Allowable Cracks Related to Penetration for Part-Through Cracks in Pipes Subjected to Bending Stresses

Fully plastic collapse stresses for circumferentially part-through cracked pipes subjected to bending stresses are estimated by Limit Load Criteria provided by the ASME Code Section XI. Allowable crack depths were determined by using the Limit Load Criteria and that are tabulated in the ASME Code Section XI for different plant service level conditions. On the other hand, crack penetration bending stresses for part-through cracked pipes were estimated by using the Local Approach of Limit Load Criteria. By using these Criteria, the study presented in this paper obtained allowable crack depths at penetration for circumferentially part-through cracked pipes. Comparing the allowable crack depths obtained by both methods for each service level, it is evident that the allowable crack depths at penetration calculated by the Local Approach of Limit Load Criteria are almost always smaller than those at fully plastic collapse stresses calculated by the Limit Load Criteria. It was found that the allowable crack depths provided by the ASME Code Section XI are less conservative for crack penetrations.

J Predictions for Defective Pipe Elbows via the Reference Stress Method

In R6, the J-based failure assessment diagram (FAD) method is used in the fracture assessment, and is underpinned by the reference stress J scheme. Therefore, an assessment using the R6 FAD method is equivalent to a J prediction using the reference stress method. In this paper, the effect of global and local limit load solutions for defective elbows on the reference stress and hence the J predictions is investigated using published three dimensional elastic-plastic finite element (FE) J results, in order to create guidance for users to follow when performing structural integrity assessments of defective elbows using the R6 procedure. The results show that using the global limit load solutions recommended in this paper can lead to good and reasonably conservative J predictions. However, the availability of global limit load solutions is very limited. The results also show that using the local limit load evaluated from the local limit load model recommended in this paper can lead to conservative J predictions for most of the cases considered.

Load capacity of the board grillage with two stringers under ice loading

Снизить повреждаемость бортовых перекрытий при ледовых нагрузках можно за счет совершенствования расчетных зависимостей по оценке их несущей способности. Далеко не всегда такие зависимости, приводимые в справочных изданиях, дают верные рекомендации из-за не вполне ясного характера распределения нагрузок в сложных статически неопределимых системах. В справочнике по СМК приводится расчетная зависимость, позволяющая определить несущую способность регулярного перекрытия с двумя стрингерами при действиии локально распределенной нагрузки в пределах прямоугольника. Цель данной работы заключалась в оценке несущей способности реального бортового перекрытия ледокола типа Wind с помощью МКЭ при параметрах ледовой нагрузки, определяемой рекомендациями Морского Регистра РФ, и последующем сравнении полученных результатов с расчетами по теоретической зависимости, приведенной в справочнике. Полученные данные показали, что зависимость в справочнике для оценки несущей способности перекрытия дает удовлетворительно согласующиеся с МКЭ результаты после соответствующего уменьшения числового коэффициента в ней. При анализе несущей способности перекрытия варьировались шпация, толщина обшивки, высота стенок стрингеров и площадь приложения нагрузки. Установлено, что текучесть наблюдается в опорных сечениях шпангоутов и посредине их пролета, а из-за большой ширины присоединенного пояска обшивка у контура перекрытия практически никогда не течет. Полученные МКЭ результаты показали наличие обратно пропорциональной зависимости между предельной нагрузкой и шпацией при фиксированной площади нагружения. Отмечено, что увеличение толщины обшивки несущественно влияет на величину предельной нагрузки при остальных неизменных параметрах перекрытия. Выполненные расчеты позволяют кроме предельной нагрузки оценить также и величины прогибов при упругопластическом деформировании перекрытий, которые затруднительно подсчитать аналитически. To low damage of the board grillages under ice loading is possible by improving analytical relations on estimation of their load capacity. Not always such relations, bringing in manuals, give true recommendations because of complex character of the loads distribution in static indeterminate systems. Im manual on ship structural mechanics is giving analytical relation for determination of load capacity of regular grillage with two stringers under action of localy distributed load in rectangular area. Purpose of this study is to estimate load capacity of real board grillage of icebreaker of type Wind with help of FEM under parameters of ice load recommended in Maritime Register of RF, and following comparison of obtained results with calculation on analytical relation, given in manual. Obtained results show that relation in manual for estimation of load capacity of grillage give satisfactory results corresponding to FEM only after corresponding reducing of numerical coefficient in it. Under analysis of load capacity of grillage, it was changing frame space, thickness of plating, depth of stringers and area of application of load. It was estimated that most loaded zones of frames are their sections near supports and in the mid-span. Because of big width of associated plate the plating near contour of grillage is never yielding practically. Results obtained by FEM show existence of inversely proportional relation between the limit load and space framing under fixed area of loading. It was noticed that increasing of the plating thickness influent not essentially on value of the limit load under all other parameters of grillage unchangeable. Performed calculations allow to estimate limit load and value of deflections under elasto-plastic deformation of grillage, which is difficult to calculate analytically,

Using the criterion of resistibility to assess of a structural limit state

Introduction. Subject of research: behaviour characteristics of an arbitrary structure under the loads that approach the limit load value. Goals: development of an objective and sufficiently universal methodology for the identification of the bearing capacity of a structure, which could allow to stop using any subjective assessments of their limit bearing capacity. Materials and methods. Behaviour characteristics are assessed by analyzing a curve of equilibrium states. The curve is constructed using the characteristic displacement, understood as the generalized displacement q, which energetically matches applied generalized force λ in the sense that the product of λdq is the growth of work performed by generalized force λ in respect of the growth of displacement dq. Results. The article shows that the system’s response, no matter what fixed conditions it is in, is not always sufficient for the assessment of the reliability of the system in case of the variable interaction with the environment. The co-authors use the V.V. Katyushin concept about supplementing the notion of the limit state with the characteristics of the system’s beha­viour determined by the velocity of a change in the system’s response caused by the change in the external action. According to the co-authors’ suggestion, the meter should represent the reduction in the slope of the curve of equilibrium states, which characterizes the loss of resistibility and, consequently, it can be used to assess the closeness of the structure to the state of failure, which arises if the resistibility of the system is equal to zero. The suggestion is to use the value of the slope of the curve of equilibrium states as the limit state, when the resistibility has reduced, and the velocity of deformation intensification has gone up 100 times if compared with the behaviour of an unloaded system. This suggestion is illustrated by the case of the analysis of a reinforced concrete diaphragm of a building. Conclusions. The proposed calculation methodology can be applied in the design of loadbearing structural elements, whose finite-element computational model has components that are different from the rod ones.

Considerations for Analytical Qualification of Tubular Connections for Thermal and HPHT Wells

It is important to complete thermal and high-pressure/high-temperature (HPHT) wells with tubular connections that possess adequate structural integrity and sealing capacity under the severe load conditions typically experienced by these wells throughout their life cycle. Individual premium connection designs are required to be evaluated and qualified through physical tests to broadly adopted industry protocols, such as ISO/PAS 12835: 2013 for thermal wells that experience temperatures from 180°C to 350°C, and ISO 13679:2019 and API RP 5C5:2017 for HPHT wells which experience peak temperatures up to 180°C and pressures greater than 70 MPa. Recognizing the time and capital expenses associated with completing full-scale physical testing of product lines with multiple connection designs of different tubular diameter, weight, and grade, industry is developing a hybrid approach that supplements results from physical qualification tests with numerical/analytical simulation, such as Finite Element Analysis (FEA). The key challenges associated with analytical evaluation are the lack of evaluation criteria and suitable guidelines for analysis methodologies. This paper provides a review of recent work related to the development of sealability evaluation criteria; and presents guidelines to facilitate performance evaluation of tubular connections in thermal and HPHT wells through advanced FEA. For thermal well applications, this paper presents a methodology for quantitative evaluation of sealability of casing connections, as a supplement to the determination of a biased test population using FEA following ISO/PAS 12835:2013 requirement. For HPHT wells, this paper presents considerations for analyzing various testing loads, such as Test Series A (internal and external pressure cycles), Test Series B (internal pressure with bending), Test Series C (thermal and mechanical cycles), and Limit Load Cases. Analysis examples with generic premium connections are presented to demonstrate the use of the proposed analysis methodologies.

Analytical Limit Load Procedure for The Axial Complex Shaped Defect in a Pressurized Pipe

The paper is devoted to elaboration of the analytical O-procedure for limit load analysis of complex shaped axial defect in a pressurized pipe. It is based on the classical lower bound theorem of the theory of plasticity, and consists in construction of the statically admissible solution, where distribution of stress satisfies to the equilibrium equations and strength conditions. O-procedure is an optimization process to get the most favorable stress distribution for providing the maximal pressure. It allows to explicitly account for the variable geometrical and physical parameters. Contrary to other approaches, the derived formula for rectangular defect is only a particular case of the general procedure application. Four different methods for the complex defects are compared. They are: first, ASME, A-, rectangular defect formula combined with RSTRENG, R-, procedure, i.e., A-R approach; second, PCORRC, P-, formula with R-procedure, P-R approach; third, Orynyak's, O-, formula with R-procedure, O-R approach; and fourth, our universal O-procedure. The verification begins for rectangular defects where both theoretical and experimental comparison is performed for A-, P-, and O- formulas. The difference between them is small, provided that all three employ the same characteristic of material, here the ultimate strength. Then theoretical comparison for A-R, P-R, O-R approaches and O-procedure is performed for the artificial complex defects, for two symmetrical rectangular defects, for triangular defect. Experimental comparison between four methods is made based on the well-known University of Waterloo full scale tests.

An Accurate Limit Load Solution for an Anisotropic Highly Undermatched Tension Specimen with a Crack

Plastic anisotropy significantly influences the behavior of structures subjected to various loading conditions. The extremum principles in the theory of rigid plastic solids are convenient and reliable tools for plastic design. The present paper combines the upper bound theorem and Hill’s quadratic yield criterion for orthotropic materials to evaluate the plastic collapse load of a highly undermatched welded tensile panel with a crack in the weld. The base material is supposed to be rigid. The shape of the crack is quite arbitrary. The orientation of the principal axes of anisotropy varies through the thickness of the weld. The upper bound solution is based on an exact solution for a layer of an anisotropic material. This feature of the upper bound solution is advantageous for increasing its accuracy. A numerical treatment is only necessary to find the solution for the uncracked specimen. This specimen has two axes of symmetry, which simplifies the solution. Simple analytic formulae transform this solution into a solution for the cracked specimens with one axis of symmetry and no symmetry. It is shown that the through-thickness distribution of anisotropic properties significantly affects the limit load.

A Study on the Shape Selection of Mechanical Fastening for the Repair of Fighter Wing

A study on optimal shape selection of a mechanical fastening for the repair of crack defect of ROK Air Force F-5 fighter wing was conducted. The crack defect occurred in the spar of the wing, and the technical manual does not specify the repair method. However, ROK Air Force decided to develop a repair technology for this defect in consideration of various logistic conditions. Three repair shapes for the proper repair were devised and the finite element analysis was performed to examine the structural safety of these three connection members. As a result of the structural safety review, two connection members except one were structurally safe with safety margins over zero because the calculated stress values were at or below the yield strength level. Therefore, two connection members were determined to be able to use for repair under the condition that the aircraft operated within the design limit load. The results of this study would be very useful if the same defect occurs in long-term aircraft operated by the ROK Air Force.

Dynamic response and parameter analysis on the vehicle–bridge coupling of cable-stayed bridge under over-limit transportation

PurposeOver-limit transportation has the characteristics of large axle load, large number of axles and lateral distribution width. Under the action of over-limit load, the coupling vibration effect of vehicle–bridge is more obvious, and the deformation of bridge components is large. Thus, research and analysis of the vehicle–bridge coupling dynamic response of long-span bridges under over-limit transportation has practical engineering significance.Design/methodology/approachBased on the principle of invariable elastic potential energy, this paper derives dynamic model of over-limit transportation n-axis flat vehicle. The numerical simulation method is used to model and calculate a cable-stayed bridge, and the static effect of the cable-stayed bridge and the dynamic response of vehicle–bridge coupling under different parameters are compared and analyzed.FindingsThe focus is on the influence of vehicle load and vehicle velocity parameters on the stress and amplitude of different cables under over-limit transportation, and the corresponding variation law is obtained.Originality/valueThe research on the coupled dynamic response of cable-stayed bridges has attracted the attention of many scholars, but there are relatively few studies on the coupled vibration of out-limit vehicles and bridges. In this paper, based on finite element software, a vehicle–bridge coupling model under bulk transportation is established.