ISO 12944 – Steel structure design and corrosion

ISO 12944 – Steel structure design and corrosion

Corrosion must be considered early in the design of steel structures

If left unprotected in corrosive environments, steel structures are liable to corrosion that can be both costly and put lives in danger. One way to control corrosion is to use paints and coatings. ISO 12944 is the internationally recognised standard that provides instruction and guidance to those working with steel structure design, including planners, painters, inspectors, maintenance, and manufacturers of coatings.

The third part of the standard provides guidance to those designing steel structures that are to be coated with protective paint systems, setting the criteria for design to avoid premature corrosion of the asset.

Why is steel structure design important?

How a steel structure is designed has a real bearing on the ability to protect it against corrosion. Poorly designed structures may have corrosion traps which are difficult to protect and from which corrosion can spread rapidly. To help prevent this, designers should consult with corrosion experts as early as possible in the design phase to consider the following elements of design that may affect corrosion:

  • The shape of the structure
  • The use of the structure
  • Structural elements such as method of joining
  • Environmental factors

Effective design of steel structures

The basic steel structure design criteria that may be exposed to corrosive environments include keeping the design simple and minimising surfaces that may be exposed to corrosive pressures. The designer will need to ensure that maintenance and inspection work is facilitated by the design, that appropriate joins are made, and that they consider how the structure will be transported and erected.

Here are the primary areas of concern that this section of ISO 12944 covers (but is not limited to):

·         Accessibility

Those who are applying, inspecting and maintaining coatings need access to the areas to be protected for their work to be effective. Design should allow this; for example, by providing for fixed walkways and the fitting of maintenance equipment (such as anchorages for scaffolding).

Safety of all operators should also be considered when designing for accessibility. For example, the surfaces to be coated and maintained should not only be accessible, they should also be within safe, easy reach and with plenty of space to work in.

In box members and tanks, openings should be large enough to allow easy access, and ventilation holes should be included.

·         Prevention of trapped water

Designers should incorporate design elements to prevent water being trapped and where foreign matter may combine to increase the potential for corrosion. Design features that might be considered include inclined surfaces, drainage systems, and chamfered edges.

·         Welding and bolting

The standard also makes it clear that welding should be clear from imperfections that make it difficult to protect effectively. Bolts, nuts and washers should be protected against corrosion, and to the same protection durability as the structure itself.

 

·         Treating gaps

Narrow gaps and blind crevices are particularly prone to potential corrosion, as they tend to retain moisture, foreign bodies and soluble salts. Very narrow crevices such as the enclosed spaces between two back-to-back flat surfaces can take up moisture by capillary action. The oxygen-deficient conditions within the crevice can set up an aggressive accelerated electrochemical concentration cell, leading to rapid pitting within the crevice. This type of corrosion is particularly dangerous as it is not visible (possibly until a structural failure), and the lack of access makes it very difficult to detect and repair.

Either filling or sealing will be needed to prevent corrosion in these gaps, with welding also used. Where steel transitions to concrete, the designer will need to pay specific attention to ensuring that gaps are treated.

Treating Sharp Edges

Liquid coatings in common with other liquids display surface tension. The surface tension of an applied coating film can cause the coating to pull away from a sharp edge (e.g. the edge of a splice plate or the flange toe of an I-section girder), resulting in a reduced film thickness along the sharp edge compared to the same system applied on a surrounding flat area. Sharp edges can therefore be vulnerable to premature breakdown unless they are given a supplementary coat(s) of protective coating (so-called ‘stripe coat’), or the design of the structure incorporates the provision for grinding of sharp edges, to provide a radiused edge profile which will allow the coating to follow the edge without a reduction in film thickness.

·         Preventing galvanic corrosion

Galvanic corrosion is possible should an electrically conducting joint exist between two dissimilar metals, with the less noble of the two metals corroding subsequently. The standard provides instruction on the type of joints that should be used to avoid this, but where it cannot be avoided then the surfaces should be electrically isolated by painting of both surfaces. However, cathodic protection may also be employed to protect against electrochemical corrosion.

·         Transportation and erection

Design of a structure should also consider how it will be transported and erected, as there will be potential for damage to occur to the corrosion protection used. The designer should include lifting points and fixings that may be needed to transport and erect the structure.

Summary

In summary, corrosion must be considered during steel structure design. The designer should enlist the advice of a corrosion expert, and deliver a structure whose design does not hinder the correct application and inspection of the specified corrosion protection coating system, coupled with subsequent inspection and maintenance of the corrosion protection measures.

In providing guidance and instruction for the design of steel structures liable to corrosion across a range of applications and in a range of corrosive environments, ISO 12944 provides recommended minimum dimensions for:

  • Accessibility
  • Openings for access to confined areas
  • Narrow spaces between surfaces
  • Treatment of gaps

It also provides detailed examples for design features to avoid retention of water and deposits, avoidance of sharp edges, and stiffener design.

If design considerations for corrosion protection are not implemented early enough in the design process, there is a greater chance that the structure will be adversely affected by corrosion. This will certainly result in greater expense in the long term, while increasing the potential for avoidable human cost.

It is far more cost-effective to implement corrosion protection on a ‘right first time’ principle rather than having to implement costly maintenance procedures later in the life of the asset. It must be borne in mind that maintenance does not just mean the cost of labour and materials for repainting the asset. Factors such as installing scaffolding and shutting down areas of a working asset could significantly multiply the cost of a maintenance project. In our next article in this series covering ISO 12944, we discuss part 4 of ISO 12944: types of surface and surface preparation. In the meantime, to learn about the Institute of Corrosion Coating and Inspection Training Courses – presented by IMechE Argyll Ruane and Corrodere – contact us today.

ISO 12944 – The Corrosive Environment

ISO 12944 – The Corrosive Environment

Categorising corrosivity by type of environment

In a recent article, we introduced you to ISO 12944, the internationally recognised standard that provides the guidelines for the use of paint and coatings to protect assets from corrosion. The second part of the standard discusses the corrosive environment. This article introduces you to this part of ISO 12944 and the changes that were introduced in the latest revision in 2018.

What is the corrosive environment?

The corrosive environment describes the environment in which the asset to be protected is situated. There are many variables within corrosive environments. Combined, these determine how corrosive the environment is, and therefore the types of protective paint systems that are needed to help prevent corrosion (covered in part 5 of the standard).

When discussing the corrosive environment, two terms are used:

  • The local environment, which describes the atmospheric conditions around a particular component
  • The micro-environment, which is the environment at the interface between an element of a structure and the local environment

The environmental factors that determine an environment’s corrosivity are:

  • Climate (the weather, which is established by reference to historical data)
  • Atmosphere (the gases – including aerosols and particles – that surround the asset to be protected against corrosion)

The classification of environments considers temperature, relative humidity, and the time of wetness (the length of time that the metal surface is likely to be covered in a film of electrolyte that can cause atmospheric corrosion). In brief, atmospheric corrosivity calculations are made by summing the hours when the relative humidity is above 80% and the temperature is above 0°C.

Corrosivity is dependent on the corrosive agents present in the environment, especially gases such as sulphur dioxide, and salts such as chlorides and sulphates.

Types of corrosive atmospheres

When specifying the protective coatings that should be used on assets, ISO 12944 considers the type of atmosphere in which the asset is located, and categorises these from rural (away from corrosive agents such as sulphur dioxide) through to marine (where airborne salts are present).

If the asset is indoors, the potential for corrosion is usually lower because atmospheric pollutants are usually reduced. However, if the indoor asset is poorly ventilated or suffers from high humidity, then this increases the potential for condensation and, therefore, corrosion.

The categories of corrosivity are taken from a separate standard, ISO 9223;2012 – “Corrosion of metals and alloys — Corrosivity of atmospheres — Classification, determination and estimation”.

The scientific method for determining corrosion rate is determined by calculating the rate of metal loss on sample coupons (mild steel or galvanized steel) that are placed in the given environment. In practice, this is rarely performed for the determination of corrosivity for a paint specification. The corrosivity is determined by an objective estimation of the general description of the environment based on the descriptions in the standard, and the professional assessment by all parties involved in drawing up the corrosion protection specification.

Location of asset and corrosivity

When protecting assets from corrosion, ISO 12944 also considers whether the asset is in soil or water. Where assets are only partially buried in soil or partly immersed in water, the corrosion is usually localised to where the rate of corrosion can be highest.

Corrosion of assets that are immersed in water depends upon the type of water (fresh, brackish, or salt), how much oxygen is present in the water, the water’s temperature, and the substances that are dissolved in the water. There are three different ‘zones’ for corrosion, transitioning from the splash zone (wetted by spray), through intermediate (where wetting is fluctuating), to fully immersed.

Corrosion of those assets that are buried in soil depends on factors that include the minerals present in the soil and its water and oxygen content. The type of protection coating needed for buried-in-soil assets may differ along the length of the asset, because it is more likely that they will be buried in different soils – in such cases, the rate and severity of corrosion will differ.

Changes to ISO 12944 in 2018

There are three major changes in environmental categorisation as described in ISO 12944. There are now five environmental categories for onshore assets, ranging from C1 (very low corrosivity, typically in a climate-controlled indoor environment) to C5 (very high corrosivity environments, such as a coastal refinery).

A new environmental category has been introduced – the CX category, which covers offshore environments. This category is now covered in detail in a new section of the standard – part 9.

The IM categories, covering immersed assets, now include a new category (IM4) that deals with immersed assets with cathodic protection.

Key takeaways

In summary, the environment in which an asset is sited has a significant effect on the potential for it to corrode, and therefore the design of corrosion prevention system used. Factors that determine corrosivity of the environment include temperature, humidity, condensation, and corrosive pollutants in the atmosphere.

In classifying corrosion environments, ISO provides a reliable guide for the design, implementation and maintenance of structures and corrosion prevention systems and the applicable characteristics of paints and coatings that may be used.

In our next article in this series covering ISO 12944, we examine the section of the standard that deals with steel structure design. In the meantime, to learn about the Institute of Corrosion Coating and Inspection Training Courses – presented by IMechE Argyll Ruane and Corrodere – contact us today.

Corrosion Protection – A Week of Webinars

Corrosion Protection – A Week of Webinars

Bringing the corrosion conversation to you

After the huge success of the week of webinars to combat corrosion, the Marine Corrosion Forum and the Institute of Corrosion are collaborating once more to bring five more exceptional webinars into your homes and places of work, as we discuss some of today’s corrosion protection issues.

These webinars, presented by some of the world’s leading corrosion experts, will follow the same format as before: one each day for five days, each presented at a time to allow as many people as possible to attend. You’ll need to be quick to register, though – there is a limit of 200 people for each webinar, and places will be allotted on a first-come-first-served basis.

Online delegates to this series of webinars are in for a real treat – with a big focus on offshore wind and other renewables, and a ‘dip-in/dip-out’ timetable that allows you to attend the webinars individually without needing to commit to attending all five. Oh, and registration for these corrosion protection webinars is free.

Before a summary of each webinar, let’s introduce the presenters – it’s quite a line-up.

Roger Francis corrosion expertDr Roger Francis

Dr Roger Francis is one of the UK’s leading experts in corrosion-resistant alloys – both stainless steels and copper-based. Director at RF Materials, Dr Francis won’t mind us telling you that he has amassed four decades (and counting) of experience in areas that include marine, oil and gas, chemical and process, power, desalination, and mining. He has authored six books, and edited several more, as well as publishing over 80 technical papers. His consultancy work includes failure analysis, materials advice, and training in various aspects of corrosion. A founder member of the Marine Corrosion Forum and a Fellow of the Institute of Corrosion, Roger never fails to deliver an informative and enjoyable paper.

Dr Adnan Syed corrosion expertDr Adnan Syed

With a PhD in Energy Materials, Dr Adnan Syed is currently a Research Fellow at Cranfield University. There, he is involved in the field of high-temperature material degradation and investigating the effects of environment on the static and stress corrosion life of alloys used for gas turbine blades. This includes the use of thermodynamic software for better understanding of the corrosion mechanisms and advanced microscopy techniques for the alloy’s microstructure details. His PhD title was ‘Fireside corrosion study of superheater materials in advanced power plants’. Dr Syed’s extensive career experience, includes working for organisations to provide chemical solutions to R&D and technical teams via Failure Mode Effects & Analysis (FMEA) toward the development of products and processes.

Lars Lichtenstein corrosion expertLars Lichtenstein

You couldn’t wish for a more accomplished corrosion mitigation voice from the world of renewables, especially offshore wind. Lars Lichtenstein is the lead principal specialist within Renewables Certification for corrosion protection issues at DNV GL – the responsible expert for the DNVGL-RP-0416 corrosion protection for wind turbines. Extremely influential in setting and interpreting DNVGL codes and rules in this sector, you’ll discover that Lars is also an extremely competent and accomplished presenter.

 

Brian Wyatt corrosion expertBrian Wyatt

Just when you thought it would be impossible to add to the expertise of our presenters, we bring you Brian Wyatt. Members of the Institute of Corrosion will recognise Brian as a past president of ICorr and Director at Corrosion Control Limited. An acknowledged expert in cathodic protection, Brian has been heavily involved in transferring best practice from the oil and gas sector to the offshore wind sector and is active in the preparation of the new EN ISO 24656 standard “Cathodic Protection of Offshore Wind Turbine Structures”.

Andrew Woodward corrosion expertAndrew Woodward and Chris Matthews

The week starts strongly, and it certainly doesn’t fizzle out. The last of the week’s webinars delivers a ‘two-for-the-price-of-one’ experience (except, of course, there is no cost – all the webinars are free).

Andrew Woodward is Marketing Manager at Connector Subsea Solutions including MORGRIP. Andrew has a BEng and an MSc in mechanical engineering from Aston University. Andrew has over 10 years of experience in technical sales and estimation in specialist applications and joined the MORGRIP team in 2016.

Joining Andrew ‘on stage’ is Chris Matthews, Project Engineer at Subsea……

Chris Matthews joined the MORGRIP team in 2014 shortly after finishing a BEng in Aerospace Systems Engineering at Coventry University. After a short period working with standard products Chris was engaged in a high-profile project for Mechanical Connectors for Deep Water Repairs which lasted 2 years. After that Chris was a leading figure on the engineering team developing the new MORGRIP CLiP Connectors which are the subject of today’s presentation.

The agenda for this week of webinars

Without further ado, let’s take a glimpse at each of the webinars. Each will be a one-hour presentation by the subject expert. A Q&A session via the chat box immediately follows the presentation.

Improving the Corrosion Resistance of Duplex Steel Welds (Dr Roger Francis)

Monday 6th July 2020, 12pm BST

Register for this webinar here

Modern duplex stainless steels have been in common use since the early 1980s, and how to weld these alloys satisfactorily is well understood. Despite this, corrosion failures of welds still occur. This talk will discuss the important parameters to produce satisfactory welds in duplex stainless steels.  There are further things that can be done to improve the corrosion performance of duplex welds, and these are discussed along with test data. It is important that testing over and above that in ASME IX is carried out on duplex weld Procedure Qualification Records (PQRs) and some suitable tests are proposed. The corrosion resistance of welds and parent metal to different sorts of corrosion will be discussed.

Hot Corrosion Mechanisms for Gas Turbines (Dr Adnan Syed)

Tuesday 7th July 2020, 12pm BST

Register for this webinar here

Hot corrosion mechanisms were first proposed more than half a century ago, but we are still learning about them and they continue to be a focus for manufacturers of aero and industrial gas turbines.

The understanding of corrosive salt and target alloys are both crucial topics to enable improved mechanisms. Corrosion mechanisms vary due to the composition of the alloys and deposit salt chemistries.

The concept of acid and basic flux on the alloy surface due to induced deposits on the alloy’s surface is also well defined; however, further investigation is still required.

Along with laboratory corrosion experiments, the use of thermodynamic software is a key tool to help identify the likely phases formed, which in turn enables a better understanding of the mechanisms involved.

The talk will include the possible hot corrosion mechanisms occurring in the gas turbine combustion environment, and support some of the challenges the industry is facing in its understanding and managing of turbine component degradation. The talk will also present the laboratory setup for hot corrosion testing and techniques used for evaluation of material performance.

Improvements of the DNVGL-RP-416 and DNVGL-RP-B401 – Upcoming Revisions (Lars Lichtenstein)

Wednesday 8th July 2020, 12pm BST

Register for this webinar here

This is a must-attend webinar for those working in the wind turbine industry. You’ll receive the inside track on material selection for bolts and stainless steel, and the boundary conditions that should be considered.

The recommended practices issued by DNV GL on corrosion protection for wind turbines are being reviewed internally. Learn what the items and considerations under review are, and become updated on how the process of review is used to address and improve the overall quality of corrosion protection for offshore wind.

The current key DNV GL documents for corrosion mitigation and CP in this sector are DNVGL-RP-0416 and DNVGL-RP-B401. Formally, DNVGL-RP-0416 is issued from Renewables Certification, part of the energy business, while DNVGL-RP-B401 is owned by the oil and gas business. Therefore, this presentation will mainly deal with the items and considerations being dealt with for the revision of DNVGL-RP-0416, but relevant topics in relation to DNVGL-RP-B401 can also be addressed and discussed.

Since 2016, when DNVGL-RP-0416 was first published, these recommendations were applied to numerous offshore wind projects. We have been part of the certification process for many of these projects and could gain experience and feedback on the content we have issued. Generally, there has been positive feedback, but some guidance lacks sufficient detail. Some of these areas need to be addressed to improve the overall quality of corrosion protection for offshore wind.

Several relevant standards have been revised since 2016 (e.g. ISO 12944 or ISO 2063), new standards like VGB/BAW have been introduced, and new ISO standards are currently being written in several working groups. Improvement of the guidance given is needed and possible. We want to address the most relevant items with new revisions of our RPs.

This seminar will provide more guidance on the useful coating lifetime as introduced in DNV-OS-J101:2011 for the first time, and the relation with fatigue calculation and surface preparation. What level of quality is needed at the end of the lifetime? How much effort shall be put into inspection and repair of 15-year-old+ coating systems? You will gain insight on material selection for bolts and stainless steel, as well as what boundary conditions should be considered. This seminar will also study the issue of coating breakdown factors with regards to CP system calculation and on currency drain of buried structures. The revisions of the documents are not yet finished, and therefore input from this event will be able to influence the development of future recommended practices.

Cathodic Protection of Offshore Renewable Energy Infrastructure (Brian Wyatt)

Thursday 9th July 2020, 12pm BST

Register for this webinar here

External surfaces of offshore structures, including offshore wind turbine foundations and tidal/wave energy structures are routinely protected from corrosion by cathodic protection [CP] using aluminium alloy galvanic anodes. Design codes for this are provided by several sources; the most commonly used for offshore wind applications being DNVGL-RP-B401.

These codes have been produced primarily for jacket structures used in deep water for oil and gas developments. They are inadequate for structures required for offshore energy infrastructure such as offshore wind turbine monopile [MP] foundations, tidal turbines, or wave generators – all of which need to be installed in near-shore shallow water environments. For these conditions, there are special considerations over and above those defined in these codes, notably the impacts of higher tidal flow, a greater proportion of the shallow structures being in the tidal zone and of wave action. All result in high levels of oxygenation at the steel/water interface which demand more robust CP designs, both in mechanical and electrochemical terms. The nature of the support structures, and limited scope for lower-cost onshore anode installation, also lead to challenges to uniform anode distribution, particularly on MPs.

Although DNV GL has addressed some of these issues in its DNVGL-RP-0416, written specifically for offshore wind applications, it has not addressed all of the environment issues, and the requirements remain largely biased towards the use of RP-B401 for CP design.

A new International Standard, EN ISO 24656 ‘Cathodic Protection of Offshore Wind Turbine Structures’ is under development to address these issues more fully. It will soon be published for public comment. It will reflect a significant change in the design process for cathodic protection, to reflect the particulars of offshore wind foundations and their environments.

This seminar concentrates on these additional considerations for the design of external CP for near-shore offshore energy infrastructure. It also, briefly, discusses the special and different requirements for internal CP of wind turbine monopiles.

Use of CRAs in Subsea Pipelines and Repair of Clad Pipeline Connections (Andrew Woodward and Chris Matthews)

Friday 10th July 2020, 12pm BST

Register for this webinar here

Since 2009 the MORGRIP team has been engaged with major operators to develop a mechanical connector solution specifically designed to meet the unique challenges of Clad and Lined Pipeline systems. A traditional mechanical connector seals on the outer diameter of the pipe and is used as an alternative to welding for straight cut pipe ends. For a clad or lined pipe this type of connector does not adequately protect the pipe end and parent pipe from the corrosive attack of the aggressive sour line media.

The CLiP Connector was developed over 2 phases of a Joint Industry Project part funded by Chevron and Woodside. The aim of the JIP was to take the existing MORGRIP connector technology and integrate a mechanism to protect the exposed end of a clad pipeline from the aggressive line media after installation.

The seal takes advantage of the corrosion resistant and ductile properties of Alloy 625 when subjected to specially controlled heat treatment as well as extensive testing and track record of graphite in order to create a seal module that conforms to NACE MR0175 / ISO15156-3. The seal forms around all pipeline manufacturing tolerances and even localised irregularities such as internal weld seams. The seal can be easily integrated into existing mechanical connector configurations and is able to be adapted for both diver installed and remote repairs.

The technology qualification was completed to DNVGL-RP-A203 through a combination of analysis, 3rd party material testing, component testing and culminating in full scale testing of a production unit. This resulted in the award of a DNVGL Type approval for the product range in accordance with the requirement of DNVGL-ST-F101 for submarine pipelines and DNVGL-RP-F113 recommended practice for pipeline repair.

Don’t miss out on these webinars

We’re anticipating strong demand for these extremely current webinars. Not only because of the subject matter, but because of the authority of the presenters. Don’t miss out – register now. As the year progresses, we plan to bring you more events that bring the corrosion conversation to you –another example of the benefits of membership of the Institute of Corrosion.

For details about membership of the Institute of Corrosion, visit our membership page.

Introducing Cathodic Protection – 7 Cathodic Protection Myths Exploded

Introducing Cathodic Protection – 7 Cathodic Protection Myths Exploded

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.

Introducing Cathodic Protection – How Does Cathodic Protection Work?

Introducing Cathodic Protection – How Does Cathodic Protection Work?

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.

Introducing Cathodic Protection – Electrochemical Corrosion

Introducing Cathodic Protection – Electrochemical Corrosion

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.