Analisa Kelelahan Pipa Pada Saat Instalasi Di Berbagai Sudut Stinger Dan Ukuran Pipa

Dalam beberapa kasus saat instalasi pipa di lepas pantai, terkadang beberapa kendala teknis tidak dapat dihindari. Kendala teknis ini dapat meliputi kerusakan pada alat instalasi seperti tensioner, mesin las, generator ataupun kerusakan pada system mooring, navigasi, tenaga penggerak kapal dan lain-lain. Hal tersebut bisa berakibat terhentinya proses instalasi pipa untuk waktu yang cukup lama. Dalam kondisi ini, pipa dapat diturunkan ke dasar laut atau dipertahankan selama durasi tertentu hingga pipa mencapai batas kelelahan yang diijinkan sesuai dengan hasil analisa, analisa tersebut akan menghasilkan berapa lama durasi pipa dapat digantung. Dalam DNV OS-F101 2013 Section 5 D.811, dijelaskan bahwa biasanya allowable yang digunakan antara installation, as laid, and operation is 10%,10% and 80%. Dimana pada bagian instalasi perlu perhitungkan umur kelelahannya. Pada pipa 24 inch dengan sudut stinger 60 mengalami over stress serta pada pipa 16 dan 20 inch juga mendekati over stress . Stress range didapat dari analisa dinamik karena adanya gelombang yang menyebabkan stress pada pipa berubah-ubah. Dari stress range yang terjadi dapat dihitung umur kelelahan pipa, Dengan adanya penambahan sudut stinger mampu mengecilkan stress yang terjadi pada pipa agar tidak over stress dan juga akan berpengaruh pada lamanya umur pipa akibat beban siklik yang terjadi. Umur standby time terkritis adalah pada pipa 24 inch terhadap sudut stinger 80 sebesar 0,138 hari atau 3.312 jam. ======================================================================================================================== In some cases during the installation of offshore pipelines, sometimes some technical problems unavoidable. Technical constraints can include damage to the installation tool such as tensioner, welding machines, generators or damage to the mooring system, navigation, propulsion boats and others. This can result in interruption of process piping installation for quite a long time. In this condition, the pipe can be lowered to the seabed or maintained for a specific duration until the pipe reaches the allowable fatigue limit according with the results of the analysis, the analysis will produce how long the pipe can be hung. In DNV OS-F101 2013 Section 5 D.811, explained that normally the allowable are used between installation, as laid, and operation is 10%, 10% and 80%. Where in the installation should calculated the fatigue life. In the 24 inch pipe with an angle of stinger 6° has over stress and the 16 and 20 inch pipe was also approached over stress. Stress range obtained from dynamic analysis because of the waves that cause stress on the pipe changeable. From stress range that occur can be calculated the fatigue life of the pipeline, with the addition of stinger’s angle is able to shrink the stress that occurs in the pipe in order not to over-stress and will also affect on the length of life of the pipeline due to cyclic loading that occurs. The most critical standby time is in the 24 inch pipe on stinger’s angle 8° amounted to 0,138 days or 3,312 hours