Patent Number: 048760560
Section: summary

This invention relates to a method and an apparatus for measuring the flow of a fluid in a duct, and particularly though not exclusively for measuring the flow of liquid in a sub-sea pipeline. According to the present invention there is provided a method for measuring the flow of a fluid in a duct having at least a length thereof immersed in a saline sea, the method comprising locating a container adjacent to the duct, with the container having an inlet communicating with the sea to allow ingress, as a test fluid, of sea water from the sea, causing the test fluid to enter the container, storing the test fluid in the container, irradiating the test fluid in the container with neutrons so as to generate atoms of a predetermined radioactive nuclide in the test fluid, injecting at spaced time intervals a sample of the irradiated test fluid from the container into the duct, detecting, at a location spaced apart along the duct from the location at which the injection takes place, radiation emitted by the predetermined radioactive atoms, and determining, from the elapsed time between the injection of the test fluid and the detection of the radiation, the flow rate of the fluid. An advantage accruing from use of sea water as a test fluid obtained from the environment of the duct is that the apparatus can operate for a long period of time without any need for servicing; the period of operation is not limited by the storage capacity of the container. It is therefore suited to use in remote or hostile locations such as on the sea bed. The invention is especially suited to measuring flow in under-sea pipelines carrying oil, for example from an oil well. Sea water typically contains sodium ions at a concentration of about 10 g/liter. As a consequence of neutron irradiation, sodium-24 nuclides are created. These decay with emission of beta and gamma radiation and with a half-life of 14.8 hours.