Analytical methodologies for buried pipeline design in geohazard areas

In geohazard areas, buried pipelines are subjected to permanent ground deformations, which constitute major threats for their structural safety. Geohazards include seismic fault movement, liquefaction-induced lateral spreading and slope instability, and the corresponding deformations induce severe strains in the pipeline. Calculation of these strains is necessary for assessing pipeline integrity. In the present paper, an analytical methodology is presented and compared with existing analytical and numerical methodologies for stress analysis of buried pipelines. The proposed methodology is also compared with full-scale available experimental results and offers significant intuition on the behavior of buried pipelines subjected to permanent ground deformations. Using the proposed analytical methodology, one may predict the strains developed in the pipeline wall quite efficiently and with good accuracy. Copyright © 2016 by ASME

Analytical model for the strain analysis of continuous buried pipelines in geohazard areas

In geohazard areas, buried pipelines are subjected to permanent ground-induced deformations, which constitute major threats for their structural safety. Geohazards include seismic fault movement, liquefaction-induced lateral spreading, slope instability or soil subsidence, and are associated with the development of severe strains in the pipeline. Calculation of these strains is necessary for assessing pipeline integrity. In the present paper, an analytical methodology is presented that allows for simple and efficient pipeline strain analysis in geohazard areas. The methodology is compared with existing more elaborate analytical methodologies and finite element predictions. The analytical formulation results in closed form expressions and the model contributes to better understanding of buried pipeline behavior subjected to permanent ground-induced deformations. The proposed methodology is directly applicable to fault actions, but it can be also applicable to a wide range of geohazards. Furthermore, using this methodology, one may predict the strains developed in the pipeline wall due to ground-induced actions in a simple and efficiently manner and is suitable for the preliminary design of pipelines. © 2017 Elsevier Lt

Strain-based design of a large-diameter steel water pipeline crossing ground settlement areas

This paper describes the structural design of a large-diameter buried steel pipeline crossing two areas of substantial soil settlement, which impose fault-type actions in the pipeline. Those ground-induced deformations are associated with the development of high levels of strain, well beyond the elastic limit of the pipe material. The present paper describes the application of "strain-based" design approach, towards economically efficient solution, while increasing pipeline safety and reducing risk. Strain demand is calculated first, using a global analysis, through finite element models, developed for the purposes of the present design. The numerical models employ "pipe elements" to simulate the pipeline and "soil springs" to describe the soil and its interaction with the pipeline. Subsequently, the ground-induced strains are calculated and compared with the allowable values. The design makes use of a newly developed concept, the "projection" concept, which increases pipeline resilience and improves lap welded joint performance. The effects of soil conditions on pipeline performance are also discussed. © 2021 ASCE

Fatigue of welded tubular X-joints in offshore wind platforms

The paper is part of the European research program JABACO (2015-2018), on the optimization of design and construction of offshore jacket platforms for supporting large wind turbines (5 - 10 MW) in water depths ranging from 30m to 80m. In particular, the paper describes an experimental investigation on the high-cycle fatigue performance of welded tubular connections, subjected to in-plane bending loading. Experimental results from seven (7) X-joint specimens are presented. The specimens were manufactured with 18-inch-diameter tubes and a brace-to-chord-diameter ratio equal to 1. Furthermore, the brace-to-chord-thickness ratio is equal 0.6, and the brace-chord angle is 90-degrees. The specimens are made of regular carbon steel grade 355, and have been fabricated using two different welding techniques: (a) manual (semi-automatic) welding (5 specimens); and (b) robot (automatic) welding (2 specimens). The comparison of the fatigue design life of those welding methods is a major objective of the present study. Prior to testing, numerical simulations have been performed to determine the critical locations around the weld toe, for proper instrumentation of the tubular specimens in terms of strain gage locations. This research work aims at a critical evaluation of available design standards, towards the development of more reliable design tools and reduction of the construction cost of the platform. Copyright © 2019 ASME

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