An Overview of Orifice Meters in LNG Applications: Structure and Function

Orifice meters are essential instruments used to measure the average velocity and flow rate of fluids, particularly in LNG (liquefied natural gas) applications. In this article, we will delve into the structure, function, and significance of orifice meters in the context of LNG systems.

Orifice Plate Structure

The orifice plate plays a crucial role in the functioning of an orifice meter, and its design and characteristics can vary based on several factors.

Factors Influencing Orifice Plate Design

- Plate thickness

- Hole placement

- Bore size

- Number of bores

Placement and Purpose

The orifice plate is typically positioned between the flanges of two pipe sections and fastened with a nut. Its main function is to restrict fluid flow, reducing pressure without causing excessive turbulence downstream.

Tapered Bore Design

To optimize pressure reduction, the hole diameter in the orifice plate is tapered, increasing in size in the direction of fluid flow.

Eccentric Orifice Meters

In applications involving fluids with particulate solids or slurries, eccentric orifice meters are utilized. Their off-center bore design prevents the build-up of solids within the pipe.

Working of Orifice Meters

The orifice meter's operation depends on the fluid's convergence as it approaches and passes through the plate, resulting in a pressure decrease.

Convergence and Pressure Decrease

As the fluid converges, its pressure decreases proportionally. This convergence continues until the fluid reaches the vena contracta point, characterized by maximum velocity and minimum pressure.

Avoiding Cavitation

Proper design is critical to ensure that the fluid's pressure does not fall below its vapor pressure, preventing vaporization in the vena contracta region and subsequent cavitation, which can damage the piping system.

Pressure Measurement

A manometer or pressure gauge is employed to measure the pressure decrease, providing valuable data for understanding and optimizing fluid flow in LNG applications.

Orifice meters play a vital role in measuring the average velocity and flow rate of fluids in LNG systems. By understanding their structure, function, and proper design, these instruments can optimize fluid flow management and ensure the safe and efficient operation of LNG infrastructure.