Analisis Kegagalan Hanger Tube Outlet Section Secondary Superheater Boiler PLTU Ditinjau dari Aspek Metalurgi

Syahbania, Sastya Adzani (2023) Analisis Kegagalan Hanger Tube Outlet Section Secondary Superheater Boiler PLTU Ditinjau dari Aspek Metalurgi. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Boiler merupakan salah satu peralatan penting pada Pembangkit Listrik Tenaga Uap (PLTU). Dalam boiler terdapat komponen yang berfungsi untuk menghasilkan uap kering, yaitu superheater. Pada superheater ditemukan adanya kegagalan berupa pecahnya hanger tube outlet section secondary superheater. Hanger tube merupakan tube yang menopang pipa-pipa secondary superheater. Kegagalan yang terjadi pada boiler akan menghentikan produksi listrik, untuk itu penyebab dan mekanisme terjadinya kegagalan hanger tube outlet section secondary superheater perlu ditelusuri agar dapat meminimalisir kegagalan serupa. Ketika terdengar suara gemuruh dari boiler dan terjadi peningkatan make-up water, dilakukan inspeksi pada boiler dan ditemukan adanya kegagalan pada hanger tube secondary superheater PLTU PT X dengan pola patahan fish-mouth berdinding tipis yang mengindikasikan kegagalan dengan mode short-term overheating, serta ditemukan pula adanya scale sebagai produk korosi pada permukaan dalam dan luar tube. Setelah itu, dilakukan analisis data berdasarkan hasil pengujian material. Untuk menganalisis penyebab kegagalan dari aspek material, dilakukan pengamatan visual secara detail dan pengujian komposisi kimia. Untuk menganalisis penyebab kegagalan dari aspek interaksi antara material dan lingkungan, dilakukan pengujian metalografi, pengujian kekerasan, dan pengujian Scanning Electron Microscope (SEM). Untuk mengetahui karakterisasi lapisan scale, dilakukan pengujian X-Ray Diffraction (XRD) dan pengujian Energy Dispersive Spectroscopy (EDS). Interaksi antara material dan lingkungan operasi dengan temperature tinggi, serta adanya impurities yang terbawa bersama feed water pada aliran steam dapat menyebabkan terbentuknya scale. Kegagalan hanger tube outlet section secondary superheater dengan mode short-term overheating terjadi akibat adanya pengelupasan scale pada inner surface tube secara lokal yang menyebabkan hilangnya lapisan magnetit sehingga tube rentan terkorosi. Hal itu dibuktikan dengan adanya scale pada permukaan dalam dan luar tube sebagai produk korosi dan ditemukannya penipisan ketebalan tube hingga mencapai 1,3 mm di bagian fish-mouth. Scale yang terkelupas dapat terakumulasi pada bend tube sehingga terjadi blockage aliran steam yang menyebabkan aliran steam selanjutnya berkurang. Akibatnya panas dari luar tube tidak terserap secara optimal oleh steam sehingga terjadi lokalisasi panas pada tube yang menyebabkan degradasi material. Hal itu dibuktikan dengan adanya perubahan struktur mikro dimana perlit mengalami spheroidisasi dan butiran kristal membesar sehingga menyebabkan penurunan nilai kekerasan. Adanya penurunan nilai kekerasan dari 253 HVN di bagian jauh dari kerusakan, hingga 185 HVN di bagian fish-mouth, menyebabkan penurunan kekuatan material. Di sisi lain, adanya tekanan dari secondary superheater outlet header tube pada tube yang mengalami degradasi material menyebabkan pecahnya tube dengan pola patahan ulet akibat ketidakmampuan dalam menahan tekanan internal fluida.
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Boiler is one of the important equipment in Steam Power Plant (PLTU). In the boiler there is a component that functions to produce dry steam, namely the superheater. In the superheater, a failure was found in the form of rupture of the hanger tube outlet section secondary superheater. Hanger tube is a tube that supports the secondary superheater pipes. Failures that occur in the boiler will stop electricity production, for this reason the causes and mechanisms of the failure of the hanger tube outlet section secondary superheater need to be traced in order to minimize similar failures. When a rumbling sound was heard from the boiler and there was an increase in make-up water, an inspection was carried out on the boiler and a failure was found on the hanger tube secondary superheater PLTU PT X with a thin-walled fish-mouth fracture pattern indicating a failure with a short-term overheating mode, and scale was also found as a corrosion product on the inner and outer surfaces of the tube. After that, data analysis was carried out based on the results of material testing. To analyze the cause of failure from the material aspect, detailed visual observation and chemical composition testing were conducted. To analyze the cause of failure from the aspect of interaction between material and environment, metallographic testing, hardness testing, and Scanning Electron Microscope (SEM) testing were conducted. To characterize the scale layer, X-Ray Diffraction (XRD) testing and Energy Dispersive Spectroscopy (EDS) testing were conducted. The interaction between the material and the operating environment with high temperatures, as well as the presence of impurities carried along with the feed water in the steam flow can cause scale formation. The failure of the hanger tube outlet section of the secondary superheater with short-term overheating mode occurs due to the peeling of scale on the inner surface of the tube locally which causes the loss of the magnetite layer so that the tube is susceptible to corrosion. This is evidenced by the presence of scale on the inner and outer surfaces of the tube as a corrosion product and the discovery of thinning of the tube thickness up to 1.3 mm at the fish-mouth. Exfoliated scale can accumulate on the bend tube resulting in blockage of steam flow which causes further steam flow to decrease. As a result, heat from outside the tube is not optimally absorbed by the steam resulting in heat localization on the tube which causes material degradation. This is evidenced by changes in microstructure where pearlite is spheroidized and crystal grains enlarge, causing a decrease in hardness value. The decrease in hardness value from 253 HVN at the far side of the damage, to 185 HVN at the fish-mouth, caused a decrease in material strength. On the other hand, the pressure from the secondary superheater outlet header tube on the degraded tube caused the tube to break with a ductile fracture pattern due to the inability to withstand the internal fluid pressure.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Fish-mouth, Hanger tube, Superheater, Rupture.
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ263.5 Boilers (general)
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis
Depositing User:	Sastya Adzani Syahbania
Date Deposited:	24 Oct 2023 03:54
Last Modified:	24 Oct 2023 03:54
URI:	http://repository.its.ac.id/id/eprint/101355

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