Abstract: 9Ni steel has good mechanical properties, weldability and low temperature toughness and has been widely used in LNG cryogenic storage tanks.Yet due to the existence of residual weld height in LNG storage tanks and the different ray absorption of weld and base material, it isoften difficult for the substrate quality to meet the standard requirements, which brings great difficulties to radiographic testing. By comparing and analyzing the imaging effects of digital radiography and conventional film technology, it was concluded that the imaging quality of digital radiography technology is better than that of film technology.Then through reasonable process settings, the testing problem of 9Ni steel welded joints was solvedsuccessfully.In addition, taking an LNG cryogenic storage tank with a volume of 200,000 m³ as an example, this paper also introduced the application of digital radiography technology in LNG installation projects, and the application results show that digital radiography has significant advantages in terms of imaging quality and testing time, and is expected to be further popularized and applied.

Key words: LNG storage tank, 9Ni steel, Digital radiography, butt joint