Understanding Cathodic Corrosion Protection for Underground Tanks - Part 1

Underground Storage Tanks offered key benefits for communities and industries when it comes to appearance, cost and security. They are also protected from the effects of fire. Mainly the reason why most of the owners preferred to install it underground.

With more owners and customers choosing to hide their propane tanks with popular underground installations, the need to protect steel vessels from moisture and chemicals in the soil has never been greater. UG tanks can rust and cause problems for the owners.

Last year, the Environment Department of Dubai Municipality had release a code for installation of Fuel storage Tank requiring each underground (UG) tanks installed must have a cathodic protection system or similar internationally recognised method to help prevent corrosion of the tank. There are also requirements for testing the effectiveness of the system on a specified schedule, to document the testing, and to maintain the test results for a specified time.

Why Do Underground Tanks Need Cathodic Protection?

• To minimize the rusting of steel tanks and connected piping which can cause a release of a regulated substance.

• To eliminate the cost associated with environmental clean-ups caused by a release from the UST system.

• To extend the operational life of the UG tank.

Preventing Corrosion

Protecting underground tanks from corrosion is easily achieved by the use of two commonly applied protection methods: external coating and cathodic protection. These two methods are complementary and should be used in conjunction with the other.

Cathodic protection prevents corrosion at those defects by applying DC current from an external source, forcing the tank to become cathode. Application of sufficient DC current to the tank will prevent any corrosion from occurring. The two general types of cathodic protection systems are sacrificial and impressed current. Sacrificial systems are used when the amount of current required for the protection is small, such as in underground propane tanks. Impressed current systems are more commonly used for large structures such as large diameter pipelines. Electrical isolation of the tank from metallic piping systems and electrical grounds is critical for the cathodic protection system’s effectiveness.

Sacrificial systems work by creating a galvanic connection between two different metals. The most common anode material is magnesium, which when coupled to steel results in DC current flow from the magnesium to the steel. The open circuit potential of steel is about -0.50 volts referenced to a copper sulfate electrode. The open circuit potential of magnesium is about -1.55V to -1.80V. By connecting the two metals together, the difference of 1 to 1.25V volts results in current flow to the tank that overcomes the natural corrosion cells that exist on the tank. With this current available to the tank, no corrosion occurs.

BATTLING CORROSION ABOARD SHIPS - Part 3

Strategies for Prevention

Preventive measures will decrease maintenance costs, early system failures, and an overall improve service life of ships granted they are detected in enough time.

a. Modifying the Corrosive Environment

Hence, Inhibitors are salt water or electrolyte solutions which are controlled. Anodic inhibitors migrate to the anode creating a protective barrier which as a result, stops corrosion in its tracks. Therefore, Cathodic Inhibitors migrate to the cathode which prevents the absorption of oxygen or hydrogen.

In addition, Cathodic protection uses sacrificial metal to act as the anode which creates a protective barrier. This metal deteriorates first instead of the ships protected layers.

For example on the hull of a ship, zinc plates prevent corrosion of any sub-surfaces.

b. Protecting the Corrosive Environment

As a result, in the hope of protecting the vessel coat it with three different paint solutions.

Binders – Therefore, the binder is a film forming component of paint.

Pigments/Extenders – these powders mix with the binder at various particle sizes and enhance the overall effectiveness of the binders.

Solvents -Eventually evaporate from the surface and help for easy application.

In conclusion, it is important to have the proper plating before the equipment is put to work. As a result the equipment will last longer and will become resistant to the elements.

Battling Corrosion aboard Ships - Part 2

Impressed current cathodic protection (ICCP) systems are the ultimate state-of-the-art, long-term solution to corrosion problems, and are recognized as a superior alternative to sacrificial anode systems, which require frequent replacement. Impressed current cathodic protection systems are preferred by ship owners because they reduce fuel cost and maintenance.

ICCP systems work by supplying a controlled amount of DC current to submerged surfaces using highly reliable mixed metal oxide anodes and zinc reference electrodes. This electrical current, constantly monitored and regulated by the system itself to prevent the electrochemical action of galvanic corrosion before it begins.

For more than 25 years, sea-going vessels of every type and size – oil tankers, LNG carriers, cruise ships, pleasure craft, workboats, semi-submersibles, and more – have benefited from the 24-hour protection provided by Impressed current cathodic protection systems against the costly, corrosive effects of electrolysis.

Reference Cell / Electrode
ICCP systems are controlled to assure optimum protection. This control is obtained by inserting a third electrode between the anode and the cathode. The third cell/electrode is insulated and does not receive any anode current. This cell/electrode is freely corroding and it becomes the starting point — or reference — in eliminating corrosion. Cell/Electrodes constructed of Zinc are used exclusively with the ICCP system.

Zinc Reference Electrode

Power Supply Unit / Control Panel
Each standard ICCP system utilizes a solid-state controller which monitors and controls the protection as measured by the Zinc Reference electrode. Anode current automatically increases when the electrode potential falls below the designated control value. An over- and under-potential alarm is provided with the system package. We also offer optional digital control, state-of-the-art technology with every system. The computer controller (shown below is more accurate and provides central control, monitoring, data storage and hard printout.

Mixed Metal Oxide Anodes
Mixed Metal Oxide anodes of are used exclusively for ICCP systems. ICCP anodes are manufactured in Linear Loop , Elliptical and Circular designs with insulating holders. They are available in a single unit capacity of 75 to 225 amperes, as required for various installations.

Impressed Current Corrosion Protection System – MMO-TI Linear Strip Anode– MMO-TI Disk Anode

System Advantage

·         Increased life of rudders, shafts, struts and propellers as well as any other underwater parts affected by electrolysis

·         Anodes are light, sturdy and compact for easy shipping, storage and installation

·         Anodes, reference cells and automatic control systems maintain just the right amount of protection for underwater hulls and fittings, unlike standard zinc anodes, which can’t adjust to changes in salinity or compensate for extreme paint loss

·         Automatic control equipment ensures reliable, simple operation

·         Optimum documented corrosion protection at minimum overall cost

·         Only one installation required for the life of the vessel or structure

·         Increased dry-dock interval

Battling Corrosion aboard Ships - Part 1

All areas of the marine industry fight a constant battle against corrosion.

The shipping industry is one that continually faces the corrosion challenges stemming from marine environments, particularly seawater.

Because seawater contains a significant concentration of dissolved salts and is very corrosive to steel, infrastructure and assets in or near marine environments are particularly susceptible to corrosion. Efforts to mitigate corrosion in marine environments continue as industries develop and implement solutions to prevent asset degradation.

The most frequent forms of corrosion found on chemical tankers are uniform corrosion, pitting corrosion, crevice corrosion, galvanic corrosion, and microbiologically influenced corrosion. 

The most efficient system for combating underwater corrosion is 'cathodic protection'. The basic principle of this method is that the ship's structure is made cathodic, i.e. the anodic (corrosion) reactions are suppressed by the application of an opposing current and the ship is thereby protected.

CATHODIC PROTECTION USING SACRIFICIAL ANODES: THE BASICS

 How does corrosion take place in ships?

 Ships are made of steel; whose main component is iron. Iron is an electrochemically positive element, i.e., it has a tendency to give up electrons to become a free ion. Sea water is composed of oxygen and hydrogen, and it produces electrochemically negative hydroxyl ions which can accept the electrons given by Iron. This way the Iron ions combine with the hydroxyl ions of water to form Iron Hydroxide. This is called the oxidization of Iron, and this oxide is what we call as the brown color rust.

 The basic idea of using sacrificial anodes is to use a metal like Zinc/Aluminium and create its contact with the surface to be protected.

The simplest picture which comes to mind is simply using a flat bar of the metal and fix it to the surface to be protected. This is actually the method commonly used to protect the outer ship’s hull.

To protect steel successfully using cathodic protection, it is therefore only necessary to lower its potential by around a quarter of one volt (250mV). 

Cathodic protection using sacrificial anodes produces a decrease in the potential of the ship by connecting the vessel to a metal which takes up a reversible potential of less than –850mV (S.C.E.) and allowing the sacrificial metal to produce the electrons rather than the corrosion reaction of the steel.

Anode Classification

Anodes can be classified based on their shape, size, material, mounting method and method of securing to the surface to be protected.

 The following are some widely used shapes for anodes:

• Flat or block shaped

• Cylindrical or semi-cylindrical

• Tear-drop anodes

• Bracelet anodes

• Disc shaped

• Tubular anodes

 Anodes can be of different shapes based on their applicability. The selection of the shape of anode depends on several factors. Some of these factors are:

• shape of the surface to be protected,

• availability of space,

• accessibility,

• ease of installation

• special considerations, e.g., effect on resistance for small boats 

For example, flat anodes are used mostly for flat, large surfaces like the ship’s hull. Tear-drop anodes are used in high speed boats where streamlining of water is important as flat anodes will increase the boat’s resistance. Bracelet anodes are used for pipelines and propeller shaft, while tubular anodes are used for cables. There are no fixed rules here though, and the choice depends on the availability, cost and flexibility in design. For example, cylindrical anodes can also be used to protect pipelines, and it is not necessary to use bracelet anodes if they are costlier.

Anode Material

Usually for marine applications, Zinc or Aluminium anodes are deployed. Zinc has been traditionally used for corrosion protection, though Aluminium is now widely used. The two properties which measure performance of an anode are listed below.

1.       Closed Circuit Potential – the first parameter, Closed Circuit Potential signifies the ease with which the anode will be corroded. The more negative the value, the more readily the anode will get corroded. Generally, a potential of less than -0.08 Volts is required for cathodic protection of shipbuilding steel to be effective.

2.       Electrochemical Capacity (in Amp-hr/kg) – The second parameter, the Electrochemical Capacity, signifies the rate at which the anode material will be consumed.

The two parameters for Zinc and Aluminium are listed in the table below:

Properties of Anode Materials (Source: DNV RP-B401)

We can see from the above table that Aluminium has a higher closed circuit potential – so it will more readily start working compared to Zinc. It also has higher Electro-chemical capacity compared to Zinc, and will be longer lasting for the same anode size.

Further, in fresh water application, Zinc tends to develop a calcareous coating on the anode surface, which prevents their effective working.

However, Zinc anodes have sometimes been found more reliable in environments with low oxygen, e.g., marine sediments or areas with high bacterial activity. Thus, while Aluminium is the more efficient one, Zinc may be more effective in some cases.

Further, Aluminium anodes, if falling from a height on oxidized steel, can create sparks. Thus they are not recommended to be used inside cargo tanks of tankers. The maximum height above tank bottom which they must be placed is 28/W meters, where W is the weight of the anode in kgs.

Hence, the selection of the material depends on the type of environment it is going to be used, and should be carefully carried out.

Anode Mounting Method

The next important consideration for installation of anodes is the mounting method, i.e., the configuration of the tubular insert, and the positioning of the anode vis-à-vis the surface to be protected.

Based on mounting technique, there are two major types of anodes which are used in ships:

1.       Flush mounted anodes – in this type of anode, the anode material (Aluminium or Zinc) is in direct contact with the surface to be protected. The insert is generally a flat bar which can be welded or bolted to the surface.

Flush Mounted Anode

2.       Slender stand-off anodes – In these types of anodes, the anode material is not in direct contact with the surface to be protected, and there is a gap (hence the name stand-off). The insert is generally a tubular one which can be welded or bolted to the surface.)

The benefit of a stand-off design is that it is a more compact design, and the anode material is better utilized in a stand-off design. This is quantified by a parameter called ‘anode utilization factor’. This is the fraction of the anode material which is actually utilized over the lifetime of the anode. For flush anodes, this is around 80%, while for stand-off anodes it is 85 to 90%. Thus, stand-off anodes are better utilized over their lifetime.

Further, in case of flush anodes, due to constant contact between the anode material and the surface, the surface may suffer from embrittlement caused by deposition of ions from the anode material to the cathode (the protected surface).

That said, stand-off anodes protrude from the surface on which they are installed. When used on external hull of a vessel, these affect the streamlined shape of the vessel, and lead to increased drag and higher powering requirements. In comparison, flush anodes are closer and more compliant to the vessel’s geometric shape and have lower effect on resistance. Thus, flush anodes are usually preferred on outer hull due to their low drag properties.

Both Flush mounted and slender stand-off anodes are further classified into Short and Long, depending on their ratio of length to width. The length affects the resistivity of the anode and thus its current capacity.

References:

https://thenavalarch.com/ship-corrosion-cathodic-protection-sacrificial-anodes/

Facts of Early Detection of Concrete Cancer and our Best Solution

The Middle East is well known for the presence of a very aggressive salty water table that sits barely a few meters below the surface. As we all know, salt and water coupled with heat are the perfect blend to create corrosion nightmare of concrete structures.

Some Facts

Concrete Cancer, often identified by flaking concrete or rust stains, which originate deep within the concrete is a serious problem caused by corroding/rusted reinforcing steel from within the concrete. As steel rusts it can expand up to 7 times its original size causing the surrounding concrete to crack. As the steel pushes the concrete away, more water gets to the steel expediting the process.

The process is generally due to:

·       Presence of large quantities of water and salt

·       The ends of reinforcing being too close to the surface allowing water to seep through concrete and react with the steel

·       Poorly treated reinforcing steel being used in the original pour of the slab

·       Fractures in the concrete allowing water to penetrate the concrete and react with the steel

What do we do?

Spalled concrete can be a safety hazard. Concrete cancer and delaminated concrete should be treated immediately as deferring the treatment will inevitably lead to increased problems into the future.

Similarly, treating the visual aspects such as rendering over the steel are short-term solutions as the rusting process will continue below the surface causing the steel to again displace the concrete and in some cases, rust so badly the steel eventually needs replacement. This approach – we call it the ‘make up’ approach – is aesthetic. In essence, the ugly bits are removed and given a nice clean looking finish, however the underlying problem is very much still present. Within a short time, the area adjacent to the area repaired is cracking and breaking and requires repair. You are back to square one.

The Real Stuff…

The appropriate and effective treatment necessary is cathodic protection – an electrochemical method of arresting corrosion for an extended period of time – ranging from 5 years to 50 years.

Ducorr’s SHIELD™ technology is easy to install into dilapidated atmospherically exposed concrete areas and achieve excellent corrosion protection. The system uses permanent power to provide sustained protection by simply making the corrosion reaction impossible to occur. There’s lots of thermodynamic theory behind, which would be too long for this article – but in essence cathodic protection is the ONLY method that address corrosion at an elemental level eliminating the possibility of any further damage.

3 Corrosion Disasters of the Far East

Bhopal Accident - India

On the night of the 2-3 December 1984 water inadvertently entered the MIC storage tank, where over 40 metric tons of MIC were being stored. The addition of water to the tank caused a runaway chemical reaction, resulting in a rapid rise in pressure and temperature. The heat generated by the reaction, the presence of higher than normal concentrations of chloroform, and the presence of an iron catalyst , produced by the corrosion of the stainless steel tank wall, resulted in a reaction of such momentum, that gases formed could not be contained by safety systems.

As a result, MIC and other reaction products, in liquid and vapor form, escaped from the plant into the surrounding areas. There was no warning for people surrounding the plant as the emergency sirens had been switched off. The effect on the people living in the shanty settlements just over the fence was immediate and devastating. Many died in their beds, others staggered from their homes, blinded and choking, to die in the street.

It is been estimated that at least 3000 people died as a result of this accident, while figures for the number of people injured currently range from 200,000 to 600,000, with an estimated 500,000 typically quoted.

Sinopec Gas Pipeline Explosion - China

On Friday, November 22, 2013, the Donghuang II oil pipeline suddenly exploded in Qingdao in eastern China, ripping roads and sidewalks apart, turning cars over and sending thick black smoke over the city. The blast killed 62 people and injured 136 —China's deadliest spill since the benzene oil spill in the Songhua River in 2005.

 In January 2014, Sinopec published a statement on the explosion that blames worker error and corrosion for the accident; Huang Yi, a spokesman for the State Administration of Work Safety, said that the initial oil leak at the pipeline wasn’t properly inspected and that both the pipeline’s operator and local government departments bore responsibility for the explosions. The direct cause of the explosion was the ignition of vapors produced from oil leaking from a corroded under-ground pipeline when workers used a hydraulic hammer that wasn't explosion-proof, resulting in sparks that triggered the blasts. 

Fukushima Nuclear Plant Tank Leak - Japan

On March 11, 2011, a 9.0 magnitude earthquake took place 231 miles northeast of Tokyo, Japan, causing a tsunami with 30 foot waves. The earthquake and tsunami caused a full meltdown of the Fukushima nuclear plant. At the start of 2014, three miles from the plant the roads are still closed, and radiation levels are 100 times higher than normal. All four reactors are still emitting radiation. Tokyo Electric Power Co. (Tepco), the company that owns the plant, injects hundreds of tons of water daily into the highly radioactive reactors to keep them cool, but groundwater is pouring into the damaged reactors and has to be pumped out and stored. The steel tanks that are used to store the contaminated water can’t be built fast enough--400 tons of contaminated water needs to be stored every day.

In August 2013, 300 metric tons of contaminated water leaked from a storage tank. The leak, first detected on August 19, was described by Japan's nuclear regulator as the worst accident at Fukushima since the earthquake and tsunami of 2011 caused reactors to melt.

Tepco concluded that the tank leak was probably caused by corrosion around faulty seals. The Fukushima plant has more than 1,000 tanks holding in excess of 380,000 tons of water irradiated from contact with reactor fuel. About 300 of the tanks are of the same bolted variety as the leaking tank. Tepco had rushed to build the tanks out of steel, but with the salt and all the radiation, they corroded quickly. At the time of the leak, only two inspectors were checking 900 tanks at any one time, so this highly radioactive leak went unnoticed for a month.

Interesting Facts About Corrosion

• Corrosion is a natural mechanism that occurs to all metals

• There are 6 main types of corrosion

• Corrosion failures cost the world in excess of over $2 trillion dollars

• Corrosion can result even in the absence of oxygen

• Corrosion protection is best addressed in the design stage

• Cathodic protection works to make the corrosion reaction thermodynamically unfavorable 

Towers, Corrosion & Sustainability - Part 3

Cathodic protection is an extremely powerful technology in that it has the power to almost completely stop corrosion on the structure it is deployed on. Most corrosion protection methods are passive in nature – such as paints. Cathodic protection is very much active. It attacks the corrosion problem at its heart.

Towers, Corrosion & Sustainability in Dubai’s Economy - Part 2

In our last notes, we discussed how a leaky basement is a recipe for disaster waiting to happen. Why? Because clearly all the elements required for an effective corrosion cell (the basic building bloc of corrosion) to easily form and self replicate are present….in abundance.

But really, how bad can this corrosion get? Is it something that will make my building collapse? Is it something to worry about? Is it something to think about? How will it affect the sustainability of the building?

Lots of questions…

For starters, let us discuss how sustainability and corrosion are interlinked. If your building can be made to last an additional 20 years by stopping corrosion, then the technology that allows you to do this is a sustainable technology. This is the link between corrosion mitigation and sustainability.

What about our leaky basement? What can we expect in terms of how bad the corrosion can get.

The biggest risk posed to any structure from corrosion would be if the corrosion were to initiate in a ‘structurally sensitive’ area and remain accelerated and localized in that area. You can imagine what this would like; a gradual but accelerated reduction of the reinforcing steel diameter in an extremely short span of time. This is the nightmare situation for any building. It happens often. I have seen corrosion of structural columns in basements in under 5 years after completion that have caused massive cracking. It’s quite ugly and frightening. What does this tell us about how bad things can get? It’s very difficult to point to a specific rate of corrosion because corrosion is mix of so many factors – electrical, electrochemical reactions, temperature, moisture, pH and much much more. So in essence, it is difficult to predict – but who is prepared to take the chance? Would you? I wouldn’t! It is something to worry about.

The thing about corrosion is that it grows and gets worse as time passes – much like a tumor would. As a matter fact, in Australia, it is nicknamed  ‘concrete cancer’ - and unless you move quickly to snuff it out, its going to destroy the building and cost you an arm an a leg.

Many owners have gone about attending to leaky basements in a strange kinda way. As soon as leak is seen, it is plugged by crack injection. Sometimes the situation is so bad that the top layer of concrete is removed and reinstated – all in the hope of …..wait for it…removing the salt chlorides. Now why would I care so much about the chlorides. Primarily because it is a corrosion initiator and when present in excess of a certain amount, corrosion is guaranteed.

If only we had a technology that would stop corrosion in an inexpensive way irrespective of how much chlorides were present! Well it exists. Cathodic Protection. In our next part on this blog, we will discuss how this technology works for basements.

3 Reasons Why Corrosion Protection is the Sustainable Way for Buildings - Part 1

In the UAE and in the region in general, the geology of our coastal cities in the Middle East require the use of pile or raft slab foundations built from reinforced concrete to be used. These very large underground structures are typically constructed in the water table. Waterproofing attempts typically fail to stop all water ingress, and the basements are often times leaky and inundated with groundwater or significant leaks. Sometimes I have seen entire basements flooded almost to the ceiling of the basement.

 The question we should be asking ourselves is, once the leaks are plugged and the water pumped out, do we still have a problem or are we in the clear?

Do we still have a problem or are we in the clear?

To be sure this is not a one liner. Let’s consider the situation. The floor is made from reinforced concrete. It is now fully laden with chlorides, even after removing all the offending water...

We certainly can’t see the chlorides, but they are there – unless you have somehow managed to miraculously to suction out the chlorides from within the concrete matrix.

With the chlorides present in party like quantities, you now have the main recipe for corrosion;

• Salt

• Water (moisture in the concrete)

• Oxygen

Unfortunately for corrosion engineers, and fortunately for owners, the initiation of corrosion is not something that you can see. If the waterproofing fails…poof….and there is a leak

If corrosion begins….there is only silence. You won’t hear anything, you won’t see anything, at least not until it is too late.

So while the owner goes about renting out his building and counting his rental income, the corrosion reaction also goes about eating away at his steel foundation.

What are the owner’s options?

 There are a plethora of remedies available. All claim to stop this phenomenon in some way or form. But to be honest there is only one method, which will in effect freeze the corrosion in its tracks. Cathodic Protection. In the next part of this blog, we discuss in more detail the corrosion problem, cathodic protection and sustainability.

Cathodic Protection of Reinforced Concrete Diaphragm Walls

The Middle East with its high temperatures and extremely high saline content of its sea-water & ground water forms an extremely aggressive environment in terms of corrosion. When constructing structures that are exposed to this environment the challenge is how to ensure corrosion durability.

For diaphragm walls that are cast in situ, this is a special challenge for two reasons.

The first reason is that during construction, some methods employed involve the boring of the excavation, lowering the steel cage into the bored excavation and then casting. The excavation is typically inundated with bore -hole chemicals to ensure that the excavation does not collapse. During this period, it can be expected that chlorides from the surrounding groundwater permeate the excavation walls. Therefore it follows that the reinforcing steel cage will, once it is lowered, be immediately exposed to potentially high levels of chloride.  

The second reason that diaphragm walls are a challenge in terms of ensuring durability, is the exposure after construction. On one side the reinforcing steel is exposed to highly saline sea-water, while on the soil side, the wall is exposed to highly saline ground-water. The wall is seemingly sandwiched between to very corrosion environments.

By deploying a well-designed cathodic protection system using impressed current, the corrosion of the reinforcing steel can be stopped or significantly reduced to a negligible amount. Cathodic protection (CP) is a technique used to control the corrosion of a metal surface by making it the cathode of an electrochemical cell. A simple method of protection connects the metal to be protected to a more easily corroded "sacrificial metal" to act as the anode. These systems (also known as sacrificial cathodic protection)  can be designed with a service of approaching 20 years.

For longer service life systems, the ‘sacrificial metal’ method above is not sufficient. Metals made from coated titanium cast into the concrete matrix. These provide a means to create electrochemical cell, by introducing direct current onto the steel to be protected, in this case the reinforcing steel. The source of the direct current is typically located close to the structure in an electrical room. These systems can be designed in excess of 50 years.

Once deployed, these systems can be monitored with extreme ease remotely. Many asset owners fret about the upkeep of these systems. In fact, the upkeep is insignificant. With IoT devices, Ducorr has already developed systems that can be monitored from your smart phone or tablet, sending you updates at intervals you chose.

These systems are extremely powerful durability tools providing a hands-on and active approach for managing corrosion – almost unheard off a few decades ago.

Beyond The Pool: Corrosion Problems Involved in Swimming Pools

Many swimming pools were built as part of leisure facilities or schools. These typically comprised of a cast in situ reinforced concrete base and walls with cast in situ promenade decks around the pool. These structures are now often in severe distress due to corrosion of the reinforcement in the walls and promenade decks.

All swimming pools experience galvanic corrosion if they use chlorine sanitizer. Chlorine is salt based, so by adding chlorine to a pool you are actually adding salt. A saltwater pool, however, has approximately ten times the salt level of a traditional chlorine pool. If a saltwater pool has ten times as much salt as a traditional chlorine pool, it means that the rate of galvanic corrosion also increases ten times.

Corrosion prevention, often referred to as "cathodic corrosion prevention," is a massive field that touches an incredibly broad spectrum of industries, including maritime shipping, manufacturing, petrochemical, water distribution, food processing, major construction and even dairy farming.

The use of cathodic protection to stop this degradation of the reinforcement has been developed to be the standard repair method. The use of anodes in the pool water has become the most popular system of cathodic protection of swimming pools. The anodes are installed in boxes, recessed into the pool side walls of the swimming pool. The economic benefits of this form of repair are so impressive that it is now being used worldwide.  

In this installation, the swimming pool walls and base are protected using anodes in the pool water. The support columns and other concrete parts which also suffer from reinforcement corrosion are protected by internal anodes placed in holes drilled in the concrete. The cathodic protection system is computer-controlled. This gives an accurate continuous control of the output current to each part of the structure based on real-time readings from reference electrodes. This gives a better and more even protection from corrosion, increases the life of the anodes and switches off the anodes in the water when bathers are in the pool. The computer control system has a modem and a telephone connection allowing remote monitoring and control of the system.

Every swimming pool, and especially every saltwater pool, should have a sacrificial anode installed. The addition of this simple and low-cost device will dramatically reduce the damage a pool experiences as a result of galvanic corrosion. While you may still experience localized anodization and oxidation of metals in a pool, especially in situations where two different metals are in direct contact, a sacrificial anode is the bare minimum level of protection that every pool needs. It is absolutely silly to not have one of these — plus they can easily be adapted to any existing system.

Importance of Corrosion Protection During Storage and Transportation

Products that are transported for a longer period of time or stored for an extended period are often in need of corrosion protection. Corrosion protection packaging prevents corrosion without having to treat the metal with oil, grease or paint.

Corrosion is a significant problem in the handling, storage and shipping of products. Bare metal parts corrode easily. Temperature changes, contaminated air, sea salt and moisture, all create corrosion. 

Due to temporary corrosion, time is diverted to handling complaints and customer loyalty is potentially lost. Delayed deliveries due to reworking of corroded components translate to avoidable losses. Therefore, planning for corrosion protection during temporary storage and transportation is a logical strategy to minimize these losses.

There are several different solutions for protecting the product from corrosion depending on parameters such as: product type, means of transportation, and the length of the transit time.

The Importance of Temporary Corrosion Protection

There are many industrial applications where temporary corrosion protection during transit and storage is critical for the final processing and end use of parts and components. If semi-finished or machined components are left unprotected, or roller bearings are not coated with a rust inhibitor during storage, or internal combustion engines are transported and stored without corrosion prevention, then they may deteriorate or become damaged due to corrosion. Any subsequent rust removal will not restore a component to its original quality and geometrical accuracy. 

Permanent corrosion protection cannot be used for temporary applications because it must be removed before further processing or assembly. Because corrosion can appear within hours or days a temporary corrosion prevention method must be implemented.

During transportation and storage, fasteners (e.g., wedges, springs, bolts, nuts, washers, screws) and associated tools require protection from corrosive chemical reactions on their surfaces. 

General Care for Preventing Corrosive Deterioration

Desiccants to control air humidity are used to prevent corrosive deterioration during storage and transport. Silica gels and molecular sieves are occasionally used as desiccants to absorb excess air moisture. Sealed films of high pressure polyethylene and special waterproof and airproof packaging systems are used for critical applications.

Cost, Safety and Health

Allowing temporary corrosion and rust on materials during interstage processes and transportation is costly due to the direct and indirect costs involved in rework and warranty damages. When carefully chosen, preventive solutions are cost effective for both application and subsequent removal.

For confined spaces, authorized specialists must be consulted. Ensure compliance with personal protective equipment (PPE) and firefighting regulations.

The combustion products of coatings can be highly toxic. Hence exposure control must be planned for in advance. Precautions should be taken to avoid eye contact and skin exposure with proper PPE suitable for the application method used. Respiratory protection might be needed in a few cases.

Problems of Durability and Reinforcement Measures for Concrete Tunnel Structures

A tunnel or bridge structure exposed to salt water can expect corrosion of the embedded steel during its service life. Cathodic Protection (CP) has proven itself as the only permanent repair of existing corroded steel reinforced concrete.

Many underwater tunnel structures have been experiencing water leakages worldwide. Tunnel structures experiencing water leakages are not only old, but also new in some case. The concrete tunnels structures located underwater are generally protected by waterproof membranes as the first defence to prevent water leakages and rebar corrosion. However, once water leakage occurs, the corrosion mechanism is quite different from other concrete structures which are exposed to marine or de-icing salt environments. When rebars corrode in concrete, the accumulating corrosion products develop expansive force and crack the concrete. When the concrete cracks grow, the concrete spalls and falls to the roadway. For the based slab, concrete spalls create potholes on the driveway. Therefore, it is important to clearly understand the corrosion condition of the rebars in the tunnel caused by salt water leakage.

Loss of Durability

Why does the durability of bridges, multi-level car parks, supporting walls, tunnels and sea water structures decrease?

The main problem is the de-icing salt on the streets. These salts contain chlorides which penetrate into the constructions and destroy the protective layer of the rebar - the consequence: corrosion.

These factors together with a too thin concrete cover and too low density as well as changing weather conditions and humidity lead to an increased risk of corrosion. Corrosion of the rebar reduces the steel cross section and as a consequence the support safety. Furthermore, it cause cracks due to the increased volume of the rust.

Factors of influence on the corrosion risk of the rebar.

Concrete Remediation Works

Certain methodology must be developed to remediate the corroding steel and mitigate further corrosion on mild steel components and reinforcement. This would allow the tunnel to achieve its required life with minimal ongoing maintenance. This involved the repair of damaged concrete, encapsulation of mild steel bolts and application of cathodic protection.

Design Options for Cathodic Protection System

There are various design options to be considered to provide cathodic protection for tunnel reinforcement. The three main options were:

a) Ribbon/discrete anodes in slots/ drilled holes in the concrete.

b) A distributed anode system along the full length of the tunnel.

c) Installation of remote anode groundbeds at the two ends of the tunnel

Treating Reinforced Concrete Corrosion In Parking Structures- Part 2

Levels of Corrosion Protection for Reinforced Concrete

There are three basic levels of active (electrochemical) corrosion protection available. These are generally referred to as:

• Corrosion prevention;

• Corrosion control; and

• Cathodic protection

All levels are essentially similar in that a protective current is provided to prevent or reduce the corrosion activity of the reinforcing steel. They differ in terms of the intensity of the protective current and suitability for a given range of applications.

Corrosion Prevention

Corrosion prevention is defined by the National Association of Corrosion Engineers (NACE) as “Preventing corrosion from initiating even though the concrete may be sufficiently contaminated with chlorides to favor corrosion.”

For owners or managers who suspect corrosion is already underway and damage is occurring, the first step is to identify the extent of the problem. Unless corrosion is severe enough to force off the outer face of the concrete, reinforcing steel is generally hidden within the concrete slab, making any visual identification of early stages of corrosion difficult or impossible. Instead, the concrete is evaluated through field and laboratory testing to determine whether conditions conducive to corrosion exist within the concrete structure.

Chloride ion content testing identifies the concentration of chlorides in concrete at various depths to evaluate the probability a corrosive environment exists. Dust samples from incremental depths through the concrete slab are extracted and sent to a testing laboratory for analysis.

Half-cell potential testing determines the electrochemical behavior of embedded steel by measuring its electrical potential (i.e. the difference in charge from one area to the next). The greater the electrical potential, the greater the risk corrosion is occurring. Conducted onsite, the test involves removal of concrete cover over reinforcing bar, followed by the connection of exposed steel to an electrode through a voltmeter. Half-cell potential readings can be used to generate an electrical potential map, indicating areas with the greatest and least risk of corrosion.

Loss of steel reinforcement is a concern for areas where corrosion has progressed at an advanced rate. Where reinforcing bar is exposed or where concrete is cracked, delaminated, or spalled, a structural engineer should evaluate the remaining slab’s structural capacity to determine whether corrosion has compromised its loadbearing ability.

Where corrosion-induced spalls have been previously repaired, a characteristic ‘halo effect’ might be observed, with a ring of corrosion staining appearing around the patch site. Patching delaminated and spalled concrete with conventional concrete can lead to an electrochemical reaction at the interface between the existing chloride-contaminated concrete and the new concrete. The large difference in electrical potential between the two, combined with the short distance between anode and cathode, leads to accelerated corrosion. Usually, such patches need to be repaired again in just a year or two.

CORROSION CONTROL

Corrosion control is defined by NACE as “Providing a significant reduction in the corrosion rate of actively corroding steel in concrete.” Corrosion control can result in an increased service life of the rehabilitated targeted sections of precast members at a relatively low incremental cost. This is how sacrificial corrosion protection or mitigation is most often used. Corrosion control may or may not completely stop ongoing corrosion, but the reduction in corrosion activity will significantly extend the service life of existing corroding structures. In corrosion control applications, the conditions for corrosion (such as chloride contamination) already exist and corrosion may have already initiated in some areas, although have not progressed to the point of concrete damage. The applied current necessary to address corrosion activity (after corrosion initiation) is higher than the current required for corrosion prevention. Therefore, either larger and/or closer spaced galvanic anodes will be required to provide corrosion control.

CATHODIC PROTECTION

One way of protecting the steel is through cathodic protection. ln this method, the corrosion is stopped by reversing the processes of electrochemical action that cause the corrosion. By applying a direct current to the rebar in opposition to the current causing the corrosion, the corrosion causing current is overcome.

An effective way to achieve long-term corrosion protection of existing chloride contaminated structures, or to provide extended service life to target locations on new precast members, is to use sacrificial protection systems. Galvanic protection is achieved when two dissimilar metals are connected. The metal with the higher potential for corrosion will corrode in preference to the more noble metal. As the sacrificial metal corrodes, it generates electrical current to protect the reinforcing steel. With this type of cathodic protection system, the galvanic protection system voltage is fixed and the amount of current generated is a function of the surrounding environment. Galvanic anodes will generate higher current output when the environment is more corrosive or conductive—for example, where there is higher chloride concentrations, and where current output exhibits a daily and seasonal variation based on moisture and temperature changes. Sacrificial protection systems are low-maintenance, do not require an external power supply, and are compatible with prestressed and post-tensioned steel.

As discussed with our previous Blog article, when sacrificial anodes cannot deliver sufficient current to prevent corrosion, impressed current cathodic protection (ICCP) may be used. As with passive cathodic protection, ICCP reverses the electrochemical process of corrosion through the action of an applied electric potential—in this case, the current arises not from the inherent properties of the materials themselves, as it does with galvanic coupling, but from an external power source.

Treating Reinforced Concrete Corrosion in Parking Structures - Part 1

Facility Management Contractors are often tasked with maintenance of parking structures. Made of concrete and steel, these multi-level hubs provide visitors and their vehicles with shelter from the elements and often provide access to housing or office space. However, protecting the structure itself from the constant attack of environmental stressors and wear-and-tear comes with its own set of challenges.

Vehicles regularly entering parking garages leave water, oil and dirt behind that can corrode the structure’s concrete and steel support system.

One of the greatest issues related to the deterioration of parking structures is the corrosion of embedded reinforcement. Structural concrete used in parking structures is strengthened by means of steel reinforcement bars, or “rebar,” which is embedded into the concrete to improve resistance to tensile and compressive stresses. Ordinarily, the surrounding concrete protects this embedded steel from the corrosive effects of water and dissolved salts in the environment. However, breaches in the concrete, whether due to cracks, flaws, thin coverage, or poor concrete composition, can allow steel reinforcement to come into prolonged contact with corrosive elements. As the steel corrodes, it expands, leading to further damage to the concrete, greater water infiltration, and additional corrosion in a self-perpetuating cycle of deterioration. If not arrested early on, the progressive nature of the cracking and corrosion can eventually lead to an unsafe structure and can cause costly repair.

There are several ways contractors can retrofit concrete parking structures to ward off the effects of chloride-induced corrosion. 

One of the effective ways to stop corrosion is the use of a cathodic protection system.

Corrosion is the electrochemical process of reinforcing steel losing electrons and decomposing to iron oxide. Reinforcing steel that loses electrons acts as an anode. One way to stop further loss of electrons, and t h e re f o re stop corrosion, is to reverse the current flow and turn the steel into a cathode.

Passive cathodic protection controls steel corrosion by connecting the reinforcing bar to a sacrificial anode, a metal that is more active than steel and so will corrode preferentially. In the presence of the sacrificial metal, the steel surface becomes polarized to a more negative potential, until the driving force for the oxidation of the steel is removed. The galvanic anode will continue to corrode until it is consumed by the electrochemical reaction and must be replaced. Galvanized rebar is one example of passive cathodic protection, where the zinc coating acts as the sacrificial anode. Other commonly used galvanic anodes include magnesium and aluminum-based alloys.

Where galvanic anodes cannot deliver sufficient current to prevent corrosion, impressed current cathodic protection (ICCP) may be used. As with passive cathodic protection, ICCP reverses the electrochemical process of corrosion through the action of an applied electric potential; in this case, the current arises not from the inherent properties of the materials themselves, as it does with galvanic coupling, but from an external power source. Care must be taken in designing and installing ICCP systems in parking structures, however; excessive current density may cause the alkaline concrete to react with acid generated by the anode, leading to concrete damage. In an ICCP system, it is difficult to provide protection at any significant distance from the anode, since current distribution within concrete is poor. Therefore, anodes must be placed no more than about a foot apart, and the anode material must remain continuous throughout the structure. The ICCP system must take into consideration differing proportion and placement of reinforcement throughout the parking structure, so as to avoid voltage drops from one area to another.

Choosing the Right Strategy

Different approaches nowadays may or may not guarantee protection against reinforcement corrosion for all parking structures. Determining the best way to prevent and treat the underlying causes of corrosion involves consideration of garage conditions and exposure, concrete quality and construction, environmental contaminants, and other factors specific to the structure and situation. Initial cost and maintenance demands are also important decision criteria. Often, the most successful strategy involves a multi-component approach, one which combines preventive treatment with an ongoing program of assessment and repair to keep corrosion at bay. Ultimately, the time and expense required to prevent corrosion and treat early warning signs is far less than that of rehabilitating a garage that succumbs to corrosion induced structural failure.

Highlights 2018: A selection of our Key Projects

2018 was an eventful year for Ducorr, in which our clients continued entrusting us with many varied and challenging works. In this compilation, we show you some of our successfully completed projects.

Concrete Corrosion Problems of Hotels near Marine Environment

Corrosion of reinforcing steel in concrete is a worldwide problem that causes a range of economic, aesthetic and utilization issues. However, if corrosion effects are considered in the design phase and the right decisions are made prior to construction, public-use buildings such as hotels can be built to last and protect against corrosion for 50 and more years.

Regular and planned asset maintenance is vital for reinforced concrete structures. Such maintenance should not be a ‘cosmetic repair’ but rather a proper root cause analysis that must be carried out to identify and understand the actual source of the problem.

Many of the hotels in MENA Region are situated near marine environments that results in rapid occurrence of concrete corrosion.

Usually, the most exposed elements deteriorate first – but the underlying corrosion is unseen. Active corrosion in the steel beneath may take five to 15 years to initiate cracks in the concrete, but much of the corroded reinforcement is not visible.

Corrosion affects all concrete buildings and structures around the world to some extent, with annual costs in the billions to national economies. With hotel assets, corrosion is often an issue of aesthetics and falling concrete where spalling occurs creates public safety risks. Hotel operators do not want scaffolds, cables, and exposed metalwork on display for extended periods of time. The corrosion of steel in concrete is accelerated in harsh environments, especially in coastal, tropical or desert environments where high salt levels or extreme temperatures can accelerate the rate of decay.

Common Causes of Concrete Corrosion

The two most common causes of concrete corrosion are carbonation and chloride (salt attack). In broad terms, when carbonation, chlorides and other aggressive agents penetrate concrete, they initiate corrosion that produces cracking, spalling and weakening of the concrete infrastructure. As reinforcing rods rust the volume of rust product can increase up to six times that of the original steel, thus increasing pressure on the surrounding material, which slowly cracks the concrete. Over the course of many years, the cracks eventually appear on the surface and concrete starts to flake off or spall.

Degradation of reinforcing steel and the subsequent weakening of the concrete occurs from the inside and may be unseen for many years. It is often referred to as “concrete cancer.”

Repair and Prevention

Impressed Current Cathodic Protection

One of the alternative ways to protect assets from corrosion is by deploying a Cathodic Protection System. One type of CP is  impressed current cathodic protection (ICCP) which is a technique where a small permanent current is passed through the concrete to the reinforcement in order to virtually stop steel corrosion.

The main benefit of ICCP is that the removal and repair of concrete is vastly reduced, with only the spalled and delaminated concrete requiring repairs.

Once installed, corrosion can be controlled for the long term, eliminating future spalling and deterioration even in severe chloride or carbonation contaminated concrete.

Proper anode system selection is the most vital design consideration for a durable and efficient ICCP system. Incorrect selection and placement of the anode system can result in poor performance and a vastly reduced installation lifetime.

EARLY CORROSION DETECTION TO AVOID COSTLY REPAIRS OF CONCRETE STRUCTURES

The protection of assets from corrosion is a key commercial, safety and environmental issue.

Deterioration of concrete structures can become a challenge for the owners of structures such as bridges, walkways, high rise buildings, etc. It is important to identify these defects on time and plan appropriate repair strategies. Concrete deterioration can occur through scaling, disintegration, erosion, corrosion of reinforcement, delamination, spalling, alkali-aggregate reactions, and cracking of concrete. Moreover, corrosion of reinforced steel is the main cause in modern concretes.

Successful contractors understand the importance of adding value to their clients' assets/structures. One of the best ways to do this is to offer additional services that provide a cost-effective benefit to the client. Contractors can provide value added service to their clients through the application of cathodic protection. Cathodic protection system stops the corrosion cycle in concrete by utilizing an electrical current. It can be an add-on service for the concrete contractor and a cost-effective benefit to the client.

How does cathodic protection work?

In the simplest terms, a small DC electrical current is discharged off of an anode and flows through the concrete to the reinforcing steel. This protective current prevents corrosion from occurring. A small power supply unit converts AC power available at the site to DC power to provide the negative charge, which is used to arrest the natural corrosion process. Typically these systems use very little power -- not much more than a conventional 120 Watt electric light bulb. The contractor has a wide range of decorative top coats available to finish the process while meeting the aesthetic requirements of the project. For more than 20 years, this proven technology has been employed successfully on numerous installations in coastal environments.

Contractors should be encouraging their clients to consider cathodic protection when major repair projects are undertaken. The first reason is the most important -- quite simply, cathodic protection stops the repair cycle by preventing further corrosion. When the client/owner completes a major concrete repair only to find that more corrosion is occurring just a few years later, there is an unhappy client eager to blame the initial repair contractor. Cathodic protection stops future corrosion which in turn stops the vicious restoration cycle.

Corrosion in Reinforced Concrete Structures in the Middle East

Corrosion of reinforced concrete structures, both underground and above ground are a significant drain on the economy of most Middle Eastern countries. The majority of reinforced concrete structures in the Arabian Peninsula are chloride contaminated. As buildings and structures age, the chloride levels increase due to both chloride loading from atmospherically carried chlorides, and from capillary action which transports chloride laden ground water into concrete structures, where the water evaporates concentrating the salt above ground level. Allowing reinforced concrete structures to corrode freely results in buildings and structures that require repair or demolition due to structural failure.

One scenario of concrete damage due to corrosion happened in one of the Port in the Emirates which was constructed during 1970 and consists of pre-cast reinforced concrete beams and slabs with in situ concrete topping, supported by tubular steel piles. The first signs of deterioration were recorded after 7 years, evidenced by cracking of the lower corners of the pre-cast beams. Observing this, a series of detailed inspections were carried out.

An impressed current cathodic protection system incorporating metal oxide coated titanium anode was used to prevent further deterioration. The main advantage of impressed current cathodic protection (ICCP) lies in its much greater output capacity as compared to galvanic anode systems. Therefore, whenever corrosion protection is required for large poorly coated or bare structures, ICCP would be the system of choice. ICCP systems requires the use of an external DC power supply and metal anode in direct contact with concrete. This is achieved by embedding a durable conductive anodic overlay. This method is called reinforced concrete cathodic protection (CP).