FAILURE ANALYSIS ON HEMISPHERICAL HEAD OF S-50 AMMONIA CONVERTER PRESSURE VESSEL IN AMMONIA PLANT

• Main Author: Nugraha Saputra, Irwan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/46104
• Institution: Institut Teknologi Bandung

S-50 Ammonia converter is a pressure vessel with a type of radial flow converter where the conversion process from process gas to ammonia occurs at high pressure and temperature using the help of catalysts inside the vessel. From the inspection results, it was found that the crack failure penetrates from the catalyst support (internal) welds to the outer surface of the bottom head after operating for around 15 years. Several similar plants have reported the failure of the S-50 ammonia converter with 2 ¼ Cr – 1 Mo as the material to the plant licensor. However, the support catalysts weld failure was the first case that occurred. Failure analysis at the bottom head was carried out to determine the root cause and the failure mechanism of the ammonia converter. From the inspection results, the obtained data were the length of the crack, depth of the crack, and hardness test (Brinell) on the outer surface of the crack. Thickness verification and static strength calculation were performed to check the design according to AD 2000 Merkblatt standard. In addition, weld strength calculation, fatigue strength calculation, fracture mechanic approach, historical data equipment, and stress simulation based on operating pressure and temperature were used to strengthen the cause of failure. The root cause of failure was the crack initiation from the catalyst support transverse fillet weld to bottom head due to the accumulation of hydrogen in that area. Embrittlement of the material that occurs was caused by the phenomenon of hydrogen embrittlement (HE) so that the strength and fracture toughness of the material in the cracked area decreases. From maintenance historical data, the welds area were not checked periodically since the operation until failure occurs.