Effect of Welded Joint Imperfection on the Integrity of Pipe Elbows Subjected to Internal Pressure (original) (raw)
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Journal of engineering & processing management, 2021
The defects in pipe elbows can, depending on their size and position, affect the integrity and safe service, as well as deformation ability of the piping systems in exploitation. Incompletely filled groove, which is the type of defect examined here, was observed by ultrasonic measurement on the pipeline in the regulation system of the hydro power plant Djerdap. Three-dimensional finite element analysis is performed using Simulia Abaqus software package. First, the models with dimensions of the defects observed by non-destructive examination are formed. Stress and strain fields for different loading types are shown and commented. The influence of the defect dimensions on the pipe elbow load-carrying capacity is determined through plastic collapse loads, which are obtained from bending moment-rotation angle diagrams. Twice elastic slope (TES) technique is applied. Additionally, some more severe defects are considered, in the form of sharp pre-cracks at the bottom of the defect; plastic collapse loads are also determined for these geometries. Both opening and closing bending moments are taken into consideration and the results are discussed and compared to two closed-form solutions from the literature. The influence of the boundary conditions applied for examination of the pipe elbows is commented.
Assessment of the integrity of welded pipes
Zastita materijala, 2014
Assessment of the integrity of welded pipes The subject of the paper is analysis of the integrity of welded pipes made of API J55 steel by high frequency contact welding (HF). Experimental research on the mechanical properties of the base material was conducted on pipes withdrawn from exploatation after 70 000 hours at service. Defect influence of the surface crack on the integrity of pipes was tested using hydrostatic pressure of pipes with axial surface crack in the base material. Fracture behaviour was tested using modified compact specimen (CT), with the initial crack in the base material, welded joint and heat affected zone (HAZ). Critical value of the tensile strength factors K Ic was determined based on the critical value J of the integral J Ic. Apart from the experimental research, based on the derived values of K r and S r and by applying fracture analysis diagram (FAD) an assessment of the integrity of welded pipes with axial surface crack on the outer surface area was conducted.
Marine Structures, 2008
In this paper, analytical expressions for stress concentration factors in pipes subjected to internal pressure and axial force are derived for a number of design cases based on classical shell theory. The effect of fabrication tolerances in simple butt welds is assessed. Analyses based on classical mechanics are compared with results from axisymmetric finite element analyses for verification of the presented methodology. Stress concentration factors are presented for circumferential butt welds in pipes welded together from pipes with different thicknesses, welds at buckling arrestors, welds at flanged connections in pipelines, and welds at ring stiffeners on the inside and the outside of the pipes. It also includes stress concentration factors at end closures in pipes for gas storage. Larger pipes are fabricated from plates with a longitudinal weld. This fabrication process introduces out-of-roundness in the pipes. The actual out-of-roundness is a function of internal pressure. An analytical expression for the bending stress in the pipe wall due to this out-of-roundness is presented. The derived stress concentration factors can be used together with a hot spot stress S-N curve for calculation of fatigue damage.
Damaged welded pipes for oil and gas rigs exposed to internal pressure - failure estimation
Ecf19, 2013
The paper deals with the integrity assessment of API J55 steel casing pipes for drilling rigs, manufactured by high frequency contact welding procedure. The influence of corrosion defects on the pipeline load carrying capacity is determined through pressure test of a pipe with corrosion damages simulated by machining the circular holes. Finite element analysis of the damaged pipe subjected to internal pressure is used for determining the stress/strain conditions in the damaged area of the pipe. Also, numerical model was used for establishing the load carrying capacity of the pipe with different damage levels (i.e. defect depth and length). Several expressions from the literature are used for estimation of the maximum pressure in the damaged section of the pipe, and the solutions are compared with the predictions of finite element models and experimental results.
Structural Integrity Assessment of Welded Pipeline Designed with Reduced Safety
Tehnicki vjesnik - Technical Gazette, 2020
The main goal of this paper was to assess the integrity of welded joints in the main pipeline of the reversible hydropower plant "Bajina Bašta". Japanese steel Sumiten 80P (SM 80P) was used as the parent material. European recommendation for pipeline safety factor is equal to 1.7 and this value was used for calculations of the RHPP "Bajina Bašta", whereas the value recommended by Japanese standards is 2.1. A relatively small safety factor, which is different from the Japanese recommendation (since the material itself is Japanese), represented one of the main reasons for a detailed investigation of the pipeline structural integrity and safety, using the prototype. In the case of pressure vessels, the welded joint is a location of stress concentration, which can act in the same way as residual stresses. Assessment of prototype test results is possible to perform based on stress and strain calculations of vessels with ideal geometry. For this reason, the solution for thin-walled vessels is given, both in elastic and elastic-plastic areas. Numerous tests were performed in order to obtain a reliability assessment necessary for the construction of the pipeline, since the consequences of potential failure would be disastrous in this case. A numerical simulation, based on the experimentally determined mechanical properties of the material used, was also performed in order to obtain the stress/strain distribution. These results were then compared to the experimentally obtained ones, and it was concluded that there is a good level of compliance between numerical and experimental results.
International Journal of Automotive and Mechanical Engineering, 2022
Pipelines are structures used primarily for the pressurized transport of flammable substances, which have higher safety requirements due to the risk of leakage or explosion [1]. New pipelines are needed to meet the growing demand for energy, such as gas and oil, among industrial users. Indeed, over the last 50 years, the latter has emerged as the most costeffective and safest mode of long-distance transportation for large amounts of energy [2]. The length of pipelines in Europe was multiplied by four between 1970 and 2007. For the same time period, however, the failure rate was divided by six [2]. To improve the profitability of this mode of supply, manufacturers have increased both the operating pressure and the pipe diameter. Between 1910 and 2000, the largest pipeline's diameter increased fourfold, while transport pressure increased sixtyfold [3]. All of this was made possible by research that improved the mechanical properties of pipelines as well as tools that allow the severity of defects in these pipes to be assessed. Undoubtedly, as with every metal structure, flaws in the pipeline may develop over time and cause it to rupture. Pipe defects can occur during installation, routine maintenance excavations, or new civil engineering work near the pipes [4]. For example, during pipe maintenance operations, mechanical damage may occur as a result of negligence, clumsiness or a lack of precautions. If site workers are unable to precisely locate the buried pipe, this structure may be subjected to shock by a tool like bucket teeth or construction machine. Most of the time, the incident goes unnoticed or unreported. Mechanical interference caused by foreign object contact accounts for approximately 50% of pipeline damage in Europe and 53.5% in the US [5]. This confirms that external damage causes the vast majority of pipeline ruptures, whether on land or at sea. These flaws can take the form of dents, cracks, or a combination of the two [6]. The structural damage induced by the presence of these deficiencies can be exacerbated if the pipeline is subjected to internal pressure of variable amplitude loading, such as water hammer waves [7]. In fact, transient flows in the pipeline network can be created by pump failure, pipe rupture, or a sudden change in the state of the valve that controls the flow of fluid through the pipeline. This can cause a pressure pulse to travel at high speeds along the pipeline in the form of a pressure wave, causing vibrations that can eventually burst the pipe [8]. The industrialists who specializes in the area of piping networks are concerned about the safety of the population as well as the environment, given the impact that a major failure can have, especially in the case of flammable gases or explosives [9]. Besides that, economic and financial aspects must be considered, as financial losses in terms of public works, pipe replacement, and operating losses are substantial. Thus, breakage prevention is critical, and it is achieved through inspection and analysis of the harmfulness of discovered defects [10, 11]. This analysis necessitates the use of specialized tools in order to assess the potential damage caused by a defect in an internally pressurized pipe. There are several methods in the literature for determining the severity of a crack, dent, notch, or corrosion defect in a pipeline [9-14]. They are frequently developed using limit analysis, fracture mechanics, and notch fracture mechanics. Depending on the type of defect, the appropriate tool is selected. The limit analysis is frequently used to assess defects such as corrosion or dents [9]. In the case of defects such as weld cracks, sharp notches, or a combination of a dent and a notch, a mechanical fracture approach is preferable. ABSTRACT-Pipelines are commonly used to transport energy over long distances. If this structure is subjected to an internal pressure of variable amplitude loading, such as water hammer waves, the structural damage caused by the presence of a defect can be exacerbated. Previous research by the authors resulted in the development of finite element models to evaluate crack and dent defects separately. Each model was used to compare and classify defects in their respective categories based on their nocivity in a metal pipe subjected to internal pressure. The primary objective of this paper is to compare the severity of various defect categories on the same scale. A numerical damage assessment model that considers the interaction effect, as well as the loading history, is used to achieve this goal. It takes the output of the two finite element models, as well as the pressure spectrum caused by the water hammer, as inputs. This model is used to analyze the effect of key parameters that influence the severity of the defects, as well as to compare and classify the various types of dent defects with the various types of crack defects found in pipes subjected to variable amplitude loading.
The Consequences of cracks formed on the Oil and Gas Pipelines Weld Joints
International Journal of Engineering Trends and Technology, 2017
Weld cracking is one of the main failure modes in oil and gas (O & G) pipelines. Cracks are the most severe of all weld defects and are unacceptable in most circumstances. A simple existing defect on the pipeline after welding can generate a catastrophic fracture. The major cause of a crack is when internal stresses exceed the strength of the weld metal, the base metal, or both. If undetected, the cracking defects can act as stress concentration sites which lead to premature failure via fatigue, as well as offer favourable sites for hydrogen assisted cracking and stress corrosion cracking. For welded metal products such as deep sea oil and gas transportation pipes, such defects heighten the risk of catastrophic in-service failures. Such failures can lead to devastating environmental, economic, and social damage. Knowing the basics behind why cracks happen, a welder can prevent those cracks from occurring in the first place. Using different literatures, this paper reviews on the consequences of cracks on the oil and gas pipelines weld joints focusing on favourable welding processes for pipeline manufacturing, causes and effects of various types of weld cracks. It further highlights the importance of inspection, maintenance and repair of weld joints cracks. Hence, the knowledge of weld joint cracks mechanisms for any person that deals with pipelines is very important.
Strength of Welded Pipe-plate Joints
The distribution of stresses of the welded pipe-plate joints is complicated. To study the strength of the joints, the parameter analyses were undertaken using nonlinear finite element method and uniform design approach. The pipe diameter, thickness, the plate width, height, and thickness were considered. Three kinds of loading conditions on the plate-the axial force, the moment, the combined axial force and moment were analyzed. The strength formulas of the joints are proposed by regression analysis. The verification tests demonstrate the reliability of the formulas.
The local stress state of the pipeline with axial and angular weld misalignment
Scientific journal of the Ternopil national technical university, 2019
The paper is devoted to the evaluation of the stressed state of the shell containing two common defects in the weld shapeangular and axial misalignment at the same time. Expressions for stress resultants and stress concentration factors for axial and angular misalignment are proposed. The analytical approach is tested by means of numerical calculations for the internal pressure.
The structural integrity of high-strength welded pipeline steels: a review
International Journal of Structural Integrity, 2020
PurposeThe key purpose of conducting this review is to identify the issues that affect the structural integrity of pipeline structures. Heat affected zone (HAZ) has been identified as the weak zone in pipeline welds which is prone to have immature failuresDesign/methodology/approachIn the present work, literature review is conducted on key issues related to the structural integrity of pipeline steel welds. Mechanical and microstructural transformations that take place during welding have been systematically reviewed in the present review paper.FindingsKey findings of the present review underline the role of brittle microstructure phases, and hard secondary particles present in the matrix are responsible for intergranular and intragranular cracks.Research limitations/implicationsThe research limitations of the present review are new material characterization techniques that are not available in developing countries.Practical implicationsThe practical limitations are new test methodol...