극저온용강 이재 용접부의 안전성 평가에 관한 연구

Abstract

Recently, the importance of the environment is increasing due to the continuous expansion of ships, and environmentally friendly ships are being discussed. Ships that use environmentally friendly energy such as LNG, hydrogen and ammonia are being discussed. Currently, through IMO 2020, many bunker C oil vessels are being ordered with desulfurization equipment or eco-LNG vessels. This LNG-propelled ship requires an LNG storage tank, but the cryogenic steel currently registered in the IGF code is Al-alloy, austenitic STS steel, and 9% Ni steel. Up until now, 9% Ni steel has been used a lot, but there are problems with weldability and material quality. Therefore, high Mn(H-Mn) steel with high Mn content is emerging as an alternative. In this study, the evaluation for applying the newly developed H-Mn to LNG storage tanks was performed as follows. First, a sample is prepared by welding cryogenic steel such as H-Mn, 9% Ni, STS and STS304 pipes. Residual stress after welding of cryogenic steel HAZ was analyzed by experimental method such as cutting method and analytical FEM analysis. Secondly, the test specimen made of extremely low temperature steel and STS304 pipes was changed from low temperature (-165℃) to normal temperature (25℃) to confirm stress caused by temperature change experimentally and analytically. Third, the actual LNG carrier C-Type tank was modeled and the residual stress after welding was estimated analytically using the MSC Marc commercial program. Finally, we modeled the actual LNG carrier C-Type tank and applied temperature changes to analyze the stress changes due to temperature. As a result, it was determined that the factors affecting the weld HAZ of cryogenic steel and STS304 pipes had a greater effect on the stability of residual stress after welding than on the stress changes caused by temperature changes.