Tips for Valves
Best Practices: How to get the Most out of Valves
Preventative Maintenance for Valves
As testing has proved, even minor scratches, on the ball surface, can lead to a valve leakage during gas testing. These scratches will continue to erode into larger leak paths if a preventative maintenance program is not in place.
The seat sealant system should be topped up with light grade synthetic lubricant or sealant. As the seat sealant system is filled, the previously injected sealant will be extruded into the valve body adjacent to the ball and seat ring interface. A valve technician should be called to inspect the valve thoroughly to ensure that the sealant is protruding around the circumference of the seat ring. Excess sealant should be smeared around the circumference of the seat ring to fill in the gap between the ball and seat ring and leveled so as not to overflow into the valve bore.
Methods such as blast cleaning should be avoided as this method could be a bit harsh on the internal parts of the valve. Sand, dirt, pebbles, sand blasting material, hand tools, timbers, are some of the many contaminants normally discovered in valve bodies, pig receivers and scraper / filter devises after start-up. Minor valve seat leakage is often the result of scratches to the seating surfaces caused by these contaminants. It would be ideal to keep a spool piece, in place of valve, while the pipeline is flush cleaned. However, this may not be feasible or practical in many sites.
Hydrostatic Testing Specifications
Hydrostatic testing when done should be in line with the valve manufacturer’s specification. First, the pipeline is filled with water, from one end of the pipeline, with all valves in the fully open position. This will push all construction debris downstream to the end of the test section, where it can be drained off. Once the water runs clean, shut the drain off point.
Prior to pressure testing, keep the valve in a half open position, as only the valve joints will get pressure tested. It is advisable to drain the valve cavity of accumulated dirt or foreign particles. Then, shut the drain plugs.
After all valves are kept in half open position, slowly increase the pressure, in stages. Check for body joints, stem top, sealant injection points, drain / vent threads for any possible leaks. T hen increase the test pressure to full rated pressure, as per pipe line commissioning procedures. All leak points shall be repaired prior to the introduction of gas into the system. Upon completion of a successful hydrostatic test, the valve should be operated in the full open position. The seat sealant system in the valve should then be topped up. Also, the valve should never be kept in the half open position for a long time. This can result in the elastomers or soft inserts in the seat ring to become deformed, resulting in severe seat leakage. After this, the pipelines or valves must be completely drained and dried.