AC Corrosion Management

Summary

Alternating current (AC) corrosion can be defined as corrosion caused or influenced by AC. If the AC component is removed or limited below a certain level, the corrosion will be diminished or completely mitigated.

AC corrosion in buried pipelines has increasingly become a concern as shared right-of-ways with high-voltage power lines have become common practice in the so-called energy corridors where the AC is induced in the pipeline through extended length of parallelism between the pipeline and the interfering power source.

Why select Vecor as your technical service provider?

The highly qualified staff of engineers and technicians of Vecor Pipeline Integrity has completed a series of challenging AC mitigation studies and installations for different pipeline operators in the gulf region. Our process illustrated below, has proven to be successful for mitigating AC corrosion on pipelines and we are proud of our track record in the design, installation and commissioning of numerous AC mitigation systems.

Our services include:

• Accurate studies and surveys to determine AC influence voltaje,
• Design, supply, installation and commissioning for AC mitigation systems
• Design, supply and installation of monitoring systems.
• Monitoring services

When a pipeline runs parallel, or cross a HVAC transmission line, some interferences could arise due to capacitive, inductive, and conductive effects but the main effect acting on the grounded pipeline is the electromagnetic induction, which is a combination of the magnetic field generated by the AC and inducing voltage. To prevent such negative effects on the pipeline, it is necessary designing and installing AC mitigation systems. Methods for mitigating AC corrosion typically addresses both the AC component and the adjustment and control of the CP level. In general, the mitigation involves the following steps:

1.- Data Collection and Analysis

Vecor methodology for designing AC mitigation systems includes gathering basic information regarding the pipeline of matter and HVAC power line paralleled with the pipeline in preparation for induced AC calculations and recommendations for optimized earth electrode positions. about the Gathering of historical data for existing HVAC and Pipeline along the segment where pipe and power line run parallel or cross each other; collecting existing AC potentials, soil conditions and AC current density.

2.- AC Mitigation Design

AC mitigation system design phase involve build and running an AC model with collected input parameters from the previous data collection phase. The results will be compared with field measurements to validate the model. If good agreement is obtained, quick runs will be made for steady state (normal operating) conditions as well as fault current conditions to determine if the predicted results dictate that a mitigation system be installed on the existing pipeline. If the induced voltages are found to be greater than the industry accepted norm, Vecor would proceed with the engineering study and design an AC mitigation system.

During this phase, the goal is incorporating all parameter into a comprehensive AC mitigation system that includes protection for both personnel and pipeline itself. The personnel protection can be achieved using Gradient Control Mats (GCMs) to create a safe area adjacent to the aboveground appurtenance. The protection of the pipeline typically involves the combination of DC decoupling devices connecting to natural drains and the use of coupon test points for effective monitoring AC potential & AC current density.

3.- Validation

The final phase involves detailed numerical simulations with greater resolution to investigate the voltage and current levels on the pipeline during steady state and fault conditions and allow for optimization of the mitigation system. Runs of both steady state and fault current conditions will also be run after the mitigation system is designed and ‘installed’ on the pipeline. This will demonstrate the effectiveness of the proposed AC mitigation system.

4.- Monitoring and Management

Vecor offers support defining and stablishing the most suitable monitoring system to document the safe operation of pipeline with regard to AC corrosion. We can specify, supply and install coupons or probes for the evaluation of AC corrosion in locations where the AC corrosion likelihood needs to be evaluated.