독립형 LNG 화물창의 공학적 결함 평가

• Published in: 大韓造船學會 論文集 Vol. 60; no. 4; pp. 213 - 221
• Main Authors: 서재훈(Jae Hoon Seo), 박규식(Kyu-Sik Park), 차인환(Inhwan Cha), 정준모(Joonmo Choung)
• Format: Journal Article
• Language: Korean
• Published: 대한조선학회 2023
• Subjects: 조선공학; LNG(액화천연가스); Stress intensity factor(응력확대 계수); Independent type-B tank(독립 B형 화물창); ECA(공학적 결함 평가); Crack growth rate(균열 진전 속도); B
• ISSN: 1225-1143; 2287-7355
• DOI: 10.3744/SNAK.2023.60.4.213

The demand for Liquefied Natural Gas (LNG) carriers and LNG-fueled ships has significantly increased in recent years due to the sulfur-oxide emission regulations by the International Maritime Organization (IMO). The main goal of this paper is to introduce the process for the Engineering Critical Assessment (ECA) of IMO independent type-B cargo tanks made from 9% nickel alloy. A methodology proposed by the British Standard was used to conduct ECA for any structure with initial flaws. Based on this standard, a Matlab code was developed to perform ECA. Coarse mesh Finite Element Analysis (FEA) was performed on an independent type-B LNG cargo tank with a capacity of 15,000 m3. The location with the highest development of maximum principal stress was identified at the bottom of the cargo tank. Fine mesh FEA was performed to obtain the stress range required for ECA. The dynamic cargo tank loads used for FEA were determined using some ship rules presented by Det Norske Veritas. As a result of performing a 20-year long-term crack propagation analysis with a semi-elliptical surface crack, the fracture-to-yield ratio exceeded the Fracture Assessment Line (FAL) and some structural reinforcement was necessary. Performing a 15-day short-term crack propagation analysis, the fracture-to-yield ratio remained within the FAL, and no significant LNG leaks were expected. This paper is believed to provide a guide for performing ECA of LNG cargo tanks in the future by providing the basic theory and application sample necessary to perform ECA.