QUANTIFYING ISOLATION VALVE LEAKAGE

摘要

Valve leakage is quantified by measuring a variable that is commensurate with a heat transfer characteristic of the pipe wall (30) and comparing the measurements to data stored in a database (84) which embodies a quantitative relationship between an index commensurate with the heat transfer characteristic variable and a range of valve leakage rates that could occur for the given value. In a straight forward implementation of the invention, a thermal hydraulic analysis of the specific valve and associated piping are performed a priori to establish a database of pipe wall temperature downstream of the valve as a function of steam flow rate. The wall temperature is simply measured and compared with the database. In another embodiement, an air cooled sleeve (54) is installed around the pipe (48) downstream of the valve (50) and a controlled flow of air is passed through the annulus (62) between the pipe and the sleeve. The temperature rise of the flowing air is measured and is used to compute the flow rate of steam leaking through the valve. In yet another embodiment, the valve leakage is quantified by monitoring and controlling heat input into a local section of a horizontal pipe (94) upstream of the valve. The center zone (106) of the heaters (96) is controlled to raise the pipe temperature a certain amount above the steam temperature and the power required to maintain the temperature is measured. The database provides a quantitative relationship between such power input and stream flow through the valve.