Joint structure for metallic pipes

A joint structure for metallic pipes comprising:

• a first metallic pipe made of a material containing one of a first metal element and a second metal element different from the first metal element as a main component;
• and
• a second metallic pipe made of a material containing the other of the first metal element and the second metal element as a main component, wherein
• the first metallic pipe includes an expanded-diameter connecting part at an end part of the first metallic pipe, an inner diameter of the end part being greater than an inner diameter of an adjacent part adjacent to the end part,
• the second metallic pipe includes a connecting end part at one end part of the second metallic pipe, the connecting end part lying in the expanded-diameter connecting part from an open end of the expanded-diameter connecting part to a base end of the expanded-diameter connecting part,
• a brazing filler layer lies between an outer surface of the connecting end part of the second metallic pipe and an inner surface of the expanded-diameter connecting part, and is made of a material containing the first metal element or the second metal element as a main component,
• an intermetallic compound layer lies at an interface of the first metal element and the second metal element located between the brazing filler layer and the first metallic pipe or the second metallic pipe, and is made of a material containing both the first metal element and the second metal element, and the intermetallic compound layer has a smaller thickness at a leading end of the connecting end part of the second metallic pipe than at a leading end of the expanded-diameter connecting part of the first metallic pipe,
• the thickness of the intermetallic compound layer varies from the leading end of the expanded diameter connecting part of the first metallic pipe to the leading end of the connecting end part of the second metallic pipe, without increasing the thickness of the intermetallic compound layer.