FPSOs & Mooring Systems David Brown, BPP-TECH London

Transcription

1 David Brown, BPP-TECH London 1

2 David Brown, BPP-TECH London 2 Professional Naval Architect and Mechanical Engineer Engineering Director at BPP-TECH, specialises in FPSOs & moorings Chairman of ISSC Floating Production Systems Committee (from ) Committee mandate: Concern for the design of floating production systems. Specific emphasis shall be given to FPSO hulls and the recent industry experience that influences the design methodology. Consideration shall be given to identification and quantification of uncertainties for use in reliability methods.

3 COMPANY OVERVIEW History: Established in 1981 Sectors: Oil & Gas, Renewables, Insurance 3 BPP-TECH Specialist Engineering Consultancy provides: Concept and feasibility studies for floating offshore systems (vessels, moorings, risers, pipelines, umbilicals, power cables) Procurement support for subsea systems (SURF) Engineering for insured risk reduction & claims (failure analysis) Offshore monitoring and instrumentation BPP-CABLES -Formed recently to satisfy needs of offshore power cable market

4 Introduction FPSOs & Mooring Systems 4 Introduction Expanding market Vulnerability Hardware Codes Environment Life cycle - design, installation, operation & maintenance, retirement Failure modes Losses Risk reduction

5 Introduction 5

6 Introduction 6

7 Introduction Drivers: Global demand for oil growing Middle East/N Africa supply disruption Oil prices at $100/bbl Deep water drilling rigs will boost fleet by 38% Huge pre-salt discoveries offshore Brazil Existing fleet: 250 units in service, including TLPs, Spars & Semis Doubled since (ref IMA rpt 3/11, Upstream 5/11)

8 Introduction 8

9 Introduction 9 Source

10 Introduction 10 Source

11 Expanding market 11 Source: Upstream 5/11

12 Expanding market 12 New units 55 - current bids or final design (next 18 mths) 139 planning phase 194- in total Source: Upstream 5/11

13 Expanding market 13 Source: Upstream 5/11

14 Expanding market 14 Source: Upstream 5/11

15 Expanding market Prelude FLNG 488m by 74m hull 600,000 Tonne 100m high turret 15 Source: The Engineer 09

16 Expanding market 16 Source: Upstream 5/11

17 Vulnerability Vulnerability: 17 Class Rules evolving from seafaring background Tanker conversions to FPSOs New developments Speedier, smaller operators, remote environments, deeper water, more subsea assets, increased asset values Existing developments -Equipment replacement considered as repairs, obsolete class codes continue to be used, many legacy systems in place for many years (eg SPMs & offloading tankers) Limited redundancy in mooring system, chain as strong as its weakest link Difficult to inspect & maintain, degradation & retirement issues Rapid incident escalation (eg cascading failure) in hostile environments Consequences can lead to major loss including damage to subsea architecture

18 Hardware 18 Dahlia FPSO Source: Upstream 5/11

19 Hardware 19

20 Hardware 20 Spread mooring

21 Hardware 21 Typical single point mooring - external turret Source: API RP 2SK

22 Hardware 22 Catenary anchor leg mooring hawsers & fixed yoke (Source API RP 2SK)

23 Hardware 23 Most permanent moorings use studless chain Studded chain: studs loosen, crack & fracture at weld Studless chain: ~10% lighter, same Tbreak, lower fatigue life DNV-OS-E301, Oct 2010 Diameter upto 6 1 link weighs 0.5T, 0.9m long Kenter shackle not allowed for long term mooring

24 Hardware 24 Typical wire rope & permanent mooring socket Galvanized jacketed spin resistant is best, yr life expectancy Ability to inspect? (API RP 2SK)

25 Codes Various authoritative documents on mooring initial design, eg: API RP 2SK (Oct 2005), GoM2008 addendum DNV E301 (Oct 2010) ISO (2005) - new standard being developed There is little guidance on detailed design or mooring operational phase. Some inspection standard & retirement criteria given in: API RP 2I 3 rd ed.(apr 2008) API RP 2SM synthetic fibre lines Intl Assocof Class Socs(IACS) No 38 Oct

26 Codes Oil & Gas UK: Mooring Integrity Guidance 08 Develop Mooring Integrity Management System Recognise that manuf. & deployment contribute to reduced life Strategy on operational intent wrtinspectability, op & survival limits AND plan if breached Detailed risk review Monitoring to confirm actual behaviour & deviation from as designed Inspection driven by the risk review System to track findings & anomalies 26

27 Environment 27

28 Environment 100 yrhs (typhoon) S China Sea m Timor Sea - 5.5m Mooring design limit = 8m STS wind speed > 48 kn Annually high probability of unavoidable annual storms have wind speed > mooring design limit 28 Average number of Storms of STS severity and higher per annum in the South China Sea ( ) high probability of wind speed > Typhoon Koppu (65 kn)

29 Life cycle - design Offshore Standard DNV-OS-E301, Oct 2010 Position Mooring Criteria, guidelines on design & construction Environmental conditions & its direction Loads - wind, wave & low freq (drift), current, VIV Mooring analysis ULS (extreme env) ALS (failure of 1 line, 1 thruster, etc) FLS (line cyclic loading, steel) Thruster assisted moorings Mooring equipment inc. anchors & piles Testing 29 Directionality : W Africa (non correlated) Other: Wave 0 deg, wind 30 deg, current 45 deg

30 Life cycle - design 30 Design criteria: Tension limits & safety factors (API RP 2SK)

31 Life cycle operation & maintenance API RP 2I In-service Inspection of Mooring Hardware, Apr Covers steel permanent moorings & fibre ropes Also MODU moorings in tropical cyclone areas Inspection 3 systems (O&G UK Mooring Integrity Guidelines 2008) Divers, successful history but safety risks (near surface & saturated), dedicated dive vessel required ROVs, large work class vehicles working from welded down platforms on FPSO or work vessel, smaller ROVs becoming more versatile (eg can be transported by helicopter) AUVs, specifically inspect detailed condition of mooring system, coming onto the market (Norwegian JIP)

32 Life cycle operation & maintenance Inspection systems - Vessel & seabed sonar - Hull mounted cameras - Pressure sensors - Tension monitoring by turret strain - Tension measurement in line - Strain measurement - ACSM (Alternating Current Stress) - Tension monitoring near touchdown - Seismic detection - Tension monitoring at stopper - Hydro-acoustic - Strain wire O&G UK mooring integrity guidelines 2008 EgWelaptega Chain Measurement System ROV based Wear, corrosion & pitting, plus link/link erosion Establishes link length & bar stock diameter Compares data with rejection criteria Ageing & degradation can be established 32

33 Life cycle operation & maintenance Visual Inspection: Link deformations Corrosion Interlink contact zones Welds Wear marks/cracks etc Factors noted on each link: Stud condition: - missing stud: - loose stud: - Gap between stud and link: Bend in link: Abrasion/wear: Corrosion state: Are there any visible cracks: Measurements (mm): Chain no.: Link no.: 33 Observations: Images: Corrosion state of the stud: Length (L) = D 2L = Breadth (B) = D 2W = D 1L = D 3 = D 1W =

34 Line failure Hazard Failure Group Hazard Failure Group 34 Input Data Design Seabed, Metocean, Vessel, Mooring comps Code, Method, Spec Corrosion General, Galvanic, Biological /SRB,Chemical, Hydrogen embrittlement StrengthSoF, Snatch load, Bend radius, Means of securing Wear /erosion Fatigue With connected item, Internal, with seabed Axial, Bending, Torsion Contact Motion Manufacturing Vessels, Seabed, Dropped object, During inspection of attachment point or external item, Seabed scouring O&G UK mooring integrity guidelines 2008 Deployment

35 Line failure Failure Modes defined for each Failure Group, eg: Input Data 35 Metocean (occurred & contributed to failure) Weather data not up to date Data from too short observation period Poor density or sea temp information Insufficient data on LAT, tide & storm ranges Squall risk not identified No time series data (wind, wave, current combinations) O&G UK mooring integrity guidelines 2008

36 Line failure Failure Modes defined for each Failure Group, eg: Deployment 36 Deployment (occurred & contributed to failure) Physical damage due to poor handling Side loading on chain links & shackles, increased SCF Cold bending or local heating (spot welding) causing reduced fatigue life Wrong shackle sizes Inappropriate deployment, lines dog-legged Anchors non-aligned to pull direction Worn pockets in chain gypsies, causing link bending O&G UK mooring integrity guidelines 2008

37 Line failure Common problems observed in used wire ropes Broken wires Wear Corrosion Loss of lubrication Change in rope diameter Distortion of the rope (kinking, bending, scrubbing, crushing, flattening, birdcaging) Thermal damage 37

38 Line failure Terminations: 38 Hawse tubes - Highest tension with additional bending, twisting stresses &contact wear of the links Touchdown - Heavy contact with sea floor which may contain rock of comparable hardness to steel -> severe localized wear Main Factors Influencing Long-Term Mooring Integrity Also inspection and maintenance, mooring jewellery Touchdown - Accelerated corrosion (aerobic) as chain moves above & below mudline, parent metal exposure Source: HSE 2006 study

39 Line failure 39 Disconnectable assets Remaining on station during hurricane events Remaining connected during monsoons Inability to disconnect during short notice typhoons

40 Line failure 40 Source: API

41 Line failure 41 Mooring degradation disconnectable vessels riding-out storms causing accel degradation Mooring systems operating beyond design life Moorings designed to out-dated codes

42 Line failure Indicative stats (based on N Sea FPSOs) 42 50% of units cannot monitor line tensions in real time, 33% of units cannot measure offsets from the no-load equilibrium position, 78% of units do not have line failure alarms, 67% of units do not have mooring line spares available, 50% of units cannot adjust line lengths. Single line failure costs 50,000 bpd N. Sea FPSO 2m 250,000 bpd W. African FPSO 10.5m Source: HSE 2006 study

43 Losses Girassol Offloading Buoy Mooring Spring 2002, buoy broke free of moorings Chain failed in buoy's hawser, due to fatigue loading Lessons learnt (Design) new failure mode, chain out of plane bending under tension in hawser 43 (Ref HSE Report: Floating production system -JIP FPS mooring integrity)

44 Case Study FPSOs & Mooring Systems Losses Recent GoM tropical storms Ivan, 2005 Katrina & Rita, 2007 Gustav & Ike (Source Numerous drilling rigs broke moorings, 255 pipelines damaged in Katrina, 206 in Rita Lessons learnt design to 10 yrenv, API GoM2008 addendum, top end line failure, anchor drag (soils) (Source - thomko.squarespace.com) 44

45 Losses Gryphon 45 Retrieved subsea arches (Upstream 9/11) Loss 2/11 Winds > 55 kn, 9m waves, 10 leg mooring Cascading events.. low tension line failure, DP miscalculates wind & wave forces, turns FPSO beam on, 21 deg roll, 3 more legs lost, blackout, 200m movement ripping prod & inj lines & umbilicals 2008 chain failure 2009 DP problems (software)

46 Losses Cascade Chinook 46 Loss 3/11 Faulty weld repair causes fracture in single chain link near butt weld Post-heat treat made chain vulnerable to hydrogen induced stress cracking Chain was T air can supporting hybrid riser released Upstream 5/11 Pictures:

47 Risk reduction Questions to the assured: Are Oil & Gas UK Mooring Integrity Guidance (2008) procedures followed? 2. Are line tensions and offsets monitored & stored? 3. Are there functioning line failure alarms on board? 4. Are line spares available? 5. Can line lengths be adjusted? 6. What inspection/reclassification is carried out should line tensions exceed design limits (eg drift off DP issue or non-disconnect)? 7. What is the policy on monitoring and retirement of ageing assets?

48 CLIENTS For more info please contact: 48 David Brown