Joint Strength or "Efficiency" Factors of Steel Lap Welded Joints for Use in Water Conveyance

Joint "efficiency" factors are proposed for pressure vessels, piping, and pipelines by ASME standards. For the particular case of non-radiographically-tested lap-welded joints, a low value of joint "efficiency" is proposed. This low value has raised some concerns regarding the use of welded lap joints in geohazard or seismic areas, where significant axial stresses and strains are developed, as a result of ground movement. The paper discusses the joint efficiency concept, mainly in relation with the corresponding failure mode of the pipeline, based on recent experimental observations and numerical simulations. The conservativeness of the ASME "joint efficiency" values for lap-welded joints is demonstrated. Furthermore, based on experimental evidence, it is shown that lap welded joints can sustain significant deformation, without loss of pressure containment. The conclusions from this paper support the argument that lap welded joints constitute a simple, efficient, and economical solution for pipeline joints in seismic areas. © 2019 American Society of Civil Engineers

The effect of spiral cold-bending manufacturing process on pipeline mechanical behavior

Large-diameter spiral-welded pipes are employed in demanding hydrocarbon pipeline applications, which require an efficient strain-based design framework. In the course of a large European project, numerical simulations on spiral-welded pipes are conducted to examine their bending deformation capacity in the presence of internal pressure referring to geohazard actions, as well as their capacity under external pressure for offshore applications in moderate deep water. Numerical models that simulate the manufacturing process (decoiling and spiral cold bending) are employed. Subsequently, the residual stresses due to cold bending are used to examine the capacity of pipe under external pressure and internally-pressurized bending. A parametric analysis is conducted to examine the effect of spiral cold forming process on the structural behavior of spiral welded pipes and the effect of internal pressure on bending capacity. The results from the present study support the argument that spiralwelded pipes can be used in demanding onshore and offshore pipeline applications. © Copyright 2016 by ASME

Buckling of internally-pressurized spiral-welded steel pipes under bending

The mechanical behavior of spiral-welded large-diameter steel pipes is simulated, with the purpose of defining their bending deformation capacity against local buckling. The steel pipes are candidates for hydrocarbon onshore pipeline applications with diameter-to-thickness ratio D/t equal to 53 and 69, and are subjected to longitudinal bending under internal pressure levels ranging from zero to 75% of the nominal yield pressure. Initial geometric imperfections are considered in the form of short-wave axial wrinkles and girth weld misalignment, whereas residual stresses are taken into account as computed from a special-purpose finite element simulation of the spiral bending process, which also accounts for both de-coiling process and hydrotesting. The sensitivity of critical bending curvature on the level of internal pressure is examined, the value of buckling wave length is discussed and the effects of hydrotesting after spiral forming on structural performance are also investigated. Finally, the value of critical bending curvature is compared with analytical and empirical equations, widely used in pipeline design applications. The results of the present study determine the main parameters affecting the buckling deformation capacity of large-diameter spiral welded pipes in a strain-based design framework, and indicate that these pipes can be used in demanding pipeline applications, such as in geohazard areas. © 2018 Elsevier Lt

Modelling of spiral-welded pipe manufacturing and its effect on pipeline structural performance

The increasing use of large-diameter spiral-welded pipes in demanding hydrocarbon pipeline applications constitutes an engineering challenge, which requires the definition of an appropriate strain-design framework. In the course of a large European project, numerical simulations on spiral-welded pipes are conducted to examine their bending deformation capacity in the presence of internal pressure, and their capacity under external pressure. The manufacturing process of spiral-welded tubes consists of two steps: (a) the decoiling process and subsequently, (b) cold bending process. Numerical models are developed in finite element software ABAQUS/Standard for the simulation of the above manufacturing steps. Upon completion of the manufacturing process, the residual stresses due to cold bending are calculated, and are used to examine the capacity of pipe under external pressure and bending capacity. The results from numerical models are compared with available experimental results. Furthermore, a parametric analysis is conducted in order to examine the effect of spiral cold forming process on the structural behavior of spiral welded pipes. © Copyright 2016 by the International Society of Offshore and Polar Engineers (ISOPE)

The effect of spiral cold-bending manufacturing process on pipeline mechanical behavior

Large-diameter steel pipes, fabricated through the spiral-welding manufacturing process, are extensively used in onshore pipelines for the transmission of energy (hydrocarbon) and water resources. However, their use in demanding applications, such as geohazard areas or in offshore applications has been very limited. Safeguarding the structural integrity in such areas of those pipes requires an efficient strain-based design framework. Bending deformation capacity in the presence of internal pressure is the major loading case under geohazard actions, whereas external pressure capacity governs the mechanical design in moderate-deep offshore applications. To predict accurately the structural performance of spiral-welded pipes, the cold-bending manufacturing process should be taken into account. In the present paper, numerical models are developed simulating both the cold-bending process (decoiling and spiral bending) and the structural response of the pipe subjected to the loading conditions under consideration. The numerical modes have been verified against experimental results of spiral pipes conducted in the framework of a European research project. A parametric analysis is also conducted to examine the effect of spiral cold forming process on the structural behavior of spiral welded pipes. The results from the present study indicate that spiral-welded pipes can sustain significant amount of bending deformation and external pressure, in favor of their use in demanding onshore and moderately deep offshore pipeline applications. © 201

Experimental Results of Steel Lap Welded Pipe Joints in Seismic Conditions

Welded lap joints are commonly used in large-diameter steel pipelines for water transmission. Their structural performance constitutes a key issue for safeguarding pipeline structural integrity with no loss of pressure containment, required even after a severe seismic event. Full-scale experiments are presented herein, and are part of an extensive project sponsored and coordinated by Northwest Pipe Co. on the structural performance of welded lap joints under severe ground-induced (seismic) actions. In the companion paper "Numerical Simulation of Steel Lap Welded Pipe Joint Behavior in Seismic Conditions" numerical simulation of the experiments are presented. The paper describes a series of large-scale experiments on welded lap joints in 25.75 in outside diameter steel pipes, with wall thickness of 0.135 in (3 specimens) or 0.250 in (3 specimens). The specimens were internally pressurized to 40% of yield pressure, and then subjected to four-point bending. Measurements of the bending load, characteristic displacements, and local strains at the joint area are reported. In all tests, the welded lap joints tested were capable of sustaining remarkable bending deformation, without any loss of pressure containment. This behavior supports the argument that welded lap joints, if appropriately constructed, can be used in seismic areas where severe and permanent ground-induced actions in the pipeline may occur. © 2018 American Society of Civil Engineers

Finite Element Analysis of Steel Lap Welded Joint Behavior under Severe Seismic Loading Conditions

The present paper extends the experimental and numerical research presented at the ASCE 2018 conference. The paper is numerical, based on a shell finite element simulation of the welded lap joint subjected to internal pressure and structural loading, which accounts for the bell formation process, the corresponding residual stresses, and the presence of initial (geometric) imperfections of the cylindrical pipes. Previous numerical simulations of the experiments presented in the 2018 conference, have shown a very good comparison between the numerical results and test data. The present paper has the following two purposes: (a) extend the numerical results for the case of axial compression loading, in addition to the case of bending; and (b) examine the effects of pressure on the mechanical response of welded lap joints. Towards the above purposes, two 24-inch nominal diameter pipes with thickness equal to 0.135 in. and 0.25 in. will be considered, similar to those tested in the prior experiments. The pipes contain welded lap joints with single and double weld and are pressurized first to a certain level (up to 50% of yield pressure) and subsequently, they are subjected to either axial compression or bending, well into the plastic regime of the steel material. The numerical results are used for elucidating some interesting issues of welded lap joint behavior under severe axial and bending deformation, allowing for determining the ultimate load deformation capacity of those joints in geohazard and seismic areas, where severe ground-induced actions are expected, towards minimizing the risk of failure. © 2019 American Society of Civil Engineers

A new concept for improving the structural resilience of lap-welded steel pipeline joints

Lap-welded steel joints are widely used in steel pipelines for water transmission, and their structural resistance is essential for safeguarding pipeline integrity and functionality after severe earthquakes or other geohazards. These pipelines are thin-walled with a diameter-to-thickness ratio ranging between 100 and 240 and are susceptible to buckling. The present paper is part of a longtime research project on the structural performance of lap-welded steel pipeline joints subjected to severe inelastic deformations, motivated by the need of pipeline safety in geohazards areas. The work described in the present paper focuses on the mechanical behavior, analysis, and design of a new seismic resistant lap-welded joint which was developed to improve the structural performance of lap-welded steel pipelines. Analysis consists of extensive finite element simulations, supported by a series of special-purpose full-scale experiments, on the mechanical response of the new lap-welded joints subjected to severe structural (axial and bending) loading conditions. The proposed joint consists of the standard lap weld configuration, enhanced by a small geometric projection introduced at a specific location near the field-applied fillet weld. The numerical and experimental results demonstrate that under severe compressive loading, this enhancement of the standard lap-welded joint results in consistent and preferential buckling of the steel pipe cylinder and not the lap-welded joint. The proposed joint effectively allows for the steel pipeline resistance to not be limited by the compression capacity of the standard lap-welded joint and offers an efficient, reliable, and economical solution for lap-welded joints in steel water pipelines constructed in geohazard areas. © 2021 Elsevier Lt

Bending response of lap welded steel pipeline joints

The paper presents a combined experimental and numerical investigation of the bending response of lap welded joints in pressurized steel water pipelines. It is motivated by the structural performance of large-diameter steel pipelines used for water transmission in seismic and geohazard areas, where the pipeline may be subjected to severe permanent ground-induced actions. A series of large-scale four-point bending experiments on lap welded joints has been performed, and rigorous finite element numerical models have been developed for conducting extensive numerical simulations. The numerical models account for the bell forming process and the corresponding residual stresses, as well as the presence of initial geometric imperfections on the pipeline wall. A very good comparison has been found between experimental results and numerical simulations in terms of both global response and local strains developed at the vicinity of the weld. The finite element models are also employed for elucidating some interesting features of lap welded joint behavior under severe bending deformation, towards determining the joint strength, its deformation capacity and the evolution of strain at different deformation stages. The experimental and numerical results indicate that lap welded joints, can sustain a significant level of bending deformation and strain, without loss of pressure containment, and can be used in geohazard areas, where severe permanent ground-induced strains on the pipeline wall are expected to develop. © 2020 Elsevier Lt

A Novel steel pipe joint for enhancing pipeline seismic resilience i: Development and validation

During the last four years, an extensive experimental project has been launched to determine the structural performance of lap welded joints under ground-induced deformations, mainly due to severe seismic events. The research consists of full-scale physical experiments, supported and validated by numerical finite element simulations. Previous experimental results indicated a remarkable strength and deformation capacity of the standard lap welded joints without loss of water containment. The latest phase of the research focuses on the behavior, analysis, and design of a new seismic resistant lap welded joint. Results of a series of additional full-scale experiments on the structural performance of the new lap welded joint under strong axial and bending loading conditions are presented, supported by finite element simulations. The new lap welded joint comprises the standard lap weld configuration with an additional small geometric projection introduced at a specific location near the field applied fillet weld, resulting in consistent buckling of the steel pipe cylinder and not the lap weld joint, during extreme loading. The proposed joint, referred to as Seismic Resilient joint or SR-joint (patent pending), offers an efficient, reliable, yet economical solution for welded joints in steel water pipelines constructed in seismic areas. © ASCE