Corrosion is a natural mechanism that occurs to all metals
There are 6 main types of corrosion
Corrosion failures cost the world in excess of over $2 trillion dollars
Corrosion can result even in the absence of oxygen
Corrosion protection is best addressed in the design stage
Cathodic protection works to make the corrosion reaction thermodynamically unfavorable
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Cathodic protection is an extremely powerful technology in that it has the power to almost completely stop corrosion on the structure it is deployed on. Most corrosion protection methods are passive in nature – such as paints. Cathodic protection is very much active. It attacks the corrosion problem at its heart.
In our last notes, we discussed how a leaky basement is a recipe for disaster waiting to happen. Why? Because clearly all the elements required for an effective corrosion cell (the basic building bloc of corrosion) to easily form and self replicate are present….in abundance.
But really, how bad can this corrosion get? Is it something that will make my building collapse? Is it something to worry about? Is it something to think about? How will it affect the sustainability of the building?
Lots of questions…
For starters, let us discuss how sustainability and corrosion are interlinked. If your building can be made to last an additional 20 years by stopping corrosion, then the technology that allows you to do this is a sustainable technology. This is the link between corrosion mitigation and sustainability.
What about our leaky basement? What can we expect in terms of how bad the corrosion can get.
The biggest risk posed to any structure from corrosion would be if the corrosion were to initiate in a ‘structurally sensitive’ area and remain accelerated and localized in that area. You can imagine what this would like; a gradual but accelerated reduction of the reinforcing steel diameter in an extremely short span of time. This is the nightmare situation for any building. It happens often. I have seen corrosion of structural columns in basements in under 5 years after completion that have caused massive cracking. It’s quite ugly and frightening. What does this tell us about how bad things can get? It’s very difficult to point to a specific rate of corrosion because corrosion is mix of so many factors – electrical, electrochemical reactions, temperature, moisture, pH and much much more. So in essence, it is difficult to predict – but who is prepared to take the chance? Would you? I wouldn’t! It is something to worry about.
The thing about corrosion is that it grows and gets worse as time passes – much like a tumor would. As a matter fact, in Australia, it is nicknamed ‘concrete cancer’ - and unless you move quickly to snuff it out, its going to destroy the building and cost you an arm an a leg.
Many owners have gone about attending to leaky basements in a strange kinda way. As soon as leak is seen, it is plugged by crack injection. Sometimes the situation is so bad that the top layer of concrete is removed and reinstated – all in the hope of …..wait for it…removing the salt chlorides. Now why would I care so much about the chlorides. Primarily because it is a corrosion initiator and when present in excess of a certain amount, corrosion is guaranteed.
If only we had a technology that would stop corrosion in an inexpensive way irrespective of how much chlorides were present! Well it exists. Cathodic Protection. In our next part on this blog, we will discuss how this technology works for basements.
In the UAE and in the region in general, the geology of our coastal cities in the Middle East require the use of pile or raft slab foundations built from reinforced concrete to be used. These very large underground structures are typically constructed in the water table. Waterproofing attempts typically fail to stop all water ingress, and the basements are often times leaky and inundated with groundwater or significant leaks. Sometimes I have seen entire basements flooded almost to the ceiling of the basement.
The question we should be asking ourselves is, once the leaks are plugged and the water pumped out, do we still have a problem or are we in the clear?
Do we still have a problem or are we in the clear?
To be sure this is not a one liner. Let’s consider the situation. The floor is made from reinforced concrete. It is now fully laden with chlorides, even after removing all the offending water...
We certainly can’t see the chlorides, but they are there – unless you have somehow managed to miraculously to suction out the chlorides from within the concrete matrix.
With the chlorides present in party like quantities, you now have the main recipe for corrosion;
Water (moisture in the concrete)
Unfortunately for corrosion engineers, and fortunately for owners, the initiation of corrosion is not something that you can see. If the waterproofing fails…poof….and there is a leak
If corrosion begins….there is only silence. You won’t hear anything, you won’t see anything, at least not until it is too late.
So while the owner goes about renting out his building and counting his rental income, the corrosion reaction also goes about eating away at his steel foundation.
What are the owner’s options?
There are a plethora of remedies available. All claim to stop this phenomenon in some way or form. But to be honest there is only one method, which will in effect freeze the corrosion in its tracks. Cathodic Protection. In the next part of this blog, we discuss in more detail the corrosion problem, cathodic protection and sustainability.
Many swimming pools were built as part of leisure facilities or schools. These typically comprised of a cast in situ reinforced concrete base and walls with cast in situ promenade decks around the pool. These structures are now often in severe distress due to corrosion of the reinforcement in the walls and promenade decks.
All swimming pools experience galvanic corrosion if they use chlorine sanitizer. Chlorine is salt based, so by adding chlorine to a pool you are actually adding salt. A saltwater pool, however, has approximately ten times the salt level of a traditional chlorine pool. If a saltwater pool has ten times as much salt as a traditional chlorine pool, it means that the rate of galvanic corrosion also increases ten times.
Corrosion prevention, often referred to as "cathodic corrosion prevention," is a massive field that touches an incredibly broad spectrum of industries, including maritime shipping, manufacturing, petrochemical, water distribution, food processing, major construction and even dairy farming.
The use of cathodic protection to stop this degradation of the reinforcement has been developed to be the standard repair method. The use of anodes in the pool water has become the most popular system of cathodic protection of swimming pools. The anodes are installed in boxes, recessed into the pool side walls of the swimming pool. The economic benefits of this form of repair are so impressive that it is now being used worldwide.
In this installation, the swimming pool walls and base are protected using anodes in the pool water. The support columns and other concrete parts which also suffer from reinforcement corrosion are protected by internal anodes placed in holes drilled in the concrete. The cathodic protection system is computer-controlled. This gives an accurate continuous control of the output current to each part of the structure based on real-time readings from reference electrodes. This gives a better and more even protection from corrosion, increases the life of the anodes and switches off the anodes in the water when bathers are in the pool. The computer control system has a modem and a telephone connection allowing remote monitoring and control of the system.
Every swimming pool, and especially every saltwater pool, should have a sacrificial anode installed. The addition of this simple and low-cost device will dramatically reduce the damage a pool experiences as a result of galvanic corrosion. While you may still experience localized anodization and oxidation of metals in a pool, especially in situations where two different metals are in direct contact, a sacrificial anode is the bare minimum level of protection that every pool needs. It is absolutely silly to not have one of these — plus they can easily be adapted to any existing system.
Products that are transported for a longer period of time or stored for an extended period are often in need of corrosion protection. Corrosion protection packaging prevents corrosion without having to treat the metal with oil, grease or paint.
Corrosion is a significant problem in the handling, storage and shipping of products. Bare metal parts corrode easily. Temperature changes, contaminated air, sea salt and moisture, all create corrosion.
Due to temporary corrosion, time is diverted to handling complaints and customer loyalty is potentially lost. Delayed deliveries due to reworking of corroded components translate to avoidable losses. Therefore, planning for corrosion protection during temporary storage and transportation is a logical strategy to minimize these losses.
There are several different solutions for protecting the product from corrosion depending on parameters such as: product type, means of transportation, and the length of the transit time.
The Importance of Temporary Corrosion Protection
There are many industrial applications where temporary corrosion protection during transit and storage is critical for the final processing and end use of parts and components. If semi-finished or machined components are left unprotected, or roller bearings are not coated with a rust inhibitor during storage, or internal combustion engines are transported and stored without corrosion prevention, then they may deteriorate or become damaged due to corrosion. Any subsequent rust removal will not restore a component to its original quality and geometrical accuracy.
Permanent corrosion protection cannot be used for temporary applications because it must be removed before further processing or assembly. Because corrosion can appear within hours or days a temporary corrosion prevention method must be implemented.
During transportation and storage, fasteners (e.g., wedges, springs, bolts, nuts, washers, screws) and associated tools require protection from corrosive chemical reactions on their surfaces.
General Care for Preventing Corrosive Deterioration
Desiccants to control air humidity are used to prevent corrosive deterioration during storage and transport. Silica gels and molecular sieves are occasionally used as desiccants to absorb excess air moisture. Sealed films of high pressure polyethylene and special waterproof and airproof packaging systems are used for critical applications.
Cost, Safety and Health
Allowing temporary corrosion and rust on materials during interstage processes and transportation is costly due to the direct and indirect costs involved in rework and warranty damages. When carefully chosen, preventive solutions are cost effective for both application and subsequent removal.
For confined spaces, authorized specialists must be consulted. Ensure compliance with personal protective equipment (PPE) and firefighting regulations.
The combustion products of coatings can be highly toxic. Hence exposure control must be planned for in advance. Precautions should be taken to avoid eye contact and skin exposure with proper PPE suitable for the application method used. Respiratory protection might be needed in a few cases.
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.
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
Lack of teamwork
Stress and fatigue
Lack of resources
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.
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.
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