Pipe coupling structure and refrigeration cycle apparatus

A pipe coupling structure comprising:

• a first refrigerant pipe that has a first portion, a first expansion portion, a second portion, a second expansion portion, and a third portion arranged in order;
• and
• a second refrigerant pipe that is inserted into the first refrigerant pipe, has a fourth portion facing the second portion and a fifth portion facing the third portion, and has a fourth expansion portion between the fourth portion and the fifth portion, wherein
• the second portion has an inner diameter larger than an inner diameter of the first portion, and the third portion has an inner diameter larger than the inner diameter of the second portion,
• the first expansion portion is an area of the first refrigerant pipe, an inner diameter of which gradually changes from the inner diameter of the first portion to the inner diameter of the second portion,
• the second expansion portion is an area of the first refrigerant pipe, an inner diameter of which gradually changes from the inner diameter of the second portion to the inner diameter of the third portion,
• the fourth expansion portion is an area of the second refrigerant pipe, an outer diameter of which gradually changes from the outer diameter of the fourth portion to the outer diameter of the fifth portion,
• the fourth expansion portion is in contact with the second expansion portion,
• the outer diameter of the fifth portion is larger than the outer diameter of the fourth portion, and
• the fifth portion and the third portion are solder material.