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Solving downslope pipeline walking on non-linear soil with brittle peak strength and strain softening

Solving downslope pipeline walking on non-linear soil with brittle peak strength and strain softening
Solving downslope pipeline walking on non-linear soil with brittle peak strength and strain softening

In 2000 the first case of pipeline walking (PW) was properly documented when this phenomenon seriously impacted a North Sea high pressure and high temperature (HP/HT) pipeline (Tornes et al. 2000). By then, the main drivers of this problem were accordingly identified for the case studied. On the other hand, to study other aspects related not only to PW, the industry joined forces in the SAFEBUCK Joint Industry Project (JIP) with academic partners. As a result, other drivers, which lead a pipeline to walk, have been identified (Bruton et al. 2010). Nowadays, during the design stage of pipelines, estimates are calculated for pipeline walking. These estimates often use a Rigid-Plastic (RP) soil idealization and the Coulomb friction principle (Carr et al. 2006). Unfortunately, this model does not reflect the real pipe-soil interaction behavior, and in practice time consuming finite element computations are often performed using an Elastic-Perfectly-Plastic (EPP) soil model. In reality, some observed axial pipe-soil responses are extremely non-linear and present a brittle peak strength before a strain softening response (White et al. 2011). This inaccuracy of the soil representation normally overestimates the Walking Rate (WR) (a rigid plastic soil model leads to greater walking). A magnified WR invariably leads to false interpretations besides being unrealistic. Finally, a distorted WR might also demand mitigating measures that could be avoided if the soil had been adequately treated. Unnecessary mitigation has a very strong and negative effect on the project as whole. It will require more financial and time investments for the entire development of the project - from design to construction activities. Therefore, having more realistic and pertinent estimates becomes valuable not only because of budgetary issues but also because of time frame limits. The present paper will show the results of a set of Finite Element Analyses (FEA) performed for a case-study pipeline. The analyses - carried out on ABAQUS software - used a specific subroutine code prepared to appropriately mimic Non-Linear Brittle Peak with Strain Softening (NLBPSS) axial pipesoil interaction behavior. The specific subroutine code was represented in the Finite Element Models (FEMs) by a series of User Elements (UELs) attached to the pipe elements. The NLBPSS case is a late and exclusive contribution from the present work to the family of available pipeline walking solutions for different forms of axial pipe-soil interaction model. The parametric case-study results are benchmarked against theoretical calculations of pipeline walking showing that the case study results deliver a reasonable accuracy level and are reliable. The results are then distilled into a simplified method in which the WR for NLBPSS soil can be estimated by adjusting a solution derived for RP and EPP soil. The key outcome is a genuine method to correct the WR resultant from a RP soil approach to allow for peak and softening behaviour. It provides a design tool that extends beyond the previously-available solutions and allows more rapid and efficient predictions of pipeline walking to be made. This contribution clarifies, for the downslope walking case, what is the most appropriate basis to incorporate or idealize the soil characteristics within the axial Pipe-Soil Interaction (PSI) response when performing PW assessments.

American Society Of Mechanical Engineers (ASME)
Castelo, Adriano
3a38834f-a2b0-4f54-a457-026ec50a7a68
White, David
a986033d-d26d-4419-a3f3-20dc54efce93
Tian, Yinghui
f7bbae79-c2c1-4a75-acc1-fb9606be92fb
Castelo, Adriano
3a38834f-a2b0-4f54-a457-026ec50a7a68
White, David
a986033d-d26d-4419-a3f3-20dc54efce93
Tian, Yinghui
f7bbae79-c2c1-4a75-acc1-fb9606be92fb

Castelo, Adriano, White, David and Tian, Yinghui (2017) Solving downslope pipeline walking on non-linear soil with brittle peak strength and strain softening. In Pipelines, Risers, and Subsea Systems: ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. vol. 5B-2017, American Society Of Mechanical Engineers (ASME). 13 pp . (doi:10.1115/OMAE2017-61168).

Record type: Conference or Workshop Item (Paper)

Abstract

In 2000 the first case of pipeline walking (PW) was properly documented when this phenomenon seriously impacted a North Sea high pressure and high temperature (HP/HT) pipeline (Tornes et al. 2000). By then, the main drivers of this problem were accordingly identified for the case studied. On the other hand, to study other aspects related not only to PW, the industry joined forces in the SAFEBUCK Joint Industry Project (JIP) with academic partners. As a result, other drivers, which lead a pipeline to walk, have been identified (Bruton et al. 2010). Nowadays, during the design stage of pipelines, estimates are calculated for pipeline walking. These estimates often use a Rigid-Plastic (RP) soil idealization and the Coulomb friction principle (Carr et al. 2006). Unfortunately, this model does not reflect the real pipe-soil interaction behavior, and in practice time consuming finite element computations are often performed using an Elastic-Perfectly-Plastic (EPP) soil model. In reality, some observed axial pipe-soil responses are extremely non-linear and present a brittle peak strength before a strain softening response (White et al. 2011). This inaccuracy of the soil representation normally overestimates the Walking Rate (WR) (a rigid plastic soil model leads to greater walking). A magnified WR invariably leads to false interpretations besides being unrealistic. Finally, a distorted WR might also demand mitigating measures that could be avoided if the soil had been adequately treated. Unnecessary mitigation has a very strong and negative effect on the project as whole. It will require more financial and time investments for the entire development of the project - from design to construction activities. Therefore, having more realistic and pertinent estimates becomes valuable not only because of budgetary issues but also because of time frame limits. The present paper will show the results of a set of Finite Element Analyses (FEA) performed for a case-study pipeline. The analyses - carried out on ABAQUS software - used a specific subroutine code prepared to appropriately mimic Non-Linear Brittle Peak with Strain Softening (NLBPSS) axial pipesoil interaction behavior. The specific subroutine code was represented in the Finite Element Models (FEMs) by a series of User Elements (UELs) attached to the pipe elements. The NLBPSS case is a late and exclusive contribution from the present work to the family of available pipeline walking solutions for different forms of axial pipe-soil interaction model. The parametric case-study results are benchmarked against theoretical calculations of pipeline walking showing that the case study results deliver a reasonable accuracy level and are reliable. The results are then distilled into a simplified method in which the WR for NLBPSS soil can be estimated by adjusting a solution derived for RP and EPP soil. The key outcome is a genuine method to correct the WR resultant from a RP soil approach to allow for peak and softening behaviour. It provides a design tool that extends beyond the previously-available solutions and allows more rapid and efficient predictions of pipeline walking to be made. This contribution clarifies, for the downslope walking case, what is the most appropriate basis to incorporate or idealize the soil characteristics within the axial Pipe-Soil Interaction (PSI) response when performing PW assessments.

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More information

Published date: 2017
Venue - Dates: ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2017, Trondheim, Norway, 2017-06-25 - 2017-06-30

Identifiers

Local EPrints ID: 418057
URI: https://eprints.soton.ac.uk/id/eprint/418057
PURE UUID: c4831458-041a-4795-a790-17d0899e1bde
ORCID for David White: ORCID iD orcid.org/0000-0002-2968-582X

Catalogue record

Date deposited: 21 Feb 2018 17:30
Last modified: 14 Mar 2019 01:24

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