Safe Flow Meter Installation and Flow Monitoring in Hazardous Environments

Neil Hannay offers some practical advice

FLOW meters are used in a wide variety of industries, processes and applications and are installed in a broad range of environments, including hazardous atmospheres. Because of this spectrum of variables, flowmeter manufacturers supply detailed technical datasheets and installation instructions for each specific flow measuring device. These documents should be fully reviewed by the design engineer to ensure the chosen meter is fully applicable for the process conditions.

Suppliers of flow measuring devices will be familiar with most process scenarios that their products are applicable for, as well as common specification and installation errors encountered by their customers. So it is always worthwhile to communicate early with the supplier to ensure the correct meter is chosen and trouble-free installation occurs.

General safety considerations for safe flow measurement

Safety covers a wide array of scenarios with liquid flow measurement, ranging from the requirement for safety-critical measurement to installing within an explosive atmosphere.

Key areas of focus for the design engineer will be the process liquid chemical and physical attributes within the required operation parameters; the required safety operation and accuracy of the measurement; and the environmental conditions the instrument will have to endure. Coupled with all these they should also ensure the practicalities of installation and maintenance are taken into consideration to help the installation engineer who has to fit the meter and ensure its correct operation.

As the specialist for an application process, the design or process engineer will have more specific knowledge of the chemical and physical operation concerns and should therefore liaise with the flow meter manufacturer where possible, highlighting these. Often customers send a basic operation specification and ask for a guarantee from the flow meter manufacturer that the meter is appropriate. This is not always possible however, as the chemicals and process conditions may be outside the capability of the devices in question. For example, chemical compatibility of materials is key to a safe installation, but data relating to the most appropriate material for the conditions in question may not be available. The specialist engineer should always check that the specification from the supplier is correct and most suited to the specific system – choosing the wrong material can be catastrophic to a system install.

Physical conditions must also be designed in. Typically, a customer will know the general operation maximum and minimums, such as temperature and pressure; and will share that with the manufacturer. What should also be shared is the level of cycling of these parameters the equipment is likely to see. Most processes operate at relatively stable conditions, which all instruments are designed to cope with. But if large cycling of pressure and/or temperature is expected, the manufacturer should be consulted as this will reduce the life span of the device and potentially incur catastrophic failures from fatigue or moisture ingress. As a rule, flow meters do not perform well in large cycling conditions, so manufacturers will always request this is minimised where possible.

Once the general process conditions are satisfied, we then come to the environment that the meter is installed in. As already mentioned, temperature and pressure conditions need to be accounted for and environmental conditions will contribute to these. Additional environmental conditions will include, UV, water and dust, pressure (eg submerged), vibration, electromagnetic and hazardous or explosive atmospheres.