Monday, February 13, 2012

Offshore Platform Structure

One month ago my lecturer gave me some material about offshore platform. now i am trying to give explanation about these material. Offshore platform has been used in oil and gas industry as early as 1930 in Venezuela. The first offshore platform was made by wood material. The steel type platform was then used in 1947 in a 6 m depth of water in the Gulf of Mexico. Since that period, various types of offshore platform has been developed and used as main offshore facility in oil and gas industry. Offshore platform can be used in many ways. A full offshore oil and gas facility can have many platforms such as quarters platform, wellhead platform, process platform, compressor platform, etc.
Type of structure and the support configuration of offshore platform are in consideration with depth and difficulties in erecting the platform. Therefore, there are many types of offshore platform. Based on the type of structure, offshore platform can be divided as :
  • Concrete gravity platform
  • Fixed steel platform
  • Semi submersible platform
  • Tension leg platform
  • Guyed tower platform

A ‘Statfjord’ gravity based structure under construction in Norway.
1, 2) conventional fixed platforms; 3) compliant tower; 4, 5) vertically moored tension leg and mini-tension leg platform; 6) Spar ; 7,8) Semi-submersibles ; 9) Floating production, storage, and offloading facility; 10) sub-sea completion and tie-back to host facility.

In addition to that classification, depending on the number of legs & jacket type, fixed offshore platform can be divided into :
  • Monopod platform
  • Bipod platform
  • Tripod platform
  • 4, 6, or 8 pile platform
A common offshore platform is consisted of platform deck, jacket, and pile. Deck is the place where all production equipments are placed. Jacket is a tubular steel structure that serves as a lateral load support for the platform while pile serves as a vertical load support. For come cases, jacket is not used because the lateral load of platform is neglect able.
In a common Offshore platform, deck, jacket, and pile are fabricated onshore. The first stage of platform erection is transporting the jacket and putting it in the designated place. After the jacket is fixed in the right place, pile is driven via the jacket hollow tube to the sea bed. Finally, the deck part is placed and connected at the top of support structure.
For safety and ergonomic reasons, platform layout should be carefully designed. Platform north should be facing to deeper water. This north part is also used as the area for jack up drilling rig and foundations spud can or mat. The south side platform is used for boat berthing, pipeline riser and subsea pipeline. Layout of platform should also be designed by considering drilling sequence, prevailing wind, and other utility such as helipad.
Load acting on platform is vital in a platform’s design stage. In designing a platform, load can be divided to load at deck structure and load at jacket structure. In general, the working load in an offshore platform consisted of the following load.
Load at Deck structure:
  • Topside load : Deck structure, piping, equipment, life load, crane load, helicopter load, drilling work over load.
  • Lateral load : Wind and earthquake.
Load at Jacket structure:
  • Vertical load : Deck structure and buoyancy
  • Lateral load : Wind, wave, current, earthquake, and added hydrodynamic mass.
Some of applicable engineering standards for offshore platform design are:
  • API RP2A Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms
  • AISC Specifications for Design, Fabrication and Erection of Structural Steel Buildings
  • API Spec 2B, Fabricated Structural Pipes
  • AWS D 1.1, section 8 and 10
  • ISO 19902 Petroleum and Natural Gas Industries – Fixed Steel Offshore Structures
  • ISO 19901-2 Petroleum and Natural Gas Industries – Specific requirements for offshore structures Part 2 Seismic Design Procedures and Criteria

A Letter from "Mom and Dad"

My child,

When I get old, I hope you understand ‘…n have patience with me

In case I break the plate, or spill soup on the table because I’m losing my eyesight, I hope you don’t yell at me.

Older people are sensitive, always having self pity when you yell.

When my hearing gets worse ‘n I can’t hear what you’re saying, I hope you don’t call me ‘Deaf!’

Please repeat what you said or write it down.

I’m sorry, my child.

I’m getting older.

When my knees get weaker, I hope you have the patience to help me get up.

Like how I used to help you while you were little, learning how to walk.

Please bear with me, when I keep repeating myself like a broken record, I hope you just keep listening to me.

Please don’t make fun of me, or get sick of listening to me.

Do you remember when you were little ‘n you wanted a ballon? You repeated yourself over ‘n over until you get what you wanted.

Please also pardon my smell. I smell like an old person.Please don’t force me to shower.

My body is weak.

Old people get sick easily when they’re cold. I hope I don’t gross you out.

Do you remember when you were little? I used to chase you around because you didn’t want to shower.

I hope you can be patient with me when I’m always cranky. It’s all part of getting old.

You’ll understand when you’re older.

‘n if you have spare time, I hope we can talk even for a few minutes.

I’m always all by myself all the time, ‘n have no one to talk to.

I know you’re busy with work.

Even if you’re not interested in my stories, please have time for me.

Do you remember when you were little? I used to listen to your stories about your teddy bear.

When the time comes, ‘n I get ill ‘n bedridden, I hope you have the patience to take care of me.

I’m sorry if I accidentally wet the bed or make a mess.

I hope you have the patience to take care of me during the last few moments of my life.

I’m not going to last much longer, anyway.

When the time of my death comes, I hope you hold my hand ‘n give me strength to face death.

‘n don’t worry..

When I finally meet our creator, I will whisper in his ear to bless you. Because you loved your Mom ‘n Dad.

Thank you so much for your care.

We love you. ! ♥

Friday, February 3, 2012

"Being in Competition...DARE U!"

The tittle of my article is really offensive manner. i am very sory to those who always living in comfort zone. i am personally hate with this word. yeah " Competition" the word which will distingush people into two kind, the looser and the winner.

Life is a a competition. I’ve heard many people complained about this statement. They argue that perceiving life as a competition would make life feel un-enjoyable and full with seriousness. Let me elaborate why I think life need to be a competition and will always be.

Firstly, whether we realizing it or not, competition will make us better. Being in a competition, someone will always try to improve his/her performance which in the end, whether (s)he win or not, will improve his overall capability. One of my professor explained why many overseas chinese and indians are more successful than their family in their home country. His answer is because these chinese and indians areexposed to a competitive world, either in US, europe, or anywhere else.

I do agree that our life need not to be a stressful life; however, I’m even more disagree if we think that this life is just to be enjoyed, whether not to pray to the God at all or doing the good thing in a slow pace. Having in mind that this is a competition, competition between us and ourselves and a competition between us and the time.

Lastly, in term of applicability, when I was a junior high school student, I think a round 10 years ago, even though I was studying in a countryside area, I always think that I have to improve my knowledge, because I want to be on the same level of competency with the students in Java (because java is the most developed region in Indonesia). When I was studying at the university, even though I was studying in the best university in Indonesia, I stress my mind that I have to be as smart and competent as the harvard student. believe me, all of this mind suggestion work.

Bearing in mind that we are competing in this life, it will makes us want to do more and to improve more. So, ready to be in the race? Good luck!

Thursday, February 2, 2012

Kenapa Harus Struktur BAJA??

Baja telah mengganti kedudukan besi tempa sebagai bahan utama bangunan logam sejak abad ke- 19. Hingga tahun 1960-an, baja yang dipergunakan dalam konstruksi, menurut klasifikasi ASTM (American Society for Testing and Materials), tergolong sebagai baja karbon A7 dengan spesifikasi tegangan leleh minimum sebesar 33 ksi. Pada saat itu, baja struktur lainnya seperti baja paduan rendah yang khusus tahan korosi (A242) dan baja yang lebih siap di las (A373), memang sudah tersedia namun masih jarang digunakan pada bangunan.
Lain halnya dengan saat ini, sekarang telah tersedia baja dengan berbagai pilihan, sehingga bahan tersebut sudah mungkin digunakan dengan kekuatan lebih besar maupun pada tempat-tempat yang tegangannya sangat tinggi tanpa mamperbesar ukuran batangnya. Dewasa ini baja telah memiliki tegangan leleh dari 24000 sampai dengan 100000 psi (pounds per square inch) (165 - 690 MPa) dan telah tersedia untuk berbagai keperluan struktural.
Dalam dunia offshore, baja juga memiliki peranan penting karena baja saat ini merupakan material utama yang digunakan untuk membuat platform. Apalagi bagi tipe platform di Indonesia yang didominasi oleh tipe jacket platform. Pengetahuan yang cukup bagi seorang perencana mengenai bahan atau material ini akan sangat bermanfaat terutama untuk mengoptimalkan antara kekuatan struktur dengan biaya konstruksi maupun perawatan.
Baja memiliki sifat-sifat yang menguntungkan untuk dipakai sebagai bahan struktur yang mampu memikul beban statik maupun beban dinamik. Alasan lainnya sehingga baja banyak digunakan dalam perencanaan struktur anjungan lepas pantai adalah sebagai berikut :
1. Isotropi
Baja mempunyai kekuatan yang sama terhadap tarik maupun tekan. Hal ini akan sangat menguntungkan bila struktur mengalami beban siklis seperti beban gelombang.
2. Daktilitas
Baja mempunyai daktilitas yang besar sehingga struktur dapat mengalami deformasi yang besar tanpa penambahan beban. Hal ini dapat dijadikan sebagai tanda (warning) sebelum struktur sepenuhnya runtuh.
§ Dapat dibentuk sesuai keinginan
Baja dapat difabrikasi lebih mudah sesuai bentuk yang diinginkan, baik bentuk penampangnya maupun bentuk rangkanya.
3. Perbandingan antara kekuatan dan berat yang besar
Hal ini menguntungkan karena dapat menghasilkan desain yang efisien. Bangunan struktur baja mempunyai keunggulan dalam hal rasio cukup kecil antara berat sendiri dengan daya dukung beban yang dapat dipikulnya jika dibandingkan dengan bangunan struktur beton. Dari sisi lain hal ini juga memiliki kekurangan, yaitu struktur menjadi langsing, sehingga perilaku responsnya kurang menguntungkan ketika menerima beban-beban dinamik yang umumnya bekerja horisontal.
Baja-baja struktur diberi nama oleh ASTM (American Society for Testing and Materials) serta oleh para pembuatnya. Untuk keperluan desain, tegangan leleh tarik menjadi kuantitas acuan yang digunakan oleh spesifikasi-spesifikasi, seperti AISC, sebagai variabel sifat untuk menentukan kekuatan atau tegangan ijinnya. Terminologi tegangan leleh (yield stress) digunakan baik untuk menyatakan “titik leleh” (yield point), yakni suatu penyimpangan yang jelas dari elastisitas sempurna yang ditunjukkan oleh kebanyakan baja struktur biasa; maupun “kekuatan leleh” (yield stress), yakni tegangan satuan pada suatu titik perpindahan regangan untuk baja-baja yang tidak memiliki titik leleh yang jelas