Non-invasive flow measurement of sea water

A petrochemical company in China sources large volumes of seawater to reduce its reliance on groundwater. The seawater is transported via a 2680 mm (~105.5 inches) pipeline to an adjacent desalination plant, where it is processed into utility water.

To ensure transparency in the amount of seawater delivered, the company was searching for a reliable flow instrumentation. Due to the pipeline's large diameter and the corrosive nature of seawater, the operator decided against an inline flowmeter. While robust electromagnetic and ultrasonic inline flowmeters with corrosion resistant wetted materials could have been used, the company did not require the high absolute accuracy these meters provide. Instead, they preferred a cost-effective, non-invasive solution with good accuracy and repeatability. However, identifying a suitable non-invasive flowmeter capable of measuring through the glass fibre reinforced plastic (GRP) pipeline proved challenging.

KROHNE supplied several OPTISONIC 6300 clamp-on flowmeters for seawater monitoring along the pipeline. The non-invasive ultrasonic flowmeters were mounted directly onto the GRP pipes without the need to open or cut the pipeline. Given the large pipe diameters of more than 2600 mm (~102 inches), the version with large stainless-steel sensor rails was selected for installation. Each sensor rail set included two rails with integrated transducers. The sensors were connected to the field-mounted converter version of the clamp-on flowmeter.

Most of the flowmeters were installed with the recommended straight inlet and outlet runs to ensure the most favourable flow profile. In some locations, these requirements could not be fully met. However, testing demonstrated that the flowmeter’s performance was robust enough to maintain reliable measurements even where the clamp-on installation had reduced straight runs. These measuring points now serve as redundant measurements.

The non-invasive ultrasonic flowmeter is highly flexible and can be easily repositioned to the installation location with the most favourable conditions. During commissioning, KROHNE Service polished the GRP pipes to provide a smoother surface for transducer mounting, resulting in better acoustic coupling and improved signal transmission quality.

The operator benefits from reduced flowmeter costs for monitoring flow in his large seawater pipelines. Since the plant operator required a highly reliable and repeatable flowmeter with good – but not the highest – absolute accuracy typical of inline flowmeters, the clamp-on flowmeter proved to be the ideal solution. The advanced clamp-on technology of the OPTISONIC 6300, combined with the expertise of local KROHNE service engineers, ensures reliable and cost-effective flow measurement of saltwater in a challenging environment – without the need to alter existing infrastructure. The clamp-on flowmeter features robust stainless-steel sensor rails that, thanks to their ingress protection, can remain permanently mounted on the customers’ pipelines located outdoors.