Analisa Kegagalan High Pressure Water Wall Seamless Tube pada Subcritical Boiler di PLTU Pangkalan Susu Sumatera Utara

Hadi, Viki Sofyan (2022) Analisa Kegagalan High Pressure Water Wall Seamless Tube pada Subcritical Boiler di PLTU Pangkalan Susu Sumatera Utara. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Keandalan boiler memegang peranan penting dalam menjaga performa Unit PLTU Pangkalan Susu OMU Medan. Kegagalan tube boiler mempengaruhi kestabilan operasi secara menyeluruh sehingga harus dianalisa penyebabnya. Hal ini dilakukan untuk meminimalisir kegagalan serupa di masa mendatang. Boiler tube rear water wall seamless tube material GB5310-20G line 132 elevasi 29.8 mdpl dan 37 mdpl terdeteksi mengalami kebocoran pada Maret 2022. Kagagalan terjadi pada usia boiler yang masih muda yaitu 7 tahun sejak Comercial Operation Date pada tahun 2015 karena boiler di desain untuk beroperasi selama 30 tahun. Hasil pengamatan visual dan pengukuran dimensi menunjukkan pola kegagalan membentuk fish-mouth rupture panjang 100 mm dan lebar 42 mm elevasi 37 mdpl. Hasil pengukuran ketebalan tube mengalami penurunan nilai ketebalan dibawah MWT berdasarkan standard ASME Section I. Kebocoran juga diamati pada elevasi 29.8 mdpl ditemukan kegagalan dalam bentuk lubang. Hasil identifikasi pada tube kegagalan fish-mouth komposisi kimia menunjukan material GB5310-20G. Nilai kekerasan 139 HB tepi rupture lebih tinggi dari daerah yang jauh dari kegagalan 113 HB. Pengamatan metallography pada tepi fish-mouth rupture menunjukkan terjadi degradasi struktur mikro peralite yang melepaskan unsur carbon sehingga terbentuknya spherodized carbide, masuk dalam kategori C ke D sesuai standar ERA. Hasil SEM daerah fish-mouth menunjukkan retakan transgranular yang merupakan ciri khas dari short-term overheating. Pengujian deposite dan EDS menunjukan senyawa magnetite pada daerah kegagalan, hal ini karena oksigen terlarut dalam air boiler yang berlebih bereaksi dengan Fe pada suhu tinggi membentuk Fe3O4 dan terjadi pengikisan tebal material. Mekanisme kegagalan fish-mouth diawali dari penurunan debit air rear water wall tube akibat kebocoran elevasi 29.8 mdpl menciptakan hot-spot line pipe 132. Penyerapan panas berlebih terjadi pada elbow elevasi 37 mdpl, proses kelebihan panas 370 ◦C mengakibatkan degradasi C pada pearlite yang lepas menjadi spherodized carbide. Dan senyawa ferromagnetite (Fe3O4) ditemukan pada deposite memicu kenaikan kekerasan serta didukung dengan perubahan struktur butir yang kasar. Kondisi ini menyebabkan munculnya insiasi crack dari area spherodize carbide sehingga menjalar secara transgranular akibat dikenai pressure 14 Mpa secara continue dengan bentuk kegagalan fish-mouth karena kelebihan penyerapan panas pada elbow elevasi 37 mdpl dengan pola kegagalan short-term overheating
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Boiler reliability plays an important role in maintaining the performance of the PLTU Pangkalan Susu OMU Medan Unit. The failure of the tube boiler affects the stability of the overall operation so that the cause must be analyzed. This is done to minimize similar failures in the future. Boiler tube rear water wall seamless tube material GB5310-20G line 132 with an elevation of 29.8 masl and 37 masl was detected as having a leak in March 2022. The failure occurred at a young boiler age of 7 years since the Comercial Operation Date in 2015 because the boiler was designed to operate for 30 years. The results of visual observations and measurement of dimensions showed a failure pattern to form a fish-mouth rupture with a length of 100 mm and a width of 42 mm with an elevation of 37 meters above sea level. The results of the measurement of tube thickness experienced a decrease in the thickness value below MWT based on the ASME Section I standard. Leaks were also observed at an elevation of 29.8 masl and failure was found in the form of holes. The identification results on the fish-mouth failure tube chemical composition showed the material GB5310-20G. The hardness value of 139 HB at the rupture edge was higher than the area far from failure of 113 HB. Metallography observations on the edge of the fish-mouth rupture showed that there was a degradation of the microstructure of peralite which released carbon elements so that the formation of spherodized carbide was categorized as C to D according to ERA standards. SEM results of the fish-mouth region show transgranular cracks which are characteristic of short-term overheating. Deposite and EDS tests showed magnetite compounds in the failure area, this was because excess dissolved oxygen in boiler water reacted with Fe at high temperatures to form Fe3O4 and thick material was eroded. The mechanism of fish-mouth failure begins with a decrease in rear water wall tube water flow due to leakage at an elevation of 29.8 mdpl creating a hot-spot line pipe 132. Absorption of excess heat occurs at the elbow elevation of 37 mdpl, the process of excess heat at 370 C results in C degradation of the loose pearlite. to spherodized carbide. And the ferromagnetite compound (Fe3O4) found in the deposit triggers an increase in hardness and is supported by changes in the coarse grain structure. This condition causes the emergence of crack initiation from the spherodize carbide area so that it spreads transgranular due to being subjected to a continuous pressure of 14 MPa with a fish-mouth failure form due to excess heat absorption at the 37 mdpl elevation elbow with a short-term overheating failure pattern.

Item Type:	Thesis (Other)
Additional Information:	RTM 621.197 Had a-1 2022
Uncontrolled Keywords:	Rear water wall tube, short term overheating, tube erosion
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ263.5 Boilers (general)
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21101-(S2) Master Thesis
Depositing User:	Mr. Marsudiyana -
Date Deposited:	13 Feb 2025 01:42
Last Modified:	13 Feb 2025 01:42
URI:	http://repository.its.ac.id/id/eprint/118703

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