Air inleak monitoring overcoming the `superheat` problem

Air inleak monitoring has been carried out for many years by Performance Engineers making the appropriate measurements of flow, temperature and absolute pressure. Instrumentation packages were produced in the late 1980s that brought together these measurements and made the necessary calculation, using firstly analog and subsequently digital techniques. These units used readings taken at one point long the air extraction pipework (Fig. 1). This single point approach has been shown to work satisfactorily on a number of installation, particularly those with large air inleak rates. There are, however, many installations where the procedure cannot work as a result of their being in `superheated mode`. The selection and design of sensors and sensing points to meet the fundamental physical requirements of the calculation process has resulted in the ability to monitor air inleak rates in a very wide range of conditions of both superheat and non-superheat for low and high air inleak rates. The paper discusses the observations made on installations in conventional and nuclear stations and the effect of changing pumping rates and other plant variables.