Production processes in the oil and gas industry are associated with process variables like pressure, temperature, level and flow. Process instrumentation allows plants to measure and control these variables in real time, making their processes run effectively and allowing them to meet safety, environmental and quality objectives.

Though the availability of a vast number of sophisticated instruments has led to improved product quality, many issues still arise. Every device has its range of measurement accuracy, sensitivity and cost; hence, instrument engineers are often overwhelmed when selecting a particular technology for a specific application. A wrong choice could lead to recurring malfunctions and failures of the instruments.

Instrument selection criteria

Here are some of the considerations end-users must make to ensure success while dealing with process instrumentation technology.

Environmental conditions

Some environmental conditions are unfavorable for specific instruments. End-users who are keen on using these instruments in such environments will have to make provisions for the protection of the instrument or modification of the system. For instance, sheathed thermocouples and thermometers should be used for temperature measurements in corrosive environments and environments where vibration and mechanical stresses are prevalent.

Collect process data

The suitability of a particular instrument largely depends on the data pertaining to the processing fluids. Physical properties such as density and viscosity of the fluid must be known before instruments are selected. Other data such as phase, flow rate, presence of contaminants, and corrosiveness must also be predetermined to prevent malfunctioning or failure of instruments. For instance, an instrument designed to handle single-phase flow will most likely be unsuitable for two-phase flows common in oil and gas production.

Effect on measured system

It is not strange to have the measured system altered when process parameters are measured. For instance, pressure losses are sometimes associated with some techniques of flow measurement. These changes are negligible in some cases and quite significant in others. Process engineers must determine if the extent of disturbance on the measured system is significant to their processes and desired product quality.

Identify operating cases

Fluid properties during normal operation differ from properties during start-up and emergency operation. Instrument engineers must be aware of process requirements in all cases before selecting a particular instrument and control technology.

Durability, maintainability and operability

Engineers must also consider the durability, maintainability, and operability of different process instrument technologies before selecting one.

Common pitfalls

Inadequate training

When process engineers lack adequate training required for the specifications of instrument technologies, issues arise. Many engineers are quick to follow the recommendations of sales representatives who lack the qualification to review details.

Although properly recruiting instrumentation engineers comes with benefits, much work is needed. Advancement in technology is common in the process industry, and engineers must be continually trained to keep them abreast of these changes.

Preference for Lower-priced products

Engineers who have a preference for lower-priced products will end up tackling issues plaguing their process system. Before choosing a particular product, an end-user must weigh price against process requirements as it ensures that higher-priced products are not excluded.

Lack of synergy between different departments within a facility

The saying “no man is an island” very much applies to the process industry. Process instrument selection requires an end-user to have knowledge about many engineering fields. Yet, many instrumentation engineers hesitate to ask for help from other departments within the facility. For instance, a mechanical engineer will be of great assistance to the instrumentation engineer on matters concerning a new control valve.

Recent technology developments

The last two decades have seen advancement in instrumentation and control technology as devices are now able to meet more stringent requirements and suit a wider range of applications. Examples include the Coriolis flow meter and the clamp-on ultrasonic flow meter.

The Coriolis flow meter directly measures mass flow rates of liquid and gases. Unlike many other flow meter technologies, it is extremely fast and accurate since it doesn’t rely on corrections of temperature, pressure, or density to compute mass flow. Instead, the Coriolis flow meter simultaneously measures other process variables such as density and temperature. These parameters can be used to compute other parameters such as concentration and volume flow rate. The Coriolis flow meters are usually compact and used in pipes with a diameter of 1 to 4 inches. Newer models now cover the needs of larger pipes.

Clamp-on ultrasonic flow meters have also gained popularity in the oil and gas industry. They are commonly used for gas flow measurement in offshore facilities, where there exist challenges of accessing thick-walled pipes with wet gas at relatively low pressure. These meters do not interfere with the fluid flow, as they have transducers that are attached to the outside of the pipe.

As long as process engineers and instrument engineers adhere to the guidelines presented in this article, process instruments will be selected correctly, and malfunctions will be greatly reduced.