Welcome at our Masterclass. Centre Line Aligned assembly of cans

Transcription

1 Welcome at our Masterclass Centre Line Aligned assembly of cans

2 Daniel Butterworth DNV GL

3 What is Centre Line Alignment? OD Aligned ID Aligned CL Aligned Stress at ID circa 2% lower than stress at OD Preferential to have a larger SCF internally than externally for double sided welding Fatigue life for worse on the side with the thickness transition For single sided welding best ID aligned as root has a worse fatigue classification F3. SCF internally becomes 1.

4 The norm DNVGL-ST-0126 tolerances defined in DNVGL-OS-C401 Ch2 Section 11 δ t = Change in thickness δ m = Fabrication misalignment δ 0 = Inherent factor within SN curve 0.05t double sided, 0 for single sided or ground (table 3-1) 4

5 SCF s SCF s defined in DNVGL-RP-C203 Section 3, SCF butt welds at thickness transitions at girth welds in tubulars External (3.3.5) Internal (3.3.6) 5

6 Typical SCF s Where fatigue is critical it is governed by the side with the misalignment External SCF OD 1.0 to 1.05 (eqn 3.3.6) ID 1.0 to 1.45 (20mm step) (eqn 3.3.5) CL 1.0 to 1.1 (10mm step) (eqn 3.3.5) Internal SCF 1.0 to 1.45 (20mm step) (eqn 3.3.5) 1.0 to 1.04 (eqn 3.3.6) 1.0 to 1.1 (10mm step) (eqn 3.3.5) 6`

7 Potential Thickness reductions 7

8 Where is it Beneficial At all fatigue sensitive step changes in wall thickness CL alignment allows larger step changes in can thickness Influence of array cable hole can be limited to a single thicker can Driving damage reduction at CL welds 8

9 Driving induced fatigue Lower SCF = Lower Driving induced damage Thinner walls reduce pile tip energy For 10mm tinner over 45% of pile - blowcount > by 7% Damage at unalterred section 90% to 105% Stress per blow reduces below thinner section For 10mm thinner section CL alignment damage 60% of OD aligned At larger step changes driving damage will reduce further Differences will increase when driving is hard. 9

10 Cones SCF from Equations & 13 A - FE analysis required not covered by parametrics B - No other SCF s required if transition is outside at the base, and inside at the top C Internal transition at base would require eqn in addition to conical SCF A B C 10

11 Conical SCF Variations A good reason to avoid thickness transitions at conical junctions Can be improved with longer Tapers, CL alignment & FE 11

12 Life Extension Centreline alignment will mean additional fatigue life relative to OD or ID aligned for the same pile weight Capacity redistributed better Lower Driving induced fatigue as SCF lower Does not change other details cable entry holes, & attachements Reliable corrosion control measures needed for extended design life coatings ICCP... Does not influence parts of the structure with constant wall thickness often these are not fatigue driven Option to remove sensitivity to large step changes useful at cable entry cans As WTG s get larger, % of strucure driven by D/t increases CL allows sensitive portion to be optimised 12

13 Colin Emmett Atkins

14 Benefit of Centre Line Alignment Three real design case studies to understand the implications of the classical vs. Centre Line alignment welding: Triton Knoll offshore wind farm Another recently installed monopile project offshore wind farm, and A recent deepwater jacket offshore wind farm Risks and Rewards Geotechnical implications 14

15 Benefit of Centre Line Alignment Monopile design drivers What governs a MP s design? Fatigue Limit State (FLS) Attachments Circumferential welds Ultimate Limit State (ULS) Natural Frequency Servicibility Limit State (SLS) Accidental Limit State (ALS) Connection characteristics 15

16 Benefit of Centre Line Alignment Potential weight savings Weight reduction of 27.2 tonnes per pile 16

17 Benefit of Centre Line Alignment Triton Knoll 17

18 Benefit of Centre Line Alignment Weight savings Triton Knoll Concept development Classical Centre Line Change Transition Piece T T 0 T Monopile T T 15.9 T Total T T 15.9 T Average saving across 90 foundations tonnes across the site 18

19 Benefit of Centre Line Alignment enhanced integrity Triton Knoll lifetime damage Classical Centre Line TP CW TP CW MP CW MP CW MP CW MP CW MP CW MP CW MP CW At the critical location this equates to a reduced probability of failure of about 20% 19

20 Benefit of Centre Line Alignment Jacket pin-piles What governs a pin-pile s design? Connection characteristics Fatigue Limit State (FLS) Circumferential welds Ultimate Limit State (ULS) Servicibility Limit State (SLS) 20

21 Benefit of Centre Line Alignment Jacket Pin Piles Limited application for the CL alignment welding Only 2 thickness transitions in the pin- pile Achievable in a single transition with a saving of approx. 1 tonne per pile 344 piles - this equates to between 3 and 4 piles worth of steel saved 21

22 Applying Centre Line Alignment Geotechnical implications Clays Driving shoes are often used to aid driving Where used, there is no need for limitations on the use of CL welding Sands Reduced resistance of sections following a thicker can Short term effect reconsolidation Chalk Low skin friction used in design minimal effect 22

23 Applying Centre Line Alignment Geotechnical risks Possible reduced capacity? Not appreciable for thickness changes less than 15mm Sands short term Chalks - Permanent(?) 23

24 William Lafleur Sif Netherlands

25 The standard Stress concentrations at tubular weld connections are due to eccentricities resulting from different sources e.g. out of roundness or differences in thickness of joined tubulars. Where the differences in plate thickness of butt welds exceeds 4 mm the thicker plate shall be tapered not steeper than 1:3. Butt joints prone to fatigue loading shall be tapered not steeper than 1:4 (DNVGL-OS-C401). The transition shall be smooth and gradual. 25

26 The standard Some standards or codes indicate that the transition may be formed by any process that will provide a uniform taper (ASME BPVC VIII UW-9). The transition may be formed by adding additional weld metal beyond what would otherwise be the edge of the weld. The normal interpretation of DNVGL is that the taper starts on the bevelled edge from the thicker part. 26

27 The standard From a fabricators point of view (align with DNVGL requirements), thickness jumps up to 4 mm can be accommodated in the weld joint and do not require tapering. 27

28 Transition in butt welds of unequal thickness Butt weld No. 1 Thicker part T1 [mm] Thinner part T2 [mm] Change in thickness [mm] Non-Symmetrical (offset alignment) DNVGL-OS-C401: 2017 Symmetrical (centre alignment) 80 0 No taper No taper No taper. Transition incorporated in the weld No taper. Transition (on each side) incorporated in the weld Taper 1: Taper 1:4 on each side 28

29 T A ΔT Sif fabrication Taper (inside) is preferably made by machining in flat condition after which the plate is formed to a shell or shell segment by cold rolling. Inside max l plate Taper length of 100 mm can be performed by machining in flat condition, but this length is further restricted by the rolling process to approximately max. 75 mm. 29

30 Sif fabrication Inside tapers, when made in flat condition, end just before the longitudinal joint preparation, as to maintain a full cross section and facilitate longitudinal welding. Taper Machined taper Circumferential joint preparation Longitudinal joint 30

31 Sif fabrication Plate bevelling (with or without taper) executed at plate mill or at Sif. 31

32 Sif fabrication Outside tapers and inside tapers with a length 75 < l < 200mm, must be made by flame cutting & grinding after cold rolling longitudinal welding re-rolling. 32

33 Centre line alignment fabrication aspects Advantages Less machined tapers needed -Thickness jumps up to 8mm can be equalized in the weld. Applied in Oil & Gas industry experience. No new feature. Enhanced integrity / Potential weight savings. No impact on back milling and welding process. Rotational speed due to different diameters is automatically compensated by the roller beds. Disadvantages More welding passes needed when taper is accommodated in the weld joint slightly increased weld width. Measuring misalignment slightly more difficult. Symmetrical taper additional fabrication activity to perform outside taper. Both sides of the taper need to be restored by grinding (at the longitudinal weld location). Flush grinding of girth welds (if required), will take more time and require more caution during execution. 33

34 Thank you for your attention