Novel Design of Small Diameter Pipelines on Uneven Seabed

2011 ◽  
Author(s):  
Frode Hove ◽  
Tore H. So̸reide ◽  
Anne Cecilie Nordsve ◽  
Sigurd D. Trier
Keyword(s):  
Crack Growth ◽  
Local Buckling ◽  
Small Diameter ◽  
Design Procedure ◽  
Bending Moment ◽  
Potential Cost ◽  
Traditional Design ◽  
Separate Control ◽  
Major Attention ◽  
Girth Welds

The paper deals with design philosophy for small diameter HP/HT flowlines on uneven seabed with major emphasis on controlled snaking expansion design of free spanning flowlines subject to fishing gear interaction loads. The response from trawl pull-over is given major attention as part of the overall design procedure including ECA (Engineering Criticality Assessment), covering high and low cycle crack growth. The background for the design procedure is reference projects in the Norwegian sector, where REINERTSEN performed the flowlines detail engineering. Iceberg plough marks make an irregular seabed with partly sharp and deep valleys crossing the flowline routes, resulting in free spans. The bathymetry and extent of unevenness varies for the lines, resulting in different behavior and design approaches, especially for trawl pull-over. The major criterion for a robust design is strong sectioning by intermittent rock berms. For operation loads these serve as locking points and as such they are termed ARBs (Anchoring Rock Berms), whereas for trawl pull-over axial motion through the berms is allowed, depending on seabed profile, and as long as the pipeline deforms without unacceptable crack growth in girth welds. Design criteria for the ARBs are presented, covering the expansion phases of buckle initiation, post-buckle and shutdown, respectively. For trawl pull-over separate control of the intermittent rock dumps is shown, covering the cases of section interaction and complete locking, respectively. Criteria for the choice of trawl design approach are evaluated. Traditional design handles the trawl impact capacity of pipelines by a local buckling criterion, in which axial force and bending moment are the response parameters. For expansion control this is a relevant approach, however for a concentrated and curvature. Applying the latter criterion is illustrated by numerical example in view of displacement- or load controlled behaviour. A summary on rock saving potential is made for a typical reference project from a traditional design involving infill of spans to the new approach where free spans are allowed also for trawl pull-over. The potential cost saving for seabed intervention work by rock dumping is found to be well above 5000 NOK/m (>1000 $/m) for very irregular seabed, while typically in the order of 1000 $ for normal uneven seabed.

Upheaval Buckling of Small Diameter Pipelines Induced by Strong Ground Shaking

2012 ◽  
Author(s):  
Hiroyuki Horikawa ◽  
Yoji Tsunasawa ◽  
Hajime Shinkai ◽  
Nobuhisa Suzuki
Keyword(s):  
Local Buckling ◽  
Small Diameter ◽  
Field Tests ◽  
Bending Moment ◽  
Design Guidelines ◽  
Combined Loading ◽  
Pipe Material ◽  
Effective Parameters ◽  
Ground Shaking ◽  
Upheaval Buckling

Upheaval buckling of small diameter gas pipeline occurred due to strong seismic excitation during the 2007 Niigata-ken Chuetsu-Oki earthquake whose diameters were 4″ and smaller. This paper deals with investigation of the upheaval buckling of gas pipes conducted by Ministry of Economy, Trade and Industry of Japan to establish seismic design guidelines to mitigate upheaval buckling. Sand box and field tests were conducted using small diameter pipes to simulate the upheaval buckling behaviors and construct a simple finite element model. The results clarified that the tensile properties of pipe material and pipe-soil interaction were the most effective parameters to explain the buckling behaviors. Interaction curve of pipes can be found in the relationship between compression and bending moment in the combined loading tests. The deformation behaviors of the buried pipe tests followed the interaction curve and local buckling of buried pipes occurred in lower bending moment than that of pipes not buried.

Issues on Design of Piled Raft Foundation

2018 ◽  
Vol 14 (1) ◽  
pp. 6057-6061 ◽  
Author(s):  
Padmanaban M S ◽  
J Sreerambabu
Keyword(s):  
Contact Area ◽  
Concrete Slab ◽  
Design Procedure ◽  
Bending Moment ◽  
Foundation Design ◽  
Detailed Review ◽  
Piled Raft ◽  
Piled Raft Foundation ◽  
Raft Foundation ◽  
Influencing Parameters

A piled raft foundation consists of a thick concrete slab reinforced with steel which covers the entire contact area of the structure, in which the raft is supported by a group of piles or a number of individual piles. Bending moment on raft, differential and average settlement, pile and raft geometries are the influencing parameters of the piled raft foundation system. In this paper, a detailed review has been carried out on the issues on the raft foundation design. Also, the existing design procedure was explained.

Crack Growth During Full Scale Reeling Simulation of Pipes With Girth Welds

2004 ◽  
Author(s):  
Oddvin O¨rjasaeter ◽  
Olav Jan Hauge ◽  
Guy Ba¨rs ◽  
Per Egil Kvaale
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
High Strain ◽  
High Stress ◽  
Strain Range ◽  
Full Scale ◽  
Small Scale ◽  
Final Fracture ◽  
Lack Of Fusion ◽  
Girth Welds

Installation of pipelines by reeling has proved to be an effective method. However, the pipe bending results in very high stress and strain and cannot be handled by conventional design rules, as stated in design codes, e.g. [2]: High strain crack growth must be assessed according to specific case-by-case selected criterions. In the present work the performance of 10” and 12 3/4” pipes with typical weld defects is studied — from initiation of cracks at notches to final fracture. Information was obtained from several sources: full scale cyclic bending of pipes, FE simulations, and small-scale tests. The plasticity during reeling operations results in substantial non-linear behavior due to varying cross section properties, cyclic creep, and different material response at tensile and compression side of the pipe. Hence, a full scale reeling simulation must be carefully planned and include sufficient tolerances. Critical cracks in pipe girth welds initiate mainly from the surface (undercuts, lack of penetration, or lack of fusion), but potentially also internally (lack of fusion or large pores). Various configurations of these parameters were investigated in full scale pipe tests. It was possible to verify both crack propagation during the reeling cycles, and the point of final fracture (for ECA verifications). In pipe design on must assure safe conditions for both reeling operations and for later in-service loading. Proper design tools must be available. Several methods for high strain crack growth analysis were considered and also compared to small-scale specimen data. Conventional strain-life methodology failed to predict the crack propagation accurately. A new approach including a tensile strain range parameter offered promising results.

Reeled CRA Clad/Lined Pipeline Installation: Seastate Optimisation From Fatigue and Fracture Perspective

2018 ◽  
Author(s):  
Daowu Zhou ◽  
T. Sriskandarajah ◽  
Heidi Bowlby ◽  
Ove Skorpen
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Superposition Method ◽  
Cycle Fatigue ◽  
Limit States ◽  
Simplified Approach ◽  
Fatigue And Fracture ◽  
Girth Welds

The deformation mechanism in reel-lay of corrosive resistance alloy (CRA) clad/lined pipes can facilitate defect tearing and low cycle fatigue crack growth in the girth welds. Pipe-lay after straightening will subject the CRA welds to high cycle fatigue. The permissible seastate for installation will be governed by failure limit states such as local collapse, wrinkling of the liner, fatigue and fracture. By means of a recently completed offshore project in North Sea, this paper discusses seastate optimisation when installing pipelines with CRA girth welds, from a fatigue and fracture perspective. The additional limiting requirement in CRA welds to maintain CRA liner integrity can lead to significant assessment work since all critical welds shall be examined. AUT scanned defect data were utilised to maximise permissible seastates based on fatigue allowance from a fatigue crack growth calculation. An alternative simplified approach to derive the crack growth based on a superposition method is studied. It enables a straightforward real-time prediction of crack growth and has the potential to be used during the offshore campaign to improve the installation flexibility. Post-installation fracture assessment under more critical seastates is examined for CRA partial over-matching welds. A comparison of CDF between conventional ECA procedure and 3D FE is provided.

Using ECA in Structural Integrity of Submarine Pipelines for Optimalization of Intervention Work

2010 ◽  
Author(s):  
Ragnar T. Igland ◽  
Trond Lamvik
Keyword(s):  
Structural Integrity ◽  
Bending Moment ◽  
Pipeline System ◽  
Unstable Fracture ◽  
Axial Capacity ◽  
Detail Design ◽  
Management Scheme ◽  
Residual Capacity ◽  
Girth Welds ◽  
Intervention Costs

The paper deals with the design methodology to define the design loads and determine the maximum allowable size of girth weld defects. The motivation for this work is reduced intervention costs obtained by opening all free spans as these are governing for rock infill volumes. 20–30% reduction of the intervention work is obtained. Structural integrity of the pipeline related to the interference with fishing gear is an important design scenario. Trawling in free span, pull-over loads with clump weight as an ALS condition is the main issue. REINERTSEN observed during detail design a lack of acceptance criteria for ALS conditions in the DNV OS-F101 design code, Ref. [1] for interference between trawl gear and subsea pipelines with low D/t ratio. Curvature in the trawl pull-over point as a function of time is found approximately constant while trawl load is increasing. The membrane forces carry most of the trawl load a few seconds after the trawl impact while bending moment decreases. This is in accordance to the philosophy that the strain and the curvature will be nearly constant for increased loading. The global load bearing mechanism is membrane and less bending. This means that we have control on the strain and that the pipeline system maintains its stiffness against loading for this high axial capacity of the flowline. These observations leads to a deformation controlled trawl load approach where an ECA of the flowline can be used to document structural integrity. Engineering Criticality Assessment (ECA) analysis is applied to evaluate the integrity of the flowlines with respect to risk for unstable fracture in girth welds due to impact from trawl equipment. The fatigue load effects from installation, temporary and operational phases are included in the ECA analysis. Geometric effects and external/internal pressure are included using the tailormade softwares LINKpipe, Ref. [7] and Crackwise4, Ref. [8]. The residual capacity of the flowlines is calculated with emphasis on fatigue during operation after the trawl pull-over. The fatigue life should be within the inspection interval, reflecting the Integrity Management Scheme.

Advanced Closed-Form Ultimate Strength Formulation for Ships

2001 ◽  
Vol 45 (02) ◽  
pp. 111-132 ◽  
Author(s):  
Jeom Kee Paik ◽  
Owen F. Hughes ◽  
Alaa E. Mansour
Keyword(s):  
Ultimate Strength ◽  
Structural Damage ◽  
Lateral Pressure ◽  
Local Buckling ◽  
Bending Moment ◽  
Stiffened Panels ◽  
Initial Imperfections ◽  
Ship Hulls ◽  
Collapse Column ◽  
Side Shell

The aim of this paper is to develop an advanced ultimate strength formulation for ship hulls under vertical bending moment. Since the overall failure of a ship hull is normally governed by buckling and plastic collapse of the deck, bottom, and sometimes the side shell stiffened panels, it is of crucial importance to accurately calculate the ultimate strength of stiffened panels in deck, bottom and side shell for more advanced ultimate strength analyses. In this regard, the developed formulation is designed to be more sophisticated than previous simplified theoretical methods for calculating the ultimate strength of stiffened panels under combined axial load, in-plane bending and lateral pressure. Fabrication-related initial imperfections (initial deflections and residual stresses) and potential structural damage related to corrosion, collision, or grounding are included in the panel ultimate strength calculations as parameters of influence. All possible collapse modes involved in collapse of stiffened panels, including overall buckling collapse, column or beam-column type collapse (plate or stiffener induced collapse), tripping of stiffeners and local buckling of stiffener web, are considered. As illustrative examples, the paper investigates and discusses the sensitivity of parameters such as lateral pressure, fabrication-related initial imperfections, corrosion, collision and grounding damage on the ultimate strength of a typical Cape size bulk carrier hull under vertical bending.

Fracture Toughness Testing and Validation of Pipeline Girth Weld Flaw Acceptance Criteria for Sour Service Under Large Strain

2011 ◽  
Author(s):  
You You Wu ◽  
Wen Guo Yuan ◽  
Tse Ven Steven Chong ◽  
Jens P. Tronskar
Keyword(s):  
Fracture Toughness ◽  
Oil And Gas ◽  
Large Strain ◽  
Axial Strain ◽  
Laboratory Data ◽  
Local Buckling ◽  
Acceptance Criteria ◽  
Service Environment ◽  
Girth Welds ◽  
Sour Service

Fracture toughness is one of the most important input parameters for assessment of pipeline girth weld failure capacity. For many new subsea pipeline projects there is a need to develop flaw acceptance criteria for pipeline installation considering the operation phase which may involve the transport of sour oil and gas and where the pipeline is exposed to large axial strain due to local buckling. Engineering Critical Assessment (ECA) performed using laboratory data based on conservative KISSC testing gives small acceptable flaw sizes which may be below the workmanship criteria for pipeline laying. DNV has conducted extensive research based on the requirements of DNV-OS-F101 and DNV-RP-F108, aiming to establish a method to develop J-R curves applicable for ECA of pipeline girth welds in sour service environment and a methodology to validate the ECA by segment testing in a laboratory-simulated sour service environment as per DNV-RP-F108.

Offshore Installation of Welded Pipe: Local Buckling Evaluation

2010 ◽  
Author(s):  
Luciano Mantovano ◽  
Richard E. Bravo ◽  
Sebastian Cravero ◽  
Hugo A. Ernst
Keyword(s):  
Numerical Models ◽  
Local Buckling ◽  
Good Control ◽  
Plastic Instability ◽  
Lead Times ◽  
Geometrical Parameters ◽  
Seamless Pipe ◽  
Project Costs ◽  
Girth Welds ◽  
Welded Pipe

Up to the present, most of the pipes used in offshore applications installed with methods introducing plastic deformation have been seamless pipes; however, welded pipes can also be used. Welded pipes offers benefits over seamless pipe in terms of improved lead times, lower project costs, tighter dimensional tolerance and good control of mechanical properties and chemistry resulting in excellent weldability. During installation of welded pipes, failure by fracture, plastic collapse and local buckling may occur. In this work, the occurrence of the local buckling phenomenon, produced during the installation method, was evaluated. Numerical models were developed to study the effect of materials and geometrical parameters on the local bucking of pipes subjected to bending. Specifically, the loads and strains at which the plastic instability occurs were determined for each particular condition. In addition, the influence of longitudinal and girth welds on the local bucking occurrence was assessed.

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