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Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers

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AC Corrosion Mitigation Strategies with RMUs

By Della Anggabrata
Published: April 4, 2023
Presented by MOBILTEX
Key Takeaways

Corrosion due to alternating current can be mitigated. One of the best strategies is with the use of remote monitoring units.

Source: iStock/Manuel-F-O

Corrosion can be, and often is, the primary cause of damage to various types of infrastructure, such as steel bridges, reinforced concrete structures, pipelines, and marine platforms.

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When metallic pipelines are installed underground, the pipes can be corroded due to electric currents. This article discusses the pipe corrosion that is caused by currents, as well as the use of Remote Monitoring Units (RMU) to resolve common operational problems.

Metallic pipes near high voltage power transmission lines, lighting or other power sources are subjected to electric currents. These currents are Alternating Current (AC). AC corrosion typically happens when metallic pipe runs parallel to high voltage power lines. AC corrosion creates pipe pitting. On the other hand, Direct Current (DC) is often an issue in urban settings. DC (commonly called "stray current") induces galvanic corrosion that usually occurs in urban locations where there is high intensity of metallic utility pipe congestion. (Read also: 5 Ways to Avoid Galvanic Corrosion.)

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Regardless of current type, it impacts pipeline integrity where it interfaces and can contribute to corrosion. The corrosion damage depends on AC current density, level of DC polarization, defect geometry, local soil composition and resistivity.

An AC current can pass in different ways, such as:

  1. Through charging and discharging of the electrochemical double layer i.e. as current passing through a capacitor.
  2. Through electrochemical reactions carrying a charge, such as oxidation and reduction reactions, which may cause corrosion.

Risks and Challenges

The main operational risk posed by stray currents is in regards to safety. The danger was tragically realized through an incident where a worker was electrocuted while working on a pipeline near a power line.

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Additionally challenging, corrosion mitigation introduces significant cost to the infrastructure projects for cathodic protection, AC mitigation, monitoring, and other related items.

Owners often have limited access to understand the voltage/ transmission data on the pipeline infrastructure. AC mitigation test stations can be difficult to access/monitor because a linesman or special trained licensee is required.

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The mitigation for AC current should be integrated with DC. Often the project issue is that the AC & DC Mitigation designs are completed separately. The owner will need a corrosion engineer to provide specifications and have the corrosion protection design be integrated and coordinated for both AC and DC Mitigation. Otherwise, the inefficiency will incur extra cost for the owner.

The most frequent sources of stray current are light rail transit and subways, which are also main traffic tools, particularly with continuously accelerating urbanization all over the world. Stray currents from these systems may easily flow into nearby metallic structures, making stray current-induced corrosion the most severe form of damage to buried structures, such as tunnels, pipelines, and various underground reinforced concrete structures. Corrosion damage is not always visible to the public but nevertheless can lead to structural failure, loss of life, loss of capital investment and environmental damage. (Read also: Stray Current Corrosion and Preventative Measures.)

Mitigation Strategies

AC Mitigation is designed and installed to decrease the induced voltage on the pipeline. This may be accomplished by the installation of different grounding methods such as linear zinc ribbon and/or grounding rods attached to the pipeline with decouplers for DC isolation. As well, controlling the current density, cathodic polarization and preventing AC-DC conversion can be an effective mitigation.

Traditional AC/DC Mitigation often involves:

  1. Connection to available natural drains. Natural drains are existing structures such as steel casings, which operators can identify during field testing and utilize to provide AC grounding.
  2. Providing additional grounding. Additional grounding options include horizontal linear ground systems or deep vertical-point ground (DVPG) systems.
  3. AC & DC Coupling Devices. DC decoupling devices are also key to protecting pipelines from induced AC Corrosion. They establish electrical connections to various components of the AC Mitigation system, allowing continuous passage of AC energy while simultaneously blocking DC current flow, thus maintaining the DC electrical isolation required for effective operation of the Corrosion Protection system.
  4. Installing coupon test stations to understand the interference. Coupon test units, like the CorTalk RMU1-SUB and CorTalk RMU1 from MOBILTEX, are another key component of any AC Mitigation system. The coupon is effective for the monitoring of both AC potential and AC current density by providing a steel surface exposed to the surrounding soil. The steel surface is representative of coating holidays. Coupons should ideally be placed in areas where geometric alignment changes to co-locate exist, since there will be a peak in AC voltage.
  5. Sacrificial anode and impressed current system. This is often used for DC Mitigation.

Both natural drains and additional grounding systems require consideration of existing soil characteristics and right-of-way/easement availability. AC current is dynamic and changes frequently especially as the peak currents enter the system.

Traditional data loggers often miss the fluctuation or multiple dynamic current readings, despite seeming to offer some cost savings. Data loggers’ disadvantages typically are safety concerns and no ability to obtain real-time data.

On the other hand, RMUs record readings approximately every 30 seconds. Additional advantages to using RMUs are that they:

  • Provide instantaneous real-time data results.
  • Minimize travel needs.
  • Reduce cost expenditures.
  • Are well-suited for sites in extreme conditions and remote locations. An RMU enclosure is watertight and rated for full submersion in water.

The figure below illustrates the application of the RMU system integrating satellite and cellular networks to deliver the real-time data directly to the client. The client can access the data via desktop and mobile device.

Figure 1: Mobiltex Remote Monitoring Unit (RMU) Network at operation transmitting data to the customers.

Technology Advancements with RMU

MOBILTEX RMUs capture and transmit all the data to a web-based platform called CorView.Cloud which enables clients to access the data with ease from any computer or mobile device with an internet connection.

CorView.Cloud Cathodic Protection Monitoring Platform

CorView is a MOBILTEX's backbone software that stores all the data, delivers secure communication and reports to the entire range of MOBILTEX CorTalk remote monitoring devices. This software can be an important component for any corrosion monitoring program for metallic pipeline infrastructure. Its instantaneous data collection and generation helps improve the management, efficiency and decision making. Customers can easily access the program through an app on their mobile devices. The CorView cloud server is equipped with full redundancy and automatic backup system.

Several examples of the RMU devices are as follows:

CorTalk RMU1 Test Station Remote Monitor

Supported by a satellite network, the CorTalk RMU1 stores and provides Corrosion Protection data every few hours. This provides a highly detailed view of the Corrosion Protection system and locations which helps identify any potential issue quickly. The device is compact, weather-proof and fits inside a standard test station. It also saves installation time and cost as it only takes 20 minutes for complete installation.

CorTalk RMU1+INT1 Test Station Remote Monitor with GPS Sync’d Interruption

The INT1 can be easily connected to the RMU1 with a single cable. CorTalk INT1 is part of the RMU1 Generation 4, which is a two-way communication device that provides remote data generation supported with a geo-positioning system. As the INT1 pairs with the RMU1, it simplifies close interval survey (CIS) activities by eliminating the need to install portable interrupters at test stations or to physically break bonds between pipelines, foreign rectifiers and structures.

CorTalk RMU1-LITE Test Station Remote Monitor

The CorTalk RMU1-LITE assists pipeline owners to collect multiple pipe-to-soil potential measurements. It provides information on seasonal variations or short-term operating irregularities between the metallic pipe and its surrounding environment (soil). It acts as an indicator and helps early detection and prevention of corrosion on the pipeline infrastructure. It enables pipeline operators to affordably achieve high volume deployment and generate operational data that provides new insights into system dynamics.

CorTalk RMU1-SUB

The new RMU1-SUB delivers a discrete yet powerful tool for remote monitoring of Structure-to-Elecrolyte potential readings, CP single or double coupons and structure bond applications — engineered to perform in the most demanding subgrade applications utilizing B&T standard valve boxes for bullet-proof installations. The RMU1-SUB installation delivers a unique and intelligently designed solution for your most challenging urban and rural applications that improves safety, reduces expenditures, and optimizes integrity programs to become proactive, not reactive.

What to Look for in an RMU System

When assessing a remote monitoring unit system, it's important to evaluate what they offer and how it can meet your needs. You may want to consider:

  • Proven platform that can effectively collect instant and real-time data from any location
  • Extended service lifetime (+10 year life expectancy).
  • Robust design, ingress protection, and extreme temperature ratings
  • Long battery runtimes and autonomy
  • Multiple data connection backhauls with flexible data plans
  • Advanced cloud-based platform with multi-tenant architecture and enterprise level security
  • Resilience to lightning strikes, surge and over-voltage to remain in-service without an immediate need for replacement.
  • Compact sized equipment designed for standard test stations and enclosures

RMU Case Study

The City of Calgary has to manage corrosion in the city’s watermain networks. The City employs galvanic and impressed current cathodic protection systems to mitigate damage on metallic pipes and lengthen their lifespan. Any damage to the watermain system can lead to legal challenges as well.

Galvanic cathodic protection is typically used on the metallic portion of the City’s distribution pipes, while impressed current is reserved for the City’s larger steel transmission mains, which are considered critical assets. While the results are effective, monitoring and maintaining a rectifier on an impressed system can be expensive.

Manual inspections are slow, resource-intensive and cost-ineffective. The inspections can also present safety issues, introduce human error, and, due to the need for regular field inspections, contribute to carbon emissions and greenhouse gases. Maintenance or repair often requires shutting down high-traffic areas to provide access for the crew. It results in complaints from the public and business owners.

Since 2008, the City of Calgary has deployed CorTalk RMU systems for their cathodic protection remote monitoring applications, which are ideal for automated monitoring of rectifiers, test points, and bonds. Their CorView account monitors more than 121 km of steel watermain pipelines. The collected real-time data-sets are regularly shared amongst various City’s departments including Asset Management. Overall, the City is aided in the decision-making process, and optimization of timelines and budgets for the Waterwork’s Operational and Maintenance planning.

CP RMUs have delivered safety, operational, and budget efficiencies for the City of Calgary. Is it time for your organization to adopt RMUs for Cathodic Protection Monitoring?

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Written by Della Anggabrata

Della Anggabrata

Della is a civil engineer with extensive and progressing experience in a consulting industry with a unique technical skill that combines civil and geotechnical engineering. Her work primarily focuses on underground infrastructure projects in the Lower Mainland of British Columbia, Canada. Some of her projects are large diameter watermains, water and wastewater treatment plants, sanitary forcemains and land development. She is a key contributor to the engineering design and project management, and also provides a solid foundation for every success that the team has achieved.

Della attained a bachelor’s degree of Civil Engineering from the University of British Columbia, Vancouver, where she graduated with a Distinction recognition. In her free time, she is a foodie who cooks, loves travelling and playing tennis. She is always eager to taste and experience new cuisines and recipes.

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