2.3 MAINTENANCE PRIOR TO FLUSHING a- If the period between installation and flushing of the of the pipeline is longer than six months a preventative maintenance operation is suggested. • Lubricate the stem through the stem injector (if applicable). • Remove valve from line and remove any debris and reflush. 2.4 FLUSHING THE PIPELINE Flushing washes away all welding slag, dirt, sand, solids and debris collected in the pipelines during construction prior to turning the valve and potentially damaging the seat. Flushing where deemed necessary is the most dangerous activity for the valve, and it happens before they are put into service. Should it be required to flush potential debris from the seat area, (or lubricate sticky valves). We recommend the following: - 1. Find a good grease for natural gas or your service. The grease must be insoluble. It must be resistant to breakdown or shearing of the gel structure under high pressure injection and under the pressure between seating surfaces. It must be stable over a wide range of temperatures, and not freeze. It must not react chemically with the fluid and become solid, or rubber like (i.e. polymerize). Depending on the service, the best greases are fully synthetic; if you have any doubt or concern, consult a valve maintenance expert. Field experience has shown that greases and sealants may cause severe problems with the seat and seal arrangement if used regularly during preventative maintenance. Of course, be warned any type of grease, especially synthetic grease can become hard or sticky causing torque problems and seat spring jamming in which case a line flushing agent like Clare 601 Valve Cleaner may be required. Of course, for leaking seats a heavier sealant like Clare 601 lubricant must be used for temporary emergency sealing. Australian Pipeline Valve - Installation, Operation and Maintenance Manual 9 API6D THROUGH CONDUIT EXPANDING GATE VALVE - AP400-405 SERIES If greasing through valve sealant fitting to dislodge debris or to lubricate, beware of greases made of synthetic oil with a mineral thickener. The natural gas (or storage prior to use) washes away the oil, leaving the thickener behind. The thickener is like a powder that caulks or bakes hard on the seats, increasing the operating torque. Always wipe the seats clean as much as possible prior to installation. To prevent damage to the valve, APV recommends first installing a spool piece instead of the valve whilst flushing the pipeline. If a spool piece is not an option, install strainers at critical locations upstream from the location to remove foreign debris. It is pertinent that the valve remain in the full-OPEN position during flushing.