Decommissioning of offshore structures by means of …. Niras Demex.pdf · Decommissioning of offshore structures by means of explosives ... preferable method for many years ... •

Decommissioning Conference

11 October 2007, Esbjerg

Decommissioning of offshore structures by means of explosives

AuthorsErik K. Lauritzen, Johan F. Gjødvad and Claus Gormsen

NIRAS DEMEX

Presented byJohan F. Gjødvad



Content

• Presentation of NIRAS DEMEX• Challenges of demolition of offshore

structures• Demolition and recycling of structures• Demolition by explosives – one of many

tools• Decommissioning of Norwegian offshore

structures by blasting • Decommissioning of wind turbines by

blasting • Design of decommissioning• Q&A



• Agriculture

• Building and industry

• Civil works

• Energy

• Environment

• Management sciences

• Urban planning

• Transportation

• Social sciences

• Hazardous waste

• Defence & security

Consulting Engineers and Planners:



Introduction - NIRAS

• The number four consulting engineering company in Denmark

• 1,000 employees

• 14 offices in Denmark

• Subsidiaries in Poland, Sweden, Ukraine, Finland, Bulgaria, Greenland, Tanzania and Zambia

• Turnover: $ 120 mill annually



DEMEX Defence and Security Technologies

Demolition

Protection of vehicles againstexplosions

Decommissioning of militaryinstallations

Mine & UXO clearance

Security for Danish embassies

Blasting for construction



Selected Offshore References

• Proposal for blasting of Drogden Lighthouse 2003

• Pre-planned dismantling of marine windturbines, 2001

• Review of cost estimation, Frigg Field, 2000

• Norwegian offshore structures, decom. study, 1999 - 2000

• Study of demolition Ekofisk Tank by blasting, 1998

• Proposal for disposal of Brent Spar, 1994



Challenges of demolition of offshore structures

• Heavy concrete and/or steel structures

• Marine environment

• Sensitive environment

• High risk operations



Barrow Offshore Wind, monopile arrangement



Demolition and recycling of structures

1. Before demolition all environmental problematic materials must be removed (e.g. asbestos, PCB, oil and chemicals etc)

2. Striping of structure – removal of all installations, doors, windows, floors, machinery etc.

3. Selective demolition of structure – downsizing of bearing steel/concrete members and sorting of the fractions on site.

4. Transportation to disposal site or treatment site

5. Recovery, recycling, reuse or disposal of waste materials

6. Cleaning up and hand over of the site



Technologies for demolition of structures

Types of demolition:

• Total demolition

• Partial demolition

Type of demolition methods:

• Downsizing, treatment of materials of site

• Downsizing, treatment of materials on site

• Dismantling of structure members by cutting and crane lifting

Demolition technologies:

• Concrete breakers

• Steel cutters

• Chain and ball

• Hydraulic jack hammers

• Blasting

• Water jetting

• oxygen cutting



Demolition by blasting - advantages

• No need for big machines – only drilling machines explosives

• Modern technologies e.g. shaped charges and MINIBLASTING made possible to control the effects and risks.

• Blasting is carried out as a remote tool

• Blasting very applicable to dismantling methods



Practical Experience of Mini-Blasting:

Blasting of Foundation Piles



Practical Experience of Mini-Blasting



Dismantling1. Drilling

2 Charging

3. Hook on crane

4. Blasting

5. Cutting of bars

6. Lifting



Demolition of offshore structures by blasting

Total demolition of offshore structures has been a preferable method for many years (e.g US platforms). However, the environmental impact, especially the impact to fish from big explosives charges has been is a great problem.

Blasting was the only possible method for removing several damaged structures after the Hurricane Katerina, 2005

To day new blasting technologies with small explosives charges and designed protection means open new application for blasting as a supplementary demolition tool.



Demolition of offshore structures by blasting

Typical applications:

• Blasting of concrete structures by explosive

charges in drill holes

• Cutting of mono-pile foundations by explosive

cutting charges

• Cut of top site structures for dismantling by crane

• Blasting of damaged offshore structures

• Blasting of anchors, risers etc.

• Weakening of structures before demolition.



Dismantling of offshore concrete structuresby blasting

Experiences of the project ”Removal Offshore ConcreteStructure” conducted by a number of Norwegianoffshore industries in 2000.

DEMEX was subcunsultant to Dr. Tech. Olav Olsen, Oslo on the study of dismantling the structures ofGulfaks by blasting, including:

• Dismantling of shafts

• Dismantling of tri-cells

• Risk assessment



Dismantling of Shafts

Blasting of Shaft Structure,

Dismantling of three element < 300 t

Drill holes

For crane lifting

0.5 m

12 m

6.6 m

For crane lifting

Drill hole




Blasting of Shaft Structure,

Dismantling 300t-3,000t

For crane lifting

40 m

6.6 m

Bore holes

0.5 m

0.5 m




0.65 m 0.65 m

Reinforcement barsDrill hole

0.65 m

2.0 m

Ri = 6.60 m

0.65 m

Blasting of shaft structure, fragmentation



Dismantling of Tri-Cells

Supplementary holes

for fragmentation

Area chrushed

by blasting

1.40 m

0.7 m

0.7 m

1.40 m

0.70 m

3.60 m

1.40 m

Blasting of Tri Cell structure, weakening

Blasting of Tri Cell structure, dismantling



Dismantling of offshore steel structures by blasting

Cutting of steel using shaped charges

Types of shaped charges



Dismantling of offshore steel structures by blastingusing shaped charges

Principles of the effect of shaped charges



Perfolit 16 kg

16 kg charge

Filled with Bonogel(PTEN based explosive) (possibly with Dynamite or other explosive)

Can be used at an underwater depth of approx. 70 m



Explosive cutting tape (ECT) BLADE



BLADE/ECT



BLADE/ECT



BLADE/ECT



Proposed cut of mono-pilesHorns Rev 1, 2001

Dismantling of mono-pile of wind turbine, 2 MW:

1) Nacell and tower shaft are removed.

2) Interior ballast inside the mono-pile removed

3) Shaped charge, designed for cutting the still, 50 mm thick, mounted inside the mono-pile 1 m below bottom line.

4) Crane hook on the shaft.

5) Detonation of the explosive charge.

6) Removal of the shaft.

DENSIT fixture

- 11.00

- 12.00

0.0

4.0 m

Thickness 50 mm











Conclusions

�Blasting of concrete and steel structures has an important

role in the demolition industry

�Remote cutting of steel and concrete structure by blasting

is quick and safe

�The blasting methods must be designed and compared

with traditional demolition methods

�The risk of blasting is of the same level of other demolition

technologies

�Dismantling of concrete and steel offshore structures is a

favourable demolition method



Any Questions ?

Thanks for the attention

Johan F. Gjø[email protected]

Documents

Decommissioning of offshore structures by means of …. Niras Demex.pdf · Decommissioning of offshore structures by means of explosives ... preferable method for many years ... •