( بسماللهالرحمنالرحيم)
COLOR=#000000 لِيَجْزِيَهُمْ اللَّهُ أَحْسَنَ مَا عَمِلُوا وَيَزِيدَهُمْ مِنْ فَضْلِهِ وَاللَّهُ يَرْزُقُ مَنْ يَشَاءُ بِغَيْرِ حِسَابٍ ([/color]38) وَالَّذِينَ كَفَرُوا أَعْمَالُهُمْ كَسَرَابٍ بِقِيعَةٍ يَحْسَبُهُ الظَّمْآنُ مَاءً حَتَّى إِذَا جَاءَهُ لَمْ يَجِدْهُ شَيْئاً وَوَجَدَ اللَّهَ عِنْدَهُ فَوَفَّاهُ حِسَابَهُ وَاللَّهُ سَرِيعُ الْحِسَابِ (39) أَوْ كَظُلُمَاتٍ فِي بَحْرٍ لُجِّيٍّ يَغْشَاهُ مَوْجٌ مِنْ فَوْقِهِ مَوْجٌ مِنْ فَوْقِهِ سَحَابٌ ظُلُمَاتٌ بَعْضُهَا فَوْقَ بَعْضٍ إِذَا أَخْرَجَ يَدَهُ لَمْ يَكَدْ يَرَاهَا وَمَنْ لَمْ يَجْعَلْ اللَّهُ لَهُ نُوراً فَمَا لَهُ مِنْ نُورٍ (40)
* صدق الله العظيم *
( 24 - سورة النــور )
[LEFT][RIGHT]Edit by alaa refit waheed hekail bhit 5th civil departement2007©
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[RIGHT]contents
CHAPTER 1
HESTORICAL OVERVIEW of offshore structure
CHAPTER 2
GENERAL INTRODUCTION OF OFFSHOER STRUCTUER
CHAPTER 3
KIND OF OFFSHOER STRUCTUER
CHAPTER 4
GENERAL INTRODUCTION OF TLP OFFSHOER STRUCTUER
CHAPTER 5
TENSION LEG PLATFORM SYSTEM
CHAPTER 9
INTERNET SITES[/right]
[LEFT][RIGHT]Edit by alaa refit waheed hekail bhit 5th civil departement2007©
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[RIGHT]CHAPTER 1
Index
HESTORICAL OVERVIEW of offshore structure[/right]
[LEFT][RIGHT]Edit by alaa refit waheed hekail bhit 5th civil departement2007©
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HESTORICAL OVER VIEW
One after the other of spectacular structures, 22 in total, have been placed on the sea bed in the North Sea reaching up to 30 m above sea level and down to 303 m at the deepest location, making this structure one of the tallest concrete structures in the world (Holand and Lenschow, 1996).
The most innovative period was around 1970, when the Ekofisk concrete platform was towed to its location, and the first of the many Condeep platforms was on the drawingboard.
( The Ekofisk tank, completed 1973 (by courtesy of Aker Maritime )
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Furthermore, offshore concrete structures have proved to be highly durable and to have good resistance against corrosion (Fjeld and Morely, 1983), provided that the concrete is dense, have a minimum of cracks and sufficient cover over the rebars. The Norwegian Standard NS 3473 requires 40 mm for permanently submerged parts and 60 mm in the splash zone. In the North Sea even larger rebar covers have normally been used.
Recent concrete projects are:
· in the Netherlands: F3, concrete gravity base 1992
· in the North Sea, Norwegian sector: Troll gas fixed platform, Heidrun tension leg platform and Troll oil catenary anchored floating oil platform , all completed in 1995
· in the North Sea, British sector: The BP Harding Gravity Base Tank completed in 1995
· in Congo: N’ Kossa, concrete barge 1995
· in Australia: Wandoo B, Bream B, West Tuna, concrete substructures completed 1996
· on the Canadian continental shelf outside Newfoundland: Hibernia 1997
· in the North Sea, Danish sector: South Arne, to be completed in 1999.
Although the recent development has not favoured concrete platforms, there are several concept studies ongoing in the design offices. As promising floater concepts, new generations of tension leg platforms and a concrete Spar shall be mentioned. (Chabot, 1997), (Brown and Nygaard, 1997).
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[RIGHT]At present work is ongoing to develop more cost-efficient concrete structures for development of smaller hydrocarbon fields. The F3 field in the Dutch offshore sector, mentioned above, is an example; a concrete structure installed at Ravenspurne North in the British sector is another.
Design concepts
1- Cylindrical tanks:-
The first concrete platform was the Ekofisk platform, that was built according to a French-Canadian concept and completed in 1973.
The decision to launch the Ekofisk platform made way for the development, not only of offshore structures but also for a development of the concrete material, design methods, construction methods, load predictions, quality management and safety evaluations.
Three additional designs in the North Sea followed mainly the Ekofisk concept (Frigg CDP1 1975, Frigg MP-2 1976 and Ninian Centre 1978) (FIP, 1996). The huge platform built by Mobil at the Hibernia field in Canadian waters and completed in 1997 is also mainly of the same type
2- Condeeps and similar gravity based structures:-
the Condeep,which became the winning concept for a period of time, was based on a cellular base with circular cells and one to four hollow columns (shafts), and thus had the advantage of a slim shape through the wave zone. Beryl Alpha, the first Condeep platform, was placed on the UK continental shelf in 1975. Up to 1995 a total of 14 Condeeps have been installed in the North Sea (Agnes, 1997). shows the largest of these structures .
Other designs were based on the same principles, except that the cells in the raft were rectangular (four platforms in the North Sea completed 1976-78, and also BP Harding in UK waters, 1995, and South Arne on Danish Continental shelf, 1999)
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