Boiler Tube and Boiler Tube Unit and Furnace

A boiler tube having a longitudinal extension, comprising:

• a radially inner tubular portion extending along at least a first part of the longitudinal extension;
• a radially outer tubular portion extending along the first part of the longitudinal extension, the radially outer tubular portion being metallurgically bonded to the radially inner tubular portion;
• and
• a sensor space arranged between the radially inner tubular portion and the radially outer tubular portion, wherein the sensor space is configured to accommodate a sensor arranged to detect a physical property of the radially outer tubular portion,
• wherein a duct is connected to the sensor space and extends through the radially outer tubular portion to an exit portion of a surface of the radially outer tubular portion,
• wherein the radially inner tubular portion and the radially outer tubular portion comprise materials of different chemical composition,
• wherein the sensor space and the duct are formed by a tube partially positioned on the radially inner tubular portion and extending through the radially outer tubular portion,
• wherein the radially outer tubular portion is built up around the tube, and
• wherein the radially outer tubular portion is formed by means of hot isostatic pressing of a metal powder, whereby the radially outer tubular portion is metallurgically bonded to the radially inner tubular portion.