David Jessop looks at the use of satellite communications for cathodic protection monitoring where pipeline access is difficult.
The need for cathodic protection monitoring, often driven by national and state safety and environmental legislation, is well known. Likewise, the monitoring regimes required to ensure the systems are effective are also well established thanks to the recommendations of organisations such as the National Association of Corrosion Engineers and the Institute of Corrosion. What is still evolving is the equipment to allow such remote monitoring.
New technology can reduce the need and cost of periodically transporting CP engineers to remote pipelines. By more frequent monitoring, it can also detect failures in the cathodic protection system before significant deterioration of the pipeline occurs.
A further benefit is that the measurements, such as the Instant Off potential, can be made more consistently than with manual techniques. With better monitoring, the workload of maintenance teams can be reduced and prioritised resulting in the pipeline life being extended.
The ability to communicate with all sections of a remote pipeline is crucial for the success of an automated CP monitoring system.
For remote monitoring, GSM/Cellnet technology provides a very effective solution but has limited geographic coverage.
It is the areas of low population with no coverage – where pipeline access is difficult and costly – that remote monitoring is most desirable. Dedicated radio telemetry is possible but is relatively expensive to install and has a limited range compared to pipeline lengths.
By contrast, cathodic protection monitoring equipment such as Satamatics’ CPME units – Transformer Rectifier (TR) and Test Post (TP) – using Inmarsat D+ satellite communications technology, offers global coverage.
How it works
Each data acquisition system on the pipeline is fitted with a satellite terminal. This communicates via a secure global satellite network to Ground Earth Stations.
At the Ground Earth Station, the radio frequency signals from the dish are converted into a digital message format and routed via a dedicated line to a Message Handling System at a centralised Data Centre. Using a secure internet connection or dedicated lines, the user is able to send and receive messages to the remote satellite terminals from his personal computer or workstation.
The measurement and control can be integrated into a monitoring application to provide a high level user interface.
In addition to the communication system, other factors determine the selection of monitoring equipment.
The requirements need to be considered for pipeline monitoring at both Transformer Rectifier (TR) stations and Intermediate Test Posts (TP). It is important to ensure that the right functions are available and, just as important, that the measurement integrity of the equipment will ensure reliable results in a pipeline environment.
David Jessop is Principal Engineer with Satamatics Limited, Tewkesbury, Gloucestershire, UK. www.satamatics.com"