Pipa elbow biasanya digunakan sebagai sambungan (fitting) ketika terjadi perubahan orientasi yang cukup ekstrim pada jalur pipa transmisi. Jalur pipa transmisi biasanya ditanam didalam tanah (underground) yang rentan terhadap korosi eksternal sehingga perlu dilakukan analisis keandalan. Analisis keandalan dilakukan dengan menggunakan simulasi Monte Carlo dengan terlebih dahulu mengukur pH, resistivitas tanah dan menghitung laju korosi eksternal. Keandalan pipa elbow pada segmen I adalah 39.56%, segmen II adalah 75.68%, dan segmen III adalah 99.99% Nilai resistivitas tanah pada segmen I berada pada level very corrosive (<500Ω-cm), segmen II berada pada level corrosive (500-1000 Ω-cm), dan segmen III berada pada level moderately corrosive (1000-2000 Ω-cm). Nilai pH berada pada rentang 5-7 untuk semua segmen. Laju korosi pipa elbow berkisar antara 0.029-0.765 mm/year, dan meningkat seiring penurunan nilai resistivitas tanah. Pengamatan struktur mikro menunjukkan ukuran butir pipa elbow adalah sebesar 16,5 µm. Hasil permodelan Autodesk Inventor memperlihatkan bahwa terjadi konsentrasi tegangan pada pipa sebesar 160 MPa , sementara itu hasil permodelan Caesar II.5.1 menunjukkan bahwa bending stress pada pipa elbowmerupakan stress paling tinggi (666-679 kg./sq. cm) pada saat kondisi operasi.
Elbow pipe is commonly used as fitting when pipeline shows an extreme change on its direction. Generally, transmission pipeline is buried underground which severe to external corrosion, thus reliability analysis is required. Reliability analysis was performed by using Monte Carlo simulation by first measured pH, soil resistivy and external corrosion rate. Reliability of elbow pipe at segment I was 39.56%, segment II was 75.68%, and segment III was 99.99%. Soil resistivity value at segment I was on very corrosive level (<500Ω-cm), while segement II was on corrosive level (500-1000 Ω-cm), and segment III was on moderately corrosive level (1000-2000 Ω-cm). pH value ranged from 5-7 for all segments. Corrosion rates ranged from 0.029-0.765 mm/year, and increased gradually as decreased of its soil resistivity value. Microstructure examination showed that grain size on elbow pipe was 16,5 µm. Autodesk Inventor modelling revealed that stress concentration was occured on innert side of elbow pipe as much as 160 MPa , while Caesar II.5.1 modelling showed that bending stress was the highest stress (666-679 kg./sq. cm) in operating condition. |
