ANALISIS DEGRADASI MATERIAL KOMPONEN BOILER DAN PERHITUNGAN SISA UMUR PAKAI BERDASARKAN UJI STRESS RUPTURE

MUJI PRIHAJATNO, Mochammad Noer Ilman, S.T., M.Sc., Ph.D.

2014 | Tesis | S2 Teknik Mesin

Boiler adalah suatu alat yang berfungsi mengubah air (boiler waterfeed) menjadi uap (steam) pada tekanan dan temperatur tertentu melalui mekanisme heat transfer. Uap tersebut dapat digunakan untuk menggerakan turbin. Boiler terdiri dari beberapa komponen yang membentuk suatu sistem untuk menghasilkan tenaga (power). Komponen boiler menerima beban kerja yang berat berupa tekanan fluida dan temperatur yang tinggi. Oleh karenannya perlu dilakukan evaluasi dan perhitungan sisa umur pakai untuk menghindari kegagalan. Proses evaluasi komponen boiler dilakukan terhadap beberapa pipa diantaranya pipa economizer, pipa water wall, pipa primary superheater, pipa secondary superheater, dan pipa reheater. Metode yang digunakan dalam evaluasi merupakan eksperimental dengan serangkaian pengujian dan pengamatan terhadap material dan produk korosi pipa boiler. Pengujian yang dilakukan diantaranya pengujian tarik, kekerasan, EDX, X-RD, dan pengurangan berat berdasarkan ASTM D-3483. Pengamatan yang dilakukan secara visual dan struktur mikro menggunakan mikroskop optik dan SEM. Perhitungan sisa umur pakai menggunakan pendekatan Larson-Miller Parameter (LMP) dengan pengujian stress rupture. Hasil evaluasi dinyatakan bahwa pipa boiler telah mengalami degradasi material. Hal ini terlihat secara mekanik terjadi penurunan nilai kekerasan dan nilai ductility. Sedangkan secara visual telah terjadi pitting corrosion, erosion corrosion, oxidation corrosion pada dinding permukaan. Struktur mikro material memperlihatkan terjadi fenomena spheroidization, graphitization, cavity, decarburizing, dan slip grainboundary. Sisa umur pakai pipa boiler beraneka ragam diantaranya pipa economizer 142.520 jam, pipa water wall 168.573 jam, pipa primary superheater 1.172 jam, pipa secondary superheater 1.518 jam, dan pipa reheater 105.713 jam. Kasus kegagalan pada pipa primary superheater terjadi karena mekanisme creep. Penyebab kegagalan akibat short-term overheating yang disebabkan oleh deposit berupa silika (SiO2) yang menempel pada dinding pipa bagian dalam sehingga menghambat laju perpindahan kalor.

Boiler is a equipment that is used to change water into steam through heat transfer mechanism. The steam is used to drive a turbine. Boiler consists of several components that allows a system to generate power. Boiler components receive a heavy workload in the form of fluid pressure and high temperature. So that it is necessary to evaluate and calculate of remaining life to avoid failure. The evaluate process of boiler components conducted include economizer pipe, waterwall pipe, primary superheater pipe, secondary superheater pipe, and reheater pipe. The method used in the evaluation is experimental with of test and observations. The performed test include is a tensile and hardness test, EDX, X-RD, and weight loss test based on ASTM D-3483. The observation is where a visual and microstructure used to optical microscope and SEM. Whereas the calculation of remaining life is performed by the Larson-Miller parameter from stress rupture testing. The results of this investigation shows that the boiler component materials have degraded. It’s seen from mechanically occur reduction in hardness and ductility. While visually in wall surfaces pipe occurs pitting corrosion, erosion corrosion, oxidation corrosion. The materials microstructural degradation including spheroidization, graphitization, cavity, decarburizing, and grain-boundary slip. The remaining life of boiler components variously including 142.520 hours of economizer pipes, 168.573 hours of waterwall pipes, 1.172 hours of primary superheater pipes, 1.518 hours of secondary superheater pipes, and 105.713 hours of reheater pipes. The case study of failure the primary superheater pipe occurs because the creep mechanism. The cause of failure due to short-term overheating caused by silica (SiO2) deposite in wall surfaces pipe so inhibits the heat transfer rate.

Kata Kunci : evaluasi boiler, sisa umur pakai, strees rupture, creep, short-term overheating, failure analysis