5.1. Kesimpulan
Setelah melakukan penelitian tentang kegagalan tube superheater package boiler, maka dapat ditarik kesimpulan sebagai berikut:
1. Diaphragma yang menghalangi aliran uap merupakan penyebab utama kegagalan tube superheater. Tube yang gagal mengalami “bulging” dan adanya “fish mouth effect”, gejala demikian menunjukkan tube telah mengalami overheating akibat menerima beban thermal stress yang berlebihan.
2. Tegangan elastis antara analisa numerik dan analitis menghasilkan tegangan yang dapat dikatakan sama. Tegangan elastis maksimum hasil analisa lebih kecil dari tegangan desain izin maksimum tube superheater. Karenanya, tube aman akibat deformasi elastis.
3. Plastic flow akibat thermal stress menjalar cepat ke arah dinding dan maksimum di bagian luar mengakibatkan tube superheater gagal dalam jangka waktu singkat.
Kegagalan tube superheater disebabkan oleh kombinasi dua atau lebih penyebab kegagagalan atau “attack mode”, yang saling bersinergi untuk mempercepat kerusakan (accelerate degradation).
Analisa kegagalan dapat dilakukan secara visual untuk mengamati karakteristik, lalu eksperimental dan analisa numerik untuk melihat respon, serta, mengevaluasi hasil guna mendapatkan penyebab untuk melakukan langkah perbaikan.
5.2. Saran
Adapun saran yang berhubungan dengan hasil penelitian ini adalah sebagai berikut:
1. Walaupun tube yang gagal akan diganti/diperbaiki, sebaiknya perbaikan lebih difokuskan pada penyebab utama, yaitu memperbaiki posisi plat diaphragma dalam header. Jika posisi diaphragma tidak segera dikembalikan ke posisi dasarnya, diprediksi akan ada kegagalan kembali pada tube superheater package boiler, yaitu tube baris 4 No. 8, mengingat posisi diaphragma yang sudah mengenai tube tersebut.
2. Pergantian/perbaikan tube dapat dilakukan pada saat shut-down rutin pada tube-tube yang sudah kurang layak dan tidak menunggu tube pecah. Support, spacer, castable yang rusak harus diganti/diperbaiki, karena komponen ini ikut mempengaruhi kegagalan.
3. Simulasi dengan geometri yang lebih kompleks, yaitu melibatkan header dan diaphragma merupakan aspek kajian lanjutan penelitian ini.
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Gambar 1. (a) Modulus elastisitas dan (b) Rasio Poison SA 213 T11 [53, 54].
Gambar 2. Reduksi luas material SA 213 T11 pada temperatur tinggi [53, 54].
Lampiran 1. Modulus elastisitas, rasio Poison, dan reduksi penampang SA 213 T11
Gambar 3. (a) Konduktivitas termal dan (b) Ekspansi termal SA 213 T11 [53, 54].
Gambar 4. Difusivitas termal SA 213 T11 [53, 54].
(a) (b)
Lampiran 7. Foto-foto Kegiatan Survey di PT PIM Lhokseumawe
3. Melakukan pengujian kekerasan 4 Berdiskusi sambil menganalisa data
5. Dokumentasi sampel tube superheater 6. Serah terima sampel tube superheater 1. Berdiskusi dengan Ka.Biro Inspeksi & K3 2. Mengamati Macchi Package Boiler
