The Effect of Piping System Non-Linearity on the Unstable Growth of a Circumferential Through-Wall Crack in a Pipe

2003 ◽  
Author(s):  
E. Smith
Keyword(s):  
Cross Section ◽  
Material Properties ◽  
Structural Integrity ◽  
Crack Size ◽  
Instability Criterion ◽  
Piping System ◽  
Linear Elastic ◽  
Piping Systems ◽  
Simple Model System ◽  
Linear Manner

During the last twenty-five years, considerable attention has been given to the structural integrity of steel piping systems, and in particular to the effect of circumferential cracks on their integrity. From a safety perspective, it is important that any crack, say for example a stress corrosion crack or fatigue crack, will not develop into a through-wall crack which will then propagate unstably, thus leading to a guillotine rupture and possibly a pipe whip scenario. One way of guaranteeing that this does not happen is to ensure that unstable growth of a circumferential through-wall crack is unable to occur. An appropriate methodology is based on tearing modulus concepts with the instability criterion being expressed in the form TAPP > TMAT where TAPP is the applied tearing modulus, a measure of the crack driving force, and TMAT is the material tearing modulus, a measure of the material’s crack growth resistance. With a piping system that behaves in a linear elastic manner, TAPP involves only the system’s geometry parameters and the crack size but not the magnitudes of the applied loadings or the material properties of the cracked cross-section; the behaviours of the cracked cross-section and the remainder of the piping system are therefore decoupled. If, however, the system behaves in a non-linear manner say, for example, as a result of excessive deformation arising as a consequence of large deformations, then TAPP also involves the material properties of the cracked cross-section; material and piping system geometry parameters are then not decoupled in the instability criterion. The paper illustrates this point by analysing a simple model system where the non-linearity arises from excessive deformation at a connection.

Piping System Structural Integrity Simulation for Post LOCA Water Hammer Loads

2002 ◽  
Author(s):  
B. W. Manning ◽  
T. Stevens ◽  
G. Morandin ◽  
R. G. Sauve´ ◽  
R. Richards ◽  
...  
Keyword(s):  
Structural Damage ◽  
Structural Integrity ◽  
Water Hammer ◽  
Piping System ◽  
Linear Modeling ◽  
Linear Elastic ◽  
Beam Elements ◽  
Loss Of Coolant Accident ◽  
Loss Of Coolant ◽  
Non Linear

The Canadian Nuclear Safety Commission (CNSC) required as part of the operating license for Ontario Power Generation’s Darlington Nuclear Generating Station, that the structural integrity of the piping following a loss of coolant accident (LOCA) be demonstrated. This is necessary to ensure that no subsequent pressure boundary failures will impede the ability to maintain fuel cooling. The injection of cold emergency coolant following a LOCA creates the potential for the occurrence of condensation-induced water hammers (CIWH) in the primary heat transport (PHT) system piping. Classical linear elastic piping analysis using the class 1 NB-3656 rules of the ASME Boiler & Pressure Vessel Code failed to demonstrate the adequacy of the piping and/or its supports that were designed using the linear elastic rules of subsection NF for nine of the twelve piping models that comprise the PHT system. A decision was made to undertake a state-of-the-art non-linear explicit analysis in order to qualify the piping. Strain rather than stress limits would be applied similar to those being developed by ASME for nuclear packaging undergoing accidental impact during transportation. In order to address the feasibility of this approach, a non-linear analysis was performed on a portion of one of the piping systems. The piping was modeled as shells and again as beam elements with and without detailed modeling of the supports. After these initial simulations, it was determined that the piping could be modeled with simplified beam elements, however, the supports would require a more detailed modeling in order to determine the extent of support damage and the effect the supports have on the integrity of the piping system itself. This paper addresses the non-linear modeling of the piping models and discusses the modeling details, assumptions and analysis results. This approach is shown to be a useful alternative for predicting the extent of structural damage that can be expected by a Level D event such as a condensation induced water hammer following a loss of coolant accident.

Estimation of Bending Stresses in Piping Systems Subjected to Transient Pressure

2020 ◽  
Author(s):  
Maral Taghva ◽  
Lars Damkilde
Keyword(s):  
Dynamic Analysis ◽  
Static Analysis ◽  
Structural Integrity ◽  
Oil And Gas ◽  
Real Life ◽  
Piping System ◽  
Transient Pressure ◽  
Operational Conditions ◽  
Piping Systems ◽  
Bending Stresses

Abstract Modifications in aged process plants may subject piping systems to fluid transient scenarios, which are not considered in the primary design calculations. Due to lack of strict requirements in ASME B31.3 the effect of this phenomenon is often excluded from piping structural integrity reassessments. Therefore, the consequences, such as severe pipe motion or even rupture failure, are discovered after modifications are completed and the system starts to function under new operational conditions. The motivation for this study emanated from several observations in offshore oil and gas piping systems, yet the results could be utilized in structural integrity assessments of any piping system subjected to pressure waves. This paper describes how to provide an approximate solution to determine maximum bending stresses in piping structures subjected to wave impulse loads without using rigorous approaches to calculate the dynamic response. This paper proposes to consider the effect of load duration in quasi-static analysis to achieve more credible results. The proposed method recommends application of lower dynamic load factors than commonly practiced values advised by design codes, for short duration loads such as shock waves. By presenting a real-life example, the results of improved and commonly practiced quasi-static analysis are compared with the site observations as well as dynamic analysis results. It is illustrated that modified quasi-static solution shows agreement with both dynamic analysis and physical behavior of the system. The contents of this study are particularly useful in structural strength re-assessments where the practicing engineer is interested in an approximated solution indicating if the design criteria is satisfied.

Structural Integrity of Flexible Piping Systems Conveying Liquids

2005 ◽  
Vol 128 (3) ◽  
pp. 341-347 ◽  
Author(s):  
Felipe BastosFreitas Rachid
Keyword(s):  
Structural Integrity ◽  
Mathematical Problem ◽  
Nonlinear Partial Differential Equations ◽  
Operator Splitting ◽  
Piping System ◽  
Damage Growth ◽  
Splitting Technique ◽  
Structure Interaction ◽  
Piping Systems ◽  
Fast Transients

This work presents a structural integrity model for piping systems conveying liquids which takes the axial fluid-structure interaction into account. The model is used to numerically investigate the influence of pipe motion on the degradation of the piping when fast transients are generated by valve slam. The resulting mathematical problem is formed by a system of nonlinear partial differential equations which is solved by means of an operator splitting technique, combined with Glimm’s method. Numerical results obtained for an articulated piping system indicate that high piping flexibility may induce a substantial increase in damage growth along the pipes.

Effects of High Frequency Hydrodynamic Loads on Structural Integrity and Mechanical Operability of Valves

2015 ◽  
Author(s):  
Yigit Isbiliroglu ◽  
Cagri Ozgur ◽  
Evren Ulku ◽  
Nish Vaidya ◽  
Kristofor Paserba
Keyword(s):  
High Frequency ◽  
Structural Integrity ◽  
Energy Content ◽  
Hybrid Approach ◽  
Piping System ◽  
Seismic Loads ◽  
Damage Potential ◽  
Element Analysis ◽  
Piping Systems ◽  
Number Of Cycles

In-line valves are qualified for static as well as dynamic loads from seismic and hydrodynamic (HD) events. Seismic loads are generally characterized by frequency content less than about 33 Hz whereas HD loads may exhibit a broad range of frequencies greater than 33 Hz. HD loads may also result in spectral accelerations significantly in excess of those due to the design basis seismic events. Current regulatory guidelines do not specifically address the evaluation of equipment response to high frequency loading. This paper investigates the response of skid and line mounted valves of piping systems under HD loads by using several independent rigorous finite element analysis solutions for various piping system segments. It presents a hybrid approach for the evaluation of the response of valves to HD and seismic loads. The proposed approach significantly reduces the amount of individual analysis and testing needed to qualify the valves. First, valve responses are evaluated on the basis of displacements since HD loads are generally characterized by high frequencies and small durations. Second, the damage potential of the loads on the valve actuators is represented by the energy imparted to the actuator quantified in terms of Arias intensity. The rationale for using the energy content is based on the fact that damage due to dynamic loading is related not only to the amplitude of the acceleration response but also to the duration and the number of cycles over which this acceleration is imposed.

Applicability of Optimal Seismic Design Methodology for Piping Systems Subjected to Seismic Waves With Various Frequency Characteristics

2007 ◽  
Author(s):  
Tomohiro Ito ◽  
Katsuhisa Fujita ◽  
Masashi Michiue
Keyword(s):  
Seismic Design ◽  
Design Methodology ◽  
Seismic Waves ◽  
Structural Integrity ◽  
Frequency Characteristics ◽  
System Model ◽  
Piping System ◽  
Optimal Conditions ◽  
Piping Systems ◽  
Support Devices

In this study, the optimal seismic design methodology which can consider the structural integrity of both piping systems and elasto-plastic support devices are developed. This methodology employs genetic algorithm and can search the optimal conditions such as supporting locations, capacity and stiffness of supporting devices. A lead extrusion damper is treated here as a typical elasto-plastic damper. Numerical simulations are performed using a simple piping system model for the various kinds of seismic waves with different frequency characteristics. As a result, it is shown that the optimal seismic design methodology proposed here is applicable to the seismic design of piping systems supported by elasto-plastic dampers subjected to the seismic waves with various kinds of frequency characteristics.

The Effect of Restraint Non-Linearity on the Instability of Growth of a Circumferential Through-Wall Crack in a Piping System

2002 ◽  
Author(s):  
E. Smith
Keyword(s):  
Simple Model ◽  
Crack Growth ◽  
Simple Approach ◽  
Instability Criterion ◽  
Piping System ◽  
Unstable Crack ◽  
Pipe Length ◽  
Unstable Crack Growth ◽  
System A ◽  
Linear Manner

The paper is concerned with the criterion for the instability of growth of a circumferential through-wall crack in a piping system. A simple approach involves representing the cracked section behaviour by a moment (M)–rotation (φ) relation. The criterion for unstable crack growth is then L* > EI |dφ/dM| where E is Young’s modulus and I is the second moment of area of the piping at the cracked section. L* can be viewed as a crack-system compliance length parameter or an “effective” pipe length. If the piping system, apart from the cracked system, behaves in a linear manner, L* is dependent on the system’s characteristics but most importantly, is independent of the magnitudes of any applied loadings and the characteristics of the cracked section. This paper is concerned with the effect of system non-linearity, and in particular restraint non-linearity, on the instability criterion, the considerations being based on the analyses of a simple model which contains a restraint which behaves non-linearly. In this case, we show that L* is no longer dependent only on the system’s characteristics, as is the case when the restraint behaves linearly.

Basic Study on Optimal Design of System Supporting Structures Subjected to Random Inputs Using the Probabilistic Vibration Theory

2012 ◽  
Author(s):  
Atsuhiko Shintani ◽  
Tadashi Nagami ◽  
Tomohiro Ito ◽  
Chihiro Nakagawa
Keyword(s):  
Optimal Design ◽  
Random Vibration ◽  
Structural Integrity ◽  
Piping System ◽  
Basic Study ◽  
Vibration Theory ◽  
Piping Systems ◽  
Random Vibration Theory ◽  
Noise Input ◽  
Supporting Structures

In this paper, we investigate the optimal design of the piping system supported by elasto-plastic damper subjected to the random input based on the random vibration theory. Using proposed optimal design, the structural integrity of both the piping systems and the elasto-plastic supporting devices are considered and the optimal conditions such as the supporting location, the capacity of the supporting devices are searched. Numerical simulations are performed using a simple piping system model for the white Gaussian noise input based on the random vibration theory.

scholarly journals Tests on SENT Specimens to Study Geometry Effects in the Brittle to Ductile Transition

2014 ◽  
Author(s):  
Patrick Le Delliou ◽  
Samuel Geniaut
Keyword(s):  
Room Temperature ◽  
Structural Integrity ◽  
Test Procedure ◽  
Crack Size ◽  
Engineering Structures ◽  
Brittle To Ductile Transition ◽  
Loading Mode ◽  
Piping Systems ◽  
Carbon Manganese Steels ◽  
Geometry Effects

The accurate prediction of ductile fracture behaviour plays an important role in structural integrity assessments of critical engineering structures under fully plastic regime, including nuclear reactors and piping systems. Many structural steels and aluminium alloys generally exhibit significant increases in fracture toughness, characterized by the J-integral, over the first few mm of stable crack extension (Δa), often accompanied by large increases in background plastic deformation. Conventional testing programs to measure crack growth resistance (J–Δa) curves employ three-point bend, SEN(B), or compact, CT. However, laboratory testing of fracture specimens to measure resistance curves (J–Δa) consistently reveals a marked effect of absolute specimen size, geometry, relative crack size (a/W ratio) and loading mode (tension vs. bending) on R-curves. These effects observed in R-curves have enormous practical implications in defect assessments and repair decisions of in-service structures under low constraint conditions. Structural components falling into this category include pressurized piping systems with surface flaws that form during fabrication or during in-service operation. This paper presents the on-going work to study geometry effects (e.g. triaxiality effects) in the brittle to ductile transition of carbon-manganese steels, the basic idea being to compare the results obtained on these specimens with the results obtained on CT specimens. A preliminary program was previously conducted at room temperature using deeply notched specimens (Le Delliou, 2012). Finite element computations were made to optimize the specimen shape and to develop the η-factor, the shape factor F (to compute K) and the normalized compliance μ. For the present program, new specimens have been machined with shallower notches (a/W = 0.4), to get a0/W = 0.5 after fatigue pre cracking. Fatigue pre cracking was conducted in 4-point bending to avoid damaging the back of the notch. Moreover, the specimens have been cut in the TS (Transverse-Short) direction of the plate to get lower toughness properties, and less plasticity during the tests. Tests at room temperature have been conducted first to validate the revised test procedure. Then, the SENT specimens have been tested at −100°C, −60°C, and −40°C, together with CT specimens.

Development of Test on Sent Specimens to Study Geometry Effects

2012 ◽  
Author(s):  
Patrick Le Delliou ◽  
Joumana El-Gharib
Keyword(s):  
Structural Integrity ◽  
Test Procedure ◽  
Crack Size ◽  
Test Procedures ◽  
Engineering Structures ◽  
Loading Mode ◽  
Piping Systems ◽  
Carbon Manganese Steels ◽  
Geometry Effects ◽  
Low Constraint

The accurate prediction of ductile fracture behaviour plays an important role in structural integrity assessments of critical engineering structures under fully plastic regime, including nuclear reactors and piping systems. Many structural steels and aluminium alloys generally exhibit significant increases in fracture toughness, characterized by the J-integral, over the first few mm of stable crack extension (Δa), often accompanied by large increases in background plastic deformation. Conventional testing programs to measure crack growth resistance (J-Δa) curves employ three-point bend, SEN(B), or compact, CT. However, laboratory testing of fracture specimens to measure resistance curves (J-Δa) consistently reveals a marked effect of absolute specimen size, geometry, relative crack size (a/W ratio) and loading mode (tension vs. bending) on R-curves. These effects observed in R-curves have enormous practical implications in defect assessments and repair decisions of in-service structures under low constraint conditions. Structural components falling into this category include pressurized piping systems with surface flaws that form during fabrication or during in-service operation. This paper presents the on-going work to develop specimens and test procedures to study geometry effects (e.g., triaxiality effects) in the brittle to ductile transition of carbon-manganese steels, the basic idea being to compare the results obtained on these specimens with the results obtained on CT specimens. A clamped SENT specimen was chosen for this study. Finite element computations have been made to optimize the specimen shape and to develop the η-factor, the shape factor F (to compute K) and the normalized compliance μ. Preliminary tests have been conducted, showing that some adjustments of the test procedure should be made. Tests on new specimens are on-going.

Tests on SENT and CT Specimens to Study Geometry Effects in the Brittle to Ductile Transition

2016 ◽  
Author(s):  
Patrick Le Delliou ◽  
Samuel Geniaut
Keyword(s):  
Structural Integrity ◽  
Crack Size ◽  
Engineering Structures ◽  
Geometry Effect ◽  
Brittle To Ductile Transition ◽  
Loading Mode ◽  
Piping Systems ◽  
Carbon Manganese Steels ◽  
Geometry Effects ◽  
Low Constraint

The accurate prediction of ductile fracture behaviour plays an important role in structural integrity assessments of critical engineering structures under fully plastic regime, including nuclear reactors and piping systems. Many structural steels and aluminium alloys generally exhibit significant increases in fracture toughness, characterized by the J-integral, over the first few mm of stable crack extension (Δa), often accompanied by large increases in background plastic deformation. Conventional testing programs to measure crack growth resistance (J–Δa) curves employ three-point bend, SEN(B), or compact, CT. However, laboratory testing of fracture specimens to measure resistance curves (J–Δa) consistently reveals a marked effect of absolute specimen size, geometry, relative crack size (a/W ratio) and loading mode (tension vs. bending) on R-curves. These effects observed in R-curves have enormous practical implications in defect assessments and repair decisions of in-service structures under low constraint conditions. Structural components falling into this category include pressurized piping systems with surface flaws that form during fabrication or during in-service operation. A research program was launched by EDF R&D to study geometry effects (e.g. triaxiality effects) in the brittle to ductile transition of carbon-manganese steels using Single-edge notch tension (SENT) specimens, by comparing the results obtained on these specimens with the results obtained on CT specimens. This paper presents the results of the tests conducted between −40°C and −100°C on a large number of specimens of both types. The toughness values of the SENT specimens appear to be included in the scatter of the CT12.5 ones, so the geometry effect between CT and SENT specimens in the brittle to ductile region is not significant. Moreover, the results of the CT12.5 cut in the L-S direction are not very different of those of the specimens cut in the T-S direction. The Master Curve methodology fits rather well the CT12.5 results, whereas the SENT results are not well covered by this methodology. The energetic approach called GP has been applied to the analysis of some tests. This approach shows that the geometry effect between both types of specimens is limited, in agreement with the experimental observations.

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