Studies on Nine Percent Nickel Steel for Liquefied Natural Gas Carriers

One of the most important issues associated with liquefied natural gas (LNG) storage tanks, such as LNG carrier cargo tanks and land LNG tanks, is their structural integrity. In order to ensure the operating life and safety of LNG storage tanks used under operating conditions such as thermal and cyclic loadings, the securing of safety evaluations for fatigue performance is considered to be of particular importance. There have been various efforts to reduce the production costs of LNG storage tanks, such as the optimum selection of materials and the development of new low temperature materials. This, the motivation of this study is to evaluate new material candidates for LNG storage tanks. This study begins with a comprehensive review of the characteristics of low temperature alloys such as SUS 304L, Invar, A5083 and 9% Ni steel that are widely used for LNG storage tanks. Then, the fatigue characteristics of a newly developed low temperature material, 7% nickel steel are investigated. Finally, the fatigue performance of 7% nickel steel is compared with that of 9% nickel steel.

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A Comparison of Fracture Toughness and Fatigue Crack Propagation Characteristics of High Manganese and Nickel Steels

Volume 4: Materials Technology ◽

10.1115/omae2018-77247 ◽

2018 ◽

Author(s):

Jeong-Yeol Park ◽

Myung-Hyun Kim

Keyword(s):

Fracture Toughness ◽

Fatigue Crack ◽

Low Temperature ◽

Natural Gas ◽

Structural Integrity ◽

Liquefied Natural Gas ◽

Manganese Steel ◽

Nickel Steel ◽

High Manganese ◽

High Manganese Steel

Recently, demands for liquefied natural gas (LNG) are increased by developing countries such as China, India and Middle East area. In addition, the International Maritime Organization (IMO) reinforced regulations to avoid the serious environmental pollution. This trend has led to manufacturing and operating various LNG vessels such as liquefied natural gas carrier (LNGC), floating liquefied natural gas (FLNG) and very large gas carrier (VLGC). In the design of LNG vessels, the structural integrity of LNG storage tank is of significant importance to satisfy the service conditions. In order to secure structural integrity, LNG storage tank is fabricated with low temperature materials. In general, low temperature materials such as SUS304L, Invar alloy, Al 5083-O, nickel alloy steel and high manganese steel exhibit excellent fatigue and fracture performances at cryogenic temperature. In particular, high manganese steel has attracted interest because they are potentially less expensive than the competing other low temperature materials. This study compares the fracture toughness and fatigue crack growth characteristics of high manganese steel with those of nickel steels. In addition, fracture toughness and fatigue crack growth rate tests for various nickel steels are conducted according to BS 7448 and ASTM E647, respectively. In order to obtain less conservative design values, the results of high manganese steel and various nickel steels were compared to those of BS7910. As a result, the CTOD value of high manganese steel is higher than that of 9% nickel steel at cryogenic temperature. In case of FCGR, the high manganese steel and 9% nickel steel are found to be similar to each other.

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An Experimental Study for Fatigue Performance of 7% Nickel Steels for Type B Liquefied Natural Gas Carriers

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4032706 ◽

2016 ◽

Vol 138 (3) ◽

Cited By ~ 1

Author(s):

Young Woo Kim ◽

Dong Jin Oh ◽

Jae Myung Lee ◽

Byeong Jae Noh ◽

Hee Joon Sung ◽

...

Keyword(s):

Natural Gas ◽

Storage Systems ◽

Nickel Content ◽

Liquefied Natural Gas ◽

Fatigue Performance ◽

Structural Safety ◽

High Price ◽

Nickel Steel ◽

Type B ◽

Butt Weld

Structural safety is one of the most important issues associated with liquefied natural gas (LNG) storage systems, such as LNG carriers, LNG Floating Production Storage Offloading (FPSO), and Floating Storage Regasification Unit (FSRU). One of the most common materials for the LNG storage systems has been 9% nickel steel over the last 50 years as it has excellent mechanical properties under cryogenic temperature. Recently, there have been efforts for lowering the nickel content due to the increased nickel price as well as the high price of nickel based welding consumables. In this respect, 7% nickel steels are recently developed for reducing the associated costs mainly for cryogenic applications. The newly developed 7% nickel steels are known to have improved toughness comparable to that of 9% nickel steels by thermomechanical control process (TMCP) and micro-alloying technology. The main objective of this study is to evaluate the fatigue performance of 7% nickel steels with a special attention to type B LNG carrier applications. Cyclic fatigue and fatigue crack growth rate (FCGR) tests for 7% nickel steels were conducted at room and cryogenic temperatures. Fatigue tests were carried out with three different types of specimens such as base metal, butt weld, and fillet weld to characterize the fatigue properties at various locations. In addition, FCGR tests were carried out using compact tension (C(T)) specimens. The difference of FCGR characteristics among base, weld, and heat affected zone (HAZ) is investigated. The fatigue and FCGR test results of 7% nickel steels are evaluated and compared with reference data of 9% nickel steel. Based on this study, it is observed that the 7% nickel steel exhibits similar fatigue performance in comparison with that of 9% nickel steel.

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