Uplift Resistance of Offshore Pipelines Subject to Upheaval Buckling

2017 ◽  
pp. 67-80
Author(s):  
Sahar Ismail ◽  
Shadi Najjar ◽  
Salah Sadek ◽  
Mounir Mabsout
Keyword(s):  
Offshore Pipelines ◽  
Upheaval Buckling ◽  
Uplift Resistance

Consolidation of Lumpy Clay Backfill Over Buried Pipelines

2009 ◽  
Author(s):  
Mahmoud Ghahremani ◽  
Andrew J. Brennan
Keyword(s):  
Pore Pressure ◽  
Clayey Soils ◽  
Buried Pipelines ◽  
Offshore Pipelines ◽  
Lump Size ◽  
Upheaval Buckling ◽  
Backfill Material ◽  
Centrifuge Tests ◽  
Uplift Resistance ◽  
External Loads

Offshore pipelines are usually buried to protect the pipe from external loads. When trenching is achieved by jetting or ploughing, some clayey soils can be cut into distinct lumps and this lumpy soil is then used as the backfill material under which the pipe is buried. To counter the effects of upheaval buckling, the resistance of the soil to pipe uplift must be known. There is still uncertainty about the performance of lumpy backfill in this regard. A series of centrifuge tests were performed with such soils as backfill, utilising a specially designed pore-pressure measuring pipe, to determine the influence of lump size, lump shape and pullout rate on uplift resistance Backfill comprising larger lumps consolidates quicker than if the backfill lumps are smaller. It is also observed that backfill comprising larger lumps provides greater resistance to pipe uplift after consolidation.

Pipeline Upheaval Buckling in Clayey Backfill and Shore Approach

2014 ◽  
Author(s):  
Alahyar Koochekali ◽  
Behrouz Gatmiri ◽  
Amirabbas Koochekali
Keyword(s):  
Water Level ◽  
Failure Mechanism ◽  
Water Levels ◽  
Burial Depth ◽  
Buried Pipeline ◽  
Soil Response ◽  
Upheaval Buckling ◽  
Soil Failure ◽  
Mean Water Level ◽  
Uplift Resistance

True estimation of soil response during pipeline upheaval buckling is a key parameter in the safe design of subsea buried pipeline. In this paper the effects of sea mean water level over the buried pipeline and the effects of pipe burial depth on the soil response during vertical buckling are investigated. For that purpose a numerical modeling of pipeline upheaval buckling in clayey backfill has been conducted. Different sea mean water levels are considered to simulate the pipeline shore approach. In addition, various pipeline burial depths are considered to predict the soil uplift resistance and the soil failure mechanism. In order to model the large penetration of pipeline into the soft clay, Arbitrary Eulerian Lagrangian (ALE) method is employed. The results reveal that in the shallow water the sea mean water level may have considerable effects on the soil failure mechanism and soil uplift resistance. In addition, as the sea mean water level and pipe burial depth increases, a new transitional failure mechanism can be observed. The mechanism is a combination of vertical sliding block mechanism and the flow-around mechanism.

A New Holistic Approach for Subsea Pipeline Upheaval Buckling Design

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
A Priori ◽  
Holistic Approach ◽  
Load Factor ◽  
Fe Model ◽  
Potential Cost ◽  
Upheaval Buckling ◽  
Structural Reliability Analysis ◽  
Uplift Resistance

For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analyzing post pipelay out of straightness (OOS) survey data incorporating appropriate safety factors based on a structural reliability analysis (SRA). The normal approach is to examine the as-laid pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation are typically performed a priori based on the assumed initial imperfections using the universal design curve methodology. A new pseudo-energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis. The approach takes into account the effects of varying effective axial force, trench imperfections, and vertical uplift resistance, by combining both axial friction and lateral resistance methods into a unified model. A new concept, effective uplift resistance and associated load, is also introduced to deal with nonuniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. A finite element (FE) model is developed to consist of three-noded quadratic pipe elements using abaqus Ver 6.12, and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.

UHB Design Approach for Multiple Pipelines Installed in Shared Trench

2019 ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Proximity Effect ◽  
Burial Depth ◽  
Field Development ◽  
Upheaval Buckling ◽  
Resistance Reduction ◽  
Failure Angle ◽  
The Common ◽  
Uplift Resistance ◽  
Mitigation Design ◽  
Offshore Field

Abstract Upheaval buckling (UHB) mitigation for trenched and buried pipelines can constitute a substantial cost element for offshore field development. There appears to have a variety of reasons for dual or more pipelines and umbilicals to be considered for installation inside the same trench. A single shared trench has been used for multiple pipelines not only for cost saving, but especially when constrained and driven by route corridor challenges. The common practice for dual pipeline trenching and UHB design is to either perform UHB design independently without due consideration of the pipelines in the proximity, potentially resulting in a compromised UHB mitigation design, or simply combine the uplift resistance required for each individual pipeline in the proximity to obtain the overall backfill/rock dumping to account for pipeline interactions. This paper re-examines the rationale of the normal practice and some fundamental aspects of UHB design for dual pipelines installation inside the same trench. The proximity effect on the uplift resistance is investigated with respect to pipeline spacing and burial depth. Its impact on the UHB mitigation is considered by a detailed analysis and a series of parametric simulations with respect to pipeline dimensions and gaps. The sensitivity of the soil slip failure angle and the dilatancy is also performed. Based on the theoretical analysis and FEA modelling, a model solution is formulated and proposed for evaluating uplift resistance reduction for multiple lines. The formulae are extended to deal with multi-layered soil and rockdump. A number of pipeline configurations have been discussed including a piggyback arrangement. A robust UHB mitigation and reduced optimum rockdumping can be achieved by considering the proximity effect through challenging the industry norms and common approach.

Environmental Loadings and Geotechnical Considerations for the Northstar Offshore Pipelines

2002 ◽  
Author(s):  
Michael J. Paulin ◽  
Derick Nixon ◽  
Glenn A. Lanan
Keyword(s):  
Oil And Gas ◽  
Limit State ◽  
Oil Production ◽  
Development Project ◽  
Loading Conditions ◽  
Design Data ◽  
Offshore Pipelines ◽  
Upheaval Buckling ◽  
Production Pipeline ◽  
Pipeline Design

BP Exploration (Alaska) Inc. completed the installation of the first subsea Arctic oil production pipeline in April 2000 for the Northstar Development Project. The drilling and production facilities are located at Seal Island, approximately 10 km offshore of the Alaskan Beaufort Sea coast. Twin 273.1 mm (10-inch) oil and gas pipeline systems run approximately 10 km from Seal Island, through a lagoon area, to a shore crossing, and then overland for approximately 18 km. The unique aspects of this design included the pipeline environmental loadings, geotechnical considerations, and the use of limit state design procedures for extreme loading conditions. Environmental loadings and geotechnical conditions (in-situ and backfill) along the pipeline route were a major factor in the design of the offshore portion of the pipelines. Data collection of environmental conditions (e.g. ice gouging and strudel scour) and proper evaluation of the same were required to provide appropriate design data. Comprehensive field and laboratory programs were undertaken to generate the necessary geotechnical data for design. The evaluation of and design for unique Arctic environmental loading conditions including ice gouging, offshore permafrost, upheaval buckling, and strudel scour are described. Trenching and backfilling aspects of the pipeline design are also discussed. The paper closes with a general overview of the pipeline operations since the start of oil production in November 2001.

Design Criteria for Upheaval Creep of Buried Sub-Sea Pipelines

1990 ◽  
Vol 112 (4) ◽  
pp. 290-296 ◽  
Author(s):  
N. J. R. Nielsen ◽  
P. T. Pedersen ◽  
A. K. Grundy ◽  
B. S. Lyngberg
Keyword(s):  
Variable Temperature ◽  
Design Procedure ◽  
Upward Movement ◽  
Pressure Loading ◽  
Buried Pipe ◽  
Creep Failure ◽  
Upheaval Buckling ◽  
Temperature And Pressure ◽  
Uplift Resistance ◽  
New Criterion

A new criterion is presented for the design against upheaval creep of buried hot marine pipelines. Observations have substantiated that the gradual upheaval of an “imperfect” buried pipe can take place when subjected to variable temperature and pressure loading. The imperfection amplitudes can thus grow until at a certain stage the overburden is insufficient to prevent upheaval (snap) buckling of the pipe. This paper shows that the “classical” upheaval buckling analysis is not applicable when designing against upheaval creep failure of an “imperfect” pipe. A new design procedure is established which determines the uplift resistance required to keep the upward movement of the “imperfect” pipe below critical values, thus preventing a progressive upheaval failure. The various aspects to be considered during the design and installation of a pipeline are highlighted, resulting in requirements for acceptable out-of-straightness of the pipe.

Subsea Pipeline UHB Design: An Improved Analysis Approach

2016 ◽  
Author(s):  
M. Liu ◽  
C. Cross
Keyword(s):  
Reliability Analysis ◽  
Structural Reliability ◽  
A Priori ◽  
Load Factor ◽  
Fe Model ◽  
Potential Cost ◽  
Subsea Pipeline ◽  
Upheaval Buckling ◽  
Structural Reliability Analysis ◽  
Uplift Resistance

A subsea pipeline operating at temperature and pressure may buckle both vertically and laterally. For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analysing post pipelay OOS survey data incorporating appropriate safety factors based on a structural reliability analysis. The normal approach is to examine the pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation is typically performed a priori based on the assumed imperfections using the methodology outlined in ref [1]. The additional rockdump schedule is derived from the crown of the pipeline imperfections regardless of adjacent profiles and overall backfill data. A new pseudo energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis. The approach takes into account the effects of varying effective axial force, trench imperfections and vertical uplift resistance, by combining both axial friction and lateral resistance methods into a unified model. A new concept, effective uplift resistance and associated load is also introduced to deal with non-uniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. An FE model is developed to consist of 3-noded quadratic pipe elements using ABAQUS Ver 6.12 and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.

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