Atlantis Oil Export SCR: Treatment of Girth Welds for Enhanced Fatigue Performance

2007 ◽  
Author(s):  
Jim Brooks ◽  
Craig Masson ◽  
David Reeves
Keyword(s):  
Water Depth ◽  
Critical Assessment ◽  
Successful Implementation ◽  
Acceptance Criteria ◽  
Mardi Gras ◽  
Steel Catenary Riser ◽  
Severe Fatigue ◽  
Oil Export ◽  
Girth Welds ◽  
Critical Portion

Suspended from the Atlantis Production Quarters Semi-submersible in over 7000 ft water depth, the 24-inch diameter Mardi Gras Oil Export Steel Catenary Riser (SCR) presented many challenges for design and installation. In particular the touchdown region of the riser was subject to severe fatigue and extreme loadings. The Engineering Critical Assessment (ECA) at the weld OD generated defect acceptance criteria that would be impractical to apply with the available inspection technology. To mitigate this, the decision was made to remove the weld caps in the most critical portion of the SCR. This paper describes the design drivers that led to this decision and the steps taken to ensure successful implementation.

An Integrated Approach to Welding, AUT and ECA for Pipeline Construction

2014 ◽  
Author(s):  
David Horsley ◽  
Jing Ma ◽  
Jan van der Ent ◽  
Casper Wassink ◽  
Martin Fingerhut
Keyword(s):  
Integrated Approach ◽  
Final Outcome ◽  
Critical Element ◽  
Unified Approach ◽  
Acceptance Criteria ◽  
Pipeline Construction ◽  
Girth Welds ◽  
Design Options ◽  
The Impact ◽  
Welding Productivity

An integrated approach for the development of welding, inspection, and alternative weld flaw acceptance criteria, as used for girth welds during pipeline construction is presented. Welding is typically the pace limiting step during pipeline construction and is critical element of pipeline integrity. As such it is vital that it be completed efficiently and with high quality. Each of these three elements is vitally important to welding productivity and quality. At the core of the approach is the coordination of the three elements such that they are developed in concert. By this coordinated effort, all design options are considered leading to optimization of the final outcome. The approach is described by providing an example alternative weld flaw acceptance criteria, and giving the logic pertaining to choices of welding setup, AUT setup, the standard used for design and construction, and the impact of choices within these three elements on the final outcome. The paper illustrates the importance of a unified approach on weld productivity and quality.

scholarly journals Critical assessment of hydrodynamic load models for a monopile structure in finite water depth

2020 ◽  
Vol 72 ◽  
pp. 102743 ◽  
Author(s):  
Loup Suja-Thauvin ◽  
Erin E. Bachynski ◽  
Fabio Pierella ◽  
Michael Borg ◽  
Jørgen Ranum Krokstad ◽  
...  
Keyword(s):  
Water Depth ◽  
Critical Assessment ◽  
Hydrodynamic Load ◽  
Load Models ◽  
Finite Water Depth

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.

Case Studies on ECA-Based Flaw Acceptance Criteria for Pipe Girth Welds Using BS 7910:2005

2007 ◽  
Author(s):  
Mohamad J. Cheaitani
Keyword(s):  
Case Studies ◽  
Pipe Wall ◽  
Single Point ◽  
Welding Residual Stress ◽  
Practical Case ◽  
Acceptance Criteria ◽  
Specific Level ◽  
Failure Assessment ◽  
Girth Welds ◽  
Selection Of

The use of an engineering critical assessment (ECA) approach to derive flaw acceptance criteria for pipe girth welds has become common practice. It allows the maximum tolerable size of weld flaws to be determined on a fitness-for-purpose basis, offering substantial advantages over the conventional workmanship approach. BS 7910:2005 is widely used to derive ECA-based flaw acceptance criteria for pipe girth welds. It offers a flexible assessment framework within the context of the well-established failure assessment diagram (FAD) approach. However, it can be relatively complex to apply and it may lead to assessments that are more conservative than codified pipeline-specific procedures. This paper illustrates, through practical case studies on assessing the significance of circumferential girth weld flaws, some of the options available to the user of BS 7910. The case studies cover the selection of the FAD (generalised or material-specific, with and without yield discontinuity), tensile properties (specified minimum or actual values); fracture toughness properties (single point CTOD values including δ0.2BL and δm, or full CTOD resistance R-curve), and welding residual stress (assumed to be uniform through the pipe wall with a yield strength magnitude, or considered to have a through-wall distribution associated with a specific level of welding heat input).

A Modified Engineering Critical Assessment Approach for Offshore Pipelines

2018 ◽  
Author(s):  
Colum Holtam ◽  
Rajil Saraswat ◽  
Ramgopal Thodla ◽  
Feng Gui
Keyword(s):  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Fatigue Loading ◽  
Critical Assessment ◽  
Offshore Pipelines ◽  
Static Crack ◽  
Production Environments ◽  
Assessment Approach ◽  
Girth Welds ◽  
Crack Growth Rates

Environmentally assisted sub-critical static crack growth can occur in offshore pipelines exposed to aggressive production environments. Recent advances in fracture mechanics testing methods have shown that slow static crack growth rates can be reliably measured in sweet and sour environments under constant stress intensity factor (K) conditions. This has potential implications for the engineering critical assessment (ECA) of pipe girth welds subject to low cycle fatigue loading with long periods of operation under constant static load between cycles, e.g. lateral buckling. This paper demonstrates the influence of including static (i.e. time dependent) crack growth as well as fatigue crack growth in a modified pipeline ECA approach.

The Role of ECA in the Development of Dynamic Riser Systems

2003 ◽  
Author(s):  
Mike Campbell ◽  
Stephen Jones ◽  
Jafar Korloo
Keyword(s):  
Critical Assessment ◽  
Acceptance Criteria ◽  
Critical Flaw ◽  
Margin Of Safety ◽  
Potential Failure ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Non Destructive

An Engineering Critical Assessment (ECA) is a procedure that may be used to define and characterise critical flaw sizes from which acceptance criteria for non-destructive examination (NDE) can be developed or confirmed. Dynamic riser systems are fatigue sensitive structures that are commonly regarded as one of the most challenging aspects of a deepwater development. An ECA provides the facility to increase confidence as it develops an understanding of the margin of safety afforded by the derived acceptance criteria based upon variations in extreme and long-term loads, material properties such as fracture toughness, quality standards for welding, control of stress concentration factors and the nature of potential failure. The paper will demonstrate the objectives, adopted methodology and explore the conclusions of an ECA with the aid of examples.

An Investigation of the Fatigue Performance of Riser Girth Welds

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Stephen J. Maddox ◽  
Julian B. Speck ◽  
G. Reza Razmjoo
Keyword(s):  
Oil And Gas ◽  
Welding Process ◽  
Fatigue Loading ◽  
Fatigue Tests ◽  
Fatigue Performance ◽  
Steel Catenary Riser ◽  
Gas Recovery ◽  
Fatigue Design ◽  
Pipeline Welding ◽  
Girth Welds

Increasing deep-water oil and gas recovery has highlighted the need for high integrity, high fatigue performance girth welds in steel catenary riser systems. Such systems include girth welds made from one side. However, the widely used fatigue design classification, UK Class F2, for such welds is not well founded, but probably overconservative for pipeline welds. In an attempt to justify upgrading current fatigue design classifications and providing a better basis for design, fatigue tests were performed on a range of girth-welded pipes produced by pipeline welding contractors. This paper presents the results of those tests and their evaluation in terms of the factors that influence the fatigue performance of girth welds, including welding process, welding position, backing system, joint alignment, weld quality, specimen type, and fatigue loading conditions. Conclusions are drawn regarding the scope for adopting higher design classifications and the conditions that must be met to justify them.

High-Cycle and Low-Cycle Fatigue Resistance of Girth Welds in Sour Service

2008 ◽  
Author(s):  
Jaime Buitrago ◽  
Stephen Hudak ◽  
David Baxter
Keyword(s):  
Low Cycle Fatigue ◽  
Water Injection ◽  
Fatigue Performance ◽  
Cycle Fatigue ◽  
Production Lines ◽  
Hydrocarbon Production ◽  
Steel Catenary Riser ◽  
Fatigue Design ◽  
Girth Welds ◽  
Constant Slope

The fatigue performance of fracture-critical production lines, such as risers and flowlines, has been shown to significantly degrade in the presence of sour hydrocarbon production caused by water injection of reservoirs. To ensure the reliability of the fatigue design under such conditions, experimental verification of the degradation effect on fatigue life due the presence of H2S is required. To that end and over the past several years, ExxonMobil has developed new testing methodologies to evaluate the riser fatigue performance for both in-air and sour conditions. This paper reviews the general elements of the fatigue qualification process and presents new sour fatigue data aimed at assessing performance at the high-cycle fatigue (HCF) and low-cycle fatigue (LCF) regimes. These new data are relevant to that seen in steel catenary riser (SCR) and flowline thermal responses, respectively. Testing methodologies for each regime are discussed and results presented. The new data are interpreted within the context of previous data in the intermediate-cycle fatigue (ICF) to provide a more robust basis for riser design. The main finding is that the new data support a constant slope S-N curve for the practical domain of fatigue lives to which offshore lines are typically designed under sour conditions.

Avoiding Local Brittle Zones in Offshore Pipeline Girth Welds for Reeling Installation Involving Large Plastic Strain

2013 ◽  
Author(s):  
Jens P. Tronskar ◽  
Vebjørn Andresen
Keyword(s):  
Fracture Toughness ◽  
Plastic Strain ◽  
Strain Curve ◽  
Structural Steels ◽  
Coarse Grained ◽  
Unstable Fracture ◽  
Large Plastic Strain ◽  
Acceptance Criteria ◽  
Offshore Pipeline ◽  
Girth Welds

Pipelines for reeling are designed to tolerate the large plastic strain associated with the reeling installation process based on widely accepted strain based design principles for subsea pipelines as described in Det Norske Veritas (DNV) Offshore Pipeline Code OS-F101: 2012 [1]. Engineering Critical Assessment (ECA) to develop flaw acceptance criteria for automatic ultrasonic testing (AUT) for girth welds subject to large plastic strain shall according to DNV-OS-F101: 2012 [1] and DNV RP-F108 [2] be carried out in accordance with BS 7910 [3], at assessment Level 3B, with amendments and adjustments described in Appendix A of DNV-OS-F101 for strain-based loading. This is a tearing analysis using the material specific failure assessment diagram (FAD), the material stress-strain curve and the fracture resistance J-R curve (or CTOD-R curve) for the HAZ or WM. It is therefore essential that the pipeline girth welds exhibit maximum load behavior and large tearing capacity to enable development of workable and practical flaw acceptance criteria for the girth welds on the stalks. Welds in offshore structural steels are known from the early 80s introduction of low carbon-manganese micro-alloyed steels, to occasionally exhibit low fracture toughness associated with so-called local brittle zones (LBZ) in the HAZ. Similarly, in the 90s LBZs were found in pipeline seam welds welded at high arc energies. Presence of such microstructures may have a dramatic effect on the coarse grained HAZ CTOD fracture toughness properties causing unstable fracture in the CTOD tests and CTOD values below 0.1 mm at test temperatures of 0°C and below. Recently low CTOD critical fracture toughness values due to pop-ins and unstable fracture initiation in the HAZ have been experienced for pipeline girth welds for reeling and investigation confirmed these were caused by LBZs. This paper makes a comparison with the situation experienced earlier for welds in structural steels and pipeline seam welds, to understand the factors influencing the LBZ formation, and to show how such problems can be avoided. To avoid LBZs formation in the girth welds is imperative for reeling installation, where the large plastic strain associated with reeling installation affects every girth weld.

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