GBO를 이용한 9% Ni Steel의 필렛 레이저 용접 공정 최적화

윤태종(Tae-Jong Yun),오원빈(Won-Bin Oh),이보람(Bo-Ram Lee),이충우(Chung-Woo Lee),나현호(Hyun-Ho Na),최주석(Ju-Seok Choi),김일수(Ill-Soo Kim) 대한용접·접합학회 2020 대한용접·접합학회지 Vol.38 No.5

Because more than 90% of the domestic manufacturing processes for the Liquefied Natural Gas (LNG) storage tanks rely on welding and processing technologies, the advancement of welding and processing technologies is directly connected to the productivity and therefore the advancement is critical to be competitive in the domestic shipbuilding industry. The welding technology using a laser light source is a more advanced technology than conventional arc welding in terms of workability, precision, and productivity. Although its application area is currently limited, this technology has been emerging as an important assembly tool in the manufacturing process of shipbuilding and offshore structures in the future. Because the LNG storage tank is a cryogenic structure, 9% nickel steel is widely used to manufacture the tank for both room temperature and low-temperature environments due to its excellent mechanical properties and fatigue strength. In terms of strength, 9% Ni steel is equivalent to 680 MPa-level high-tensile strength steel, and is usually used in applications where the operating temperature is below -150℃, such as LNG tanks with QT treatment. The 9% Ni steel has higher strength and better weldability than A5083-O aluminum alloy, has better impact toughness at cryogenic temperatures than SUS304L, and is economic. Therefore, 9% Ni steel is widely used to manufacture LNG tanks. Previous studies on the 9% Ni steel are based on butt welding, and research has been conducted according to the welding process. However, because 30-40% of LNG storage tanks are formed in a curved shape, research on the fillet welding process to overcome the limitations of butt welding has not been actively conducted to date. More specifically, research on the development of an algorithm for setting process variables, which is the core technology of fillet welding, needs to be conducted. Therefore, in this study, fiber laser welding, which is a fillet shape, is studied and performed using 9% Ni steel. The main objective of this study is to optimize the welding process variables by predicting weld properties. To derive the optimal process variables, the GBO algorithm was developed based on mathematical models. Finally, the developed algorithm showed an average error rate of 0.01831%, which ensures the high reliability of the optimal process variables.

Feasibility study on the wide and long 9%Ni steel plate for use in the LNG storage inner tank shell

정명진,김종민,김진국 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.5

This study aimed to assess the feasibility on the wide and long 9%Ni steel plate for use in the LNG storage inner tank shell. First, 5-m-wide and 15-m-long 9%Ni steel plates were test manufactured from a steel mill and specimens taken from the plates were tested for strength, toughness, and flatness to verify their performance based on international standards and design specifications. Second, plates with a thickness of 10 mm and 25 mm, a width of 4.8~5.0 m, and a length of 15 m were test fabricated by subjecting to pretreatment, beveling, and roll bending resulting in a final width of 4.5~4.8 m and a length of 14.8m with fabrication errors identical to conventional plates. Third, welded specimens obtained via shield metal arc welding used for vertical welding of inner tank shell and submerged arc welding used for horizontal welding were also tested for strength, toughness and ductility. Fourth, verification of shell plate material and fabrication was followed by test erection using two 25-mm-thick, 4.5-m-wide and 14.8-m-long 9%Ni steel plates. No undesirable welding failure or deformation was found. Finally, parametric design using wide and long 9%Ni steel plates was carried out, and a simplified design method to determine the plate thickness along the shell height was proposed. The cost analysis based on the parametric design resulted in about 2% increase of steel weight; however, the construction cost was reduced about 6% due to large reduction in welding work.

LNG 저장 탱크 운반선 9% Ni Steel의 용접성에 대한 실험분석과 메타분석 연구

박상흡(Sang Heup Park),안덕현(Duck Hyun Ahn) 한국산학기술학회 2016 한국산학기술학회논문지 Vol.17 No.12

본 연구는 LNG 저장 탱크 운반선 9% NI Steel에 대한 실험분석과 메타분석 연구이다. 본 연구는 LNG 저장 탱크운반선 9% NI Steel에 대한 선행연구에 기초해서 메타분석을 수행한 후에, 9% Ni Steel의 패스(pass)와 다층용접(multi pass)이 인장강도(tensile strength)에 미치는 영향을 분석하기 위하여 충격반응검정(impulse-response test)을 통한 실험분석을 수행하였다. 본 연구의 실험분석 결과 다음과 같은 연구결과를 얻었다, 첫째, 9% Ni Steel의 다층용접(multi pass welding)에 대한 인장강도(tensile strength)를 시험한 결과 패스 1부터 패스 3까지 인장강도가 증가하였으나, 패스 3 이후부터 다층용접의 인장강도는 감소하는 것으로 보인다. 둘째, 다층용접(Multi pass welding)이 인장강도(tensile strength)에 미치는 영향을 분석한 결과, 패스(pass), 다층용접(multi pass)이 인장강도(tensile strength) 에 유의한 정(+)의 영향을 미치는 것으로 보인다. 용접시간(welding time)이 인장강도(tensile strength)에 미치는 영향을 분석한 결과, 용접시간(welding time), 인장강도시간(tensile time)이 인장강도(tensile strength) 에 유의한 정(+)의 영향을 미치는 것으로 보인다. Laboratory and meta-analyses were done for 9% NI Steel for use in a liquefied natural gas carrier. The meta-analysis is based on a previous study. The laboratory analysis examines the effects of a single pass and multiple passes on the tensile strength through an impulse-response test. The tensile strength increased from pass one to pass three and decreased from pass four to pass ten. The pass and multi-pass welding had a positive effect on the tensile strength. Lastly, the welding and tensile time had a positive effect on the tensile strength.

Duplex ESSO 시험법에 의한 9% Ni강 취성 균열정지 특성 연구

김영균(Young Kyun Kim),오병택(Byung Taek Oh),양영철(Young Chul Yang),윤인수(Ihn soo Yoon),김재훈(Jae Hoon Kim) 한국가스학회 2020 한국가스학회지 Vol.24 No.6

취성파괴는 구조물 손상의 원인 중 하나로 대형사고로 발생할 가능성이 있다. -162℃의 초저온 LNG를 저장하는 저장탱크의 내조는 취성파괴가 발생하지 않도록 반드시 이를 확인 할 수 있도록 성능검사를 하여 건설된다. 파괴역학 관점에서는 구조물의 파괴특성을 균열생성과 균열정지로 구분하고 있다. 취성균열이 발생되지 않도록 설계하고 취성 파괴가 발생하여도 취성 파괴가 정지하는 기능이 확인되는 소재가 사용되어야 한다. 본 논문에서는 LNG저장탱크의 내조 소재로 널리 사용되는 9% Ni강 33mm, 37mm, 40mm 두께로 준비하여 취성균열정지 특성을 분석하였다. 기본적인 취성 충격 시험특성을 파악하기 위하여 샤르피 충격시험을 상온, -162℃, -196℃조건에서 수행하였다. 또한 -196℃ 환경에서 Duplex ESSO 시험을 수행하여 취성균열정지 파괴인성을 평가하고 그 결과를 분석하였다. 이러한 시험결과를 바탕으로 9% Ni강이 LNG저장탱크 내조소재로 적용되기에 충분한 균열정지 파괴인성을 가지고 있음을 확인하였다. A brittle fracture is one of the source of structural damage and can bring a fatal accident. The inner shell of LNG storage tank should be designed and applied to construction by ensure that no brittle crack will occur under -162℃ condition. In point of view of fracture mechanics brittle fracture in the structure could be referred as crack initiation and crack arrest. It should be designed no crack initiation. However, in the unlikely event of a brittle fracture occurring, a back-up function of arresting the brittle crack should be included for the design. In this paper investigated the characteristics of 9% Ni steel thick plates of having a capability of arresting brittle cracks under the thickness of 33 mm, 37mm, 40 mm. First, charpy test has performed to evaluate the fundamental brittle impact fracture property of 9% Ni steel under the temperature of 24℃, -162℃and –196℃. In addition, Duplex ESSO tests were also performed under –196℃to evaluate the capability of crack arrest for 9% Ni steel. From the experiments results, it was confirmed that all the thickness of 9% Ni steel plates exhibits sufficient brittle crack arrest fracture toughness for the application of LNG storage tank as a inner shell.

Fe계 합금 용가재가 적용된 9% Ni강 용접 조인트의 미세조직과 기계적 특성에 미치는 용접 후 열처리의 영향

최광수,정효연 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.9

A Fe-based filler material with the composition of Fe-20Ni-5Co-2.5Mn-0.2C was used for welding9% Ni steel, and the effect of post-weld heat treatment on the microstructure and mechanical properties ofthe welded joints was investigated. Post-weld heat treatment of the welded joint was performed in thetemperature range of 200 to 600 oC. After the experimental selection, the microstructure changes of the weldmetal and base metal were investigated in detail at heat treatment temperatures of 350 and 600 oC. Grainmorphology, size, and the location of precipitated cementite were studied using SEM and EBSD phase maps. The mechanical properties of the weld joint were characterized by tensile properties and micro-hardness. Based on the experimental results, this study provides key insights into the applicability of post-weld heattreatment to weld joints of 9% Ni steel prepared using Fe-based filler material to improve the mechanicalproperties, toughness and ductility of the weld joints.

9% Ni 강 지상 LNG 저장탱크의 내진에 의한 건전성 평가

김재원(Jae-Won Kim),이영신(Young-Shin Lee),이성진(Seong-Jin Lee),이영민(Young-Min Lee),김영균(Young_Kyun Kim) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1

In this study, seismic analysis of 9% Ni steel Ground LNG storage tanks was performed, and evaluate the soundness. Analysis and interpretation of the model excluding the welds were performed. Seismic analysis of the response spectrum analysis was applied to the analysis model. Workbench 12.0 was used in the analysis.

Enhancement of Impurity, Machinability and Mechanical Properties in Te-Treated 0Cr18Ni9 Steel

Jian‑bo Xie,Tian Fan,Han Sun,Zhi‑qi Zeng,Jian‑xun Fu 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6

To enhance the machinability and mechanical properties of 0Cr18Ni9 steel, free-machining element Te was introduced inthis work. By adding various quantities of Te to steel, several machining and tensile tests were carried out. Results show thatwith Te addition of 530 ppm, the number of inclusion sizes below 1 μm disappeared. With raising Te from 360 to 530 ppm,more MnTe–MnS inclusions of 10–40 μm were in spherical shape; above 50 μm2, the ratio of inclusion area at 530 ppmwas greatest among all, and the large-sized inclusions occupied a larger share. Te addition contributed to the surfaces ofmachining steels more smooth. The ultimate tensile strength of steel increased from 399 to 435 MPa. Te resulted in growthof sulfides and improved the machinability of steel.

9% Ni강의 Alloy 625 용접재료 적용에서 GTAW와 FCAW의 고온균열 발생 특성 비교

나기범,이창익,박정현,조상명 대한용접접합학회 2019 대한용접·접합학회지 Vol.37 No.4

Recently, demand for LNG storage and fuel tanks has been increasing due to the International Maritime Organization(IMO) regulations on sulfur oxides and greenhouse gas emission. In the production of LNG tanks, 9% Ni steel is used and Alloy 625 or Hastelloy wire are used as the filler materials. In the FCAW welding process using Alloy 625 consumables, when using high current to increase productivity, hot cracking frequently occurs as well as welding defects such as lack of fusion due to arc instability. In this study, the hot cracking characteristics of FCAW and GTAW using Alloy 625 consumables in 9% Ni steel welding were compared through the FISCO hot cracking test.

9% Ni 강 LNG 저장탱크 내조의 정적 구조 해석

이영민(Young-Min Lee),이영신(Young-Shin Lee),이성진(Sung-Jin Lee),김영균(Young-Kyun Kim) (사)한국CDE학회 2011 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2011 No.1

The design of LNG Tank is conducted using 2-dimensional finite element analysis in the past. But it is possible to analysis using 3-dimensional finite element analysis of recent hardware & software. In this study, a static analysis of construction of 9% ni steel of LNG strorage tank internal is conducted. The evaluation on the structural integrity is conducted using ABAQUS. The maximum stress and maximum displacement is occurred on the bottom wall.

액화천연가스 저장탱크 9% 니켈강 용접부의 방사선투과시험 필름에 나타나는 밴드형상의 지시 해석

이승현(Seung Hyun Lee),이승림(Seung Rim Lee),이영순(Young Soon Lee) 한국비파괴검사학회 2010 한국비파괴검사학회지 Vol.30 No.5

초저온 액화가스인 LNG의 저장탱크에 사용되는 9% 니켈강은 Inconel 혹은 Hastelloy 계열 용접봉을 사용하여 용접되며, 용접부는 저합금강과 오스테나이트 스테인리스강의 이종금속 용접부와 유사한 특성을 가지고 있다. 용접부에 대한 방사선투과시험 시 용접조건에 따라 밴드형태의 지시가 방사선투과 필름 상에 나타나곤 한다. 따라서 본 연구에서는 이에 대한 해석을 위하여 재료, 방사선투과시험, 초음파탐상시험, 액체침투탐상시험 및 조직시험을 통하여 의사지시 여부를 확인하였으며, 방사선투과시험 해석 및 밴드형태 지시의 발생 원인을 제시하였다. 9% nickel alloy steels used for LNG, cryogenic liquid, storage tank are welded with dissimilar Inconel or Hastelloy welding rod and the weldment shows similar characteristic with the dissimilar metal weld of low carbon steel and austenitic stainless steel. Band type indications are sometimes shown on the film during radiography test of the weldments. Thus this study identified whether the indications are non-relevant indications through material, radiographic test, ultrasonic test, liquid penetrant test and microstructure analysis and also proposed radiography film interpretation and cause of band type indications.