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.

Reference: https://www.nbcmiami.com/news/local/Waverunners-Jet-Skis-to-Blame-in-Miami-Bridge-Corrosion-488207961.html

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.

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.

Reference: https://www.corrosionpedia.com/human-error-as-a-factor-in-corrosion-failure/2/1493

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

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]

Benefits

• 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

Corrosion: Understand It to Fight It

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

CORROSION COSTS

There have been many studies about the cost of corrosion.

NACE International, formerly known as the National Association of Corrosion Engineers (nace.org, 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%.

HOW CORROSION OCCURS

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.

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.

TYPES OF CORROSION

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.

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.

KEEP IN MIND

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. 

THE BEAUTY OF MONOLITHIC INSULATING JOINTS

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.

Ref: http://www.meccanicasegrino.com/the-beauty-of-monolithic-insulating-joints.aspx

CATHODIC PROTECTION REMOTE MONITORING SYSTEM

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).

Challenge

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.

Solution

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.

Architecture

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.

References: http://www.castagra.com, http://www.sciencefocus.com

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

Background

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.

Sources:

https://www.corrosionpedia.com

https://pgjonline.com

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.

Optimisation

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 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.

Conclusion

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. 

Conventional Steel Corrosion and Durability Design

Conventional corrosion is an electrochemical redox reaction, thus when steel is in contact with an electrolyte and oxygen, then steel mass will be lost, this is more pronounce in sea water. Corrosion, compared to time is generally a linear process and is uniformly spread over the exposed area.

Table 1. Recommended value for the loss of thickness (mm) due to corrosion for piles and sheet piles in fresh water or in sea water

On the basis of this table the common method utilised in accounting for corrosion is to utilise a sacrificial thickness by increasing the thickness of the pile by at least 4mm.

However, for construction in the Arabian gulf this method may not be the optimal solution due to the climatic and seawater conditions. The gulf coastline experiences some of the most extreme weather conditions with summer temperature reaching up to mid to high forties, with the salinity of the Gulf generally being highly variable with some sections near the coast reaching a concentration of 10 % (Fookes et al). In general, the salinity of the Gulf, at 4 %, is also higher than the open ocean, at 3 %.

The sacrificial thickness specification for a pile in sea water in zone of high attack is 3.75 mm, which means that a corrosion rate of 0.075 mm/year is adopted. However, according to research presented in CIRIA C634 that is the minimum rate of corrosion reported. The average corrosion rates reported range from 0.08 to 0.2 mm/side/year. For the harsh aggressive environment of the Arabian Gulf compounded with high and variable salinity of sea water, with the high temperatures a higher corrosion rate in design is recommended for optimal durability. The highest corrosion rates range from 0.17 to 0.34 mm/side/year. For a worst-case scenario, the highest corrosion rate will see a loss of 17 mm of steel, and if a sacrificial thickness of 4 mm is utilised, it will only protect the integrity of the member for 12 years.

Table 2. Corrosion Rates found in Literature

Biodiesel Bacteria Boost Corrosion of Underground Storage

Thousands of underground diesel storage tanks may need to be replaced in the coming years because bacteria present in biodiesel are boosting corrosion, the Volkskrant has reported.

The paper bases its claim on a preliminary report by SIKB, which monitors ground pollution in relation to infrastructure. It has been compulsory to add biodiesel – fuel produced using plant or animal fats – to traditional diesel since 2007 and since then there has been an increase in corrosion reported in uncoated steel tanks, the institute says in a new report.

The decision to remove sulphur from diesel, which slowed down bacterial growth, has had an additional impact.

Although the SIKB research focused on underground tanks without protective coatings, there are also strong indications that other sorts of tanks are also affected, the report said.

The transport ministry said in a reaction it would wait for a definitive report before deciding what action to take.
 

Concrete Cancer

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.

The Dubai Water Canal is key infrastructure project that involves the construction of water canal that routes just east of Sheikh Zayed Road to the Jumeirah beach. The canal mainly consists of block wall construction. However, in a minor section of the canal, the construction incorporates a reinforced concrete diaphragm wall. The project specification requires that the reinforcing steel of this diaphragm wall be protected from corrosion using cathodic protection designed and installed by DUCORR.

Contact us to deploy your system now.