Social aspects of place experience in mobile work/life practices

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 ( ${\textstyle d}$ ), width ( ${\textstyle W}$ ) and length ( ${\textstyle L}$ ) 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].

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Figure 1. Schematic diagram of corrosion defect pipeline

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 ${\textstyle 20{\rm {m}}\times 10{\rm {m}}\times 6{\rm {m}}}$ , 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].

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Figure 2. Finite element model containing corrosion defect

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]

(1)

where ${\textstyle \varepsilon }$ is a strain, ${\textstyle \rho }$ is stress, ${\textstyle E}$ is Young’s modulus, ${\textstyle \sigma _{y}}$ is yield strength, ${\textstyle \sigma _{u}}$ is ultimate tensile strength, and ${\textstyle K}$ and ${\textstyle n}$ are R-O model parameters, which depend on the materials. It is 0.079 and 12 for X80 steel, respectively.

Table 1. Mechanical properties of X80 pipeline steels

Steel	Yield strength (MPa)	Ultimate tensile strength (MPa)	Young’s modulus (GPa)	Poisson’s ratio
X80	534.1	718.2	200	0.3

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].

Table 2. Parameters of model for soil

Young’s modulus (MPa)	Poisson’s ratio	Density (kg/m³)	Friction Angle (°)	Flow Stress ratio	Cohesion (KPa)
20	0.35	1840	30	1	29.3

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:

(2)

where ${\textstyle {\sigma }_{mises}}$ is von Mises stress, ${\textstyle {\sigma }_{1,2,3}}$ refer to three principal stress on the pipeline, and where ${\textstyle {\sigma }_{u}}$ 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 1mm ${\textstyle \times }$ 1mm ${\textstyle \times }$ 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).

Table 3. Maximum von Mises stress for different mesh number

Number of elements	Maximum von Mises stress (MPa)
30305	552.1
54105	556.2
86522	559.6
112785	578.1
128569	578.4
153674	578.6

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.

Table 4. Base condition parameters

Variable		Value
Load (MPa)	Ground overload (OLD)	1
Load (MPa)	Internal pressure (IP)	7
Loading area (m)	width ${\textstyle \times }$ length	0.8 ${\textstyle \times }$ 1.8
Buried depth (m)	H	1
Corrosion defect (mm)	d ${\textstyle \times }$ L ${\textstyle \times }$ W	5.6 ${\textstyle \times }$ 40 ${\textstyle \times }$ 32

Test

PERFIL IPE	I_t calculado	I_t Argüelles [11]	I_t Monfort [12]	I_t ArcelorMittal [16]	I_w calculado	I_w Argüelles [11]	I_w ArcelorMittal [16]
	mm⁴ x 10³	mm⁴ x 10³	mm⁴ x 10³	mm⁴ x 10³	mm⁶ x 10⁶	mm⁶ x 10⁶	mm⁶ x 10⁶
IPE 80	5.59	7.21	7.0	7	119	118	120
IPE 100	8.83	11.4	12.0	12	353	351	350
IPE 120	13.72	17.7	17.4	17	895	890	890
IPE 140	20.35	26.3	24.5	25	1989	1981	1980
IPE 160	28.20	36.4	36.0	36	3976	3959	3960
IPE 180	39.20	50.6	47.9	48	7470	7431	7430
IPE 200	51.65	66.7	69.8	70	13019	12990	13000
IPE 220	70.91	91.5	90.7	91	22774	22670	22700
IPE 240	92.80	120	128.8	129	37624	37390	37400
IPE 270	119.43	154	159.0	159	70871	70580	70600
IPE 300	155.74	201	201.2	201	126379	125900	126000
IPE 330	205.40	265	281.5	282	199841	199100	199000
IPE 360	289.26	373	373.2	373	314510	313600	314000
IPE 400	374.33	483	510.8	511	492215	490000	490000
IPE 450	510.71	659	668.7	669	794312	791000	791000
IPE 500	711.68	918	892.9	893	1254441	1249000	1249000
IPE 550	947.43	1220	1232.0	1230	1893452	1884000	1884000
IPE 600	1329.70	1720	1654.0	1650	2858298	2846000	2846000