Pressure vessel

A pressure vessel comprising:

• a pressure vessel body provided with a flow channel through which a fluid is caused to flow, having a rectangular cross-sectional shape, and formed in an elongated shape;
• and
• a circular body flange provided on at least one longitudinal end side of the pressure vessel body and including an opening portion formed of a through hole, the pressure vessel body being inserted in the body flange,
• wherein
• the pressure vessel body has a fluid inlet-outlet port which is provided in a side surface on the one longitudinal end side and provided on the body flange side of the pressure vessel body and connects with the flow channel and through which the fluid is caused to flow in or out,
• the pressure vessel further comprises an inlet-outlet header which is formed between an outer surface of the pressure vessel body and an inner surface of the body flange as a closed space connecting with the fluid inlet-outlet port and which the fluid is caused to flow into and out of, and
• the opening portion of the body flange has a space in which the pressure vessel body is insertable and a space in which the inlet-outlet header is formable.