ASPIRE for Integrity Management Support for Upstream Assets Payam Jamshidi, TWI Ltd Sebastian Hartmann, Innospection Ltd
OVERVIEW - Discussion of corroded pipe assessment procedures under combined loading - What do we need? How we derived to assessment of conductors? - Current study and our approach - Assessment of well conductors - Some results - Conclusion
Objectives The ultimate objective of this project was to integrate the collection, management and analyses of inspection data for the purpose of providing RBI and repair decision making for upstream assets. This will be achieved by the following objectives: To develop a customisable probabilistic based algorithm and software to use advanced reliability methods to assess failure scenarios for several types of non-standard geometries, loading, environment and operations; To link the software to different NDT technologies to analyse the results seamlessly; To validate the algorithm through pilot implementations on project partners identified cases. The ASPIRE TM - Project 760460 is funded by the EU under the Horizon 2020 Framework Programme
OIL & GAS ACCIDENTS - In the last 10 years, 34% of oil & gas losses happened in upstream ~ $12 billion The 100 Largest Losses 1974-2013, Large property damage losses in the Hydrocarbon Industry, 23rd Edition, MARSH
ASSETS SUBJECT TO COMBINED LOADING Engineering structures such as flexible risers, free-standing or toptensioned rigid risers, and steel catenary risers are continuously subject to global bending moments in addition to axial loads and/or internal pressure. Global bending plays an important role when the assessment is applied to deep sea offshore pipes.
CORRODED PIPE ASSESSMENT - Pressure equipment used in the oil and gas industry is typically subjected to multiple loads (internal pressure, axial stress, global bending). - There are limited numbers of research programs addressing the assessment of corrosion defects in pipeline structures subjected to global bending, compressive loading or combination - Several methods for the assessment of corroded pipeline subjected to internal pressure loading are currently available; such as ASME B31G, DNV-RP-F101 RSTENGTH, API 579, etc. - These methods do not take into account the effect of global bending or longitudinal compressive load on the failure of the corroded structure and their predictions of failure pressure are quite conservative compared to the full scale tests*. Benjamin, A.C. (2013). Prediction of the failure pressure of corroded pipelines subjected to a longitudinal compressive force superimposed on the pressure loading, The Journal of Pipeline Engineering, pp301.
Past Study at TWI - Assessment of LTAs in pipe structures subject to global bending and compressive loading and compares the results to the BS7910 reference stress solutions. - FEA is carried out to produce collapse loads of pipe structures containing corroded areas (with different LTA aspect ratios) subject to global bending, internal pressure, axial tension and ultimately combined bending and compression. - The model was calibrated against BS7910 under conditions of internal pressure and axial tension. - All models were analyzed to cover a wide range of LTA depth to pipe thickness ratios and aspect ratios so as to generate a closed-form or tabulated solution.
Past Study at TWI - The following depth to pipe wall thickness (B) ratios were analyzed: a/b = 0.3, 0.5 or 0.7 - The axial lengths given by c 1 /c 2 = 0.25, 0.5, or 1.0 The LTA was meshed densely whilst away from the LTA, the mesh was coarser.
Conclusion of Past Study at TWI - The BS 7910 equations were conservative as would be expected. - In terms of total axial stress at failure, these analyses showed that compressive loads reduce the failure load; that the failure load is further reduced under combined loading, but that the BS7910 equations could still be used to provide conservative solutions (for all cases analyzed). - The failure criterion employed in this work has been validated extensively for internal pressure loads (and internal pressure with end cap axial forces). However, little experimental work has been done to verify the FEA failure criterion for other external load combinations and therefore experimental testing should be undertaken to verify the numerical procedures.
Well Conductors Offshore well bores consist of several concentric tubes The outermost well casing, the conductor, protects the inside casings from aggressive corrosion. The conductor should not leak, nor buckle or collapse under both axial load and bending moment
Past Conductor Failures
Well Conductors Purpose To demonstrate / document viability & integrity of each of conductors For next x years Endorsement period Time/Risk Based Inspection period Avoiding any major repairs Process Review of available data Design analyses and engineering assessments Inspection scopes & results Operational history including incidents 12
Assessment Procedure Design check of well conductors is a stability check based on international best practices: Petroleum and Natural Gas Industries, Fixed Offshore Platform, ISO-19902, 2007 Institute of Petroleum, Guideline for the Analysis of Jackup and Fixed Platform Well Conductor System, 2001 Design of Concentric Tubular Members, G. R. Imm, B. Stahl, Offshore Technology Conference, 1988. Design Methodology for Offshore Platform Conductors, B. Stahl, M. P. Baur, Offshore Technology Conference, 1980. Minimum Required Thickness (MRT) is the thickness below which the required cross sectional area is not achieved and failure may occur Grouting in annulus of conductor and other internal casing/tubing will influence the MRT calculation. It will be in-conservative not to consider the effect of grouting.
Assessment Procedure In summary, design evaluation of conductors include: Determine the equivalent section of the conductor by the supports configuration. Determine the stiffness of the conductor based on effective length Calculation of the axial loads and bending moment Calculation of stress ratio MRT calculation which is the critical thickness at which the stress ratio is equal to 1.0. Conductor Subjected to Axial, Internal and Bending Strength Check Stability Check Stress Buckling Design of Concentric Tubular Members, G. R. Imm, B. Stahl, Offshore Technology Conference, 1988.
Loading Mi & Me Pi & Pe Axial Compression Pi: - Axial load due to weight of conductor, internal casings etc. Pe: - Axial load at each elevation due to weight on top of the conductor Global Bending Me: - Bending moment due to environmental condition such as 100 year storm Wave and current calculated by SACS software Mi: - Bending moment due to eccentricity of casings
Effect of Breathing Window - Breathing window in a section causes reduction in Area and consequently reducing the Second Moment of Inertia of that loading section. - Based on the size of each window (by using principles of mathematic and solid mechanic), reduction factors for Area and Moment of Inertia are multiplied in properties of the intact section.
Assessment Procedure
Assessment Procedure
MEC TECHNOLOGY - Operations - Little pipe preparation needed (no couplant) - Remote controlled deployment - NDE key points - up to 1.3 Wall Thickness, sensitive for isolated pit detection, sizing accuracy +/- 10% - inspection through coatings (Neoprene etc.) & CRA layers (Monel, Inconel, TSA ) - inspection speed (net average run speed 0.25m 0.5 m/sec) - separate C-Scan corrosion mapping of near side & far side or merged - Direct online data assessment & integrity assessing data set up Example field applications Conductor Scan Caisson/Riser scan Flexible Riser Scan
Splash Zone SPLASH ZONE INSPECTION Splash Zone Inspection & Assesment Support Riser / Caisson / Conductor -Combined cleaning & inspection -MEC & UT Technology combination -Inspecting through coatings -No operational interruptions -ROBOTIC TOP SIDE DEPLOYMENT & REMOTE CONTROLLED DRIVE
Segment 3 (Sea Water zone) Segment 2 (Splash zone) Segment 1 (Marine corrosion zone) Remaining Life Assessment External Indication SLOFEC Inspection Results Internal Indication 1 Averaged Minimum measured thickness from the SLOFEC results The retirement thickness required to meet the loading condition at each segment of the conductor 2 Distribution of RL (per segment) --- The remaining time to exceed the Probability of Failure (PoF) target will be considered as the risk based remaining life. RL t MRT mm ( i) CR Distribution of corrosion rate per segments based on thickness data or corrosion models 3 4 Cumulative Distribution Function (CDF) t CR Trd age nom 5
Splash Zone Marine Zone Corrosion Rates Current Study Literature According to HSE Research Report 016 - Guideline for use of statistics analysis of sample inspection of corrosion Zones of corrosion for Steel Piling in Seawater Estimated CR will be the 95% confidence limit Source: F. L. LaQue, Marine Corrosion cause and Precention, P. 116, john Wiley & Sons, 1975. Reproduced by permission of The Electrochemical Society.
Risk and Risk Based Remaining Life Predictive target risk date (RLI) Inspection frequency determined
Risk and Risk Based Remaining Life Distribution of Remaining Life due to the distribution in Corrosion Rate (per each section of the conductor) The remaining time to exceed the Probability of Failure (PoF) target will be considered as the Risk Based Remaining Life (RBRL). 5 Very High 4 High 10-2 BS 7910 Annex K PROBABILITY 3 2 10-3 Medium Low 10-4 1 10-5 Very Low 10-6 Water Injection OP (1) <10000 OH (1) <15000 OP (1) >10000 OH (1) <15000 OP (1) <10000 OH (1) >15000 OP (1) >10000 OH (1) >15000 Unmanned M anned or Very Low Low Medium High A B C D CONSEQUENCE Very High E
Results per section of conductors Total of 98 sections from 25 conductors Current Risk Forcasted Risk In 7 Years Very High 5 5 5 1 Very High 9 2 2 PROBABILITY 10-2 High 4 4 10-3 Medium 3 3 10-4 Low 2 2 10-5 1 1 Very Low 1 1 25 28 33 PROBABILITY High Medium Low 10-2 10-3 10-4 10-5 Very Low 2 2 2 1 1 2 4 2 3 15 22 25 10-6 10-6 Water Injection OP (1) <10000 OP (1) >10000 OP (1) <10000 OP (1) >10000 OH (1) <15000 OH (1) <15000 OH (1) >15000 OH (1) >15000 Water Injection OP (1) <10000 OP (1) >10000 OP (1) <10000 OP (1) >10000 OH (1) <15000 OH (1) <15000 OH (1) >15000 OH (1) >15000 Unmanned Manned or Unmanned Manned or Very Low Low Medium High Very High A B C D E CONSEQUENCE Very Low Low Medium High Very High A B C D E CONSEQUENCE
AUTOMATED MODELLING To reduce the level of conservatism built into these equations, finite element modelling can be used. This allows for: - Accurate/realistic modelling of the corrosion defect geometry - Incorporation of non-linear strain-hardening properties (full stressstrain curve) - Incorporation of non-linear deformation behaviour (buckling/bulging) - Combined loading conditions
FEA to validate Proposed methodology: Method 1: Applying a reduction strength factor. Method 2: Define distance criteria between two patches of corrosion
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Conclusion - Methodology for assessment of corroded pipes under combined loading was proposed. - This methodology was applied for conductors with probabilistic approach for reliability assessment. - This probabilistic risk model was designed for assessment of conductors in terms of Run Length Index (RLI) - Application of FEA proposed: distance criteria between two patches of corrosion to be defined and a reduction strength factor to be applied.