No excuse for cutting corners on corrosion downstream

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June 26, 2018
By Phil Yule, Regional Business Manager, Cosasco

Corrosion is a major challenge and essential risk to contain for any oil and gas operator. Loss of containment can mean loss of process, loss of revenue, expensive repairs and – most importantly – a potentially major safety hazard. But while a breach in a cross-country pipeline can be a major incident and environmental risk, it’s another matter downstream. Different plant and processes are tightly packed together, with all manner of hydrocarbons and other combustible fluids boiling, cooling or flowing. Workers dart in-between, never more than a few dozen feet from a potential corrosion risk. In this environment, loss of containment could be catastrophic. It doesn’t take more than a quick google search to find a multitude of incidents related to corrosion control issues.

All of which is to say that, when it comes to the downstream, the stakes are higher, and corrosion control is too important to ignore. However, in conjunction with increased risk comes increased complexity: the number of different processes and the variety of different mediums and hydrocarbons entails a diverse, heterogeneous environment for monitoring. One monitoring system does not fit all, so it can be difficult for operators to avoid a pick ‘n’ mix of systems with patchwork, incomplete coverage.

So how to manage the risk? Most, if not all, refineries and petrochemical plants employ talented and knowledgeable corrosion engineers with the expertise to do so. But to do the best job, they need the best data. That in turn requires a fully integrated monitoring system – something that has historically been in short supply.

An aggressive environment

The difficulty involved in downstream corrosion monitoring can’t be underestimated. And it’s growing.

The refining industry has many elements that can contribute to increased corrosion rates. Corrosive substances can be found in the feedstock – amines, sulphuric acid as an example and often further elements can be added and produced during the refining process itself, such as oxygen, nitrogen, trace metals, salts, carbon dioxide, and naphthenic acids. Refinery processes themselves involve extreme temperatures and velocities in many of the processes including distillation, catalytic crackers, and alkylation that all contribute to elevated corrosion rates.

Not only that, but downstream operators are dealing with more than hydrocarbons. There are a variety of fluids used in different processes, many of which can be extremely corrosive themselves. Getting corrosion right, in this instance, can be the difference between profitability and throwing money away on unscheduled repairs and maintenance.

To add to this the ripple effects of the recent downturn are still being felt across the oil and gas sector. With ageing assets, extended operating windows and high demands on production rates, one technique firms adopted in order to adapt was crude blending, mixing different qualities of conventional and TAN crudes to a level that they hadn’t before. This practice makes financial sense, TAN crudes can be a third of the cost to operators compared to conventional crudes but also make corrosion less predictable and increases risk due to their higher acid content. Prices have recovered, but not to anything like previous highs, and crude blending is still common practice. If refineries are to continue to blend crudes and remain profitable they must ensure that a robust, accurate integrated corrosion monitoring system is in place.

Keeping tabs

In this environment, corrosion is unavoidable. The key is to keep tabs and effectively monitor the issue. And accuracy is key. Underestimate corrosion, and the risk of failure rears its head, along with all the safety and business risks that come with it. However, if an operator errs too much on the side of caution, they risk unnecessary maintenance downtime, premature replacement of equipment or an overzealous corrosion inhibitor programme – all potentially expensive and avoidable mistakes.

But accurate monitoring – across a diverse downstream facility – is easier said than done. Different pipework and different processes require a different approach to corrosion.

For example, one of the most tried and tested methods for corrosion monitoring is the use of a corrosion coupon. This is a small sample of metal, inserted into the flow at selected locations, which is then subject to the same corrosive factors as the pipework. At regular intervals – perhaps as often as every few months – corrosion coupons are removed and engineers measure how much of the metal has been corroded, taking that as a representation for pipeline corrosion. A corrosion coupon can also give valuable data on the type of corrosion and potential localised pitting corrosion issues. This is appropriate in many instances, but not all.

Another commonly used monitoring method is to insert electrical resistance probes inline into the pipework. These are capable of real-time monitoring and can detect changes in corrosivity within hours, making them ideal for highly changeable applications. High resolution ER probes allow operators to directly monitor levels of corrosion in their system and react quickly to process changes in a system, rather than using a coupon as a proxy. This approach is extremely effective and the only viable method to accurately monitor and control corrosion inhibitor injection programs, as it allows operators to adjust volumes injected based on live, granular data. A huge cost saving potential.

However, as with coupons, there are certain process within the downstream industry where intrusive monitoring cannot be used due to extreme process conditions. It isn’t appropriate for all applications.

That’s why, in many cases, corrosion engineers have turned to external ultrasound thickness (UT) monitoring systems that affix directly to the outside of the pipe and require neither downtime nor intrusion to install. However, by itself the approach is no silver bullet. The trade-off for these advantages is that operators have to settle for a lower level of sensitivity, resolution and accuracy. Modern ultrasonic technology has made great progress on this front, but still doesn’t match ER probes for accuracy and response times.

So, there’s no one-size-fits-all perfect solution for corrosion engineers working downstream. Likely they will have a patchwork of different systems, selecting the best option process by process, pipe by pipe. This gives the best possible corrosion monitoring performance at the individual application level, but carries its own risks at the facility-wide scale.

The holy grail for the corrosion engineering team is an overall view of corrosion risk across the facility. Understanding which equipment is suffering from near problematic corrosion levels, and which other processes are in close proximity, helps give a more accurate gauge of overall risk to the operator and personnel. Similarly, understanding if one process is due downtime for corrective maintenance helps operators plan more effectively. For example, if one process has knock-on effects on another, it may best to schedule maintenance for both at the same time even if one isn’t quite at its corrosion limits, rather than have to shut down a second time a couple of months down the line.

The only way for corrosion engineers and operators to effectively monitor plant wide is through assimilating those disparate systems into one broader integrated system, incorporating corrosion coupon, ER probe and UT devices together feeding the data back into a central platform to give a holistic, facility-wide view of risk. Corrosion engineers are then empowered to make the most informed decisions, guarding safety while maximising asset profitability. In the past, this might have been a pipe dream. However, companies like Cosasco now have decades of accumulated experience with these individual technologies and have invested in platforms to bring them together in a fully integrated way.

So, for corrosion engineers at refineries and petrochemical plants, there’s really no excuse not to implement an integrated, multi-pronged corrosion monitoring strategy. No excuse because the risks to safety and revenue are too high to ignore, and no excuse because the technological limitations that may have once hampered such a programme are no longer insurmountable. A modern system utilises intrusive electrical resistance probes and state of the art, high accuracy non-intrusive ultrasonic ones. Feeding that data back into a central view of risk, is the logical next step in keeping the downstream sector safe and profitable.

 

Construction Concerns: Galvanic Corrosion

Fire Engineering

Article and photos by Greg Havel

“Galvanic corrosion” is damage caused when two dissimilar metals are joined in the presence of an electrolyte. The electrolyte can be one of many liquids, including plain water, acids, sea water, or salt water. When the two metals are joined in the presence of the electrolyte, one becomes the anode and corrodes faster than it would by itself. The other metal becomes the cathode and corrodes more slowly than it would by itself.

This action, the basis for wet-cell and gel-cell batteries, was first demonstrated by Alessandro Volta in 1800.

This action is also the basis for the sacrificial corrosion of one metal to protect another by use of sacrificial anodes or cathodic protection. This sacrificial corrosion is used in the protection of underground steel tanks and steel pipelines, boilers, and water-heating appliances, using magnesium or aluminum sacrificial anodes. This action was first demonstrated by Sir Humphry Davy and Michael Faraday a few years later.

A small electrical current flows between two dissimilar metals in contact in a conductive or corrosive environment. This current flow results in the increased corrosion of the least corrosion-resistant (most active) metal and in the decreased corrosion of the more corrosion-resistant (most inactive) metal. The least corrosion-resistant metal is gradually destroyed by this process, causing weakness and eventually failure of the metal.

The Galvanic Table

The Galvanic Table lists metals in order from the most active (Anodic, or most easily corroded) to the least active (Cathodic, or least easily corroded, or “noble”). This excerpt from one of these tables, based on sea water as the electrolyte, lists some of these metals:

Note: Monel is a nickel-copper alloy that also contains small amounts of iron, manganese, carbon, and silicon; with high tensile strength and resistance to corrosion.

The rate of corrosion is related to the distance between the metals in the Galvanic Table. Metals farther apart in the table will corrode more rapidly than metals that are adjacent to each other. Due to their relative positions on the galvanic table, aluminum is more easily corroded than steel when they are in contact with each other. The rate of corrosion of the aluminum will be increased in the presence of a corrosive electrolyte like road salt, whereas the corrosion of the steel will be reduced or stopped.

Galvanic corrosion does not always occur while the metals are submerged in a conductive or corrosive liquid. It can also take place in the atmosphere, where the rate of corrosion is dependent on the amount of moisture and oxygen present, the conductivity of the connection between the metals, and the temperature. This can explain why corrosion continues from exposure to salt of an aluminum-body fire apparatus even during a dry summer. If some salt remains in contact with both the steel and aluminum, and if the steel and aluminum are in contact with each other, the corrosion continues.

The corrosion rate of dissimilar metals also depends on the amount of each metal present at the connection. Aluminum rivets or screws will corrode quickly when used to join steel panels to steel frames, causing rapid failure of the connectors. Aluminum panels will corrode quickly when connected to steel frames with steel screws or rivets, causing rapid failure of the panels at the connections.

Manufacturers and materials engineers consider these points when joining dissimilar metals:

  • Avoid placing a small amount of an active metal in contact with a large amount of an inactive metal.
  • When connecting two pieces of the same metal, use fasteners of the same metal.
  • When the metals being connected are structural or load-bearing, use fasteners of the proper grade and strength, with the proper coatings to reduce the potential for corrosion.
  • When fasteners are not available of the same material as the metals being fastened, use fasteners of a material as close as possible to the material being fastened in the galvanic corrosion chart.

These points apply to buildings and structures as they do to vehicles and fire apparatus. If galvanic corrosion is not prevented during the construction of a building, its structural components or fasteners may fail early in the building’s life. One common challenge in building high-rises is the connection of an aluminum-framed glass curtain wall to structural steel framing.

When dissimilar metals must be in contact, a non-porous insulator must be used between them. Examples of this include the hard plastic strips that are often installed between steel truck frames and aluminum truck bodies; and like the non-compressible plastic tapes that are installed between steel or stainless steel door hardware and aluminum compartment doors. All surfaces of both metals must be primed and painted. This is especially important for the more active metal, like the aluminum body of a fire apparatus with a steel frame.

Galvanic corrosion can also explain some of the electrical problems that occur during the 20 to 30-year life of a fire apparatus, especially when the apparatus’ aluminum body is joined to a steel chassis. In the past, the aluminum apparatus body was electrically bonded (grounded) by copper wires to the steel chassis to complete the circuit for lights, warning lights, sirens, and other equipment. Steel is more active in corrosion than copper; and aluminum is more active than steel. The corrosion at both ends of the copper ground wires loosened connections and increased resistance to current flow. The corrosion products are also less conductive than the metals on which they are based. Either of these related conditions resulted in electrical malfunctions.

Modern vehicles and fire apparatus are equipped with two-wire circuits for each light, siren, or other accessory; and no longer depend on chassis and frame bonding to complete electric circuits. However, there are still many older fire apparatus that depend on this older bonding method for the operation of lights and accessories.

Galvanic corrosion follows the laws of physics and chemistry. We cannot assume that we or our project are so special that these natural laws will be suspended. If we do so, we, or our fire apparatus, or our building under construction, will develop problems that will be difficult to remedy. Problems caused by galvanic corrosion probably will not show themselves until after the project is complete and the warranties have expired.

For a more complete discussion of this topic, search the Internet for “galvanic corrosion” and “galvanic table.”

Download this article as a PDF HERE

 (212 KB).Greg HavelGregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 35-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 35 years of experience in facilities management and building construction; and has presented classes at FDIC International and other venues.

 

 

Construction Concerns: Galvanic Corrosion

http://www.fireengineering.com/content/dam/fe/online-articles/documents/2018/2018-06-cc-havel-galvanic-corrosion.pdf

Corrosion-Resistant Aluminum Oxide Film Is Self-Healing

Aluminum oxide.

Researchers at Massachusetts Institute of Technology (MIT) (Cambridge, Massachusetts, USA) have found that a solid oxide protective coating for metals, when applied in sufficiently thin layers, can deform as if it were a liquid, and fill any cracks and gaps as they form.

The thin coating layer is expected to be especially useful for preventing the permeation of tiny molecules, such as hydrogen gas or radioactive tritium (a heavy form of hydrogen that forms inside the cores of nuclear power plants), that can pass through most materials.

Most metals, with the notable exception of gold, tend to oxidize when exposed to air and water. This reaction, which produces rust on iron, tarnish on silver, and verdigris on copper or brass, can weaken the metal over time and lead to cracks or structural failure. There are three known elements, however, that produce an oxide that can actually serve as a protective barrier and prevent further oxidation: aluminum oxide (Al2O3), chromium oxide (Cr2O3), and silicon dioxide (SiO2).

“We were trying to understand why aluminum oxide and silicon dioxide are special oxides that give excellent corrosion resistance,” says Ju Li, a professor of nuclear engineering and science at MIT and senior author of a paper describing the new finding.

The team, led by MIT graduate student Yang Yang, used highly specialized instruments to observe in detail the surface of metals coated with these special oxides to see what happens when they are exposed to an oxygen environment and placed under stress. While most transmission electron microscopes (TEMs) require samples to be studied in a high vacuum, the team used a modified version called an environmental TEM (E-TEM), which allowed the samples to be studied in the presence of gases or liquids of interest. The device was used to study the process that can lead to stress corrosion cracking.

Metals under stress from pressure inside a nuclear reactor vessel and exposed to an environment of superheated steam can corrode quickly if not protected. Even with a solid protective layer, cracks can form that allow oxygen to reach the bare metal surface, where it can then penetrate interfaces between the metal grains that make up a bulk metal material, and cause further corrosion that infiltrates even deeper and leads to structural failure. “We want an oxide that is liquid-like and crack-resistant,” Yang says.

It turns out that aluminum oxide can have liquid-like flowing behavior, even at room temperature, if the coating layer is thin enough—about 2- to 3-nm thick.

People typically think that the metal oxide would be brittle and subject to cracking, Yang says, explaining that no one had demonstrated otherwise because it is so difficult to observe the material’s behavior under realistic conditions. That’s when the specialized E-TEM setup at Brookhaven National Laboratory (Upton, New York, USA), one of about 10 such devices available in the world, came into play. “No one had ever observed how it deforms at room temperature,” he adds.

“For the first time, we’ve observed this at nearly atomic resolution,” notes Li. This approach demonstrated that an Al2Olayer, normally so brittle it would shatter under stress, is almost as deformable when made exceedingly thin as a comparably thin layer of aluminum metal (much thinner than aluminum foil). When a bulk piece of aluminum is coated with Al2O3, the liquid-like flow keeps the aluminum covered with its protective layer, Li reports.

The researchers demonstrated inside the E-TEM that the aluminum with its Al2O3 coating could be stretched to more than double its length without causing any cracks to form, Li says. The oxide forms a very uniform conformal layer that protects the surface, with no grain boundaries or cracks, even under the strain of stretching, he says. Technically, the material is a type of glass, but it moves like a liquid and fully coats the surface as long as it is thin enough.

The self-healing coating could have many potential applications, Li says, noting the advantage of its smooth, continuous surface without cracks or grain boundaries.

Source: Massachusetts Institute of Technology, news.mit.edu.

Corrosion Basics: Protecting Fixed Structures in Seawater

Structures such as offshore drilling platforms supported by steel piles may be protected with either sacrificial galvanic anode systems or impressed current systems.

Structures such as steel bulkheads, steel piles supporting piers or wharfs, offshore drilling platforms, and other similar structures may be protected with either sacrificial galvanic anode systems or impressed current systems.

Galvanic anode systems in seawater, for the most part, use much heavier anodes than those used in soil. This is because it is possible to obtain high current from them in a low-resistivity seawater environment and because the corrodible mass is needed to provide reasonably long life.

For structures that can be polarized, a low-potential galvanic anode material such as zinc or aluminum is generally preferable to a high-potential material such as magnesium. Magnesium will work perfectly well, but may discharge more current than needed.

Zinc or suitable aluminum alloy anodes can polarize a steel structure in seawater to within a few millivolts of the potential of the anode itself. Assume that potential is 50 mV, although it can be less. This means that the anode current will stabilize at a value sufficient to maintain polarization.

If magnesium anodes are used, however, the structure does not tend to polarize beyond ~–1.1 V vs. a silver/silver chloride (Ag/AgCl) electrode (SCE) because the hydrogen overvoltage potential is reached and this results in the evolution of free hydrogen. This means that with a magnesium working voltage of ~ –1.4 V vs. SCE, there will be a driving voltage of ~0.3 V. Thus, on a comparable basis, the magnesium will discharge about five times as much current as is actually required to achieve the required polarization.

Because less powerful anodes can provide an efficient CP system, the surplus current from a more powerful anode is, in effect, wasted. However, there is one advantage. The more cathodic voltage provided by magnesium anodes tends to force the deposition, in seawater, of a thicker protective calcareous coating on the structure surface than would be obtained with less powerful anodes.

Special chemical backfills are not needed in the uniform seawater environment because galvanic anodes work satisfactorily without them.

Impressed current systems for fixed seawater structures may use suitable anode materials, without backfill, suspended in the seawater from the structure being protected or placed on the ocean floor. In the past, various materials such as treated graphite, high-silicon cast iron, platinized titanium, or lead/silver have been used as anodes. However, the introduction of highly efficient, dimensionally stable anodes (DSAs), which are basically mixed metal oxide coatings on titanium, has rendered these other anodes almost obsolete.

Particular attention must be given to the design of the rectifier placement, header cable distribution system, and anode suspension or placement details. Above-water components are subject to severe marine atmospheric attack, whereas other portions must be protected from or designed to withstand the mechanical forces exerted by moving seawater as well as by water-carried debris or shipping traffic.

This article is adapted from Corrosion Basics—An Introduction, Second Edition, Pierre R. Roberge, ed. (Houston, TX: NACE International, 2006), pp. 514-516.

Double graphene sandwich provides protection against corrosion

http://www.chemeurope.com/en/news/pdf/1155556/1155556.pdf

Using Sacrificial Anodes in Reinforced Concrete Structures

Reinforced concrete structures, such as bridges, can be exposed to aggressive chloride environments and often show evidence of corrosion after short service periods.

According to Oladis Troconis de Rincón, FNACE, with Universidad del Zulia (Maracaibo, Zulia, Venezuela); Alberto A. Sagüés, FNACE, with University of South Florida (Tampa, Florida, USA); Andrés Torres-Acosta, with Instituto Mexicano del Transporte (Sanfandila, Querétaro, Mexico); and Miguel Martinez-Madrid, with Instituto Mexicano del Transporte, authors of an article on galvanic anodes for reinforced concrete structures published in CORROSION,2 many existing structures currently have a considerable amount of corrosion in progress. Since the mid-1970s, research efforts have addressed various techniques to prevent corrosion from chloride exposure. The consensus is that the only substantiated method to arrest chloride-related corrosion of metals embedded in concrete is cathodic protection (CP). According to the U.S. Department of Transportation’s Federal Highway Administration (Washington, DC), CP is the only rehabilitation technique that has been proven to stop corrosion in salt-contaminated bridge decks regardless of the chloride content of the concrete.3

Much of the research on CP systems for steel-reinforced concrete structures has focused on impressed current CP (ICCP) systems based on the assumption that concrete’s high electrical resistance does not allow the use of sacrificial anodes. However, the authors note, in locations where there are no power lines and where maintenance and control of rectifiers is overly expensive, sacrificial anode CP systems would be highly desirable. They add that the use of sacrificial anodes for CP in reinforced concrete structures has increased in recent years due to the ease of installation, low maintenance requirements, and the desire to decrease the risk of hydrogen embrittlement of the reinforcing steel for prestressed concrete structures.

Zinc-based alloys are among the most evaluated sacrificial anode materials for concrete structures, particularly in the United States. These anodes can be utilized in many ways and in various forms. The protection capacity of zinc alloy anodes can be limited, however, based both on laboratory and on field application studies. The authors shared their findings during a symposium presentation4 at CORROSION 2017 in New Orleans, Louisiana, USA, where they reviewed the research work done in both the laboratory and the field as part of a study to identify situations where sacrificial anode use may be a practical option for steel-reinforcement protection in concrete structures.

The zinc-based anode usages studied the most are thermal spray anodes, installation of embedded anodes with moisturizing agents to promote sustained electrochemical activity, jacketed zinc anodes embedded in a Portland cement mortar cover, and small localized “point” anodes.

As an alternative galvanic CP system, thermal spray metallic coatings are low-cost and simple to implement. These coatings, typically ~50 µm (2 mils) thick, are generally produced from zinc- and/or aluminum-alloy wires that are melted with an electric arc and sprayed using pressurized air. Installation requires the delaminated concrete to be removed, and the reinforcing steel to be exposed by pressurized sandblasting before the molten anode alloy is sprayed. Generally, the electrical connection is achieved directly by the applied zinc on the exposed reinforcing steel.

Thermal spray galvanic anodes using zinc- or aluminum-based alloys can provide effective protection of the rebar in marine environments; however, the authors note the protection is limited mainly to the tidal and splash zones provided the concrete there is a good conductor. System life there can be limited by self-corrosion. Some benefit may be attained in the atmospheric zone, too, but it may be due to the sprayed metal acting as a physical barrier against aggressive agents and oxygen.

A general view of a bridge pile protected with jacketed zinc anodes. The photo on the right reveals the zinc mesh that is covered by a thin coat of mortar. Photos courtesy of the authors.

A general view of a bridge pile protected with jacketed zinc anodes. The photo on the right reveals the zinc mesh that is covered by a thin coat of mortar. Photos courtesy of the authors.

With embedded zinc anodes, byproducts generated by the dissolved zinc—such as oxides and hydroxides—can accumulate at the zinc/concrete interface and eventually cause delamination and flaws in the metallic coatings, which over time will decrease the galvanic CP system’s protective capabilities. The authors comment that both laboratory and field investigations have shown that the current provided by the galvanic system increases when humidity at the zinc/concrete interface is increased, and this also contributes to the redistribution of the dissolving coating’s byproducts into the concrete. Studies were done on the use of substances (moisturizers) that promote high humidity at the anode/concrete interface and enable the anodes to retain their protective capability. Moisturizers investigated were lithium bromide (LiBr), lithium nitrate (LiNO3), and potassium acetate (KC2H3O2). The results proved that lithium salt-based moisturizers improved the zinc anodes’ behavior, with LiBr showing the best results. They commented that the use of moisturizing agents increases zinc alloy activity in splash and atmospheric zones, but not enough to maintain it for long periods of time. Zinc-hydrogel anode applications, where a zinc sheet is embedded in an ionically conductive adhesive, also were seen to increase the zinc anode activity, and improved performance was reported.

Jacketed anode systems hold zinc-based anodes in place against a reinforced concrete surface with a jacketing material, and they have been used to protect bridge piles. The authors say that placing zinc-based anodes in a jacket system provides efficient long-term steel protection for the tidal region, where there is appreciable chloride ion ingress into the mortar, and where the influence of the submerged anode is greatest. Unlike thermalsprayed anodes, these jacketed systems allow better monitoring of the sacrificial anode system because they can be installed with monitoring systems that allow measurement of the current and potentials for both the anode and the steel reinforcement using electrodes embedded in the protected element.

The Florida Department of Transportation (FDOT) (Tallahassee, Florida, USA) started using a new version of jacketed anodes in 1994 with a configuration similar to one used for an ICCP system with jacketed titanium mesh anodes. According to the authors, this system is comprised of expanded mesh of nearly pure zinc alloy with small additions of elements intended to improve its formability and anodic performance. The anode mesh is mounted in a glass fiber jacket that provides an annular space between the mesh and the protected structure. The space is filled with a mortar mix of Portland cement, fine aggregate, and sand. The jacket is placed around the pile, starting at the lowest tide point and extending up to ~1.8 m above low tide.

Because there are no activating admixtures in the jacket filler, any activation of the anode must rely on the absorption of seawater by the filler after the jacket is placed in service. Studies have shown that zinc readily passivates in normal Portland cement concrete, and that a high concentration of chloride ions in the concrete is needed for zinc to be consistently active and able to protect the embedded rebar. Since the fill mortar is chloride free, the zinc alloy in the jacket tended to passivate in the splash and atmospheric zones and protection there is limited to physical barrier effects. This system has become a standard method of pile repairing for the FDOT, which has repaired hundreds of piles in numerous bridges with good results.

In applications such as patch repairs and other general sacrificial CP installations, localized “point” anodes are used. According to the researchers, it is well established that repairs of chloride-contaminated or carbonated concrete can create electrochemical incompatibilities between the “new” and “old” concrete that may lead to the accelerated corrosion of the steel reinforcement in the concrete near the patch repair. This is known as the “halo” effect. The resulting corrosion can induce cracking that may require extending the patching repair after a short time period (e.g., three to five years).

The idea of the localized CP anode application is that small galvanic point anodes installed in the patch repair will sacrificially corrode and reduce the possibility of a new active corrosion zone on the surrounding rebar, the authors comment. There are various versions of these anodes. Some, with an overall diameter of ~60 mm and a height of ~30 mm, may utilize a single zinc alloy core (with a mass of several tens of grams) surrounded by a cylindrical active matrix of cementitious components. Others, with larger dimensions, may incorporate multiple zinc alloy cores embedded in a common activating matrix. The zinc alloy cores are usually connected to rebar tie wires that can be easily tied to the reinforcing steel in the area to be patched before casting the repair concrete. The overall result, according to the findings of some investigators, is an appreciable extension of service life in patch repairs. The authors caution, however, that the service range of those anodes may be limited and it should be carefully evaluated against other options.

For more information on these sacrificial anode systems, see the CORROSION article available at https://doi.org/10.5006/2613.

References

1 “Materials and Methods for Corrosion Control of Reinforced and Prestressed Concrete Structures in New Construction,” U.S. Department of Transportation, Federal Highway Administration, Publication no. 00-081, August 2000.

2 O. Troconis de Rincón, A. Torres-Acosta, A. Sagüés, M. Martinez-Madrid, “Galvanic Anodes for Reinforced Concrete Structures: A Review,” Corrosion 74, in press (2018): https://doi.org/10.5006/2613.

3 “Long-Term Effectiveness of Cathodic Protection Systems on Highway Structures,” U.S. Department of Transportation, Federal Highway Administration, Publication no. FHWA-RD-01-096, April 2001.

4 O. Troconis de Rincón, A. Torres-Acosta, A. Sagüés, “Sacrificial Anodes for Reinforced Concrete Structures: A Review,” CORROSION 2017, paper no. 9078 (Houston, TX: NACE International, 2017).

New insights into molecular-level processes could help prevent corrosion and improve catalytic conversion

May 28, 2018, Environmental Molecular Sciences Laboratory
New insights into molecular-level processes could help prevent corrosion and improve catalytic conversion
An international research team peered deep into the atomic-level workings of water vapor on a nickel-chromium alloy to provide new insights that could help prevent metal corrosion. Credit: Environmental Molecular Sciences Laboratory

Engineers have long known water vapor can accelerate corrosion of metals and alloys, but the exact mechanisms remain elusive and therefore difficult to prevent. Now an international research team has peered into the atomic-level workings of water vapor corrosion. Their work reveals how the involvement of protons speeds the corrosion process.

Understanding how water vapor such as mist or steam corrodes metals and alloys can help engineers keep industrial systems working at peak performance longer. Armed with that knowledge, engineers can also improve catalytic conversion processes and enhance ionic conduction in materials.

Scientists from EMSL, the Environmental Molecular Sciences Laboratory, an Office of Science user facility, collaborated with colleagues at Pacific Northwest National Laboratory, Chinese Academy of Sciences, and State University of New York at Binghamton to study the effect of water  and elevated temperatures on a nickel-chromium alloy. Using EMSL’s environmental , they were able to directly observe oxide growth on a nickel-chromium alloy during corrosion at the atomic level. What they discovered was a complex dance of protons, cations, and anions that led to increased  and a more porous structure of the oxide. They then modeled the process through computer simulations to confirm their findings.

Their work provides insights into how  might change other materials, particularly at elevated temperatures.

More information: Langli Luo et al. Atomic origins of water-vapour-promoted alloy oxidation, Nature Materials (2018). DOI: 10.1038/s41563-018-0078-5

Read more at: https://phys.org/news/2018-05-insights-molecular-level-corrosion-catalytic-conversion.html#jCp

Construction Concerns: Corrosion

 

05/09/2018
Article and photos by Greg Havel

Corrosion of a metal can be defined as its degrading from a reaction with its environment. This degradation can cause weakening of the metal by reducing its cross section, by changing its crystalline structure, or by a gradual chemical reaction converting the metal to a compound with less strength.

Environmental concerns include the presence of oxygen, moisture (water), contact with dissimilar metals, and chemicals.

The National Aeronautics and Space Administration (NASA) suggests that most corrosion is electrochemical, taking place at the atomic and molecular level; and estimates that 90 percent of corrosion is caused by oxidation. Most of the remaining corrosion is galvanic, taking place between two dissimilar metals in contact with each other in the presence of an electrolyte, which forms a weak battery; a topic for another time.

Corroded steel rebar in a structural concrete slab

(1)

One of the most common and most destructive electrochemical oxidation reactions is one that occurs between iron or steel and oxygen, commonly called “rust.” In a simplified description of this reaction, iron atoms lose electrons, becoming positively charged iron ions. Oxygen atoms gain the electrons, becoming negatively charged oxygen ions; which combination forms iron oxide. Iron oxide has different chemical and physical properties than pure iron, including a great reduction of tensile and compressive strength. This process occurs most quickly in the presence of moisture with dissolved oxygen. Photo 1 shows the remains of the reinforcing steel (rebar) in a structural concrete slab that was corroded from years of rainwater and salty snow-melt finding its way through the cracks and fissures in the concrete, until the pressure exerted by the increased volume of the iron oxide (compared to the volume of the original steel) spalled a large area of the under-side of the concrete.

Part of the steel frame of a truck that has been severely corroded

(2)

Photo 2 shows part of the steel frame of a truck that has been severely corroded and weakened by years of exposure to weather and salty snow-melt. This steel has been so weakened by corrosion that it is no longer structurally sound and needs to be replaced.

In piping systems, the most destructive oxidation in iron or steel is the localized one resulting in pits (thin spots in the steel) and deposits of iron oxide and other minerals above them which maintain a localized environment that is especially conducive to corrosion, and which can obstruct flow of fluids through pipes.

Rebar stirrups with surface rust

(3)

Widespread or general corrosion on the surface of a metal changes its appearance but does not affect its strength. Photo 3 shows rebar stirrups with surface rust, which will become part of the rebar assembly inside reinforced concrete columns. In this instance, this mild corrosion lifts any remaining oil from the steel mill from the surface of the rebar and roughens it slightly to provide a better bond for the concrete.

In some cases, like the formation of copper oxides and aluminum oxides on the surfaces of these metals, oxidation forms a film that prevents further oxidation by preventing contact with oxygen.

Rebar stirrups that have been coated with an epoxy compound

(4)

In other cases, general corrosion and further degradation of the metal are combated by applying coatings to the metal, to isolate the metal from the oxygen in the air, moisture, and soil. Photo 4 shows rebar stirrups that have been coated with an epoxy compound for this purpose. Photo 5 shows epoxy-coated rebar that has been assembled to join a column with a structural concrete deck that will be exposed to the weather. This epoxy-coated rebar is often used today in bridges, underground structures with high water tables, and anywhere that the completed structure needs a long life expectancy and will be exposed to the extremes of weather.

Epoxy-coated rebar

(5)

Film-forming primers and paints

(6)

The lead-based, chromate-based, and polymer film-forming primers and paints (Photo 6) used on structural steel and bridges are examples of these coatings on structural steel.

Combining a metal with a less reactive metal can result in an alloy that does not oxidize as easily as the original metal. The addition of copper, nickel, chromium, and other metals to steel to form stainless steel of different grades is an example of this. Another example is the patented formula for alloy structural steel which forms an oxide coating on the surface that protects the rest of the steel structure.

Plating one metal with another can also prevent the oxidation reaction, as in the plating of steel with chromium in exposed components like automobile bumpers and hardware.

Galvanized steel electrical conduit in a wall framed with galvanized steel studs

(7)

Coating one metal with another that is more reactive in oxidation can protect the base metal from corrosion, as in coating steel with zinc, which sacrifices the zinc by corrosion rather than the steel. Photo 7 shows galvanized (zinc-coated) steel electrical conduit in a wall framed with galvanized steel studs. This is the same principle used in galvanizing (zinc-coating) steel pipes and ducts; in the “sacrificial anodes” that are used in water heaters to protect the heating elements and the tank; and the “sacrificial anodes” that are used with protective coatings to prevent corrosion of steel gas and oil pipelines from soil contact.

Uncontrolled corrosion in a building and its systems can lead to early failure of pipe and duct systems, as well as to structural collapse when the corrosion sufficiently weakens the structural steel. These potential failures may not be noticeable under normal conditions, until an abnormal even like a fire, tornado, or earthquake add stress to these already stressed systems.

For more information on the electrochemical and galvanic reactions involved in corrosion, search the Internet for

  • Corrosion
  • Corrosion types
  • Galvanic corrosion
  • Corrosion prevention
  • Corrosion protection

Download this article as a PDF HERE (1.4 MB).

Greg HavelGregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 35-year veteran of the fire service. He is a Wisconsin-certified fire instructor II, fire officer II, and fire inspector; an adjunct instructor in fire service programs at Gateway Technical College; and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 35 years of experience in facilities management and building construction; and has presented classes at FDIC International. This year ihe is presenting on “Building Construction and Fire Behavior.”

Corrosion Prevention Using Real-Time Data in Oil Fields

The corrosivity of free water in oil lines can be tested by following a side stream technique.

Modern high-resolution corrosion monitors, including electrical resistance probes, are available. These instruments can be installed in key locations and connected to a control room computer. Responsible engineers can observe the real-time corrosion trends from the control room along with other operational parameters. By seeing the corrosion data in real time, personnel can take immediate mitigation action in situations with high corrosion rates or risks.

Corrosion Inhibitor Injection

Chemical injection is an effective solution to many corrosion problems; however, injection rates below the specified dosage result in inadequate corrosion control and injecting excessive dosages is wasteful and not cost effective. Monitoring chemical treatments with data loggers obtains real-time data that can help streamline the chemical treatment process. Real-time data are helpful for maintaining the effectiveness and efficiency of the pump skids.

Corrosion inhibitor levels in injection tanks are important. Level control can be computerized and automated. In cases of low inhibitor levels, an alarm can alert the corrosion team so that the chemical supply can be promptly adjusted. This is more efficient than requiring personnel to conduct site visits, note the inhibitor level readings, and replenish the corrosion inhibitor if necessary.

Real-time chemical injection information from data loggers also can help determine the performance of the chemical treatment. Automating this process provides more accurate injection data than manual control during site visits because the inhibitor performance and chemical levels in the tanks are checked only at the time of the visit. Chemical injection quantities are then calculated based on the difference between the levels measured during the site visits. Automation is particularly useful for remote sites. By implementing automation, it is possible to continuously monitor the corrosion inhibitor injection and performance, make necessary adjustments when needed, and thereby minimize the corrosion of assets.

Monitoring Inhibitors in Pipelines

Identifying the corrosivity of fluid flowing in a pipeline or system is essential when adjusting the formulation of the inhibitors. Off-the-shelf inhibitor formulations may not always work. It is better to have tailor-made inhibitors that suit the specific conditions exactly.

FIGURE 1: Monitoring configuration for water samples.

FIGURE 1: Monitoring configuration for water samples.

The corrosivity of free water in oil lines can be tested by following the side stream technique (Figure 1). This can be carried out from a sampling point at the 6 o’clock position in the circumference of a wet crude oil pipeline. Tubing is connected from this sampling point to a small side stream separator that will yield oil-free water for testing. The water outlet of the separator is connected to a device with linear polarization resistance (LPR) probes affixed to it. By monitoring the LPR meter or using electrochemical impedance spectroscopy techniques, corrosivity can be checked.

This side stream equipment also can be used to inject and test inhibitor formulations. Preparing an inhibitor in a laboratory with collected samples may involve numerous, complex factors. There can be problems associated with dissolved oxygen (DO) ingress and liberation of dissolved gases from samples collected in containers and transported to a laboratory. Similarly, establishing system pressure, temperature, and other conditions in a corrosion testing laboratory is often very difficult.

Using side stream equipment for online sampling can simplify this work because the fluid exposed to the test electrodes is exactly the same as the pipeline fluid. Also, the system pressure, temperature, and other conditions remain consistent. Water from the side stream equipment also can be used for testing dissolved gases such as carbon dioxide (CO2), hydrogen sulfide (H2S), and DO. Additionally, chemical constituents in the water, such as dissolved iron and total iron, can be checked with the help of appropriatestandardized field test kits.

Normally, corrosion coupons are available for placement in the 6 o’clock position within pipelines. Coupon holders are also available with sample collection systems. Fluid can flow through the coupon holder to the outlet that is connected to the side stream equipment. Considerable care, however, must be exercised in unscrewing the coupon holder to allow fluid flow while avoiding holder displacement under high pressure. It is also important to confirm that the fluid flow is not blocked by particles that could impede the collection of side stream samples. This method gives real-time data of fluid corrosivity and provides data that are also representative of actual field conditions. In side stream equipment, two probes can be connected in a series to check their accuracy.

Conclusions

A dynamic approach to corrosion monitoring is essential. Acquiring and analyzing real-time data greatly facilitates corrosion prevention. Traditional methods concentrate on detecting and evaluating corrosion after it has occurred. Corrosion monitoring techniques should concentrate on collecting real-time data to identify corrosion risks in time to prevent significant losses and failures.

Bibliography

A.W. Peabody’s Control of Pipeline Corrosion. 2nd ed. R.L. Bianchetti, ed. Houston, TX: NACE International, 2001.

Munger, C.G. Corrosion Prevention by Protective Coatings. 3rd ed. L.D. Vincent, ed. Houston, TX: NACE, 2014.

Murthy, T.L.N. and G. Kannayya Naidu. “A Sour Gas Problem in Sweet Crude Oil Storage Tanks.” MP 54, 2 (2015).

Murthy, T.L.N. “A Systematic Approach to Prevent Internal Corrosion of Pipelines.” MP46, 12 (2007).

Murthy, T.L.N. “Corrosion Control—Loss Prevention.” J. Corros. Sci. and Eng. 12 (2007).

Murthy, T.L.N. “Corrosion Monitoring and Inhibitors for Production Tubing in Gas Wells.” MP 54, 10 (2015).

Murthy, T.L.N. “Corrosion Monitoring to Prevent Corrosion Problems.” Coating and Corrosion J. Quarter 4 (2007).

Murthy, T.L.N. “Monitoring of Chemical Treatment is Essential to Prevent Internal Corrosion.” MP 53, 12 (2014).

Roberge, P. Corrosion Basics: An Introduction. Houston, TX: NACE, 2006.

“Remote Monitoring System Tracks Cathodic Protection and Sensor Data.” MP 55, 1 (2016): p. 18.

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