Material properties of SUS 304 steel at low temperature and integrity assessment of loading arm for LNG

Loading arms are widely used as loading facilities for LNG etc. and made of austenitic stainless steel SUS 304 which is tough at low temperatures since LNG is the low temperature fluid of -162'C. However, due to the long time usage under the low temperature circumstances, deformation starts which is considered to be caused by martensite transformation due to thermal strain generated during the loading operation of LNG. Heretofore the data on this matter have been insufficient. In this research, the relationship between the martensite deposit and the absorbed energy while the above strain was repeatedly applied was examined through the strain loading tests in the liquid nitrogen. As the result, it was confirmed that the martensite deposit of SUS 304 under the loaded strain equivalent to the 20 year usage of the actual machine was about 10% presenting no legal problem whatsoever. In addition, as the result of the fracture toughness test, the critical value of imperfect dimension permissible until the start of fracture was found to be one half of the thickness of arm tube and it was considered that no vital brittle fracture would occur during the actual use. (15 figs, 4 tabs, 3 photos, 3 refs)