FLow Control Valve 100% open

Hello, in a LNG regasification terminal the LNG flow control valve at the inlet of an Open Rack Vaporizer tends to open 100% and as a result flow decreases and the design capacity of the ORV cannot be achieved. It seems that the operating high pressure pumps and the sendout pressure is related to this problem. Any ideas about this topic?
Thank you in advance.

The issue you’re facing at the LNG regasification terminal concerning the LNG flow control valve and the Open Rack Vaporizer (ORV) is a complex one, which may involve multiple factors. The fact that the LNG flow control valve tends to open 100% yet the flow decreases indicates a possible systemic issue related to the valve control system, fluid dynamics, or the integrity of the components involved.

Here are some areas to investigate:

Valve Control Mechanism

  1. Control System Calibration: Ensure that the PID (Proportional-Integral-Derivative) control loops associated with the flow control valve are correctly tuned. Poorly tuned control systems could be overly sensitive or too sluggish to maintain desired flow rates.
  2. Instrumentation: Ensure that the sensors giving flow rates and pressures are accurate. Incorrect sensor data can mislead the control system.
  3. Actuator Malfunction: Ensure that the actuator is functioning correctly and is capable of exerting the required force to control the valve position effectively.

Fluid Dynamics

  1. Pressure Drop: If the valve is fully open but the flow is decreasing, it could mean there is a significant pressure drop somewhere in the system, perhaps due to an obstruction, fouling, or because the high-pressure pumps are not operating at full capacity.
  2. Pump Curve: Assess the operating point of the high-pressure pumps. It should lie within the efficient zone of the pump’s performance curve to provide sufficient pressure for optimal flow.
  3. Two-Phase Flow: If the LNG is partially vaporizing before reaching the ORV, it could lead to a two-phase flow which is much harder to control and could explain the reduced flow rate.
  4. Sendout Pressure: High sendout pressure could cause a back pressure effect, affecting the flow rate. The control system might fully open the valve to counter this, but it won’t help if the cause is downstream.

Mechanical Integrity

  1. Valve Condition: Make sure the valve itself is in good condition. Any wear and tear, such as scoring on the valve seat, could result in less than optimal operation.
  2. Piping Integrity: Ensure that there are no leaks or integrity issues in the piping that could be affecting the pressure and flow rate.


  1. Data Logging and Trends: Look for any trends in the system data that might offer clues. Is the problem continuous, or does it happen in cycles?
  2. Dynamic Simulation: A dynamic simulation of the system might reveal whether there are systemic issues affecting the valve operation and flow rate.
  3. Consult Manufacturer: Sometimes the issue could be very specific to the equipment used. Consulting the manufacturer’s technical support can provide insights that are not obvious.

Given that you are experienced in instrumentation, you might want to look closely at the system controls and sensors to ensure they are correctly calibrated and operational. Likewise, since you’re also knowledgeable about electrical systems, ensure that the electrical components like actuators and pumps are receiving the correct voltages and currents for optimal performance.

This problem requires a multi-disciplinary approach, involving expertise in mechanical engineering, process control, and fluid dynamics. It would be advisable to have a detailed system audit to understand the root cause of this issue.