 1228-1231
Author(s):  
Yu Li Liu ◽  
Hai Bo Liu ◽  
Bo Wang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Concentration ◽  
Maximum Stress ◽  
Mutual Authentication ◽  
Element Analysis ◽  
The Finite Element Analysis ◽  
Edge Stress

In this paper, the sheet with hole for the finite element analysis, the location of maximum stress and maximum stress values are obtained under different load of edge of the hole, and the finite element analysis results compared with the classic Qi Erxi answers. This coincidence is not accidental, but it just shows their correctness. Therefore, we can use Qi Erxi answer when the calculation of the hole’s edge stress concentration and the condition of the force and the boundary are simple; while the it is complex, the finite element analysis can be used.

Fatigue Analysis of Stripper Bolt Under Combined Loading for Improvement of Stamping Die Design

1986 ◽  
Vol 108 (2) ◽  
pp. 222-229
Author(s):  
Sang Hoon Lee
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Impact Load ◽  
Rectangular Pulse ◽  
Die Design ◽  
Combined Loading ◽  
Element Analysis ◽  
Mass System ◽  
Stamping Die ◽  
Stamping Dies

A common problem of fatigue failure of stamping dies was experienced during the stamping operation with socket-head screws. In order to establish a design standard for the stripper bolt, a methodology for determination of the loads and the fatigue strength of the stripper bolt was developed. Stresses due to an impulsive load and a rectangular pulse were calculated based on a simplified spring mass system and the appropriate corrections were made to elaborate the solution. This approximate solution was validated by a finite element analysis. The stripper bolt should have an infinite fatigue life to survive a half million stamping operations. The fatigue problem involves a stress concentration with combined mean and alternating stresses. The Gerber parabola and the residual stress method were employed to treat the combined loading and the stress concentration. In order to enhance the fatigue life of the stripper bolt, a cushion is introduced at the surface where an impact load is applied. The cushion is found very effective in improving the fatigue life of the stripper bolt. An interactive computer program was developed as a tool for designing stamping dies.

Elastic Stress Concentration Factors (Kt) by Stress Gradient Method Using FEA

1996 ◽  
Author(s):  
Ajay Garg ◽  
Ravi Tetambe
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Maximum Stress ◽  
Elastic Stress ◽  
Stress Gradient ◽  
Nominal Stress ◽  
Element Analysis

Abstract The elastic stress concentration factor, Kt, is critical in determining the life of machines, especially in the case of notched components experiencing high cycle fatigue. This Kt is defined as the ratio of the maximum stress (σmax) at the notch to the nominal stress (σnom) in the region away from the notch effect. For simple geometries such as, plate with a hole, calculation of Kt from either closed form solution or from making simple but valid assumptions is possible [1,2]. However, for complex machine components such data is usually not available in the literature. Using Kt values from the simple geometries may lead to either over or under estimation of the real Kt for such complex geometries. Such error can then further lead to a substandard product or a product which is overdesigned and expensive. Present paper outlines a methodology for computing reasonably accurate elastic stress concentration factor, Kt, using finite element analysis (FEA) tool. The maximum stress (σmax) is readily available from the finite element analysis. The nominal stress (σnom) near the stress concentration is however can not be directly extracted from the FEA results. A novel approach of estimating reasonably accurate σnom is presented in this paper. This approach is based on selecting the correct path at the stress concentration region, post processing the stress and the stress gradient results along that path and identifying the cut of point where stress concentration effect begins to take place. This methodology is first validated using two examples with known Kt and later applied to a real world problem.

Development of Design Curve for Sweepolet Subjected to Acoustic Induced Vibration

2016 ◽  
Author(s):  
Yuqing Liu ◽  
Philip Diwakar ◽  
Dan Lin ◽  
Ismat Eljaouhari ◽  
Ajay Prakash
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Fatigue Failure ◽  
High Stress ◽  
Peak Stress ◽  
Acoustic Energy ◽  
Piping System ◽  
Element Analysis ◽  
Design Curve ◽  
High Stress Concentration

High acoustic energy has the potential to cause severe Acoustic Induced Vibration (AIV) that leads to fatigue failure at high stress concentration regions such as fittings in a piping system. Sweepolet fittings have been extensively used as mitigation to counteract the risk of fatigue failure caused by AIV. The advantages of a sweepolet are its integrally reinforced contoured body and low stress concentration. However, there are inconsistencies in published standards and regarding the design limits for sweepolet subjected to AIV. In this paper, Finite Element Analysis is conducted to simulate high frequency pipe shell wall vibration caused by acoustic energy inside the pipe. Peak stress and the associated minimum fatigue life are calculated for sweepolet and sockolet under the same acoustic excitation. By comparing the stress level to that of a sockolet whose design limit to AIV had been published, the design curve and fatigue life equation for sweepolet are developed.

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