Reliability-Based Limit States Design for Onshore Pipelines

2002 ◽  
Author(s):  
Maher Nessim ◽  
Tom Zimmerman ◽  
Alan Glover ◽  
Martin McLamb ◽  
Brian Rothwell ◽  
...  
Keyword(s):  
Wall Thickness ◽  
Traditional Approach ◽  
Large Diameter ◽  
Small Diameter ◽  
Mechanical Damage ◽  
Design Approach ◽  
Design Parameters ◽  
Pipe Failure ◽  
Limit States ◽  
Current Design

The traditional approach to pipelines design is to select a wall thickness that maintains the hoop stress below the yield strength multiplied by a safety factor. The main design condition implied by this approach is yielding (and by extension burst) of the defect-free pipe. Failure statistics show that this failure mode is virtually impossible as the majority of failures occur due to equipment impact and various types of defects such as corrosion and cracks. Recent investigations show that these failure causes are much more sensitive to wall thickness than to steel grade. As a consequence, current design methods produce variable levels of safety for different pipelines — small-diameter, low-pressure pipelines for example have been shown to have higher failure risks due to mechanical damage than large-diameter, high-pressure pipelines. In addition, the current design approach has been shown to have limited ability to deal with new design parameters, such high steel grades, and unique loading conditions such as frost heave and thaw settlement. The paper shows how these limitations can be addressed by adopting a reliability-based limit states design approach. In this approach, a pipeline is designed to maintain a specified reliability level with respect to its actual expected failure mechanisms (known as limit states). Implementation involves identifying all relevant limit states, selecting target reliability levels that take into account the severity of the failure consequences, and developing a set of design conditions that meet the target reliability levels. The advantages of this approach include lower overall cost for the same safety level, more consistent safety across the range of design parameters, and a built-in ability to address new design situations. Obstacles to its application for onshore pipelines include lack of familiarity with reliability-based approaches and their benefits and lack of consensus on how to define reliability targets. The paper gives an overview of the reliability-based design approach and demonstrates its application using an example involving design for mechanical damage.

scholarly journals Evaluation of Effectiveness of Waterjet Propulsor for a Small Underwater Vehicle

2021 ◽  
Vol 28 (4) ◽  
pp. 30-41
Author(s):  
Lech Rowinski ◽  
Maciej Kaczmarczyk
Keyword(s):  
Small Diameter ◽  
Mechanical Damage ◽  
Underwater Vehicle ◽  
Propulsion System ◽  
The Body ◽  
Head Losses ◽  
Current Design ◽  
And Performance ◽  
Semi Empirical ◽  
Surface Vessel

Abstract The goal of the project described is to replace the existing propulsion system of a small underwater vehicle with a solution less prone to mechanical damage and ensuring a lower risk of the entanglement of fibrous objects suspended in the body of water. Four typical marine screws are utilised in the current design of the vehicle. One possible solution of the problem is the application of waterjet propulsors located inside the body of the vehicle instead. The general condition of the application of the new solution was to secure at least the same motion control capabilities of the vehicle while the basic capability is its propulsion effectiveness at the required speed. Specific features of the considered waterjet propulsor, when compared with their application in surface vessel propulsion, are the lack of the head losses and the low significance of cavitation issues. One of the difficulties in the considered case is the small diameter of the propulsor in comparison to commercially available waterjet units, which have diameters between 0.1 [m] and 1.0 [m]. There is very little data regarding the design and performance of devices in the 0.02 to 0.05 [m] range. Methods utilised to forecast the performance of the new propulsion system are presented and results compared. These were semi-empirical calculations, numerical calculations and tests of real devices. The algorithm that is based on semi-empirical calculations is of particular interest while it offers possibility quick assessment of performance of a propulsor composed of several well defined components. The results indicate the feasibility of modification of the propulsion system for the considered vehicle if all the existing circumstances are taken into account.

Application of Deterministic and Probabilistic Methods in Pipeline Lateral Buckling Design

2012 ◽  
Author(s):  
Hammam Zeitoun ◽  
Maša Branković ◽  
Edwin Shim ◽  
EuJeen Chin ◽  
Benjamin Anderson
Keyword(s):  
Structural Reliability ◽  
Design Guidelines ◽  
Probabilistic Methods ◽  
Design Solution ◽  
Design Parameters ◽  
Pipeline System ◽  
Limit States ◽  
Lateral Buckling ◽  
Current Design ◽  
Subsea Pipelines

Subsea pipelines lateral buckling design has significantly evolved over the last years as more pipeline projects have moved into more challenging environments and into high temperature / high pressure (HT/HP) design application. Knowledge and understanding of pipeline lateral buckling has improved with design application resulting in refined and enhanced design approaches. Using current design approaches, it is now quite acceptable to control lateral buckle formation along the pipeline by using buckle triggers or to allow uncontrolled lateral buckles, provided that the various design limit states are satisfied. A number of design methodologies can be used to check the acceptability of uncontrolled buckling or to design for controlled buckling including deterministic, probabilistic buckle formation and full Structural Reliability Assessment (SRA) methods. Using SRA or probabilistic methods is usually an attractive design option as lateral buckling design involves dealing with a large number of uncertainties and variation in design parameters. These methods help to ensure the reliability of the proposed buckle initiation scheme. However, the use of these methods is also associated with a number of challenges such as the need to identify key parameters influencing the design and quantifying their uncertainties. Deterministic design approaches on the other hand are simpler to apply. However, they do not provide means to quantify the reliability of the proposed buckling scheme or the design risks. The choice of input parameters in a deterministic design is also relatively subjective which can possibly result in an overly conservative or unconservative design solution depending on the adopted design approach, selected design parameters and pipeline system being considered. Design guidelines and recommended practices such as SAFEBUCK (20) offer comprehensive guidelines to design for lateral buckling. However when faced with a range of complex variables, the designer needs to be aware of the effect of these parameters on the overall design. This paper describes the application of Deterministic and Probabilistic design approaches in lateral buckling design. The paper starts by describing these approaches, their advantages and limitations. The paper then explores a number of key uncertainties and variation in design parameters that the designer is faced with and its effect on the pipeline response.

Assessment on Design Factors of China’s Natural Gas Pipeline Based on Reliability-Based Design Method

2016 ◽  
Author(s):  
Zhenyong Zhang ◽  
Yawei Zhou ◽  
Jinyuan Zhang
Keyword(s):  
Natural Gas ◽  
Design Method ◽  
Large Diameter ◽  
Small Diameter ◽  
Research Report ◽  
Design Code ◽  
Limit States ◽  
Reliability Based Design ◽  
Location Class ◽  
Design Factors

Although the traditional method based on stress analysis is simple and convenient, the main limitation is that it does not reflect the actual failure mechanisms (or limit states). A pipeline network database of about 40 thousand kilometers comprising 258 design cases that represent combinations of steel grade, diameter, pressure, and location class is established, in order to evaluate and improve the design factors specified in the Chinese standard “Code for design of gas transmission pipeline engineering” (GB 50251). Referring to the research report “Target Reliability Levels for the Design and Assessment of Onshore Natural Gas Pipelines” accomplished by C-FER in 2005, the critical wall thicknesses and corresponding equivalent design factors are calculated by using reliability-based method to meet specified reliability targets. The research shows that the equivalent design factors obtained by Reliability-Based Design (RBD) method tend to increase as the pipe diameters get larger. The new design factors are smaller than those specified in the design code for pipelines with small diameter in location class 1 and 2, and larger than those in the design code for the other pipelines. Therefore, design factors are modified in each location class. The new factors are specific to pipes with small diameter (D ≤ 508mm), medium diameter (508mm < D < 711mm), and large diameter (711mm ≤ D ≤ 1219mm), thus enhancing the rationality and practicability of design factors.

Rock Berm Design for Pipeline Stability

2012 ◽  
Author(s):  
David J. Chamizo ◽  
Dean R. Campbell ◽  
Eric P. Jas ◽  
Jay R. Ryan
Keyword(s):  
Traditional Approach ◽  
Large Diameter ◽  
Mechanical Damage ◽  
Small Scale ◽  
Lateral Movement ◽  
Functional Requirements ◽  
Natural Gas Pipelines ◽  
Hydrodynamic Loading ◽  
Wave Heights ◽  
Subsea Pipelines

Stabilizing large diameter natural gas pipelines on the seabed against extreme hydrodynamic loading conditions has proven to be challenging in the northwest of Australia. Tropical storms, which affect the area annually between November and April, can generate wave heights exceeding 30 m and storm steady state currents of 2 m/s or more. Consequently, in shallow water depths, typically less than 40–60 m, subsea pipelines can be subjected to very high hydrodynamic loads, potentially causing significant lateral movement. To mitigate the risk of the pipeline suffering mechanical damage due to excessive lateral movement, quarried and graded rock is often dumped over the pipeline as a secondary stabilization solution. In order to satisfy functional requirements, the rock berm must comprise of a sufficiently large rock grading size and berm volume to withstand the design hydrodynamic loading such that the pipeline cannot break out of the berm. The design of rock berms for pipeline secondary stabilization has traditionally followed a deterministic approach that uses empirical equations for preliminary rock sizing, followed by small-scale physical modeling for design verification and optimization. Whilst the traditional approach can be effective in producing a robust rock berm design, opportunities for further optimization are inhibited by a lack of available data and an imperfect understanding of the failure mechanisms. This paper presents an overview of an improved approach for rock berm design optimization. A general overview of rock berms, the design principles, benefits and risks are also presented.

Effects on Road Safety of Converting Intersections to Roundabouts: Review of Evidence from Non-U.S. Studies

2003 ◽  
Vol 1847 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Rune Elvik
Keyword(s):  
Road Safety ◽  
Evaluation Studies ◽  
Meta Analysis ◽  
Large Diameter ◽  
Small Diameter ◽  
Traffic Signals ◽  
The United States ◽  
Design Parameters ◽  
Meta Regression Analysis ◽  
Trim And Fill

A meta-analysis of studies reported outside the United States was performed to evaluate the effects on road safety of converting intersections to roundabouts. Twenty-eight studies that provided 113 estimates of effect were evaluated. State-of-the-art techniques of meta-analysis were applied to synthesize evidence from these evaluation studies. A meta-regression analysis was performed, and the possible presence of publication bias was tested and adjusted using the trim-and-fill method. The results show that roundabouts are associated with a 30% to 50% reduction in the number of injury accidents. Fatal accidents are reduced by 50% to 70%. Effects on property damage accidents are highly uncertain, but in three-leg intersections, an increase often will occur. Evidence from the evaluation studies, although highly uncertain, suggests that the effect of roundabouts on injury accidents is greater in four-leg intersections than in three-leg intersections, and it is greater in intersections previously controlled by yield signs than in intersections previously controlled by traffic signals. Few studies have evaluated in detail the effects on safety of design parameters for roundabouts. Findings are inconsistent, but the majority of studies find that small roundabouts (a small diameter of the central traffic island) are safer than large roundabouts (a large diameter of the central traffic island).

Effect of vessel diameter on variation of fiber morphology in Acacia mangium

IAWA Journal ◽  
2020 ◽  
Vol 41 (1) ◽  
pp. 2-11
Author(s):  
Ridwan Yahya ◽  
Yansen Yansen ◽  
Suyako Tazuru-Mizuno ◽  
Junji Sugiyama
Keyword(s):  
Wall Thickness ◽  
Fiber Diameter ◽  
Large Diameter ◽  
Small Diameter ◽  
Cell Diameter ◽  
Fiber Morphology ◽  
Fiber Cells ◽  
Small Vessels ◽  
Fiber Wall ◽  
Large Vessels

Abstract Paper quality depends on fiber diameter and wall thickness, and their derivatives. Fiber deformation occurs due to pressure from the vessel during development. The diameter and wall thickness of the fibers were measured following the direction of pressure exerted by the vessel on the face of the fiber cells. Fiber cell diameter measured perpendicular to and parallel with vessel enlargement was referred to as radial and tangential diameter, respectively, and likewise for fiber wall thickness. Differences in radial and tangential diameter and wall thickness of fiber cells in relation to their distance from vessels were analyzed. The radial diameter of fibers adjacent to large vessels decreased from the first to the fifth fiber, and from the first to the second fiber adjacent to small vessels. Conversely, tangential fiber diameter increased from the first to the fifth fiber for fibers adjacent to large vessels, and from the first to the second fiber adjacent to small vessels. The fibers adjacent to the vessel seem to have thicker walls in both the tangential than radial directions up to 2 and 5 fibers for small and large vessels, respectively. The first two fibers adjacent to small diameter vessels may produce higher strength paper than those up to five fibers from large diameter vessels, because the Runkel ratio, Coefficient of rigidity and Muhlsteph ratio values of fibers adjacent to small vessels are lower than fibers adjacent to large vessels. The opposite occurs for flexibility coefficient values.

Numerical Investigation of an In-Wall Cooling Design Approach for Improved Thermal Efficiency of Additively Manufactured Gas Turbine Ring Segments

2020 ◽  
Author(s):  
Thomas Wimmer ◽  
York Mick ◽  
Bernhard Weigand
Keyword(s):  
Gas Turbine ◽  
Wall Thickness ◽  
Thermal Efficiency ◽  
Gas Turbines ◽  
Base Material ◽  
Design Approach ◽  
Design Parameters ◽  
Structural Wall ◽  
Cooling Design ◽  
Loaded Surface

Abstract Raising the combustion temperature continues to be a major driver for increasing the overall efficiency of industrial gas turbines. Therefore, active cooling has become a necessity as gas temperatures have surpassed the allowable temperature of the base material. Thus, cooling schemes need to be improved for higher heat loads. However, the thermal efficiency of cooling schemes, which can be manufactured employing conventional machining is limited. With the geometrical freedom offered by Additive Manufacturing (AM), advanced cooling designs for gas turbine parts have become viable and can provide superior thermal efficiency. A promising cooling design approach which exploits this freedom is In-Wall cooling. Here cooling channels are placed within the structural wall close to the heat-loaded surface. In order to develop this design approach further, In-Wall cooling schemes for a ring segment have been modeled numerically with different topologies and varying design parameters. These include wall thickness, channel pitch, size and length, and several more. The design parameters’ influence on thermal efficiency of In-Wall cooling schemes are quantified. The wall thickness between channels and the heat loaded surface is adapted locally. The employed approach leads to a more homogeneous temperature distribution and is reported in the paper. This work can help designers to focus on the most important factors when designing a new In-Wall cooling scheme and shows how the capabilities of AM can be employed in gas turbine cooling design.

scholarly journals Multi-step Hydroforming Process And Wall Thickness Optimization of 5A02 Aluminum Alloy Five-Way Tube With Different Branch Diameter

2021 ◽  
Author(s):  
Liming Wei ◽  
Xuefeng Xu ◽  
Yubin Fan ◽  
Ju Zhang ◽  
Congcong Yuan
Keyword(s):  
Aluminum Alloy ◽  
Wall Thickness ◽  
Large Diameter ◽  
Tube Hydroforming ◽  
Reduction Rate ◽  
Small Diameter ◽  
Branch Diameter ◽  
Hydroforming Process ◽  
One Step ◽  
The One

Abstract The different branch diameter of five-way tube affects the design of loading internal pressure in the hydroforming process, where the large-diameter branch is broken more easily than the small-diameter one due to the same ultimate stress of tube material in one-step forming method. Therefore, the first four-way and then five-way of multi-step forming (FFTF) method and the first three-way and then five-way of multi-step forming (FTTF) method were proposed to fabricate the 5A02 aluminum alloy five-way tube with two kinds of branch diameters to avoid the burst of large-diameter branch tube. The finite element simulation of five-way tube hydroforming process shows that the height of small-diameter branch tube is lower and serious wrinkles appear at the large-diameter branch tube in the one-step forming and FFTF method. By optimizing the length of punch, a five-way tube with a big branch height and uniform wall thickness was obtained with the FTTF method. The approach of lengthening the punch in the experiment increased the height of formed branch and reduced the wall thickness reduction rate of five-way tube in FTTF method. Overall, the findings mentioned above can not only offer guide in creating five-way tube with excellent quality, but also be taken as reference to the hydroforming studies on multi-way tube in the future.

Fatigue Design Criteria for Small Super Duplex Steel Pipes

2004 ◽  
Author(s):  
Steinar Kristoffersen ◽  
Per J. Haagensen
Keyword(s):  
Stainless Steel ◽  
Wall Thickness ◽  
Large Diameter ◽  
Small Diameter ◽  
High Strength ◽  
Gas Production ◽  
Steel Pipes ◽  
Fatigue Design ◽  
Duplex Steel ◽  
Design Guidance

Stainless steel pipes ranging in sizes from approximately 10 to 100 mm OD are used extensively in umbilicals for the control and monitoring of underwater installations for oil and gas production. Umbilicals are subjected to tensile loads as well as variable amplitude loading from wave and current actions. Fatigue is therefore a critical issue in the design of umbilical components. Sea water resistant high strength super duplex steel with ultimate strength of typically 800 to 900 MPa is used to save weight and reduce the wall thickness. Some umbilicals installed by Statoil have design pressure up to 1035 bar, which in combination with large dynamic loads from floating production units makes fatigue design of the umbilicals a challenging issue. While the fatigue performance of butt welded pipes for pipelines and risers are established and implemented in design guidance and codes, the experimental basis for design of small diameter piping made of high strength materials is not well documented in the open literature. However, unpublished data from in-house investigations indicate that small pipes in super duplex steel perform significantly better than larger diameter pipes in lower strength materials. It is therefore apparently scope for a “thinness effect”, i.e. a bonus effect that could be applied to the data for large diameter pipes in current codes to account for the higher S-N curves for small stainless steel pipes. This paper reviews some of the fatigue data for piping and compares these data with experimental evidence from a joint industry project. Tentative fatigue design guidance for small diameter super duplex steel piping is presented. Questions concerning special issues such as the possible influence of wall thickness, mean stress and pre-straining due to reeling are discussed.

Development of an improved design methodology and front steering design guideline for small-wheel bicycles for better stability and performance

2020 ◽  
Vol 234 (3) ◽  
pp. 227-244
Author(s):  
Milan Paudel ◽  
Fook Fah Yap
Keyword(s):  
Design Methodology ◽  
Design Guidelines ◽  
Design Approach ◽  
Design Parameters ◽  
Design Practice ◽  
Frame Design ◽  
Current Design ◽  
And Performance ◽  
Improved Design ◽  
Bicycle Design

The maneuverability and compactness of small-wheel and folding bicycles are greatly appreciated. Nonetheless, the performance of these small-wheel bicycles as compared to the big-wheel bicycles has always been questioned. They are often blamed for being less stable, wobbly, or twitchy. It is still unclear how the performance of the small-wheel bicycle designs can be improved. Both small- and big-wheel bicycles are designed with similar ergonomics; therefore, the focus has been on the front steering design. The steering design parameters of 91 big-wheel and 27 small-wheel bicycles were compared, bearing in mind the available front steering design guidelines to understand: (1) the influence of big-wheel bicycle’s frame design on small-wheel bicycles and (2) most common range of design parameters used in current bicycle designs. The analysis showed a strong influence of current big-wheel bicycle design practice on front frame parameter selection of small-wheel bicycles. Furthermore, the self-stability comparison over the most common design range confirmed the lesser stability in the current small-wheel bicycle designs at normal riding speed. However, it was also found that the lesser stability was not the result of small wheels per se, but rather owing to an inadequacy in the current design approach to addressing the complex influence of reducing wheel size and bicycle frame design on its stability and performance. Therefore, an improved design methodology was adopted by incorporating the bicycle dynamics into the current design approach and the front steering design guidelines for small-wheel bicycles have been developed. The guidelines contradict the current small-wheel bicycle design practice, as they recommend steeper headtube angles for small-wheel bicycles. The guidelines were validated with good agreement between the theoretical and experimental results on two prototype 20-inch-wheel bicycles having counter-intuitive steering geometry.

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