An apparatus adapted for use with a wellhead assembly, comprising: an ultrasonic flow meter (92; 132) including: a meter body (94; 134) adapted to operate at fluid pressures up to substantially 700 bar, the meter body including a conduit (96; 136) with inlet and outlet ports (98; 138); and an ultrasonic transducer assembly coupled to the meter body (94; 134), wherein the ultrasonic transducer assembly includes: an ultrasonic transducer within a transducer housing that includes a hollow tube for receiving the ultrasonic transducer and a cap for closing the end of the hollow tube, and is positioned within the conduit (96; 136) of the meter body (94; 134) such that, during flow of a fluid through the meter body (94; 134), the transducer housing is exposed to the fluid and is in pressure balance with the fluid, characterized in that the transducer assembly further includes: a sheath disposed about the transducer housing, wherein the transducer housing is positioned inside the sheath, such that the sheath is between the transducer housing and the conduit (96; 136) of the meter body (94; 134), wherein the sheath comprises ports or apertures that enable fluid to flow inside the sheath about the transducer housing, and a carrier coupled to the sheath. a meter body (94; 134) adapted to operate at fluid pressures up to substantially 700 bar, the meter body including a conduit (96; 136) with inlet and outlet ports (98; 138); and an ultrasonic transducer assembly coupled to the meter body (94; 134), wherein the ultrasonic transducer assembly includes: an ultrasonic transducer within a transducer housing that includes a hollow tube for receiving the ultrasonic transducer and a cap for closing the end of the hollow tube, and is positioned within the conduit (96; 136) of the meter body (94; 134) such that, during flow of a fluid through the meter body (94; 134), the transducer housing is exposed to the fluid and is in pressure balance with the fluid, characterized in that the transducer assembly further includes: a sheath disposed about the transducer housing, wherein the transducer housing is positioned inside the sheath, such that the sheath is between the transducer housing and the conduit (96; 136) of the meter body (94; 134), wherein the sheath comprises ports or apertures that enable fluid to flow inside the sheath about the transducer housing, and a carrier coupled to the sheath. an ultrasonic transducer within a transducer housing that includes a hollow tube for receiving the ultrasonic transducer and a cap for closing the end of the hollow tube, and is positioned within the conduit (96; 136) of the meter body (94; 134) such that, during flow of a fluid through the meter body (94; 134), the transducer housing is exposed to the fluid and is in pressure balance with the fluid, characterized in that the transducer assembly further includes: a sheath disposed about the transducer housing, wherein the transducer housing is positioned inside the sheath, such that the sheath is between the transducer housing and the conduit (96; 136) of the meter body (94; 134), wherein the sheath comprises ports or apertures that enable fluid to flow inside the sheath about the transducer housing, and a carrier coupled to the sheath. wherein the transducer housing is positioned inside the sheath, such that the sheath is between the transducer housing and the conduit (96; 136) of the meter body (94; 134), wherein the sheath comprises ports or apertures that enable fluid to flow inside the sheath about the transducer housing, and a carrier coupled to the sheath.