MANUAL ON INSTALLATION OF REFINERY INSTRUMENTS AND CONTROL SYSTEMS PART I-PROCESS INSTRUMENTATION AND CONTROL SECTION 8-SEALS@ PURGES@ AND WINTERIZING (THIRD EDITION)
"Section 8 discusses recommended practices for sealing@ purging@ and winterizing measuring instruments and the lines connecting them to their process. Following these guidelines should ensure reliable instrument performance. The instruments usually requiring sealing@ purging@ or winterizing are those for measuring flow@ pressure@ and liquid level@ but also may include other instruments having sensitive elements normally exposed to the process fluid such as process stream analyzers. Seals and purges are used to prevent the process fluid from entering the instrument or connecting lines and causing improper operation or damage due to vaporization@ condensation@ viscosity effects@ corrosion@ or sedimentation. Winterizing@ usually some form of heating@ is used to prevent impaired operation of the instrument and connecting lines by formation of ice@ hydrates@ and other fluids that solidify at low ambient temperatures. Heating is also used to prevent solidification of a process fluid at a temperature approaching its pour point. Analyzers often require special winterizing techniques which are discussed in API RP 550@ Part II@ ""Process Stream Analyzers."""