Method of manufacturing welded jointwelded joint, welded joint, method of designing low-temperature liquefied gas tanklow-temperature liquefied gas tank, and low-temperature liquefied gas tank

A welded joint that is used for an inner tank of a low-temperature liquefied gas tank, the welded joint comprising:

• a base metal;
• and
• a weld metal,
• wherein a linear expansion coefficient of the weld metal is larger than a linear expansion coefficient of the base metal, and,
• a CTOD value at a use temperature of the low-temperature liquefied gas tank is equal to or more than a required CTOD value which takes into account an influence of a thermal stress that occurs due to a difference between the linear expansion coefficient of the weld metal and the linear expansion coefficient of the base metal.

A method of designing a low-temperature liquefied gas tank having a butt-welded portion configured to include a base metal and a weld metal in an inner tank, the method comprising:

• obtaining a thermal stress that occurs in the butt-welded portion due to a difference between a linear expansion coefficient of the weld metal and a linear expansion coefficient of the base metal at a use temperature of the low-temperature liquefied gas tank;
• obtaining a required CTOD value for preventing the low-temperature liquefied gas tank from undergoing a brittle fracture during an operation of the low-temperature liquefied gas tank by assuming a defect in the butt-welded portion and taking into account an influence of the thermal stress;
• and
• selecting the base metal so that a CTOD value of a heat-affected zone is equal to or more than the required CTOD value.