German China India

Modernization of Process Plants

Automated Monitoring of Pipe Trace Heating Increases Availability and Reduces Costs

| Author / Editor: Thilo Glas / Dr. Jörg Kempf

If a pipe trace heating system fails in winter, the entire plant is shut down — and the damage is immense.
If a pipe trace heating system fails in winter, the entire plant is shut down — and the damage is immense. (Source: ©zorandim75 - stock.adobe.com)

In process engineering systems, it is essential that piping systems are heated in winter. Otherwise, the liquids transported in these systems would either become viscous or even freeze completely. In the case of water-based liquids, the pipes could also burst. A monitoring solution that can be individually adapted to the specific needs of older systems provides a remedy.

The more northerly the location, the more important pipe trace heating becomes. It protects the substances transported in the pipes from freezing. However, the same is also true for pipes in hot regions of the world. In Asia, for example, the crude oil transported in the pipes must be heated up so that it reaches a pumpable viscosity and does not become viscous. Therefore, if pipe trace heating fails, the entire operation usually comes to a standstill, resulting in significant financial losses.

What makes matters even worse is that the heating in older systems is often not monitored in any way. The heating systems are simply connected to the mains via a miniature circuit breaker and are switched on in the fall and then switched off again the following spring. It is also quite possible that someone will forget to switch them off. If the heating is defective under these conditions, this will go unnoticed due to the lack of monitoring equipment and will only be detected when the transported medium fails to reach its destination. This scenario can be avoided, for example, by monitoring the heating system current. An open circuit, short circuit or insulation fault can thus be identified.

Monitoring Heating System Current via Fieldbus …

The current transducer required for this type of check can be integrated into the circuit directly or via a current transformer. For example, direct measurement up to 5 A can be performed using devices from the Phoenix Contact MACX MCR product range. If a corresponding current transformer is used, such as one from the Pact series, measurements can even be performed in the kA range. The measuring transducer converts the heating system current into a 4…20 mA analog signal that can be recorded by the control technology. A direct connection to the specific control system used would be possible, but is not easy to implement due to the large distances that usually have to be covered in the system. If a fieldbus system such as Profibus, Profinet or Modbus/TCP has already been installed in the field, the signals can be connected via a remote I/O station. All that is needed is a small control box, in which the bus coupler suitable for the relevant fieldbus system is connected to the analog input modules for the 4…20 mA signals.

… or Secure Industrial Wireless Solution

In many cases, the initial situation is different, as installing signal lines in the field often involves high costs. A secure wireless connection therefore presents a possible alternative solution. Several technologies are available for this purpose. When we talk about wireless data transmission, WLAN communication is the first thing that springs to mind for many users. A wide range of hardware products are available for this wireless technology. However, distances of only around 100 meters can be covered via WLAN. A particularly good alternative here is Trusted Wireless 2.0 technology, which was developed specifically for industrial applications. When transmitting in the 2.4 GHz frequency band, distances of up to five kilometers can be covered between two devices. In the 868 MHz band, it is even possible to cover distances exceeding 32 kilometers. In addition, the Radioline product family offers a complete I/O system that can be connected directly to the transmitter module. In addition to frequency hopping (FHSS), it also provides optional 128-bit AES encryption for secure data exchange.

By combining the Radioline I/O system based on Trusted Wireless technology with a current transducer, you have a simple way to monitor the current for pipe trace heating. You just need a small control box to install the Radioline transmitter module, the analog input cards, and the MACX MCR current transducer. With a flexible number of input cards, the solution can be optimally adapted to the relevant application and covers all local sections of the heating system. For example, the Radioline system is connected to the control system via Modbus/RTU and the values can be clearly visualized there. Interface converters are available for integrating other fieldbus systems, such as Profibus.

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