Inspections: Main tool for the knowledge of the state of the integrity of the pipe

Inspections

In a protected infrastructure, during the operation phase, the inspections are the main tool for the knowledge of the state of its integrity. The data obtained will help us to calculate the remaining life of the installation, that this asset can work safely with the current operating parameters, update the inspection maintenance and repair plans.

Procainsa is specialised in inspection techniques for protected infrastructures, especially underground pipelines.

Our techniques include:

• Cathodic Protection
• Stray current studies
• Direct Current Voltage Gradient (DCVG)
• Close Interval Potential Survey (CIPS)
• DCVG + CIPS
• Alternating current voltage gradient (ACVG)
• External Corrosion Direct Assessment (ECDA)
• Soil resistivity survey
• pH analysis
• Pipeline mapping
• Pipeline locating and depth measurement

Direct Current Voltage Gradient (DCVG)

The Direct Current Voltage Gradient (DCVG) is the most accurate inspection method for coating surveys on buried pipelines and also checks the efficiency of the cathodic protection systems.

The technique is fundamentally based on measuring the voltage gradients in the soil above a cathodically protected pipeline.

This technique uses a direct current pulse generated by a current switch. Current flow through the soil causes a gradient of potential around defects in the coating. These are detected using two grounding electrodes that allow measurement using a specifically designed voltmeter. This system evaluates the electrical magnitude of the defects found.

The technicians of Procainsa SA will take the measurements and geo-locate the defects through a GPS. Defects with the highest IR percentage will be rated as the most severe. The following table shows the 4 categories of defects.

Close Interval Potential Survey (CIPS)

The technique consists of taking potentials under cycles on / off at regular intervals of the Cathodic Protection system along the buried pipeline.

This inspection method is used to evaluate the effectiveness of the cathodic protection system in buried pipes. The CIPS inspection also can locate areas affected by stray currents and coating features (holidays).

DCVG + CIPS

Procainsa SA combines both inspections to know the severity of the coating defect and to certify the type anodic or cathodic feature.

By DCVG inspection method, we detect and know the electrical severity of the coating feature, as percentage of voltage gradient (% IR) and the feature is characterised observing if it receives cathodic protection current (cathodic or protection) or if it drain current to the ground (anodic or corrosion).

Where a coating defect has been detected, the CIPS technique shall be applied to determine on/off potentials on the pipeline, these on/off potentials shall be taken in sections of 20 m, meter by meter, 10 m upstream and 10 m downstream of the localization of the defect.

Combining DCVG and CIPS inspections will obtain the defect electrical data and if the cathodic protection system is working properly in this area, therefore this information will help to establish coating repair strategies.

The detailed information provided by DCVG technology, when analysed together with other information such as on/off potentials obtained with CIPS, soil resistivity, pH, presence of stray currents, etc., allows to predict the rehabilitation requirements on the pipeline, giving priority to repair by the most effective and economic form.

External Corrosion Direct Assessment (ECDA)

This procedure should be used as an alternative to the intelligent pig inspection or in pipelines where cannot be inspected by intelligent pig (unpiggable or due to operational problems).

ECDA includes the following four steps:

• Preassessment: collects historic and current data to determine whether ECDA is feasible, defines ECDA regions, and select indirect inspection tools. The types of data to be collected are typically available in construction records, operating and maintenance histories, alignment sheets, corrosion survey records, other aboveground inspection records, and inspection report from prior integrity evaluations or maintenance actions.

• Indirect Inspection: this step covers aboveground inspections to identify and defines the severity of coating faults, other anomalies, and areas where corrosion activity may have occurred or may be occurring. Two or more indirect inspection tools are used over the entire pipeline segment to provide improved detection reliability under the wide variety of conditions that may be encountered along a pipeline right-of-way.

• Direct Examination: includes analyses of indirect inspection data to select sites for excavations and pipe surface evaluations. The data from the direct examinations are combined with prior data to identify and assess the effect of external corrosion on the pipeline. In addition, evaluation of pipeline coating performance, corrosion defect repairs, and mitigation of corrosion protection faults are included in this step.

• Postassessment: the last step covers analyses of data collected from the previous three steps to assess the effectiveness of the ECDA process and determine reassessment intervals.