Best Practices on How to Safeguard Pipeline Ball Valves

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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. Then 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.

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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.

Specifications High Pressure Gas Tests

For natural gas pipelines, high pressure nitrogen gas testing would follow the hydro test. While pressure testing the line with nitrogen, the valve should be operated first in the half open position to pressurize the body cavity and then returned to the full open position. The body vent or drain valve should then be opened and closed to drain the water from the body cavity. When all water has been removed, the valve needs to be brought back to the fully open position and lubricated further.

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With the pipeline under normal operating pressure, the valve technician can now inspect the valve for seat leakage. Then, verification of each valve being tightly sealed in both full open and full closed positions can be done. Leakage, if any, is visually monitored by opening the body vent fitting with the main valve in the fully open or in fully closed position only.

How to Deal with Valves Failures or Leaks

In the event that minor leakage persists, the valve should be topped up with more lubricant or sealant and the valve stops need to be adjusted in an attempt to achieve a perfect seal. When the sealing is achieved, the actuator stops and should be locked in to position. In the event that a seal cannot be maintained, the valve manufacturer’s representative should be consulted for recommendations. In the event that leakage is very minor, a heavier sealant may be injected upon mutual consent of the operator, contractor and valve manufacturer.

* The author is Managing Director for Valvezone Technical Services

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