SEVERE SERVICE
VALVES

The fire water system on offshore platforms (represented in Figure 6) has proven to be an extremely onerous application. KKI became involved in this application when a competitor’s butterfly valve suffered severe vibration, resulting in a failure of the system and causing a Health & Safety risk, since both the sprinkler and deluge system would not function correctly. On closer inspection of the valve, erosion (resulting from cavitation) of the vane, valve body and seating area was discovered.

It was noted that the valves were originally specified to be operating with an inlet pressure of 6 bar and a pressure drop of 1 bar. Following installation it was revealed that the operating pressure drop under test conditions was significantly higher. The pressure drop was actually 5 bar and the flow rate had increased from 250m³/hr to 340m³/hr. This meant that the existing butterfly valve had a calculated cavitation index of + 2.0 bar, which is classified as “severe”. The photograph in Figure 7 shows the type of damage that occurred on this application. The majority of the damage was to the outer edge of the vane, but there was also severe cavitation erosion damage to the valve body.

Although it was clear that a larger globe type valve fitted with a low pressure recovery would be suitable for the operating pressures, the operator required a valve that would fit into the existing pipework configuration. KKI provided the Rotrol high-performance butterfly valve as the solution. This product had undergone extensive tests both on KKI’s water test facility and at the Brown Boveri Corporation (Baden) research facility.

The special low-recovery vane enables high pressure drops to be handled without the onset of cavitation. A comparison between the respective pressure recovery characteristics of a standard vane and a Rotrol vane is shown in Figure 8. The Cavitation Index (CI) for the Rotrol valve under the most extreme condition was 0.5 bar.

The valve was installed and operated without the previous problems of cavitation and unstable control. This valve is now an accepted solution for what is still an onerous application. Find out more about our Series 63-66 rotary valves.