When installing a differential pressure (DP) flow transmitter for liquid, gas, or steam services, proper piping design is crucial to ensure accurate and reliable measurements. The design considerations and practices for each service differ due to the varying properties and characteristics of liquids, gases, and steam. Here’s an overview of how piping is carried out for different pressure flow transmitters on these services and why it is important:
Liquid Services:
Since liquids have the ability to self-drain, the transmitter is positioned below the orifice plate on liquid lines.
In liquid applications, it is essential to consider the fluid properties, such as viscosity, density, and potential for sedimentation or clogging. The piping should be designed to minimize pressure losses, prevent air pockets or vaporization, and avoid turbulence that could affect measurement accuracy. Some key considerations include:
- Selecting an appropriate pipe size based on the flow rate and maintaining a velocity within a recommended range to prevent excessive pressure drop or turbulence.
- Ensuring proper pipe orientation to avoid the accumulation of air or gases that can affect the measurement accuracy.
- Providing sufficient straight pipe runs upstream and downstream of the flow transmitter to reduce swirl, disturbances, and pressure variations caused by bends or obstructions.
Gas Services:
In a gas service, the transmitter is located above the orifice plate due to the self-ventilating and condensate forming properties of gases.
In gas applications, factors such as compressibility, density, and pressure fluctuations must be considered for accurate flow measurement.
Key considerations for piping design in gas services include:
- Selecting an appropriate pipe diameter to maintain a velocity that prevents excessive pressure drop or turbulence while avoiding issues like sonic velocity limitations.
- Ensuring a smooth and straight upstream section to minimize disturbances and provide a well-developed flow profile.
- Preventing the accumulation of condensate or moisture in the piping, which can affect the accuracy of the measurement.
Steam Services:
The transmitter is positioned below the orifice plate with condensate pots for steam service. The pots ought to be level with one another.
Steam applications require specific considerations due to the high temperature and latent heat of vaporization.
The key factors to address in steam service piping include:
- Designing the piping system to minimize condensation and prevent liquid water from entering the flow transmitter, which can cause inaccuracies or damage.
- Ensuring proper steam quality by removing any entrained moisture or impurities before it reaches the flow transmitter.
- Selecting appropriate materials that can withstand the high temperature and pressure conditions of steam.
Why is Proper Piping Important?
Proper piping design plays a crucial role in achieving accurate and reliable flow measurements. The key reasons for following good piping practices are:
- Well-designed piping minimizes pressure losses, turbulence, and disturbances, allowing the flow transmitter to provide accurate readings and reliable flow measurements.
- Improper piping can lead to excessive pressures, vibration, erosion, or corrosion, which can damage the flow transmitter and pose safety risks to personnel and equipment.
- Optimal piping design minimizes pressure drops, reducing energy losses and ensuring efficient operation of the system.
- Properly laid out piping facilitates maintenance activities such as calibration, inspection, and troubleshooting by providing easy access to the flow transmitter and associated components.