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.

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 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.


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.



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.




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).



The Impact of Corrosion on Concrete Infrastructures


In the past 50 years, U.S. Department of Transportation’s Federal Highway Administration (Washington DC & Florida) have done research on the bridges and offshore platforms that have aggressive chloride environments and show evidence of corrosion after short service periods. They found that, since mid of 1970’s, the cost of repairing or replacing of deteriorated structures has become a major liability for highway agencies. $20 Billion was spent on repairing corrosion problems in the past 10 years and it is increasing at $500 Million per year. The primary cause of this deterioration (cracking, delamination, and spalling) are due to the chloride attacking the reinforced steel.

Various Cathodic Protection techniques were developed to prevent corrosion in their bridges & offshore platforms. The U.S. Department of Transportation’s Federal Highway Administration (Publication no. 00-081, August 2000) is applying cathodic protection on their major bridges/tunnels, etc. The advantage of deploying Cathodic Protection System are:

1.    100% guaranteed service life (10 to 100 years life span)

2.    Easy installation

3.    Low maintenance

4.    Decreases (stop) the risk of corrosion in the reinforced concrete structures

In recent years, Road and Transportation Authority (RTA) of Dubai, have taken the approach of deploying Cathodic Protection System on their assets such as Dubai Water Canal and Shindagha Tunnel since it is a simpler option that allows to decrease the risk of corrosion on their reinforced concrete assets.



Culprits That Caused Miami Bridge Corrosion

#corrosion #Infrastructure #bridge

3 Culprits That Caused Miami Bridge Corrosion

Jet Skis, waverunners and other personal watercraft shooting salt water up at the underside of the MacArthur Causeway have caused extensive corrosion on one end of the bridge, necessitating repairs to beams and columns. It's also time to replace the top three inches of concrete on the bridge's surface.

The bridge connects the city of Miami to the barrier island of Miami Beach.

Residents and commuters of the notoriously traffic-jammed region should brace themselves for a long stretch of headaches on the main causeway connecting South Beach to mainland Miami.

The Miami Herald reports the Florida Department of Transportation began a two-year, $12.9 million rehabilitation project on the corrosion of the bridge in June 2018.





Ducorr Won the contract for Shindagha Bridge Project

Ducorr was awarded a contract to deploy a Cathodic Protection System for Dubai’s $107.3 million Shindagha Bridge project.

Ducorr role as cathodic protection specialist is to ensure the durability of the parts of the bridge that require corrosion protection.

Shindagha Bridge is a part of the AED5 billion Shindagha Corridor Project extending 13km along Sheikh Rashid Street as well as Al Mina, Al Khaleej and Cairo Streets.

The bridge’s iconic design features an architectural arch-shaped in the form of the mathematical symbol for infinity. The top of the infinity arch rises 42 m. About 2,400 tons of steel will be used in the construction of the bridge. 


Hassan Sheikh, Managing Director of Ducorr Middle East, said: “It is truly a great honor for us to be a part of the Shindagha Bridge Project, as Shindagha is one of the oldest and historical areas of Dubai and was home to the late Sheikh Saeed Al Maktoum, Ruler of Dubai.”





Human Error as a Factor in Corrosion Failure

  Mitigating human errors requires the same careful use of protocols, supervision, and inspection as reducing other corrosion factors.

Mitigating human errors requires the same careful use of protocols, supervision, and inspection as reducing other corrosion factors.

Corrosion failure happens for all kinds of reasons. Environmental conditions, the materials in question and the stresses that a material undergoes all play major roles. And while different materials, technologies and processes are thoroughly discussed in industries where corrosion is an issue, one of the least addressed contributing factors to corrosion is human error. It can occur for a number of reasons:

  • Lack of communication

  • Unwillingness to improve the situation

  • Lack of knowledge

  • Distractions

  • Lack of teamwork

  • Stress and fatigue

  • Lack of resources

  • Pressure

  • Lack of assertiveness

  • Lack of awareness

  • Insufficient control and supervision

Here we'll take a look at how human error contributes to corrosion failure and what can be done to mitigate its effects.

Where Human Error Occurs

Any project consists of many stages, beginning at manufacturing and design, all the way through construction, and ending with supervision and maintenance work. Human error can occur at one or all of the above stages.

The design stage of any metallic system is the most important one; if a major error occurs at this stage, it significantly raises the risk of corrosion failure. There are many factors to be considered for optimum design, including material selection, wall thickness and diameter (for pipelines), as well as corrosion allowance and corrosion control measures. 

Types of Human Error

According to Neville W. Sachs in "Understanding Why It Failed," there are six key error categories that can contribute to corrosion failure.

1. Operational Errors

Operational errors occur when a system or process operates outside of or beyond the parameters of its design. For example, if specified operating practices call for a specific operating temperature, and a worker makes a decision to exceed this temperature, accelerated corrosion may be the result.

2. Design Errors

Design errors can occur when a system's design fails to match up to its application, or when the way the system is used is changed without a thorough review. This type of error can be an engineering error, or can occur when other workers install systems or machines without proper oversight.

3. Maintenance Errors

Maintenance errors occur when maintenance personnel fail to properly maintain or repair a system, or improperly install one of its components.

4. Manufacturing Errors

Manufacturing errors occur when components in a system are improperly manufactured or include flaws that can contribute to corrosion failure.

5. Installation Errors

Original installation of a system's components can cause corrosion failure if those components are installed incorrectly or without proper oversight.

6. Supervisory Errors

Supervisory errors are said to occur when a problem is noticed, but no action is taken. Often, a worker may believe that someone else will take care of the problem, or that it's someone else's responsibility. 

How to Reduce Human Error

In order to mitigate human errors, human factors must be considered. Human factors are all those things that enhance or improve human performance in the workplace. As a discipline, human factors are concerned with understanding interactions between people and other elements of complex systems.

Human factors apply scientific knowledge and principles, as well as lessons learned from previous incidents and operational experience to optimize human well-being, overall system performance, and reliability. The discipline contributes to the design and evaluation of organizations, tasks, jobs and equipment, environments, products, and systems. It focuses on the inherent characteristics, needs, abilities, and limitations of people, and the development of sustainable and safe working cultures. In other words, mitigating human errors requires the same careful use of protocols, supervision, and inspection as reducing other corrosion factors. (Discover more management tools in Corrosion Knowledge Management versus Corrosion Management: An Essential Tool for Assets Integrity Management.)

Additionally, all work should be done according to applicable codes and standards, and should be completed by professionals.





Cathodic Protection using Tankbox System

The TankBox™ is a pre-designed factory assembled complete sacrificial cathodic protection system that can be deployed quickly and easily for underground and coated LPG or Fuel tanks.

 Figure 1: Anode Installation

Figure 1: Anode Installation

TankBox™ systems features

  •  Complete Sacrificial Cathodic Protection System
  • Pre-designed
  • Quick Installation – no welding, no splicing, no specialist technician required
  • Integrated monitoring & hazardous rated enclosure for testing 
  • Anode Array consisting of high potential magnesium anodes
  • Tank Connection Assembly
  • Monitoring Sensor Assembly
  • Hazardous rated Junction Box [Optional]


  • Entire system comes in the box
  • No need for design
  • No need for Specialists, Technicians or Engineers
  • Service life up-to 20 years
 Figure 2: Typical Installation

Figure 2: Typical Installation



Corrosion: Understand It to Fight It


Knowing what your operations are up against is crucial in preventing costly, potentially dangerous, damage.


There have been many studies about the cost of corrosion.

NACE International, formerly known as the National Association of Corrosion Engineers (, Houston), conducted research from 1999 to 2001 that found direct corrosion costs in the United States amounted to $276 million (about 3.2% of the country’s GDP). In March 2016, NACE released a study that estimated worldwide corrosion amounted to $2.5 trillion (about 3.4% of the GDP) and indirect costs doubled that.

In the 2016 study, NACE estimated that between 15% and 35% of those corrosion-related costs could be eliminated using current technology. Researchers also offered that, comparing corrosion costs in 1975 with those in 1999, an intelligent approach to automobile design and elimination of corrosion appeared to have reduced the cost to American consumers by about 52%.


Energy is needed to convert mined ores into useful metals. Corrosion is the natural result of those metals trying to revert back to their original states. Consider, for example, that there’s very little difference between the rust from corroded steel and the iron ores that were originally refined to make that steel.

 Fig. 1 Depicting a steel bar in liquid, this diagram shows how corrosion occurs. The liquid contains water. When iron ions (Fe) off the bar unite with oxygen in the water, different kinds of rust can form.

Fig. 1 Depicting a steel bar in liquid, this diagram shows how corrosion occurs. The liquid contains water. When iron ions (Fe) off the bar unite with oxygen in the water, different kinds of rust can form.

he actual corrosion process is an electrochemical reaction. Depicting a steel bar in a liquid, Fig. 2, shows how this reaction takes place. In the diagram, corrosion is attacking the anode, with iron ions being released into the solution, while hydrogen is being generated at the cathode. Water (H2O), is made up of two hydrogen ions and one oxygen ion. The iron ions from the anode (the Fe symbols) will ultimately unite with oxygen in the water, whereupon several different types of rust can form.

At the cathode site of the piece, atomic hydrogen is being released. Most of those hydrogen ions then mate with another hydrogen ion and form molecular hydrogen, the readily flammable gas we’re used to thinking about. But some of the ions remain solitary and they are the cause of the many forms of hydrogen damage including hydrogen embrittlement, cracking, and blisters.

For wet corrosion, a liquid must be present to provide the complete circuit required by the electromechanical reaction. Electrons that flow from the cathode to the anode have to eventually return to the cathode, and they do so by traveling through the liquid.

Chemicals such as road salt are in the silt. As the moisture in it evaporates, the chemical concentration increases. The chemicals, in turn, make the water more electrically conductive and significantly increase the rate of corrosion.   

Temperature is a third important factor in corrosion. Below freezing, ice can’t conduct corrosion currents. But, as the temperature increases, the corrosion rate increases. A good example is the rapid attack on hot piping with moist insulation. The exact solution chemistry has a major effect, but up to about 175 F (80 C), the corrosion rate usually rapidly increases, then drops off and ceases when the liquid vaporizes.


Uniform corrosion causes about 80% of all corrosion. It occurs where anode and cathode sites relatively uniformly swap position. Examples include the railroad-bridge-support column shown in Fig. 1, buried steel water lines, nooks and crannies on vehicles where deposits build up, and machine frames and bases in damp areas.

Pitting corrosion manifests as isolated areas of attack. With carbon steel, it may take years before leakage occurs while stainless-steel pitting might progress at a rate of 0.001 in. (0.025 mm)/day. Steel examples frequently include water and wastewater tanks. Stainless-steel examples include external areas with dirt deposits on them.    

Galvanic corrosion occurs when two chemically different metals are joined. One is always the anode and continuously attacked, protecting the other piece. A common example involves a joint between steel and copper pipe, where the steel will always be attacked. 

 Fig 2. A common example of galvanic corrosion involves a joint between steel and copper pipe where the steel will always be attacked. This joint was submerged in water for only nine months before damage occurred.

Fig 2. A common example of galvanic corrosion involves a joint between steel and copper pipe where the steel will always be attacked. This joint was submerged in water for only nine months before damage occurred.

Figure 3 shows a bronze fitting and a steel pipe that had been submerged in water. Perforation of the freshly cut pipe threads happened in only nine months.

Selective leaching is essentially galvanic corrosion within a metal. The common industrial application involves buried cast-iron water or waste lines where the graphite in the iron acts as a cathode, and the iron is eaten away, leaving a weak and brittle graphite pipe. When initially excavated, the pipe may appear almost undamaged, but sandblasting will rapidly remove the graphite leaving proof of the mechanism. (A frequent problem with buried-pipe replacement is that the new piece is always anodic to the older sections. The new one will rapidly corrode and leak, and personnel will blame the material, not knowing that the actual problem is their lack of corrosion knowledge.)

Crevice corrosion occurs in a small gap between two pieces of metal. It allows a corrosion mechanism to act in a way that’s similar to pitting corrosion. Although it’s not a common industrial mechanism, it can happen with poor joint control on welded assemblies.

Intergranular corrosion involves galvanic attack at the grain boundaries within a   metal. It’s usually associated with a poor choice in materials of construction for  chemical processes.

Erosion corrosion is a combination of actions. Corrosion results in an oxide on a metal’s surface. The oxide, though, slows the attack because it prevents fresh corrodent from reaching the surface. If there’s a fast fluid flow that scrubs the oxide off the surface, corrosion continues at a very rapid rate. A common site for erosion corrosion is the outer radius of piping elbows in steel lines with untreated waters and flow rates exceeding approximately 10 ft./sec. (3 m/sec). It’s also been seen in pumps as a result of poor choices of construction materials.

The previous seven categories/types are basically different-looking versions of galvanic corrosion. Two other corrosion types—stress-corrosion cracking and hydrogen damage—result in metallurgical damage leading to often hard-to-detect catastrophic failures.

Stress corrosion cracking (SCC) can occur with almost any metal and is the result of a combination of stress, a chemistry that attacks the metal’s structure, and a susceptible metal. Industrially, although it is sometimes seen with nitrates and steel, the most common situation involves 300 series (austenitic) stainless steels and chlorides.


The battle against corrosion is never ending. In summary, if an area is wet and metal isn’t protected, there will be corrosion. What’s worse, the seriousness of the damage caused by this scourge may not be recognized for years. 




Much of the world runs on pipelines. When you drive your car, the fuel that you use will probably have passed under pressure through pipelines at some stage. The water that you drink, likewise, just like the gas that you use to heat your dinner. And these pipelines depend on monolithic insulating joints.

This is because pipelines are subject to corrosion, just like any metal object that is exposed to the elements. Whether overground, underwater or buried underground, pipelines need to be protected against damage from water and the air, as well as electric currents generated by lightning.

Simpler, easier to use and more effective than older anti-corrosion methods

Monolithic insulating joints (or isolation joints) provide just such protection. Specially designed to be shock absorbent and insulated against the electrical charge, they isolate sections of the pipeline so that currents can only pass so far. Materials placed within the monolithic isolation joint also work by attracting electrical charge and preventing corrosion. This is achieved by something called cathode protection - where the material in the joint becomes an anode, and the pipeline becomes a cathode. The anode protects the pipeline from corrosion. You can see the same devices attached to ships, while they are also installed in concrete constructions and on bridges as well. Without them, complex engineering would be extremely difficult.

The advantages of using the monolithic isolation joint are that this kind of joint avoids small parts such as gaskets and flanges, and can be produced to exacting standards of precision. They can be ordered in whatever pipe size is required and sealed easily and safely without the need for welding. They can also be delivered to clients pre-tested and produced to the specifications of the client, avoiding the need for technicians to attend to the installation process.


Save money and prevent accidents by using the latest technology

Every monolithic insulating joint can be fully customized for the needs of each client. They are adapted for both main and service line applications and come in a wide range of different diameters.

By installing a monolithic insulating joint at periodic points along the pipeline, firms can prevent leakages in pipelines carrying liquids such as water, liquid gas and petroleum, and also stop electric currents passing through the pipe casing, improving safety. They are a cheap, effective solution to the problems faced by pipeline maintenance operations across the world.

Previously, oil and gas firms have often relied on less effective and more expensive insulating flange kits. With the need to avoid industrial accidents and financial losses through leakage greater than ever, it makes sense to invest in the most efficient way to safeguard pipelines against corrosion. That is why European and Middle Eastern firms have already embraced isolation joints, and why American operators are following suit.





Cathodic Protection is an electrochemical technique which has been used for many years to prevent the corrosion of buried and/or immersed metallic surfaces. It utilizes the application of small amounts of electrical current (DC) to the protected surface to counteract the natural corrosion currents existing at the metal surface. The whole of the structure under protection is forced to act as the cathode of an electrochemical cell, hence the term CATHODIC PROTECTION (CP).


One of the critical issues that the owners and operators of CP systems are facing nowadays is the monitoring and maintenance of the system.

Collecting CP measurements for analysis can be time consuming and a drain on personnel resources. Some installations are located in remote /difficult to access areas or under hazardous working environments. Moreover, the incorrect monitoring and maintenance regime or operation of the CP systems can result in lack of protection and may even cause harm.


Asset owners and operators have been examining a number of Remote Monitoring (RM) technologies for CP systems. Emerging wireless technologies have expanded the possibilities for remote CP application. Major corrosion events are now leading companies to look for new, low-cost alternatives for cathodic protection remote monitoring. The adoption of wireless smart sensor network technology will enable the automatic measurement, analysis, storage and transmission of real-time data. It is a proactive system – it supports the identification of potential problems as and when they occur and alerts the responsible entities immediately.

The benefits of CP Remote Monitoring System to asset owners are:

  • Reduced ‘windshield time’
  • Reduce data collection costs and improve data quality
  • Generate automatic reports and alarms
  • Reduced operator exposure to the potentially hazardous environment
  • ‘Real-time’ access to accurate system operational data, automated reporting and alarming system via inputs to existing SCADA systems
  • Enables more effective use of personnel resources to achieve timely and targeted maintenance tasks
  • Evaluate and increase infrastructures lifetime.





Corrosion Facts That Will Blow Your Mind

Corrosion is all around us. In school we were taught that when iron is exposed to oxygen, iron oxide, or rust, is formed very slowly. But when iron and oxygen come in contact with water, rust forms much quicker.

But watching rust form is like watching paint dry – only at a much slower pace. However, the science of corrosion is fascinating – mainly for how, why, and where reasons – and what companies and people do to combat this natural “disaster”.
You may already know that salt can speed up rust production, and that the combustion reaction between iron and oxygen also produces the same amount of heat as fire.
But did you know that “rust” can form in space? 

Well, in space there are ultraviolet lights that can break chemical bonds between atoms. When these atoms and ultraviolet light strike metal in space, they can produce some of the same combinations of metal and oxygen atoms found in rust. Because the density of atoms in outer space is very low, it takes many years for rust to form on any object. To get a sense of just how slowly things rust in space, just look at iron meteorites and chunks of metal that have fallen to earth from outer space. Before crash-landing on earth, these bits of metal floated through the solar system for millions or even billions of years, but were still chunks of pure metal with little rust.





Case Study: Flow lines Protection Works for Shell Iraq Petroleum Development (SIPD)


Ducorr was contracted to design and deploy a Cathodic Protection System for Shell Iraq Petroleum Development (SIPD) to protect its new and existing buried flowlines in Majnoon Oil Field,Iraq.

The Challenge

The Majnoon Oil field being development by SIPD has several existing and new buried flowlines and production facilities. The new pipelines are coated with a three (3) layer polypropylene (constructed and commissioned in 2013) & old ‘legacy’ pipelines coated with a coal-tar epoxy, FBE and PP and were mostly constructed in 2003.

These flowlines are buried in very corrosive soil and therefore require protection. As the commissioning of a permanent cathodic protection (ICCP) will require more than 6 months, a temporary protection of the new flowlines was needed in order to provide protection during this period of time.

The work was in a challenging environment and a nearby potential minefield increased safety risks.

The duration of the contract was 3 years.



Causes of Stress Corrosion Cracking In Pipelines

Stress corrosion cracking (SCC) is a type of environmentally-assisted cracking (EAC), or the formation of cracks caused by various factors combined with the environment surrounding the pipeline. SCC occurs as a result of a combination between corrosion and tensile stress. Corrosion is related to the susceptibility of the material to the environment, while stresses may be residual, external or operational.

The most obvious identifying characteristic of SCC in pipelines, regardless of pH, is the appearance of patches or colonies of parallel cracks on the external surface of the pipe.

SCC is usually oriented longitudinally, and the dominant stress that causes it is usually internal pressure. Here we'll take a look at some different types of stress corrosion cracking, and how they occur. 

Conditions that Lead to Stress Corrosion Cracking (SCC)

The occurrence of SCC depends on the simultaneous achievement of three conditions.

1. A Potent Cracking Environment
The conditions at the pipe surface are referred to as "the environment." This environment may be isolated from the surrounding soil by the pipe coating, and the conditions at the pipe surface may be different from those in the surrounding soil.

The four factors controlling the formation of the potent environment for the initiation of SCC are the type and condition of the coating, soil, temperature and cathodic current levels.

  • Pipeline Coating Types: SCC often begins on the pipeline surface at areas where coating disbondment or coating damage occurs. The ability of a coating to resist disbonding is a primary performance property of coatings and affects all forms of external pipeline corrosion. Coatings with good adhesion properties are generally resistant to the mechanical action of soils from wet/dry cycles and freeze/thaw cycles. They also are better able to resist the effects of water transmission and cathodic disbondment.

  • Soil: There are several factors relating to soils that influence the formation of an environment that's conducive to SCC. These are soil type, drainage, carbon dioxide (CO2), temperature and electrical conductivity. The amount of moisture in the soil also affects the formation of stress corrosion cracks.

  • Cathodic Protection: The presence of cathodic protection (CP) current is a key factor in the formation of a carbonate/bicarbonate environment at the pipeline surface, where high pH SCC occurs. For near-neutral pH, SCC CP is absent.

  • Temperature: Temperature has a significant effect on the occurrence of high pH SCC, while it has no effect on near-neutral pH SCC.

2. A Material that Is Susceptible to SCC
In addition to a potent environment, a susceptible pipe material is another necessary condition in the development of SCC. A number of pipe characteristics and qualities are considered to determine if they are possibly related to the susceptibility of a pipe to SCC. These factors include the pipe manufacturing process, type of steel, grade of steel, cleanliness of the steel (presence or absence of impurities or inclusions), steel composition, plastic deformation characteristics of the steel (cyclic-softening characteristics), steel temperature and pipe surface condition. (For examples of susceptible materials, see Hydrogen Embrittlement Issues with Zinc and Causes and Prevention of Corrosion on Welded Joints.)

3. A Tensile Stress that's Higher than Threshold Stress
When tensile stress is higher than threshold stress, this can lead to SCC, especially when there is some dynamic or cyclic component to the stress. (For more on this topic, read The Effects of Stress Concentration on Crack Propagation.) Stress is the "load" per unit area within the pipe wall. A buried pipeline is subject to different types of stress from different sources. The pipeline’s contents are under pressure and that is normally the greatest source of stress on the pipe wall. The soil that surrounds the pipe can move and is another source of stress. Pipe manufacturing processes, such as welding, can also create stresses. These are called residual stresses.


Types of Stress Corrosion Cracking

SCC in pipelines is further characterized as "high pH SCC" or "near-neutral pH SCC." Note that the "pH" here refers to the environment on the pipe surface at the crack location, not the pH of the soil itself.

High pH Stress Corrosion Cracking (Classic Type)
High pH SCC occurs on the external surface of pipelines where the electrolyte in contact with the pipe surface has a pH of 8-11 and the concentration of carbonate/bicarbonate is very high. This electrolyte is found at disbonded areas of coatings where the CP current is insufficient to protect the pipeline. This type of SCC may develop as a result of the interaction between hydroxyl ions produced by the cathode reaction and CO2 in the soil generated by the decay of organic matter.

This form of SCC is temperature-sensitive and occurs more frequently at higher temperature locations above 100°F (38°C). This is why there is a greater likelihood of SCC immediately downstream of the compressor stations where the operating temperature might reach 150°F (65°C).

The high-pH form of SCC is intergranular; the cracks propagate between the grains in the metal, and there is usually little evidence of general corrosion associated with the cracking. These cracks are very tight, narrow cracks.

Near-Neutral pH Stress Corrosion Cracking (Non-Classic Type)
A near-neutral pH SCC environment appears to be a dilute groundwater containing dissolved CO2. The source of the CO2 is typically the decay of organic matter and geochemical reactions in the soil. It has been found that low pH SCC occurs in environments with a low concentration of carbonic acid and bicarbonate ions with the presence of other species, including chloride, sulfate and nitrate ions.

Typically, the SCC colonies initiate at locations on the outside surface, where there is already pitting or general corrosion. This damage is sometimes obvious to the unaided eye, while at other times it is very difficult to observe.

The near-neutral-pH form of SCC is transgranular; the cracks propagate through the grains in the metal and are wider (more open) than they would be in the high-pH form of SCC. In other words, the crack sides have experienced metal loss from corrosion. Near-neutral-pH SCC is less temperature-dependent than high-pH SCC.

How Crack Growth Occurs

Stress corrosion cracking in pipelines begins when small cracks develop on the external surface of buried pipelines. These cracks are not visible initially, but as time passes, these individual cracks may grow and forms colonies, and many of them join together to form longer cracks.


The SCC phenomenon has four key stages:

  1. The initiation of stress corrosion cracks

  2. The slow growth of cracks

  3. The coalescence of cracks

  4. Crack propagation and structural failure

This process can take many years depending on the conditions of the steel, the environment and the stresses to which a pipeline is subjected. Consequently, failure as a result of SCC is relatively rare, although failures can be very costly and destructive when they do occur.




Typical Costs for Extra steel Required in Sacrificial Thickness

The pricing in the table below is an approximate price of the additional steel required in sacrificial thickness, and it is based on steel price for structural sections. This is excluding additional costs and is based purely on steel price, while also assuming the minimum sacrificial thickness allowable.


The protection offered by Cathodic Protection (CP), design life of 30 years, usually is significantly less expensive than the sacrificial thickness.

The design for corrosion protection is dependent on exposure area, as with its increase the mass of steel loss increases. By increasing the sacrificial thickness, the total mass of steel increases, whilst not guaranteeing the design life. The increase of exposure area also requires an increase in cost with CP, the reason for this is the fact that the anode mass is dependent on the area. Typically for an element without paint cover it requires an estimated (at current prices) 90 AED/m2, and for an element with paint cover it reduces to 55 AED/m2, in accordance with the DNV standard. Cathodic protection is a proven technology and the likelihood of corrosion with is significantly less.

There is a misconception of the maintenance cost of cathodic protection. Typically, once installed, these systems self regulate and require little or no on-going costs. International standards do not have a scheduled requirement and many times it is the owner’s apprehensiveness about the system that leads to excessive looking after. For example, it is possible to install a CP system on a jetty using sacrificial alloy anodes and not need to inspect for upto 3 years.


The severity of corrosion for a steel member in a marine environment varies depending on the location relative to sea water. Most design codes specify this and advise that the design can be optimised based on these corrosion rates.

 Figure 1: Corrosion Rate Distribution

Figure 1: Corrosion Rate Distribution

 Figure 2: Relative Loss in Metal Thickness

Figure 2: Relative Loss in Metal Thickness

The section just below MLW experiences some of the highest corrosion, and this section is most prone to ALWC attack. This is an area that can be actively protected by a CP system, thus inhibiting and limiting corrosion. Therefore, negating the need of excessive sacrificial thickness for protection and insuring that the structure does not deteriorate before the allotted time.


The primary reasons for corrosion protection safety for structure against failure, to prolong the life span of the element, and to reduce the total project and operation life cost. Unforeseen failure to structural elements is both dangerous and very expensive, as remedial action is far more difficult manage in comparison to providing a protective system from the beginning. A sacrificial thickness is a good methodology to obtain durability with regards to conventional, uniform corrosion. However, in conditions of extreme localized corrosion attacks it can only limit the ingress for a short period of time. For protection against these, one of two methods are recommended. First, is regular monthly inspection of all elements at risk, so that remedial action can be taken in the early stages before the reduction of safety factors. Secondly is the installation of a cathodic protection system, which is also recommended by CIRI C634, which is proven to provide protection against all forms of electro chemical corrosion, this system requires annual monitoring only.



Corrosion due to Accelerated Low Water Corrosion (ALWC)

Accelerated Low Water Corrosion (ALWC) is a relatively new phenomenon, and an extreme form of aggressive corrosion, that majority of the time occurs slightly above Lowest Astronomical Tide (LAT) level, and is reported to have occurred along submerged sections. The occurrence is on unprotected steel in tidal areas. The cause of this is due to bacterial activity, and is therefore a microbial influenced corrosion (MIC). This occurs when sulphate resisting bacteria, an anaerobic bacteria, grow on steel forming a colony, if growth is sustained for long enough it forms a biofilm. This patch of bacteria does not directly consume the steel; however, it promotes and aggressively increases the rate of corrosion as it makes the ideal environment for it.

According to CIRIA C634 this process is random, and a successful method for predicting its occurrence has not been developed. Cases of ALWC have been reported from around the world in all tidal areas, and cause of its occurrence has not been truly understood. Its high variability is baffling as variation occurs in the local geography, where some piles are found with ALWC and some piles within the same vicinity are found to be free of it. The time scale is variable also as it is a multi-stage process and not linear like in table 2, which underestimates ALWC, as the rate of corrosion varies depending on the micro-environment. However, once the biofilm has formed rates of metal wastage is very high, making it possible to see patches within a couple of years. As a rule of thumb localised corrosion rates are 1.5 to 3 times more than the general uniform corrosion rates.


Currently the only reliable method of detecting ALWC is by visual inspection together with residual wall thickness measurements. ALWC occurs as localised patches of damage, identified by a characteristic, poorly-adherent orange corrosion product over a 'soupy' black underlayer associated with rapid metal thinning. 


The strategy for management of ALWC will depend on whether the structure is new built or an existing structure. The corrosion protection measures that are currently applicable to ALWC are those based on conventional corrosion control methods such as cathodic protection (CP) and coatings of various types.