Revision as of 09:46, 14 May 2021

Abstract

eer-reviewed\nThis chapter examines the importance of “where” mobile work/life practices\noccur. By discussing excerpts of data collected through in-depth interviews\nwith mobile professionals, we focus on the importance of place for mobility, and\nhighlight the social character of place and the intrinsically social motivations of\nworkers when making decisions regarding where to move. In order to show how\nthe experience of mobility is grounded within place as a socially significant construct,\nwe concentrate on three analytical themes: place as an essential component\nof social/collaborative work, place as expressive of organizational needs and characteristics,\nand place as facilitating a blending of work/life strategies and relationships.\nACCEPTED\nPeer reviewed

Document type: Part of book or chapter of book

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2. Numerical modeling

In this study, an X80 grade steel pipeline with corrosion defect is modeled. According to the previous analysis, the local stress state of buried corrosion defective pipelines is complicated under the action of unreasonable ground overload. Meanwhile, the focus of this paper is to conduct a safety assessment of buried corrosion defective pipelines under given conditions. Generally, the shape of corrosion defects is irregular. To quantify the shape of corrosion defects, it is necessary to reasonably simplify the model corrosion defects to apply the results to various geometric shapes [19-20]. In many industry standard specifications such as DNV and modified B31G, the maximum corrosion depth (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle d}

), width (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle W} ) and length (Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle L} ) are used to describe the pipeline corrosion defects. If the defect depth profile is relatively smooth and does not present multiple major peaks in depth, a corrosion defect can be considered as a regular shape [20]. The shape of the corrosion defect of buried pipelines is simplified as a rectangular volume defects and rounded the corners in this paper, as shown in Figure 1, which is a common used method in literature [13,17,21].

Numerical analysis of the buried pipeline under the ground loads is conducted by using the FE software ABAQUS6.14. The diameter of the pipeline is 0.66m, and the wall thickness is 8mm. The length of soil along the axial is selected 30 times the pipe diameter, and the height and width are 9 times and 15 times the pipe diameter, respectively, according to the previously published article [1]. Therefore, the whole size of the soil is Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle 20{\rm m}\times 10{\rm m}\times 6{\rm m}} , and the buried depth is 1m. Considering that the model and boundary conditions have obvious symmetry, a quarter model is used for calculation, in order to improve the calculation efficiency. The FE model of buried corrosion defect pipeline under ground overload is shown in Figure 2. The equivalent pressure is used to describe the ground overload, and the ground overload directly acts on the soil surface above the corrosion defect pipeline, as shown in Figures 2(a) and (c). The pipeline corrosion defect is simplified as a rectangle with rounded corners, and the detailed local shape is shown in Figure 2(d).

The bottom boundary conditions of the model are fixed constraints, and the symmetry constraint is used on the symmetry plane (i.e. the XY plane and the ZY plane). The upper surface of the model is free, and the normal displacement of the outer end faces is restricted to prevent the soil from collapsing. The contact pair algorithm is used to simulate the interface between the outer surface of the pipe and the surrounding soil. And set the friction coefficient as 0.4 [22]. The contact algorithm is widely accepted to simulate the nonlinear behavior of pipe-soil contact, and it can truly simulate the contact force of underground pipeline and soil [2,8].

The material properties of X80 are given in Table 1, and the stress-strain method of Ramberg-Osgood (R-O) power-hardening is used in the FE model to describe real stress-strain behavior of the high grades of pipe steels, as shown in Eq.(1) [23]

where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle \varepsilon}

is a strain, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle  \rho  }
is stress, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle E  }
is Young’s modulus, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle \sigma_y  }
is yield strength, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle  \sigma_u }
is ultimate tensile strength, and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle K }
and Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle n}
are R-O model parameters, which depend on the materials. It is 0.079 and 12 for X80 steel, respectively.

Pipeline backfill soil is a heterogeneous soil with high compressibility, viscoelasticity and low shear resistance [3]. Under ground overload, the buried pipeline is mainly subjected to the top soil pressure of the backfill generated by the self-weight of the backfill, which increases with the depth of the pipeline buried depth. The soil adopts the Drucker Prager constitutive model, and the shear strength of the soil is reflected by selecting the friction angle and cohesive force. The change of the yield surface is adjusted by setting the cohesive force [24]. It is suitable for pressure-sensitive soil, because it can well reflect the unequal tension and compression characteristics of rock and soil, and is widely used. The parameters of the soil around the pipe are given in Table 2 [25].

Failure models of the buried pipeline are varied. Typical failure modes of the buried pipeline include strength failure, buckling failure and excessive deformation [10]. Under ground overload, large local stress and deformation will occur in the corrosion defect pipe. The main failure modes for corrosion defect pipeline are local strength failure and excessive deformation. Generally, the failure criterion of the pipeline is based on the elastic failure and plastic failure adopted the stress based failure criterion for defect pipeline failure pressure prediction under cyclic loads [7].

In this paper, failure criteria based stress is used to describe the failure of corroded pipes. The pipeline failure is considered to occur when the max von Mises stress exceeds the allowable value at the location of the pipeline corrosion defect. The failure criterion is:

where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle {\sigma }_{mises} }

is von Mises stress, Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle  {\sigma }_{1,2,3} }
refer to three principal stress on the pipeline, and where Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle  {\sigma }_{u} }
is the ultimate tensile strength.

The element type of the pipe and the surrounding soil adopts eight-node brick element with the reduced integral unit to improve the convergence efficiency for geometrically nonlinear modeling. In order to obtain a reasonable grid that ensure that the simulation results are sufficiently stable and reliable, multiple sets of grid independence tests are conducted. Meanwhile, local grid refinement is used in the corrosion defect area of the pipeline and the ground overload area, and the sparse grid is used in the area far from the important area. The maximum von Mises stress for different element number are shown in Table 3, and the loads and corrosion defect size are shown in Table 4. When the number of elements exceeds 112785, the maximum Mises stress area stabilizes. According to the above analysis, the number of elements finally selected 112785, and the smallest grid size sets as 1mmFailed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle \times } 1mmFailed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://test.scipedia.com:8081/localhost/v1/":): {\textstyle \times } 0.8mm. In particular, in order to ensure the accuracy of the calculation, a four-layer grid is selected for the thickness of the corrosion defect wall, and highlighted in dark red in Figure 2(d).

The model uses single-factor analysis to discuss the safety assessment and failure pressure prediction of buried pipelines with corrosion defects under ground overload conditions. The basic parameters of the model are shown in Table 4.

Test

Original document

The different versions of the original document can be found in:

http://dx.doi.org/10.1007/978-1-4471-4093-1_13

http://hdl.handle.net/10344/7664

https://ulir.ul.ie/bitstream/10344/7664/1/Gray_2012_Social.pdf

http://shura.shu.ac.uk/6578/1/Ciolfi_23.pdf,https://ulir.ul.ie/handle/10344/7664,https://link.springer.com/chapter/10.1007/978-1-4471-4093-1_13,https://dl.eusset.eu/bitstream/20.500.12015/2757/1/00512.pdf,http://shura.shu.ac.uk/6578,https://rd.springer.com/chapter/10.1007/978-1-4471-4093-1_13,https://academic.microsoft.com/#/detail/1796785663

http://www.springerlink.com/index/pdf/10.1007/978-1-4471-4093-1_13,http://dx.doi.org/10.1007/978-1-4471-4093-1_13