![Page 1: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/1.jpg)
Subsea Drop Object Analysis
Understanding of the DNV Approach
Adekola Obayomi (CEng, MIMarEST)
27 February 2018
![Page 2: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/2.jpg)
• Recommended Practice
• Object Excursion by Group
• Probability of Hit
• Simulation Examples of Object Excursions
• Conclusion
Content
![Page 3: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/3.jpg)
Recommended Practice
• The primary requirement for a dropped object study is to categorise identified dropped objectsinto sizes and weights and estimate the excursion distance from the water entry drop point.
• This is usually achieved using the categories from DNVGL-RP-F107 (Risk assessment ofpipeline protection)
Source: Table 3.1, DNVGL-RP-F107
![Page 4: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/4.jpg)
Recommended Practice
• The excursion of the object subsea is calculated based on the water depth and angular deviationusing the table below
Source: Section 5.0, DNVGL-RP-F107
![Page 5: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/5.jpg)
Other Recommendations
DNVGL-ST-N001 recommends the following for dropped object assessment
![Page 6: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/6.jpg)
Object Excursion by GroupWater depth = 99m
No Description Weight (tonnes)
Angular deviation (α) (deg)
Excursion Distance (m)
Excursion Diameter (m)
DNVGL-RP-F1071
Flat/ Long shaped<2 15 26.53 53.05
2 2 - 8 9 15.68 31.363 > 8 5 8.66 17.324
Box/Round Shaped<2 10 17.46 34.91
5 2 - 8 5 8.66 17.716 > 8 3 5.19 10.387 Box/Round Shaped >> 8 2 3.46 6.91
DNVGL-ST-N0011 General N/A 20 36.03 72.07
Excursion Distance / Diameter 36.03 72.07
![Page 7: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/7.jpg)
Probability Hit GraphWater depth = 99m
Radius x(m)
Phit
0 0.00005 0.110410 0.218620 0.421130 0.594940 0.733050 0.834760 0.904170 0.947980 0.973690 0.9875
100 0.9945110 0.9977120 0.9991130 0.9997140 0.9999150 1.0000
![Page 8: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/8.jpg)
Drop Zone Plots (20deg Excursion Angle)*
*68% probability of hit inside exclusion zone based on DNVGL normal distribution formula
![Page 9: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/9.jpg)
OrcaFlex Setup model
![Page 10: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/10.jpg)
Content
SIMULATION EXAMPLES
![Page 11: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/11.jpg)
Scatter diagram and fall profile of dropped Objects
![Page 12: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/12.jpg)
Conclusion
• It should be remembered that the lateral deviation formula in the code only gives a seabed excursion distance where 68% of objects in the category will fall.
• The most common calculation produced by subsea contractors for calculating the safe overboarding distance from assets of interest does not reflect the actual possible excursion distance the dropped object cover
• Measures in accordance with the As Low As Reasonably Practicable (ALARP) principle should always be put in place to assess and mitigate risk of a dropped object on an asset ofinterest during lifting operations which can lead to a drop event.
![Page 13: Subsea Drop Object Analysis - DROPSOnline€¦ · Subsea Drop Object Analysis. Understanding of the DNV Approach. Adekola Obayomi (CEng, MIMarEST) 27 February 2018 •](https://reader036.vdocument.in/reader036/viewer/2022062417/613d8880e1ef621e9f2dc840/html5/thumbnails/13.jpg)
ONE PARTNER.WORLDWIDE SUPPORT.
www.loc-group.com