Search

Subsea pipelines subjected to impacts are prone to generating significant deformations and residual stresses, which could reduce their structural integrity and increase the risk of failure. This paper introduces analytical and numerical frameworks aimed at predicting residual stress behavior induced by subsea pipeline impacts. An empirical formula to regulate residual stress levels in extensively deformed submarine pipelines is derived through a parameter-fitting method. This formula enables the swift and accurate computation of the residual stress magnitudes in such pipelines. Abaqus is employed to simulate the residual stresses in large-deformation submarine pipelines. The results of the finite element analysis are validated through experimental work. A comprehensive database is constructed via the finite element method to fit an empirical formula for residual stresses in large-deformation submarine pipelines. The empirical formula places particular emphasis on the influence of the diameter-to-thickness ratio and dent depth on the residual stresses. It is crucial for pipeline design and maintenance. [ABSTRACT FROM AUTHOR]

Subsea pipelines subjected to impacts are prone to generating significant deformations and residual stresses, which could reduce their structural integrity and increase the risk of failure. This paper introduces analytical and numerical frameworks aimed at predicting residual stress behavior induced by subsea pipeline impacts. An empirical formula to regulate residual stress levels in extensively deformed submarine pipelines is derived through a parameter-fitting method. This formula enables the swift and accurate computation of the residual stress magnitudes in such pipelines. Abaqus is employed to simulate the residual stresses in large-deformation submarine pipelines. The results of the finite element analysis are validated through experimental work. A comprehensive database is constructed via the finite element method to fit an empirical formula for residual stresses in large-deformation submarine pipelines. The empirical formula places particular emphasis on the influence of the diameter-to-thickness ratio and dent depth on the residual stresses. It is crucial for pipeline design and maintenance.

In this article, the concept of low-velocity impact resistance in composite materials is presented. Three existing expressions (e.g., bilinear, parabola, and exponential) that show the relationship between the dent depth and impact energy of composite laminates subjected to low-velocity impact are presented. Because of some flaws in these expressions, new supposed functions between impact energy and impact dent have been established. By means of existing ASTM D 7136 tests and simulation analysis, the new expressions are verified, and the nature of dent formation in composite materials is well explained. The conclusion is reflected in the ending part.

Suspended submarine cables are prone to likely mechanical damages due to ship anchors, which represent a significant threat to the reliability of power transmission and information communication networks. This paper is aimed at presenting a detailed investigation to the dynamic response of a ship anchor impacting the suspended section a submarine cable in order to reduce the risk of cable damage. In this regard, a three-dimensional and dual nonlinear model of the anchor affecting a subsea cable is established using ABAQUS finite element analysis software. The damage effect due to the ship anchor on the suspended and buried-in-soil sections of the cable is studied. Results show that when a ship anchor hits a suspended section of the subsea cable, the mechanical stress is concentrated at the impacted point and is progressing to both sides of the suspended section with a significant cable deformation. On the other hand, the buried section of the cable suffers from a short impact process, and the deformation is relatively small. To reduce this impact effectively, a detailed technical comparison of two common dumping and filling methods is conducted, and the better protection method is proposed.

Residential and commercial buildings often use metal roof panels. In contrast, the dent resistance of steel panel subjected to impact of hailstone is insufficiently studied. The analysis of the whole experimental setup has been carried out using a finite element model (FEM). Artificial hailstones were launched at different steel sheets based on their size at different terminal velocities for comparison with natural hailstones that remained intact after impact. Based on comparisons between experimental results and the FE model, the simulation approach and material properties are evaluated. Additionally, an equation to predict dent depth using kinetic energy and stress is presented. The results of this study provide an understanding of both hail and roof panel failure modes and their effect on dent resistance. Experimental observations and numerical simulations in this study were well matched with results obtained using analytical models. In addition, the proposed equation overestimates dent depths compared with those found in the tested steel sheets, while underestimating the ones determined by finite element models. [ABSTRACT FROM AUTHOR]

Mechanical damage can cause immediate or delayed failure of the pipe. The dent is the main form of mechanical damage. According to the Oyane ductile fracture criterion, the finite element method was used to simulate the axial simple dent caused by the construction stage. Analyzed the change of pipeline ductile damage degree in different pit sizes, pipe sizes and pipe pressures, the relationship between the dents depth and the ductile damage degree is obtained, which provides the theoretical basis for the safe design of the oil and gas pipelines with axial indentation during the construction stage.

The profile of several dents on a propeller with a diameter of about 2500 mm were measured by the stylus probe method. The predominant mechanism of action during cavitation was found to be the impact of jets occurring at an angle to the blade surface. The diameter of the jets reaches 5 mm, and the impact velocity is several hundred meters per second, while the deformation of the material of dents from single blows of the jets reaches 10%, and the depth of the dents is 0.3 mm. At such depths of dents, the thickness of the hardened layer under the surface of the wear zone can be 3 mm or more, which allows evaluating the contribution of electrochemical corrosion to the total wear of propellers during cavitation in a different way. When testing screw alloys for cavitation wear using ultrasonic magnetostrictive vibrators, the replacement of fresh water with sea water is unreasonable; the corrosive action of sea water can lead to plasticization of the surface layer of the metal due to facilitated dislocation discharge. This is unlikely on propellers, since the depths of work hardening of the blade surface layer are two orders of magnitude greater than the thickness of the plastically deformed layer obtained in experiments with ultrasonic vibrators. [ABSTRACT FROM AUTHOR]

The properties such as dent depth, residual compressive strength and compressive failure strain of 3 groups of T800 carbon fiber composite laminates with the same layer ratio and different thicknesses were tested. The results show that there inflection points are existed both in impact energy-dent depth curves and dent depth-residual compression strength curves. The inflection points of the 3 groups are at the depths of 0.70 mm, 0.76 mm and 0.45 mm respectively, which are less than the depth of dent (1.3 mm) corresponding to barely visible impact damage (BVID). With the same ply ratio, the greater the thickness of composite laminates, the better the impact damage resistance.

Offshore jacket platforms are widely used for oil and gas extraction as well as transportation in shallow to moderate water depth. Tubular cross‐sectional elements are used to construct offshore platforms. Tubular cross sections impart higher resistance against hydrodynamic forces and have high torsional rigidity. During operation, the members can be partially or fully damaged due to lateral impacts. The lateral impacts can be due to ship collisions or through the impact of falling objects. The impact forces can weaken some members that influence the overall performance of the platform. This demonstrates an urgent need to develop a framework that can accurately forecast dent depth as well as dent angle of the affected members. This study investigates the use of an adaptive metaheuristics algorithm to provide automatic detection of denting damage in an offshore structure. The damage information includes dent depth and the dent angle. A model is developed in combination with the percentage of the dent depth of the damaged member and is used to assess the performance of the method. It demonstrates that small changes in stiffness of individual damaged bracing members are detectable from measurements of global structural motion. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of High Pressure Physics is the property of Chinese Journal of High Pressure Physics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The defect of pipe dent has a great threat to the safety of oil and gas pipe transportation. In this paper, the numerical calculation model of pipe extruded by cylindrical indenter at vertical and transverse direction was established. Effects of indenter displacement, indenter radius and internal pressure on the dent behavior were discussed. The results show that different action forms of the indenter would cause different dent behaviors. A large degree of plastic deformation is formed at the edge of the cylinder end of the indenter when indenter made a vertical action. The larger the indenter radius is, the larger the plastic deformation is. But when the indenter extrudes transversely, the change in the indenter radius has little influence. For pressure pipeline, the strain in the dent fluctuates in a certain degree, and the plastic strain is larger than that in the non-pressure pipeline, but the dent depth would be lower in the end. Under different conditions of internal pressure, the laws of dent with "non-pressure" and "loading pressure" are the same, and the dented laws of "pressure" and "unloading pressure" are consistent. The strain and the depth of the dent achieve an extreme point or maximum near the edge of the dent. [ABSTRACT FROM AUTHOR]

The plate dent test is one of the simplest tools for fast determination of the detonation pressure. The test is based on the observation that the detonation pressure correlates with the depth of the dent produced by a detonating explosive on a metal witness plate. The present study is aimed at developing a model for estimating the dent depth, which is used not only to obtain the detonation pressure, but also to evaluate the brisance relative to a reference explosive. It is shown that the experimental dent depth values for CHNO and CHNOClF explosives can be successfully reproduced by a model based on few parameters, namely: loading density, number of moles of gaseous detonation products per gram of the explosive, and average molecular weight of the gaseous products, where the number of moles and the mean molecular weight of the gaseous products are calculated according to the [H2O-CO2] arbitrary decomposition assumption. Furthermore, the predicted values of the dent depth and the Kamlet-Jacobs method are used to estimate the detonation pressure for 37 explosives. The results show that the pressures obtained on the basis of the dent depth values are in better agreement with experimental/thermochemical code data than the predictions of the Kamlet-Jacobs method. [ABSTRACT FROM AUTHOR]

Dented defects pose a great threat to the safety of oil and gas pipeline transportation. In this paper, dent behavior of a pipeline caused by a spherical indenter was investigated. Effects of thickness, indenter displacement, indenter radius and pipeline internal pressure on the stress, strain and depth of the pipeline dent are discussed. The results show that internal pressure has a great effect on the pipeline dent. When the internal pressure increases, folds appear on the pipeline wall. With the increasing of wall thickness and indenter displacement, the stress, plastic strain and dent depth increase. But the radius of the indenter has a little effect on the dent's stress and strain. In general, the strain and the depth of the dent achieve an extreme point or maximum near the edge of the dent. [ABSTRACT FROM AUTHOR]

The ability to visually detect damage from impact events is a common concern for carbon/epoxy composite laminates, particularly because composite materials can sustain impact damage in forms such as delamination and backside fiber breakage that is not directly visible at the site of the impact. Therefore, a relationship drawn between the internal damage level and visibility of surface dents would be useful. An experimental investigation is presented on the relationship between visual detectability and the extent of internal damage created by low-velocity impacts. The specimens examined were 8, 16, and 24 ply carbon/epoxy panels impacted by tips of radii: 12.7, 25.4, 50.8, and 76.2 mm. In order to quantitatively describe the visibility of the damage, the depth and span of the surface dents were considered. The results indicate that there are direct relationships between visible and internal damage, but that these relationships are strongly dependent on the radius of the impact tip. Small radius impactors can leave significant visual evidence (i.e. surface dent) without creating internal damage, while the larger radius blunt impactors can create large-area internal delamination without leaving any visual evidence. Therefore, the visual detectability of impact damage is highly dependent upon tip radius, and the level of internal damage cannot be determined based on visual observation alone, especially since in practice, the radius of an impacting object is not always known. [ABSTRACT FROM AUTHOR]

Dent-corrosion defects are a typical combination of defects and pose a significant threat to the safety and integrity of energy pipelines. In general, the corrosion features rather than dents are considered the primary factor of fitness-for-service of pipelines containing a dent-corrosion defect. In this work, a finite element (FE) based model was developed to predict the failure pressure of pipelines containing a dent-corrosion defect and investigate its dominant factor. Parametric analysis results demonstrated that the presence of dents reduced the failure pressure of corresponding pipelines containing a single corrosion defect. The dominant factor of the failure pressure changed from corrosion feature to dent feature if (1) an increase in dent depth and a decrease in the pipe diameter-to-thickness ratio, (2) exceeding the critical dent depth by 8% of diameter (D), and (3) below the critical indentation radius by 10% D. Longitudinal dent gave a significant reduction of the failure pressure, making dent feature a dominant factor; Oppositely, the effect of the circumferential dent was marginal. • The presence of dents reduces the failure pressure of corroded pipelines. • Parameter effects on failure pressure of combined defected pipelines are investigated. • The dominant factors of failure pressure under different conditions are determined. [ABSTRACT FROM AUTHOR]

Dent is a common type of defect in oil and gas pipelines and the assessment on dented pipelines is carried out with major international standards and specifications based on dent depth as the evaluation criteria. However, such evaluation criteria based on depth does not account for the impact of various parameters (e.g. parameters of dent, parameters of pipeline and the internal pressure of pipeline) on the evaluation result, as a result, many dented pipelines lose their efficacy, even though they meet the depth-based standards. The influence of parameters changes on the damage degree of II-type dented pipelines is investigated on the basis of Oyane's ductile fracture criterion and by the method adopting finite element numerical calculations. Finally, the non-linear regression analysis is conducted and based on the outputs, a specific expression of dent depth and pipeline damage degree is also acquired within a certain scope of application. [ABSTRACT FROM AUTHOR]

A defect that contains both dent and crack, often known as dent–crack defect, may lead to a failure due to rupture or leak in the pipe wall. Hence, the pipeline operator becomes concerned about the performance and safety of the pipeline when a dent–crack defect is diagnosed. A research was recently completed at the Centre for Engineering Research in Pipelines, University of Windsor to study the effect of the crack depth on the safe pressure capacity (burst strength) of 30-inch diameter and API 5L X70 grade linepipe. This study found that the dent–crack defect with crack depth of 70% of wall thickness can reduce the pressure capacity by 55%. This paper discusses the test specimens, test setup, test procedure, test results, and data obtained from finite element analyses. [ABSTRACT FROM AUTHOR]

This paper deals with the origin of permanent indentation in composite laminates subjected to low-velocity impact. The three-point bending test is used to exhibit a non-closure of matrix crack which is assumed as a cause of permanent indentation. According to the observation at microscopic level, this non-closure of crack is produced by the blocking of debris inside matrix cracking and the formation of cusps where mixed-mode delamination occurs. A simple physically-based law of permanent indentation, “pseudo-plasticity”, is proposed. This law is qualitatively tested by three-point bending finite element model and is lastly applied in low-velocity impact finite element model in order to predict the permanent indentation. A comparison between low-velocity impact experiments and simulations is presented. [ABSTRACT FROM AUTHOR]

Abstract: In the present work the plastic deformation of a thin rectangular polycarbonate armor plate subjected to single and multiple impacts was investigated in detail. The impacts were conducted on a horizontal and diagonal path to explore the plate vulnerability against the in-coming single and multiple projectiles striking at various locations. Single impacts revealed the overall trend in plate dent sizes and thickness reductions on the horizontal and diagonal paths. Results were compared with previous research [Shah QH, Abakr YA. Effect of distance from the support on the penetration mechanism of clamped circular polycarbonate armor plates. International Journal of Impact Engineering 2008;35:1244–50] conducted on circular armor plate for validation purposes. The single impact data scatter necessitated to conduct repeated impact tests at reduced number of locations to search for a definite answer for the possible failure process in the vicinity of the clamped edges of the plate. An accelerated plastic deformation resulting in early perforation was found to occur in the diagonal plate corner compared to the plate center impact position or close to a straight clamped edge. Multiple impact results presented can be significantly helpful in designing rectangular shape polycarbonate armor plates to enhance safety. LSDYNA was used to simulate the impact event for the plate midpoint, the horizontal edge, and the diagonal edge. The results show a close agreement with the experimental work. [Copyright &y& Elsevier]

Abstract: Quasi-static indentation tests on composite laminates have been performed. Thermal deply and C-scan techniques are used to observe the internal damage characteristics of laminates induced by static indentation. The results indicate that the dent depth increases slowly and almost linearly as the force is lower than its maximum. The observation shows that the damage induced at this loading stage includes matrix cracking and delamination only. Once the force exceeds the maximum, the dent depth increases sharply while the force remains almost unchanged. Deply test results demonstrate that the transition to rapid increase in dent depth is due to the fiber breakage produced at this loading stage. The results also indicate that the damage resistance of a composite laminate can be characterized by the maximum contact force. On the basis of this principle and test results, it is concluded that the damage resistance of toughened composite is much higher than that of brittle one. [Copyright &y& Elsevier]

• The ductile damage degree of dented pipes was studied based on the Oyane ductile fracture criterion. • The change of the ductile damage integral value with the change of parameters during each loading process were analyzed. • The relationship between the pipeline damage and the depth of the dent were analyzed. Dent is one of the most common defects in mechanical damage of oil and gas pipelines. Most of the dents generated during pipeline construction are unconstrained dents, and rebound will occur during service of the pipeline. The dent defect can be considered as ductile damage. Taking X52 steel pipe as the research object, the rebound process of unconstrained dents in service is numerically simulated. Based on the Oyane ductile fracture criterion, the ductile damage degree of dented pipes affected by multiple factors was studied. The change of the ductile damage integral value with the change of parameters during each loading process of the pipeline and the relationship between the pipeline damage and the depth of the dent were analyzed. The results show that the analysis results based on the ductile damage model are in accordance with the conclusions of the existing research, and the ductile damage integral value of the pipeline changes with the depth of the dent in a reasonable law, which shows that the ductile fracture criterion can be used for the safety evaluation of dented pipeline. [ABSTRACT FROM AUTHOR]