Electrical Hazard Assessment for Pipelines

In the context of pipelines situated near or running parallel to high-voltage (HV) lines, the potential for electrical hazards arises. To address this, contemporary industry practices, exemplified by the Australian Standard ‘AS4853 electrical hazards on metallic pipelines,’ adopt a risk assessment approach for hazard identification and management.

Key considerations in this regard include:

• Earth Potential Rise (EPR): Occurring when faults at nearby assets transfer voltage to pipeline appurtenances through the soil.
• Low-frequency Induction (LFI): Generating voltage on the pipeline due to faults occurring over a parallel conductor.
• Capacitive Coupling: Leading to voltage on an unearthed pipeline located beneath a high voltage line, though this is generally negligible for buried pipelines.

Importantly, steady-state corrosion effects, which result in relatively lower magnitude voltages when compared to LFI due to power system faults, are typically of secondary concern in hazard assessments. These approaches collectively contribute to ensuring pipeline safety in the presence of nearby HV lines.

Hazard Assessment Levels

The assessment of electrical hazards, as per AS4853 guidelines, involves a structured approach with different levels of analysis:

• Level 1 Hazard Assessment: This initial assessment provides a conservative, preliminary evaluation of pipeline separation and exposure length. It compares these factors to predefined tables for acceptance.
• Level 2 Hazard Assessment: This stage involves a conservative analysis of calculated voltages on the pipeline. These calculations may use either detailed or conservative values. The comparison is made against pre-defined safety limits, considering typical conservative inputs like fault rates and contact scenarios.
• Level 3 Hazard Assessment: The highest level of assessment, this stage evaluates the voltage produced on the pipeline. It can involve either a simplified and conservative calculation or a more detailed model. The assessment is based on calculated safety criteria specific to the fault and contact scenario. Level 3 assessments typically require more detailed inputs and are less conservative compared to previous levels.

These assessment levels allow for a comprehensive evaluation of electrical hazards, progressively moving from a conservative initial assessment to a more detailed and specific analysis.

Current Injection Test

An alternative to complex calculations for assessing electrical hazards involves performing a current injection test. This test simulates a fault and measures the resulting voltage on the pipeline. It offers advantages of cost-effectiveness and simplicity while delivering precise results, as long as the real fault scenario can be accurately replicated.

Zero Sequence Earthing is happy to provide advice on which method is best for you installation given your goals for the assessment.

Input information required to conduct assessment

Level 1: Basic Information

• Pipeline route
• Type of pipeline
• Powerline route
• Helpful but not mandatory: Soil resistivity and fault level data if available

Level 2: Detailed Data

• Soil resistivity
•  Detailed powerline and pipeline routes with separation distances
• Powerline specifics (voltage, OHEW, conductors, construction/heights, tower/pole earthing details)
• Single line to ground fault levels, X/R ratios, and clearing times
• Load currents for steady state low-frequency induction (LFI) calculations
• Pipeline details (material, size, coating type/thickness, coating condition, burial depth, insulating joints, valve/appurtenance locations, CP points, earthed points/anode beds, surge protection, offtakes)

Level 3: Enhanced Information

• Data from Level 2
• Additional data on line fault rates, contact frequency, and duration at appurtenances/CP test points. If unavailable, suitable values from AS4853 are chosen based on line and pipeline types.