Breaking through to realities of cathodic protection

As we’ve described in our previous two articles an introduction to cathodic protection – discussing electrochemical corrosion and how cathodic protection works – cathodic protection is a highly effective method to prevent corrosion. It is used in multiple industries and environments, and without it the cost of corrosion on society, the economy and the environment would be far worse.

In this final article in the series, we dismantle seven common myths about cathodic protection.

Cathodic Protection Myth #1: Cathodic protection protects the whole structure, even if some of it is above the ground.

Reality – There is NO effect at all on the atmospheric corrosion of the piles, columns and beams above ground.

Cathodic Protection Myth #2: Cathodic protection on ONE side of a vessel (pipe/tank/lock gate) can protect both the inside and outside of the structure.

Reality – There is NO effect on corrosion on the other side of the vessel, unless there are holes that allow some cathodic protection current to flow in a common electrolyte from one side to the other.

Cathodic Protection Myth #3: If a buried pipeline is suffering from AC corrosion (AC induced from power transmission lines) it needs more CP to protect it.

Reality – NO! Don’t do it! NO! AC corrosion is complex, and an increased cathodic protection current density and more negative pipe/soil potentials will only enhance the risk of AC corrosion.

Cathodic Protection Myth #4: If I reverse the polarity of my impressed current cathodic protection system, I can pass more current. This must be better.

Reality – This has been done and proved to be incorrect. The structure supposedly being protected becomes the anode, and is consumed at around 10kg per amp per year. Entire sections of pipelines have been destroyed in this way.

Cathodic Protection Myth #5: You can reverse the current with a galvanic anode system.

Reality – In normal situations this is NOT possible. At elevated temperature there can be a reversal between zinc anodes and steel, but only if there are no chlorides present.

Cathodic Protection Myth #6: Galvanic anode CP systems are fit and forget.

Reality – If only this were true! All cathodic protection requires inspection and testing to determine if it is still functional and effective.

Cathodic Protection Myth #7: Galvanic anodes can only deliver a short design life.

Reality – It is normal for offshore structures to be well protected from immersed corrosion for more than 30 years by using aluminium alloy anodes. The early BP Forties platforms in the deep northern North Sea were protected for 40 years with a combination of coatings and large zinc anodes.

The challenges of using cathodic protection

Cathodic protection is used extensively to protect critical infrastructure from corrosion. Common uses include:

• Oil and gas pipelines
• Oil and gas storage facilities
• Offshore oil, gas and renewable energy structures
• Ships
• Reinforced concrete in bridges and other structures

However, cathodic protection is a specialised area, requiring application of corrosion science, electrochemistry, electrical engineering, metallurgy, and, often, structural and mechanical engineering.

The standards (BS EN and BS EN ISOs), that cathodic protection professionals must work to, all make it clear that cathodic protection design must be undertaken by cathodic protection specialists who have a documented and appropriate level of competence.

BS EN ISO 15257 details the competencies that are required in all sectors of cathodic protection (buried, marine, steel-in-concrete, and internal). This standard also details the work that should be undertaken by cathodic protection Data Collectors or Testers, Technicians, Senior Technicians and Specialists or Engineers. Only personnel with appropriate levels of training, experience and competence can undertake work associated with cathodic protection:

• Surveys
• Designs
• Installation
• Testing
• Commissioning
• Performance assessment
• Maintenance

In the UK, certification in accordance with ISO 15257 is increasingly required. 

Here’s one final myth that must be exploded:

Bonus Cathodic Protection Myth: There are graduate and postgraduate courses in cathodic protection engineering.

Reality – No, there aren’t! So how do you get the training and certification you need, either for your employees or as an independent cathodic protection specialist?

Breaking the catch 22 in cathodic protection training

It sounds like something of a catch 22, doesn’t it? You must be certified to work with cathodic protection engineering, but there are no specialist courses for graduates or postgraduates. Consequently, specialists may start with a degree in science or engineering – or perhaps an apprenticeship – and then take advantage of specialist training. The Institute of Corrosion offers both courses and certification in cathodic protection.

Our cathodic protection courses are perfect for companies that need their staff trained and certificated in cathodic protection, for independent specialists, and for managers who want a better understanding of what their employees and contractors in cathodic protection should be doing.

These courses provide all the training required (levels 1 to 3) by cathodic protection data collectors, technicians and senior technicians in the sectors of buried, marine, and steel-in-concrete cathodic protection.

In addition, we offer independent assessment of competence as defined in BS EN ISO 15257.

If you are a cathodic protection company or an independent cathodic protection specialist, training and certification from the Institute of Corrosion provides recognition of training, knowledge, skills, experience and expertise that is valid internationally. As the industry continues to become more regulated and standards-led, this recognition will enhance your reputation and work opportunities.

To learn more about our range of cathodic protection training courses and the experience and qualifications needed for certification, please visit our pages detailing the Cathodic Protection, Training, Assessment and Certification Scheme.

Cathodic protection methods – differences and similarities

In our last article, we examined electrochemical corrosion and introduced the major areas where cathodic protection is used to protect against corrosion in aggressive environments such as soils, waters, and chloride contaminated concrete.

In this article, we take a deeper dive into how cathodic protection works.

The two types of cathodic protection

There are two types of cathodic protection: galvanic anode and impressed current cathodic protection.

Both provide a cathodic protection current flow from cathodic protection anodes placed within the same electrolyte as the metal to be protected. The current flows from the anode into the electrolyte. It discharges onto the metal, controlling the corrosion. It must flow within the metallic circuit (the metal plus the cables) and back to the anode to complete the circuit.

Galvanic anode cathodic protection (GACP)

Galvanic anode cathodic protection works as summarised above.

The anode materials are alloys of either zinc, aluminium, or magnesium – all more active metals than, for example, carbon steel. These more active metals corrode preferentially to the steel when they are metallically connected to the steel in an electrolyte.

The corrosion current of the anode material is the cathodic protection current for the steel. The current flows through the electrolyte onto the steel, controlling its corrosion. The current returns to the anode in the metallic circuit.

You may have heard the term ‘sacrificial anodes’. However, though this terminology describes the anode materials and how they act (the galvanic anode corrodes preferentially to the steel), it was changed in Europe in the 1980s to ‘galvanic anodes’.

You may see galvanic anode cathodic protection identified by the acronym SACP or GACP.

·         How is galvanic anode cathodic protection used?

Offshore, anodes are normally cast onto structural tubular cores which are welded to the offshore structure during construction onshore.

Offshore oil and gas pipelines are protected with aluminium alloy or zinc bracelet anodes clamped over the protective coating and connected to the pipeline by short cables or welded connections. Such protection should last for 30 years or longer.

Onshore, short pipelines are often protected using magnesium anodes. These are cast onto steel cores and connected to the pipeline with cables. In soils of low electrical resistivity, extruded or continuously cast and hot-rolled zinc ribbon is used. Zinc ribbon is widely used as an earthing electrode to mitigate induced alternating current (AC) on buried pipelines.

Impressed current cathodic protection (ICCP)

Impressed current cathodic protection is provided by connecting a DC power source between the metal being protected and the cathodic protection anodes. In contrast to GACP, the cathodic protection current is supplied by the DC power source and not by corrosion of the anode itself.

The DC power supplies are typically transformer rectifiers (confusing acronyms include TR, TRU and T/R) which convert mains electricity to low voltage DC. In remote areas, solar panels and batteries are commonly used (and stolen); thermo-electric DC generators and both diesel and gas engines driving generators have also been used.

The negative pole is connected to the protected metal (‘negative drain point’), and the positive pole is connected to the anode. As with GACP, the cathodic protection current flows from the anode, through the electrolyte and onto the metal being protected.

The anodes can be scrap steel (a reasonably common practice in France, where old railway rails are often used in such applications), high silicon iron, or sophisticated ‘mixed metal oxides’ coated onto titanium. Other materials, including graphite, magnetite, lead, platinum-coated titanium and niobium, have also been used, though performance and cost have combined to reduce their use.

·         How is impressed current cathodic protection used?

Offshore, anodes are typically mixed metal oxide coated titanium (MMO/Ti). These can be used in both seawater and saline mud, though in the latter their consumption rate is greater.

For steel in concrete, most impressed current systems use MMO/Ti anodes either in mesh, strip, or tubular form. There is a tubular anode formed into a conductive ceramic of MMOs.

In onshore applications, groups of anodes are normally used in ‘groundbeds’, which may take the form of a long horizontal trench in which multiple anodes are buried in a carbonaceous backfill. This increases the surface area, reduces the electrical resistance to ground, and extends the anode life. Similarly, anodes and ‘coke’ can be used in deep boreholes or multiple shorter boreholes. Anodes are typically high silicon cast iron or MMO/Ti.

Most impressed current systems will require replacement after about 25 years.

Which form of cathodic protection is best?

If the cathodic protection system is well designed, installed, operated and maintained, both galvanic anode and impressed current cathodic protection can be equally effective. However, GACP is simpler and has proved to be more reliable offshore.

Onshore, ICCP systems are easier to access for maintenance and, once installed, their components are not subject to the challenges of offshore environments. If properly designed, ICCP can protect many kilometres of well-coated pipelines.

ICCP is also advantageous for bare or poorly coated steel as it can deliver hundreds of amps of low voltage direct current, while a typical galvanic anode will seldom deliver more than 5 amps.

Cathodic protection – a specialist operation

Cathodic protection is used extensively to protect critical infrastructure from corrosion. For example:

• It is legally mandated for gas and oil pipelines to ensure their safe operation
• Offshore gas and renewable energy structures are effectively mandated to receive effective cathodic protection by their certification bodies
• Ships benefit from extended dry-docking rules if they have effective cathodic protection
• The life of concrete bridges and structures affected by chlorides, from de-icing salts or marine exposure, is extended by cathodic protection
• Newly constructed, reinforced concrete structures in severe exposure conditions also have extended life when cathodic protection is used

However, across all functions – from design through installation to testing and maintenance – cathodic protection is highly specialised. There are standards (BS ENs and BS EN ISOs) for cathodic protection applications for different structures in different environments.

A key takeaway from the standards is that they make it clear that cathodic design must be undertaken by cathodic specialists with a documented, appropriate level of competence.

How do you gain a cathodic protection specialisation?

There are no degrees that can be gained in cathodic protection, and there are no postgraduate courses in cathodic protection engineering, either. Instead, you find that cathodic protection specialists may hold a science or engineering degree (or complete an apprenticeship) before undertaking specific training and gaining experience and expertise in cathodic protection.

The Institute of Corrosion offers courses in cathodic protection, providing the training required for levels 1 to 3 for cathodic protection data collectors, technicians and senior technicians. These courses are produced, owned and administered by the Institute of Corrosion CP Governing Board (CPGB), part of the ICorr Professional Development and Training Committee (PDTC).

These courses are designed for those seeking the certification of competence in accordance with standard BS EN ISO 15257. We also find that these courses add value to managers and others who want to know what their cathodic protection staff and/or contractors must be doing and the limits of what they should do.

Independent of the cathodic protection courses and the PDTC and CPGB, the Institute of Corrosion also offers an independent assessment of competence through its Professional Assessment Committee (PAC). This is recognised internationally as confirmation of experience, knowledge and task skills as defined in standard BS EN ISO 15257; it is valid internationally.

For cathodic protection companies and for independent cathodic protection specialists, attainment of cathodic protection training and certification will ensure demonstration of competence, experience and expertise. This translates into more effective work, improving reputational excellence, and more employment opportunities.

To learn more about our range of cathodic protection training courses and the experience and qualifications needed for certification, please visit our pages detailing the Cathodic Protection, Training, Assessment and Certification Scheme.

In our next article, we explode 7 cathodic protection myths.

Corrosion and electrochemistry from Davy to today

Cathodic protection is a highly effective method of preventing corrosion, and is used in multiple industries and environments. Its history in corrosion science really begins when Sir Humphry Davy first discovered the cathodic protection principles and applied them to electrochemical corrosion.

Davy’s experiments led to a better understanding of electrochemical corrosion and the first use of cathodic protection in 1824, when Davy successfully protected a British Navy ship’s copper sheathing from corrosion in seawater by using iron anodes.

In this article, we examine the process of electrochemical corrosion as an introduction to cathodic protection.

What is electrochemical corrosion?

Electrochemical corrosion is a process in which current flows between the cathodic and anodic areas on metallic surfaces, resulting in corrosion. There are always multiple elements in this process:

• A host metal or metals exposed in an electrolyte.
• An electrolyte is a medium that can conduct electricity by movement of ions (for example, saltwater, soil, or the pore water in concrete)
• A metallic path between the exposed metal surfaces. Examples of this include:

• • A buried steel pipeline, accidentally connected to a copper earthing system in a classical ‘galvanic couple’ (the steel being anodic to the copper)
  • A buried or immersed steel pipeline or structure on which ‘anodic’ and ‘cathodic’ areas naturally establish due to variance in either the steel composition/metallurgy or within the electrolyte

Corrosion initiates on the metal/electrolyte interface and, at these anodic areas, low voltage direct current (DC) flows off the anodic metal into the electrolyte. Charged ions are released into the electrolyte and electrons are released into the metal. By convention, DC flow is opposite to electron flow.

The simple electrochemical circuit is:

• Within the electrolyte (that is in the soil, the sea or river water, or the pore water within concrete) DC flows OFF the corroding anodic areas.
• This must complete the electrical circuit, so it flows in the electrolyte and discharges on the non-corroding cathodic areas. The DC flows in the metallic circuit electronically, by electron movement. In the electrolyte it is via ionic movement, termed ‘ionic conduction’. The cathodic areas, receiving current flow from the electrolyte, do not corrode.

The electrochemist, rather than the engineer, will describe precisely the same process as the anodic area losing ions to the electrolyte (metal loss) and electrons to the metal (electron flow); the process is the same, it just that by convention the directions of electron and ion flow are opposite to the DC current flow.

In electrochemical corrosion, the magnitude of current flow is directly proportional to the rate of corrosion: approximately 10kg of steel is consumed by 1 ampere DC passing off a steel surface for one year.

How does cathodic protection help prevent corrosion?

Depending on whether it is described by an electrochemist or an engineer, cathodic protection might be described as:

• Replacing the lost electrons from an external source, thus changing an anodic area into a cathodic area and preventing corrosion (electrochemist)
• Providing cathodic protection current to all areas of the metallic surface within the electrolyte, sufficient to make all surfaces cathodic (engineer)

Though different descriptions, these are the same process.

Where is cathodic protection used?

Cathodic protection is used around the world to protect against corrosion, especially in aggressive environments such as soils, waters, and chloride contaminated concrete. Applications include:

• Buried and immersed storage tanks – external surfaces of bases of above ground storage tanks with corrosive foundations; inside crude oil storage tanks with highly saline ‘water bottoms’; inside storage tanks for seawater or raw water
• Ships’ hulls’ externals and internally in seawater-filled ballast tanks and cooling water systems
• Offshore oil rigs, platforms, and subsea completions
• Offshore wind foundations and tidal generators
• Pipelines – buried and immersed – both onshore and offshore
• Well casings
• Flood defences and lock gates
• Reinforcement in concrete

Cathodic protection is a specialisation

Though used extensively, cathodic protection is highly specialised. To be successful it requires a combination of the application of corrosion science, electrochemistry, electrical engineering, metallurgy, and often structural and mechanical engineering.

There are effective Standards (BS ENs and BS EN ISOs) for a wide range of CP applications in different environments for different types of structures. They all have one thing in common: all make clear that CP design must be undertaken by CP specialists with a documented and appropriate level of competence.

The standards make it clear that all work associated with cathodic protection (such as design, installation, testing, commissioning, performance assessment, and maintenance) should be undertaken by personnel with appropriate training, experience and competence.

How do you become a cathodic protection specialist?

Despite the rigorous nature of the standards surrounding cathodic protection, there are no graduate or postgraduate courses in cathodic protection engineering.

Cathodic protection specialists may start with a science or engineering degree, or via apprenticeships and trade skills, then augment these with specific training, experience and expertise.

The Institute of Corrosion offers both courses and certification in cathodic protection.

·         Courses in cathodic protection

ICorr cathodic protection courses provide the training required for levels 1 to 3 for cathodic protection data collectors, technicians and senior technicians in the sectors of buried, marine, and steel-in-concrete cathodic protection.

While providing the knowledge and skills training detailed in standard BS EN ISO 15257, existing experience and task competency are required depending on the course level.

These courses are suitable for those seeking certification of competence in cathodic protection in accordance with ISO 15257, and also for managers and others who wish to have an introduction to cathodic protection so that they understand what their staff or contractors need to be able to do and the limits of what they should do, within the scope of the standards.

·         Certification in cathodic protection

Independently of the cathodic protection courses, we also operate an independent assessment of competence. The ICorr Professional Assessment Committee (PAC) assesses whether the applicant has the requisite levels of experience, training, knowledge, and task skills as defined in BS EN ISO 15257.

This certification is recognised and valid internationally. In the UK, almost all steel-in-concrete cathodic protection projects, including those for Highways England (previously the Highways Agency), require cathodic protection personnel to be certified in accordance with ISO 15257. In addition, National Grid and the distribution companies, and many marine, port, harbour and offshore operators, also require certification of cathodic protection personnel.

Sustainability in cathodic protection provision

Cathodic protection companies will experience increasing benefits from having their employees certified in line with BS EN ISO 15257. They will be better trained, more competent, and better aware of their responsibilities. Clients are increasingly purchasing services from companies whose staff are certified in cathodic protection. For independent contractors, certification will enhance your reputation, help you to work more effectively, and give greater access to employment opportunities.

To learn more about our range of cathodic protection training courses and the experience and qualifications needed for certification, please visit our pages detailing the Cathodic Protection, Training, Assessment and Certification Scheme.

In our next article, we take a closer look at how cathodic protection works.