..sedikit berbagi ilmu..

ketika ilmu begitu bermanfaat

Houston, December 2011, 3 deg Celcius

Hi guys…

Tahun 2011 gak kerasa akan segera abis yah.. and it had been almost 1 month I am here in Houston, the center of oil and gas industry (many people said like that, isn’t it). Thanks God, that’s only I can say.. It is same just like last time when I went to Paris (beginning January 2011 till April 2011), I am just supporting the engineering team of Subsea 7 under temporary assignment from my company SapuraAcergy. SapuraAcergy is a joint venture between Sapura Crest and Acergy, and Acergy is no longer exist since they have merged with Subsea 7 and they become Subsea 7. So it is pretty common for internal employee transfer like me because we are in the same company group. In the football game we used to call this as loan player transfer hehe… anyway, I am glad to be here..

For almost one month, I am supporting the engineering team here for tendering in Gulf of Mexico (damn good, finally I am working on this zone) but in the shallow water area (surely it’s still OK for me).. Our client is one of Mexican company so the area is in the Mexico side. As per my skill, this is the pipeline installation tender. The pipes are quite heavy with the 36″ OD x 0.75″ WT x 4″ Concrete leads the dry weight of 1340 kg/m and the submerged weight of 333 kg/m. This kind of pipes are pretty difficult to install since they are very heavy.. you need to have huge tension on your vessel and longer stinger to have bigger radius to minimize the bending moment since the concrete thickness is 4″ (what???)… And it happen to be our problem now.. we have to modify our stinger, make it longer and we are using almost 85% of our tension capacity in static condition. We can actually reduce our tension by reducing the submerged weight but we need plenty of buoyancy tanks to lift the pipes.. and 77km of pipelines are not a good idea to use as such buoyancy tanks. The worst is the acceptance criteria. We are not using the DNV as criteria but the company specification. Their specs are way too strengthen than DNV. They are using bending moments as the limit and not using the strain/stress. As comparison, for instance, DNV roles 87% SMYS both for stinger tip and sagbend section but their 100% bending moment criteria is equal to 70% SMYS only. And it is applicable for all the sections from overbend, stinger tip and sagbend. It makes us to have a such bigger radius to have the bending moments  as small as possible. Also, with this kind of pipe, there is no way to have such separation in the stinger tip. Offshore guys are happy to see some separation in the stinger tip to make sure the pipe is still within the catenary shape as proposed. But with this pipe, hmmm… no way! But anyway, we can put some load cell in the stinger tip to monitor the load. So when the loads are more than what we are expecting then we can increase the tension or maybe trim a bit the barge. The problem is how much tension that we have as redundancy? Or if we trim the barge then how is the effect to bending moment since it will increase the bending moment (even it is small but how much?).

Anyway, we have submitted the pre-qualification analysis that show our capability to install this pipes with some notes to be considered (need to modify the stinger, tension to be upgrade for wet buckle contingency, etc.) This analysis is based on static condition only. After we are qualified then we will continue to submit for the rest analysis (dynamic, pipe stacking, mooring, transportation, etc.). And now, I am start working on the dynamic analysis (we are confident to win this tender, great!).

Part II (December 6, 2011).

Jumpa lagi…. just to keep you update, saya lagi utak-atik OFFPIPE utk mengetahui window operation pada saat laying nanti dengan pipe segede seperti yang telah saya sebutkan di atas. Dan ternyata eng ing eng… alamaaak… karena terlimit dengan maximum bending moment sekitar 4000 kN.m, jadinya laying hanya bisa dilakukan pada Hs sekitar 0.7m (=1.3m Hmax) sahaja… beh beh beh… artinya itu laut harus dalam keadaan yang tenang bangeeeetss hehe… ya artinya sangat tidak mungkin (ya mungkin2 aja sih cuma mungkin jarang banget nemu keadaan yg seperti itu)..

Hmm… Terpaksa deh saya harus mengakali keadaan ini dengan beberapa skenario, yang pertama melakukan trim pada barge sebesar 0.5, 1.0 dan 1.5 derajat dan melihat hasilnya, kemudian skenarion ke-2 yaitu dengan memasang buoyancy 1Te dan 1.5 Te, lalu skenario terakhir adalah menggabungkan penggunaan trim dan buoyancy (saya limit dengan pakai 1Te of buoyancy aja).. lalu kita bandingkan hasilnya seperti dibawah ini.

December 4, 2011 - Posted by | Deep of Me, Lesson Learn, Offshore, oil and gas, Piping/Pipeline | , , , , , , , , ,

8 Comments »

  1. I’m thinking about the mooring load.
    Higher Lay Tension will put more tension on the mooring line, usually during start to pull. Eh, is this mooring barge of DP?

    Comment by Irwan Hamid | December 4, 2011 | Reply

    • We are using mooring bro.. I agree with your thought.. higher tension will leads higher load in the mooring… but the design of the mooring line for each vessel should accommodate the total loads that had been estimated.. for instance, if the barge have maximum tension of 200 mT then then mooring should be able to hold a such load… we just need to analysis separately what will happen on the pipe if let’s say one of the mooring line is fail due to some reasons..

      Comment by vladvamphire | December 4, 2011 | Reply

  2. Hello Vlad,
    Saya tertarik untuk diskusi tentang Strain Criteria di DNV. Saya sedang cari referensi Ramberg Osgood tentang non-linear material. Apa kamu punya?
    Ada bbrp pertanyaan tentang pipelay. Bisa diskusi disini atau di email?
    Terimakasih sebelumnya kalau berkenan untuk diskusi.

    Comment by Desy | December 5, 2011 | Reply

    • Hi Dessy..
      Thanks udah mampir ke blog saya yg ga jelas ini hehe…
      Btw, kalo RO itu kan lebih ke masing2 pipe properties dan biasanya di dapatkan pada saat kita beli pipe itu.. semua hasil uji strain nya ada di certificate nya meskipun kadang ga semua material punya data yang lengkap tp paling gak mereka ada tes strain pada beberapa point tertentu (stress). Dr situ lalu kita bisa plot utk mendapatkan strain/stress curve relationshipnya.. Atau juga curve nya bisa kita generat jika si empunya pipe bisa memberikan 2 nilai koefisien RO lalu kita plot dengan menggunakan formula biasa..
      Utk berdiskusi saya rasa bisa di sini saja jadinya banyak rekans yang bisa ikut mengkoreksi kesalahan pada diskusi kita (jika ada).

      Thanks.
      Vlad.

      Comment by vladvamphire | December 5, 2011 | Reply

  3. wouw…mantap….akhirnya menjajal gulf meksiko ya bos..yang selama ini hanya dengar dan lihat datanya di bangku kuliah aja..sukses terus buatmu bro..

    Comment by Brando | December 5, 2011 | Reply

    • Thanks bro.. sukses juga buat kmu yah…
      Keep contact!

      Comment by vladvamphire | December 5, 2011 | Reply

  4. Wah blog nya terlalu technical & ilmiah untuk saya nih…. Anyway, sukses untuk expatriasinya… Bekerja sambil traveling atau traveling sambil kerja….

    Thaksin tuk kunjungannya….

    Comment by Nin | December 5, 2011 | Reply


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