Two Technologies That Address the $138 Billion Corrosion Problem
Electro Plasma Technology & Self Healing Coatings Come To Market.
August 15, 2011
If you think for a moment about the number of structures you see each day that use steel as a key component – buildings, bridges, roads, vehicles, oil rigs – you quickly realize the impact that corrosion (or rust) has on the economy.
Ironically, the primary methods used to prevent corrosion in most applications have been around for more than 100 years. They are capital intensive, energy demanding, environmentally unfriendly and, in many cases, unable to provide the corrosion protection needed. While there have been innovations to improve performance, many of the newer techniques have proven too expensive or inefficient for wide scale deployment.
This article reviews two new technologies: Electrolytic Plasma Technology (EPT) and a Microencapsulation based Self Healing Coating Technology, which have shown potential to overcome the deficiencies of conventional methods. They seek to provide improved corrosion protection while meeting the cost, efficiency, and surface finishing requirements of industry.
Costs of Corrosion
To understand the magnitude of the detrimental effects of corrosion, consider a study conducted by the U.S. Federal Highway Administration (FHWA) and National Association of Corrosion Engineers (NACE). According to the study, more than $138 billion (see chart ) is spent annually to prevent corrosion, with the extrapolated direct corrosion costs to the US Economy estimated at 3.1% of the US GDP. On a per project basis, the direct life-cycle cost of maintenance due to corrosion for any one project is 2-5 times the initial cost, while indirect costs are estimated at 5-11 times the direct cost of repair.
In order to help prevent corrosion, steel is cleaned and then coated. However, these techniques have not been able to effectively resolve the corrosion problem as they are inefficient, costly, have restricted surface morphing ability, cause material loss and have negative environmental consequences.
Hot working processes where materials are deformed above their recrystallization temperatures and other processes that occur at high temperatures result in a discoloring oxide layer or scale on the surface. Cleaning techniques are used to remove this layer from the surface of steel and remove other impurities, such as stains, inorganic contaminants, rust or scale. A clean surface is critical to follow-on metal processing operations, especially in providing a base for an effective application of corrosion resistant coatings. Acid Pickling is the most common method used for cleaning metal surfaces. However, the method has serious limitations. It results in material loss, hydrogen embrittlement, and has negative by-products. Pickling sludge is the waste product from pickling, and includes acidic rinse waters, metallic salts and waste acid. Spent pickle liquor is considered a hazardous waste. Several countries are implementing new regulations or restrictions on the process.
For further information on the conventional cleaning methods please read more here.
Zinc and other metals like nickel, lead, copper, cadmium, tin, chromium, and aluminum are used as coating agents in industrial environments. Zinc has a self-healing mechanism and has the property of sacrificing itself slowly by galvanic action to protect the base steel. This sacrificial action continues as long as any zinc remains in the immediate area. Due to this property Zinc is able to protect steel against corrosion, and consequently protect buildings, automobiles, ships and steel structures from corrosion by the atmosphere, water, and soil.
Galvanization denotes the application of a zinc coating to the surface of a metal by any method. Hot Dip Galvanization (HDG), Electrodeposition, and spraying are a few methods used to galvanize a metal. Hot Dip Galvanization has been the mainstay of the steel coating industry for over 250 years. However, it has some inherent issues. For example, it can lead to hydrogen embrittlement in high-strength steel. This occurs during the pickling and fluxing steps of the galvanizing process. The process also leads to material loss during the galvanization stage. Electrodeposition/Electroplating is also a widely used process, however, it can be difficult to obtain a uniform thickness of coating and the process is relatively slow and expensive.
For further information on the conventional coating methods please read more here.
Technology Solution 1: Electro Plasma Technology
Electro-Plasma Technology (EPT) is a novel, surface engineering technique that has shown promise in its application on commercial scale for cleaning and coating of metal surfaces. The electro plasma process is a hybrid of the conventional techniques of electrolysis and atmospheric plasma process. This process has been in the field of research since the 1920s with the first significant work having being done in 1950 by Kellogg . Successful commercial utilization, however, has only become possible in the past few years.
A VentureLab company, CAP Technologies LLC, utilizes the principles of Electro-Plasma Technology (EPT) in a patented process for cleaning, coating and surface modification of metal surfaces. The EPT process used by CAP is able to process metals continuously in normal atmospheric conditions, which was not possible with earlier versions of plasma processing.
CAP’s EPT processing is a dynamic process that involves delivery of aqueous electrolyte into a confined chamber (EPT reactors) on the surface of the work-piece. The technique involves application of a D.C. potential between two electrodes in an aqueous media, producing discreet bubbles in which plasma is formed near the surface of the work piece. The plasma forms evenly across the surface. When the plasma bubble implodes, it produces shock waves that assist in removing surface contaminants and micro-modify the metal surface, removing oxide scale, lubricants, dirt, etc. As oxide mill scale is removed, the resulting surface is passivated due to reconstituting of a portion of the scale into alpha iron. This passivated layer is a hard non-reactive surface film that inhibits further corrosion and also increases shelf life prior to metal processing.
A principal advantage offered by the technique is that it can be used in sequence (in series) to both continuously clean and coat a substrate whereas other cleaning/coating processes do one or the other. This provides a significant efficiency improvement and reduces time and cost between operations. EPT has the ability to deposit metal and alloy coatings, such as Zn, Ni, Zn-Ni, Ni-Cu, Zn-Ni-Mo. Other key advantages include:
- Single Step Processing: Many metal applications like hot dip galvanizing use multiple-step cleaning. EPT cleans different type of surface impurities in a single step.
- Environmentally friendly: EPT does not use hazardous chemicals. A fine textured scale powder (iron oxide) is the primary byproduct, which can be captured with a simple filtration system.
- Reduced Material Loss: The technique uses benign electrolytes and preserves base material, as opposed to acid pickling which uses strong mineral acids and causes the metal to lose up to 3% of the base material. Traditional coating methods like HDG and electroplating also lead to material loss which is avoided by the EPT process. According to CAP’s estimates, 30-40% of the scale is reconstituted to alpha-iron and deposited back to the surface.
- Desired surface morphology: EPT created morphology provides uniform micro-roughness to the treated surface. The morphology produced by EPT is favorable for adhesion of lubricants and coatings as it provides much better mechanical interlocking sites as compared to the grit blasted surface. The technique provides capability to control surface profile easily by varying processing parameters and the aqueous electrolytic media.
- High deposition rates: Zn coated wire rod/wire using the EPT technique can be drawn 3 times faster than Hot Dip Galvanized Zn coating with no damage to the coating or dies
- Interfacial bonding: EPT coatings exhibit excellent adhesion with the substrate.
- Nanocrystalline grain structure: Grains formed by EPT process offer potential to improve the properties of the coating as compared to the respective large grained coating.
- Unlike hot-dip galvanizing which must be applied to the finished product, galvanized metal from the EPT process can be drawn into wire without damage to the coating as it does not create an intermetallic zone between the coating metal and the substrate.
- No Hydrogen Embrittlement – EPT process used by CAP does not lead to hydrogen embrittlement which is an issue with Hot Dip Galvanizing.
- Higher Corrosion Resistance: In salt bath cycling tests, (GM-9540P) which examines the effectiveness of coatings against corrosion, EPT processed materials have demonstrated corrosion resistance up to 5 times longer than comparable thickness hot dip galvanized coatings.
- Significantly reduced footprint and capex requirements: EPT does not require air scrubbing, wastewater capture, and acid regeneration equipment that amounts to significant capital and maintenance cost. The EPT processing equipment has a footprint approximately 5 to 8 times smaller than acid pickling baths or coating systems.
Technology Solution 2: Self Healing Coatings – Microencapsulation
Companies have been addressing the challenge of corrosion by recoating and/or by using coatings containing anti-corrosive additives. However, even with optimal use of the best available corrosion management practices available today, the FHWA report estimates that annual corrosion costs would be reduced by only 25-30%. A major reason for this is that existing corrosion prevention solutions do not provide an immediate repair to a damaged area. The underlying material becomes and remains exposed to the environment, the damage accelerates, and the corrosion propagates resulting in significant repair or replacement cost.
AMI, Inc., a VentureLab company, provides a solution to this problem. AMI develops microencapsulated self-healing agents that deliver an automatic healing response precisely when needed: immediately at the time of damage and without the need for human intervention. This automatically reestablishes the coating’s core protective mechanism: the protective physical barrier, before corrosion damage can occur or progress.
AMI’s technology involves the microencapsulation of proprietary healing agents that are added to high-performance coatings, which can then be applied to a wide range of metallic substrates. When damage occurs in a coating protected by AMI’s self-healing technology, the microcapsules are ruptured and healing agents are released. These healing agents flow to the site of damage and then polymerize. This heals the damage and restores the protective barrier the coating was intended to provide. The microcapsules are robust enough to survive the manufacturing and application process. Following are several advantages of the technology.
- Improved Coating Performance and Lifetime: Microencapsulation with these agents improves coating performance and extends coating lifetimes, which can significantly reduce costs associated with recoating, resurfacing or replacing the underlying material.
- Versatility: Compatible with a wide range of solvent and water based coating chemistries (polyurethane, silicone, epoxy, acrylic and alkyd liquid, and powder coatings). The size of the microcapsules as well as the thickness of their shell walls can be customized for various coating thicknesses and end uses. Capsules are designed to be easily incorporated into coatings during formulation and can be customized to specific end-user functions (for example, the inclusion of anticorrosive pigments).
- Cost Savings: The self-healing agents can be added directly to coatings during formulation. This means no additional customer equipment/capital cost is required. This also leads to reduced materials/replacement costs and labor costs as the frequency of recoating is reduced.
- Reduced Environmental Impact: As fewer coatings are produced and consumed there are reduced volatile organic emissions, reduced energy usage and carbon footprint, and lower toxic chemical waste production.
Looking at the Future
EPT offers a solution to the inefficiencies, costs, material losses and environmental considerations associated with the legacy cleaning and coating techniques.
Self Healing Coatings increase the longevity of the coatings and reduce the need for recoating, or replacing the underlying surface.
The steel industry is facing increasing price and margin pressures along with weak operating and utilization rates. To improve margins and lower production costs, industry participants are looking for more effective, longer lasting and, higher ROI corrosion protection systems. The Electro Plasma Technology and the Self Healing Microencapsulation Technology offer novel solutions to corrosion costs being faced by the industry today.
2. H.H. Kellogg, J. Electrochem. Soc. 97 (1950) 133
3. P. Gupta, G. Tenhundfeld, E.O. Daigle, D. Ryabkov – Electrolytic Plasma Technology: Science & Engineering – An Overview, Surface And Coatings Technology (2006)