Understanding Cathodic Corrosion Protection for Underground Tanks - Part 1

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

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

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

Why Do Underground Tanks Need Cathodic Protection?

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

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

• To extend the operational life of the UG tank.

Preventing Corrosion

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

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

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

3 Corrosion Disasters of the Far East

Bhopal Accident - India

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

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

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

Sinopec Gas Pipeline Explosion - China

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

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

Fukushima Nuclear Plant Tank Leak - Japan

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

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

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

Interesting Facts About Corrosion

• Corrosion is a natural mechanism that occurs to all metals

• There are 6 main types of corrosion

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

• Corrosion can result even in the absence of oxygen

• Corrosion protection is best addressed in the design stage

• Cathodic protection works to make the corrosion reaction thermodynamically unfavorable 

Towers, Corrosion & Sustainability - Part 3

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

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

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

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

Lots of questions…

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

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

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

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

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

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

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

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

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

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

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

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

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

• Salt

• Water (moisture in the concrete)

• Oxygen

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

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

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

What are the owner’s options?

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

Beyond The Pool: Corrosion Problems Involved in Swimming Pools

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

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

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

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

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

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

Importance of Corrosion Protection During Storage and Transportation

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

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

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

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

The Importance of Temporary Corrosion Protection

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

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

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

General Care for Preventing Corrosive Deterioration

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

Cost, Safety and Health

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

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

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

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.

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

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

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