A heat exchanger, in particular a high-pressure heat exchanger for urea synthesis, comprising multiple heat-transfer tubes for transporting a first fluid in order to transfer heat between the first fluid and a second fluid via the heat-transfer tubes, wherein an ultrasound sensor is respectively arranged on one or more of the heat-transfer tubes for determination of tube wall thicknesses of the heat-transfer tubes, wherein the ultrasound sensor is designed for a working pressure of more than 30 bar and/or a working temperature of more than 80° C., wherein the ultrasound sensor is connected to an electronic data acquisition unit for a transfer of data, in order to transfer measurement data to the electronic data acquisition unit during operation of the heat exchanger.