Fitness-for-Service Methodology Based on Variational Principles in Plasticity

2004 ◽  
Author(s):  
H. Indermohan ◽  
R. Seshadri
Keyword(s):  
Lower Bound ◽  
Hot Spots ◽  
Variational Formulation ◽  
Variational Principles ◽  
Limit Load ◽  
Pressure Vessels ◽  
Load Estimation ◽  
Estimation Technique ◽  
Simplified Procedures

A variational formulation in plasticity has been used to develop improved limit load estimation technique, such as the m-alpha method. Lower bound limit load estimates are especially germane to design and fitness-for-service assessments. The concept of “integral mean of yield” has been applied to problems involving locally thin areas (LTA) and local hot spots in the context of industrial pressure vessels and piping. Simplified procedures for “fitness-for-service” assessment, suitable for use by plant engineers, have been developed. The results are compared with the corresponding inelastic finite elastic analyses.

Fitness-for-Service Methodology Based on Variational Principles in Plasticity

2005 ◽  
Vol 127 (1) ◽  
pp. 92-97 ◽  
Author(s):  
H. Indermohan ◽  
R. Seshadri
Keyword(s):  
Lower Bound ◽  
Hot Spots ◽  
Variational Formulation ◽  
Variational Principles ◽  
Limit Load ◽  
Pressure Vessels ◽  
Load Estimation ◽  
Estimation Technique ◽  
Simplified Procedures

A variational formulation in plasticity has been used to develop improved limit load estimation technique, such as the m-alpha method. Lower bound limit load estimates are especially germane to design and fitness-for-service assessments. The concept of “integral mean of yield” has been applied to problems involving locally thinned areas (LTA) and local hot spots in the context of industrial pressure vessels and piping. Simplified procedures for “fitness-for-service” assessment, suitable for use by plant engineers, have been developed. The results are compared with the corresponding inelastic finite elastic analyses.

Fitness-for-Service Evaluation of Thermal Hot Spots and Corrosion Damage in Cylindrical Pressure Components

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
P. Tantichattanont ◽  
S. M. R. Adluri ◽  
R. Seshadri
Keyword(s):  
Hot Spots ◽  
Structural Integrity ◽  
Variational Principles ◽  
Elastic Shell ◽  
Corrosion Damage ◽  
Pressure Vessels ◽  
Alternative Methods ◽  
Linear Interaction ◽  
Reference Volume ◽  
Aspect Ratios

Thermal hot spots and corrosion damage are typical of damages occurring in pressure vessels and piping. Structural integrity of such components needs to be evaluated periodically to determine “fitness-for-service” (FFS) of the components. In the present paper, three alternative methods for level 2 FFS assessments (as described in API 579) are proposed. They are based on variational principles in plasticity, the m-alpha method, the idea of reference volume, and the concept of decay lengths in shells. Decay lengths in the axial and circumferential directions for cylindrical shells are derived based on elastic shell theories. They are used to specify the reference volume participating in plastic action and the extent of what can be called “local” damage. Interaction between longitudinal and circumferential effects is investigated. A linear interaction curve is shown to give good estimation of the “remaining strength factor” for damage of practical aspect ratios. The stretching and bulging effects due to the damage are also studied. The limit defining the threshold to dominance of stretching action is proposed by using an approximate equilibrium calculation based on yield-line analysis. The effectiveness of the proposed assessments is demonstrated through an example and verified by level 3 inelastic finite element analysis.

Integral Mean of Yield Criterion in Design and Fitness for Service Assessment

2008 ◽  
Author(s):  
R. Adibi-Asl ◽  
R. Seshadri
Keyword(s):  
Lower Bound ◽  
Variational Formulation ◽  
Yield Criterion ◽  
Hot Spot ◽  
Corrosion Damage ◽  
Limit Load ◽  
Assessment Procedure ◽  
Limit Loads ◽  
Reference Volume ◽  
Volume Method

Mura’s variational formulation for determining limit loads, originally developed as an alternative to classical methods, is extended further by allowing the pseudo-elastic distributions of stresses to lie outside the yield surface provided they satisfy the “integral mean of yield” criterion. Consequently, improved lower-bound and upper-bound values for limit loads are obtained. The mα estimation limit load method, reference volume method and the fitness for service assessment procedure (including corrosion damage and thermal hot spot damage), are all applications and extensions of the “integral mean of yield” criterion.

Integrity Assessment of Spherical Pressure Components With Local Corrosion and Hot Spots

2006 ◽  
Author(s):  
Pattaramon Tantichattanont ◽  
Seshu Adluri ◽  
Rangaswamy Seshadri
Keyword(s):  
Lower Bound ◽  
Hot Spots ◽  
Structural Integrity ◽  
Hot Spot ◽  
Corrosion Damage ◽  
Pressure Vessels ◽  
Operating Conditions ◽  
Local Corrosion ◽  
Integrity Assessment ◽  
Spherical Pressure

Corrosion damage and hot spots are typical of damages that can occur in ageing pressure vessels and pipelines used in industrial processes. Internal and external corrosion could be the result of corrosive products stored inside or harsh environmental conditions on the outside. Hot spots are caused by damage due to loss of refractory lining on the inside wall of pressure components or due to maldistribution of flow containing catalyst and reactive fluids. The structural integrity of such ageing components needs to be evaluated periodically to establish the continued suitability of the vessels under operating conditions. The present paper develops a method for Level 2 (as categorized by API 579) structural integrity evaluations of spherical pressure vessels containing local corrosion damage or hot spot. The decay lengths for spherical shells subject to local damages have been studied based on stretching and bending effects using elastic shell theories so as to identify the reference volume participating in plastic action. A limit for “local” corroded spot or hot spot is defined by the size of damage that an onset of pure membrane action occurs inside the damaged area. The size of damage indicating the crossover from dominance of stretching effects on the damage behavior to that of bending effects is also presented. The lower bound recommended “remaining strength factors” for spherical pressure vessels containing corrosion or hot spot are formulated by application of Mura’s integral mean of yield criterion and the improved lower bound mα-multiplier. Three alternative recommendations are proposed. The effectiveness of the proposed methods is evaluated and demonstrated through illustrative examples and comparison with inelastic finite element analyses.

Limit Load Analysis of a Torispherical Head With Thermal Hot Spot Damage

2018 ◽  
Author(s):  
Amir Mehrizi ◽  
Soheil Nakhodchi ◽  
Reza Adibi-Asl
Keyword(s):  
Hot Spots ◽  
Hot Spot ◽  
Limit Load ◽  
Pressure Vessels ◽  
Load Carrying ◽  
Different Shapes ◽  
Service Degradation ◽  
The Common ◽  
The Impact ◽  
Inside Wall

Vessel dished heads are widely being used in storage tanks or pressure vessels. These heads are available in different shapes including hemispherical, ellipsoidal and torispherical heads. In this paper, pressure limit load of torispherical head with thermal hotspot damage is investigated. Thermal hotspots are one of the common types of in-service degradation in some pressurized components and can be considered as damage. This type of damage is usually caused by the loss of refractory lining on the inside wall of pressure components or due to a misdistribution of the flow within vessels containing catalysts. Hotspot damage potentially jeopardizes the integrity of the components [1]. In the current research, the impact of a thermal hotspot on the load carrying capacity of various shapes of torispherical heads is investigated using numerical simulation. Also, sensitivity analysis has been performed to investigate the effect of location of thermal hot spots and thickness in the torispherical heads, with and without thermal hot spot damage.

Fitness-for-Service Evaluation of Thermal Hot Spots and Corrosion Damage in Cylindrical Pressure Components

2007 ◽  
Author(s):  
P. Tantichattanont ◽  
Seshu M. R. Adluri ◽  
R. Seshadri
Keyword(s):  
Hot Spots ◽  
Structural Integrity ◽  
Variational Principles ◽  
Elastic Shell ◽  
Corrosion Damage ◽  
Pressure Vessels ◽  
Alternative Methods ◽  
Linear Interaction ◽  
Reference Volume ◽  
Aspect Ratios

Thermal hot spots and corrosion damage are typical of damages occurring in pressure vessels and piping. Structural integrity of such components needs to be evaluated periodically to determine “fitness-for-service” of the components. In the present paper, three alternative methods for Level 2 FFS assessments (as defined by API 579) are proposed. They are based on variational principles in plasticity, the limit load multiplier m-alpha method, reference volume and the concept of decay lengths in shells. Decay lengths in the axial and circumferential directions for cylindrical shells are derived based on elastic shell theories. They are used to specify the reference volume participating in plastic action and the limit of what can be called “local” damage. Interaction between longitudinal and circumferential effects is investigated. A linear interaction curve is shown to give good estimations of “remaining strength factor” for damages of practical aspect ratios. The stretching and bulging effects due to the damage are also studied. The limit defining the threshold to dominance of stretching action is proposed by using an approximate equilibrium calculation based on yield-line analysis. The effectiveness of the proposed assessments are demonstrated through an example and verified by Level 3 inelastic finite element analysis.

Applications of Limit Load Analyses to Assess the Structural Integrity of Pressure Vessels

2005 ◽  
Author(s):  
Richard C. Biel ◽  
Chris Alexander
Keyword(s):  
Lower Bound ◽  
Structural Integrity ◽  
Plastic Material ◽  
Limit Load ◽  
Pressure Vessels ◽  
Analysis Model ◽  
External Pressures ◽  
Buckling Resistance ◽  
Engineered Systems ◽  
Elastic Plastic Material

With advances in computational modeling techniques, limit load methods are gaining wider acceptance as a tool for determining the structural integrity of pressure vessels. The objective of a limit load analysis is to size a vessel or structure considering nonlinear methods such as elastic-plastic material properties and non-linear strain-displacement relations. Case studies are presented in this paper that feature external pressures, gravity, and wind loads. The technique applies an appropriate initial magnitude for each load type and uses the analysis model to increase the load until a lower bound is calculated. The lower bound value is determined by incrementally increasing the load until convergence is not possible then the results are extracted. This paper presents how limit load techniques were used to address the structural integrity of four engineered systems including the structural stability of a corroded tower under wind and vacuum loads, determining the pressure capacity of a pressure vessel, analysis of a subsea vessel under high external pressures, and the remaining buckling resistance of a dented subsea flowline. The paper highlights the application of limit load techniques using criteria detailed in WRC 464.

Lower Bound Limit Loads Using the Reference Two-Bar Structure: An Improved Estimate Beyond Mura’s Lower Bound

2015 ◽  
Author(s):  
S. L. Mahmood ◽  
R. Adibi-Asl ◽  
C. G. Daley ◽  
R. Seshadri
Keyword(s):  
Lower Bound ◽  
Variational Formulation ◽  
Limit Load ◽  
Limit Loads

Mura’s lower bound limit load multiplier (m′) has been obtained on the basis of a variational formulation (Mura et al., 1965). However, m′ is equal to or less than the classical lower bound multiplier (mL). In this paper, a relationship between the m′ multiplier and the reference two-bar multiplier (Seshadri, R., and Adibi-Asl, R., 2007) is obtained. The nature of the bounds is examined in the context of several pressure components.

Lower Bound Limit Load Estimation Using a Linear Elastic Analysis

2012 ◽  
Vol 134 (2) ◽  
Author(s):  
C. Hari Manoj Simha ◽  
R. Adibi-Asl
Keyword(s):  
Lower Bound ◽  
Deformation Theory ◽  
Elastic Stress ◽  
Limit Load ◽  
Load Estimation ◽  
Elastic Analysis ◽  
Numerical Examples ◽  
Linear Elastic ◽  
Plastic Localization ◽  
Appl Math

We present a scheme that utilizes one elastic stress field (no iterations) to compute lower bound limit load multipliers of structures that collapse through gross (or localized) plasticity. A criterion to distinguish between these collapse modes is presented. For structures that collapse through gross plasticity, we demonstrate that the m′ multiplier proposed by Mura et al. (1965, Extended Theorems of Limit Analysis,” Q. Appl. Math., 23(2), pp. 171–179) is a lower bound in the context of deformation theory. For structures that undergo plastic localization at collapse, we present a criterion that identifies (approximately) the subvolumes of the structure that participate in the collapse. Multiplier m′ is computed over the selected subvolumes, denoted as m'S, and demonstrated to be a lower bound multiplier in the context of deformation theory. We consider numerical examples of structures that collapse by localized or gross plasticity and show that our proposed multiplier is lower than the corresponding multiplier obtained through elastic–plastic analysis and the proposed multiplier is not overly conservative.

A Finite Element Technique for Limit Analysis of Structures

1990 ◽  
Vol 112 (2) ◽  
pp. 138-144 ◽  
Author(s):  
E. G. Berak ◽  
J. C. Gerdeen
Keyword(s):  
Finite Element ◽  
Lower Bound ◽  
Limit Analysis ◽  
Variational Principles ◽  
Yield Criterion ◽  
Iteration Process ◽  
Limit Load ◽  
Upper And Lower Bounds ◽  
Algebraic Equations ◽  
Linear Algebraic Equations

Limit analysis provides an alternative to incremental elastic-plastic analysis for determining a limit load. The limit load is obtained from the lower and upper-bound theorems. These theorems, which are based on variational principles, establish the static and kinematic methods, respectively, and are particularly attractive for finite element implementation. A finite element approach using the definition of the p-norm is developed for calculating upper and lower bounds of the limit load multiplier for two-dimensional, rigid perfectly plastic structures which obey the von Mises yield criterion. Displacement and equilibrium building block quadrilateral elements are used in these dual upper and lower-bound formulations, respectively. The nonlinear finite element equations are transformed into systems of linear algebraic equations during the iteration process, and the solution vectors are determined using a frontal equation solver. The upper and lower-bound solutions are obtained in a reasonable number of iteration steps, and provide a good estimate of the limit load multiplier. Numerical results are provided to demonstrate this finite element procedure. In addition, this procedure is particularly applicable to the solution of complex problems using parallel processing on a supercomputer.

Sign in / Sign up

Export Citation Format

Share Document