ADVANCED PIPELINE PROTECTION – Page 5

To ensure that there is no danger of a pipeline rupturing, most countries require regular inspections of any company operating both onshore and offshore fields and they must be able to certify compliance.

One method of monitoring a pipeline’s CP system in the case of offshore pipelines is called Electrode Field Gradient (EFG) measurement where a Remotely Operated Vehicle (ROV) or diver swims along the entire length of a pipeline to record the field gradient of the pipeline’s CP system. Field gradient can be used as an indication of cathodic protection activity. The field gradient strength is a function of the distance between the reference electrode array and the pipeline. However, all pipeline surveys must include periodic “stabs” along its length to recalibrate the EFG readings.

One of the latest methods for surveying pipelines is to install CP test stations at a regular, calculated interval, similar to those for onshore buried pipelines. Monitoring of the test stations requires minimal survey equipment aboard a survey vessel. An ROV or diver is required to take contact readings at these test stations using a special probe. Next, a nearby anode can be located and stabbed. During both contact measurements the voltage gradient is recorded.

Unfortunately, in practice, these surveys are sometimes not conducted correctly leading to inaccurate information that is used to assess the performance of the system. One reason for this is that some companies use staff that have not been adequately trained in CP or they use inspectors that have undertaken very basic training to carry out the assessments. There is an opportunity to improve the knowledge of inspection personnel which is being addressed by the ACA.

From these readings, the survey crew can use pipeline CP attenuation modelling to determine the next appropriate survey site and report on what actions may need to be taken immediately or planned to maintain optimal operations.

Companies such as DWA and CCE have a range of corrosion control and monitoring equipment and services that can be quickly deployed to site and/or easily added to a pipeline to enhance the effectiveness of the monitoring program.

The ACA will be running a NACE Pipeline Integrity Management course in Perth from 19 – 23 June and Melbourne from 26 – 30 June. In addition, it will be running a Pipeline Technical Event in conjunction with the Australian Pipelines and Gas Association (APGA) in Melbourne on 29 June.

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