Simplified fitness-for-service assessment of pressure vessels and piping systems containing thermal hot spots and corrosion damage

2010 ◽  
Vol 87 (7) ◽  
pp. 381-388 ◽  
Author(s):  
M.M. Hossain ◽  
R. Seshadri
2005 ◽  
Vol 127 (2) ◽  
pp. 137-142 ◽  
Author(s):  
R. Seshadri

Local hot spots can occur in some pressure vessels and piping systems used in industrial processes. The hot spots could be a result of, for instance, localized loss of refractory lining on the inside of pressure components or due to a maldistribution of process flow within vessels containing catalysts. The consequences of these hot spots on the structural integrity of pressure components are of considerable importance to plant operators. The paper addresses structural integrity issues in the context of codes and standards design framework. Interaction of hot spots, as is the case when multiple hot spots occur, is addressed. An assessment method, suitable for further development of a Level 2 “Fitness-for-Service” methodology, is discussed and applied to a commonly used pressure component configuration.


2009 ◽  
Vol 131 (5) ◽  
Author(s):  
P. Tantichattanont ◽  
S. M. R. Adluri ◽  
R. Seshadri

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.


Author(s):  
Pattaramon Tantichattanont ◽  
Seshu Adluri ◽  
Rangaswamy Seshadri

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.


Author(s):  
R. Seshadri

Local hot spots can occur in some pressure vessels and piping systems used in industrial processes. The hot spots could be result of, for instance, localized loss of refractory lining on the inside of pressure components or due to a maldistribution of process flow within vessels containing catalysts. The consequences of these hot spots on the structural integrity of pressure components are of considerable importance to plant operators. The paper addresses structural integrity issues in the context of codes and standards design framework. The interaction of hot spots as is the case when multiple hot spots occur is addressed. An assessment method suitable for Level 2 “Fitness-for-Service” evaluation is discussed, and applied to a commonly used pressure component configuration.


Author(s):  
P. Tantichattanont ◽  
Seshu M. R. Adluri ◽  
R. Seshadri

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.


2006 ◽  
Vol 13-14 ◽  
pp. 127-132 ◽  
Author(s):  
Gerold Lackner ◽  
Peter Tscheliesnig

Acoustic emission testing (AT) is in Europe an already well established non-destructive testing (NDT) method. Qualification requirements as well as certification of testing personnel are laid down in European standard EN 473. A widespread application of AT deals with testing of unfired pressure vessels for re-qualification after a certain period of service (repetition test). The advantages of applying AT compared to the traditional procedure of hydrostatic test plus visual inside inspection are numerous. Just to name the most important: reduction of downtime, omitting of residual humidity and no risk of product contamination with water. It is a fact that AT provides much more useful information concerning the condition of the pressure vessel under test than a simple ‘passed’ or ‘not passed’ obtained usually by a hydrostatic test. This contribution gives two examples of practical experience, where severe corrosion defects have been detected by AT. The defects have been found in both cases on the vessel’s shell under the thermal insulation, where they have been hidden undetected for years. It can be assumed that even the vessel with the most severe damage (loss of more than 50% of the nominal wall thickness) would have passed the traditional repetition test procedure and that failure within the following service period would have occurred. In contrary to this scenario, AT enabled the vessel operator to perform appropriate repair in time.


Author(s):  
Claude Faidy

During the past 30 years the main rules to design pressure vessels were based on elastic analyses. Many conservatisms associated to these different elastic approaches are discussed in this paper, like: stress criteria linearization for 3-D components, stress classification in nozzle areas, plastic shake down analysis, fatigue analysis, Ke evaluation, and pipe stress criteria for elastic follow-up due to thermal expansion or seismic loads... This paper will improve existing codified rules in nuclear and non-nuclear Codes that are proposed as alternatives to elastic evaluation for different failure modes and degradation mechanisms: plastic collapse, plastic instability, tri-axial local failure, rupture of cracked component, fatigue and Ke, plastic shakedown. These methods are based on limit loads, monotonic or cyclic elastic-plastic analyses. Concerned components are mainly vessels and piping systems. No existing Code is sufficiently detailed to be easily applied; the needs are stress analysis methods through finite elements, material properties including material constitutive equations and criteria associated to each methods and each failure modes. A first set of recommendation to perform these inelastic analysis will be presented to improve existing codes on an international harmonized way, associated to all material properties and criteria needed to apply these modern methods. An international draft Code Case is in preparation.


Author(s):  
Ishita Chakraborty ◽  
Kannan Subramanian ◽  
Jorge Penso

Abstract Brittle fracture assessments (BFAs) of pressure vessels based on API 579-1/ASME FFS-1, Section 3 procedures are frequently easier and more straightforward to implement in comparison to the BFAs on piping systems. Specifically, the development of the MSOT curves. This is due to the complexities involved in the piping systems due to the branch piping interactions, end conditions of piping systems such as nozzle flexibilities at the pressure vessel connections, temperature changes in the length of piping especially when the piping is significantly long as seen in flare header piping systems. MSOT curves that are alternatively used for MAT curves provide a better picture to the plant personnel in understanding the safe operating envelope. Development of MSOT curves is an iterative process and therefore involves significant number of piping stress analyses during their development. In this paper, an approach to develop the MSOT curves is discussed with two case studies that are of relevance to olefin plants.


Author(s):  
Kshitij P. Gawande ◽  
Phillip Wiseman ◽  
Alex Mayes

Whenever undesirable dynamic events occur within power plant, refinery, or process piping systems, specialty supports and restraints have the task of protecting the mechanical equipment and connecting piping from damaging loads and displacements. The array of components that may be affected include, but are not limited to, piping systems, pumps, valve assemblies, pressure vessels, steam generators, boilers, and heat exchangers. In particular, the dynamic events can be classified into two distinct types that originate from either internal events or external events. The internal dynamic load generating events include plant system start-up and shut-down, pressure surges or impacts from rapid valve closures such as steam and water hammer, boiler detonations, pipe rupture, and operating vibratory displacements that may be either low frequency or high frequency vibrations. The external dynamic load generating events include wind loads, earthquake, airplane impact to supporting structures and buildings, and explosions. Most of the aforementioned dynamic load generating events can be defined quite simply as impact loads, i.e., forces and moments that are applied over very short periods of time, for example, less than one second. While earthquake loads may be applied over a total time period of an hour or so, the peak loads and resulting displacements occur on a more sinusoidal basis of peak-to-peak amplitudes. One of the most common specialty restraint components utilized in the piping industry to absorb and transfer the dynamic load resulting from impact events is the hydraulic shock suppressor, otherwise known as the snubber. The snubber is a formidable solution to protecting plant piping systems and equipment from impact loading while not restricting the thermal displacements during routine operations. In the dynamic events that may be characterized by an impact type loading, snubbers provide an instantaneous, practically rigid, axial connection between the piping or other component to be secured and the surrounding structure whether it be concrete or steel (for example). In this way, the kinetic energy can be transmitted and harmlessly dissipated. In the vibratory environment, however, neither the impact load scenario nor the rapid translations are imposed upon snubbers, thereby presenting the competing intended application of the snubber to protect against impact loads versus, in many cases, the improper selection of the snubber to dampen vibratory (other than seismic) loads. The details of the hydraulic shock suppressor design are reviewed and discussed to exemplify why a case can and should be made against the use of snubbers in piping systems within an operating vibratory environment.


Author(s):  
Henry Kwok ◽  
Simon Yuen ◽  
Jorge Penso

The overall framework for a Level 2 assessment of local thermal hot spot in pressure vessels was first developed by Seshadri [1]. The assessment procedure invokes the concept of integral mean of yield and the concept on a reference volume to determine the reduction of load capacity caused by hot spot damage. This paper investigates the accuracy of this assessment by comparing the results of the Level 2 assessment with a Level 3 assessment (inelastic finite element analysis). Three examples with varying pressure component and hot spot sizes are considered. The comparison yielded a low variance between the Level 2 and Level 3 assessments with the Level 2 assessment being more conservative.


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