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Part 5 of 6: How “Just a Little Thinner” Impacts VOC Emissions in Industrial Coatings

Chef makes a meal without a recipe

6-Part Blog Series: The Role of High-Performance Coatings in Shrinking the Carbon Footprint

In part four of this blog post series, we discussed the key data points that should be used when selecting an industrial coating system in order to accurately forecast volatile organic compound (VOC) emissions.

In this next blog post, we will examine how the human factor—such as common practices across the industrial coatings industry—can impact actual VOC emissions.

One common industry practice occurs when painters are preparing to apply industrial coatings for the first time. With catalyzed coatings, part A and part B are mixed together according to the instructions. Purely out of habit, a stir stick is then used to assess the consistency of the coating and to add thinner to the mixture until it “feels right.”

To be clear, many of these craftsmen who add thinner to feel can effectively “lay it down as smooth as glass”—producing some of the most beautiful, seamless finishes. This is similar to a seasoned chef who does not measure, but instead adds ingredients and spices “to taste.” Although this method works in some cases, it’s not ideal if you are not a trained chef or have specific dietary restrictions. In the industrial coatings industry, if low VOC emissions are required, the painter needs to carefully measure the thinner and find alternatives wherever possible.

Let’s take a look at the effect on total VOC emissions if “just a little extra” thinner is added to an industrial coating. Assume, for example, that an annual maintenance program will use 1,000 gallons of epoxy paint. For this illustration, let’s say the epoxy used is 75% solids by volume, and the 25% volatiles are VOCs with a weight of 1.8 lbs per gallon. At 1,800 lbs of VOC emissions, this would be considered a high-solids, low-VOC epoxy that falls well within the acceptable VOC limits in most legislative regions.

That 1,000 gallons of epoxy can protect upwards to 200,000 ft² of steel surface. In the big picture of sustainability, the ability to protect large areas of steel from corrosion is a very good thing. That said, it’s important to still be mindful of the VOC emissions—especially those that are unnecessary.

Let’s next consider the effect of adding 10% extra thinner to the coating, whether or not it is actually needed. For this illustration, we’ll assume the thinner contains 7 lbs of VOCs per gallon. In addition to the 1,000 gallons of epoxy, an additional 10%—or 100 gallons—of thinner is added to the 1,000 gallons of paint prior to application.

As you can see, the VOC emissions “cost” for protecting 200,000 ft² of steel from corrosion rose from 1,800 lbs VOCs to 2,500 lbs—a nearly 40% increase!

Suitable thinners for industrial coatings are absolutely necessary. They are required to clean equipment and, at times, to improve the application characteristics of a coating when environmental conditions are not ideal. For instance, hot and windy conditions, or even cold weather, may require special thinners to achieve a successful application.

Although thinners are often a necessary part of the application process, spray equipment can be adjusted to handle higher-viscosity coatings instead of using thinners with VOCs to lower the viscosity of the coatings. This small adjustment can have a big impact on reducing VOC emissions.

In the final part of this blog post series, we will explore the various strategies that can be used to reduce VOC emissions by painting less.

Need Help Selecting the Right Coating for Your Project?

Contact a local sales representative from Carboline’s Technical Service team.

Part 4 of 6: Using Data to Select an Industrial Coating with Low VOC Emissions

A project estimator calculates the true coverage and VOCS for a coatings project

6-Part Blog Series: The Role of High-Performance Coatings in Shrinking the Carbon Footprint

In part three of this blog post series, we began our discussion on how to evaluate the volatile organic compounds (VOCs) produced by high-performance industrial coatings, as well as the data points related to VOCs that are commonly used when choosing an industrial coating system.

In this next blog post, we will take a deep dive into the key data points that should be understood by specifiers and environmental, health and safety (EH&S) personnel who select and approve industrial coatings in order to accurately forecast VOC emissions.

Let’s start out by evaluating paint emissions. A good way to estimate total VOC emissions is in the same way that estimators price out a paint job. When evaluating different paint systems in a coating specification, estimators always ask two questions: what is the cost per gallon, and what is the percentage of volume solids? Because the specified dry film thickness (dft) of a coating is already provided in the specification, these additional data points allow estimators to calculate and compare the costs per square foot, or square meter, of the coating systems.

Calculating Cost Per Square Foot

To calculate the cost per square foot, multiply the theoretical coverage of a liquid at 1 mil (or 1604²) by the volume solids percentage of the coating, then divide the result by the specified dft in mils. This provides the coverage rate of a paint at the specified film thickness after the evaporation of solvents.

Next, divide the cost per gallon by the square-foot coverage of the coating to determine the theoretical cost per square foot, as shown below:

For example, let’s calculate the theoretical cost per square foot for a coating that has been specified to achieve 5 mils dft. The coating has a volume solids of 75% and has been quoted at $50 per gallon.

So, we can multiply our theoretical cost per square foot—20.8 cents—by the total estimated square footage of the job to determine our material costs, right? Not quite.

Theoretical Versus Practical Application Rates

Most readers have probably picked up on the repeated use of the word “theoretical.” This is because the theoretical cost per square foot assumes a 100% transfer of the coating from the bucket to the surface being coated—which we know is impossible. For instance, depending on the application method, some paint could be lost to overspray or even left embedded in the roller or brush.

In the industrial coatings industry, this is usually referred to as either the “loss factor” or “consumption rate.” Regardless of the terminology, a practical coverage rate is needed in order to estimate a more realistic cost per square foot.

The loss rate of a coating application typically ranges from 10% to 40%, depending on the application method and geometry of the structure being painted. Estimators should know the loss factor to plug in for the type of project they are estimating.

Taking our above theoretical coverage rate per gallon (240.6 ft²), and let’s say a 25% loss is expected for this type of job. Based on this, what is the practical coverage rate?

When the cost per gallon of $50 is divided by the practical coverage rate of 180 ft², the cost per square foot equals out to $0.277 per square foot.

Other factors certainly come into play when applicators select a coating system, such as ease of application and service level of the manufacturer. However, every estimator who prices out jobs should be able to tell you to the penny—or even the tenth of a penny—the estimated material cost per square foot.

Calculating VOC Emissions by Coverage Rates

VOC emissions per square foot can be estimated in a similar way to cost per square foot. Start by calculating the coverage rate per gallon, as shown above. However, instead of dividing the cost per gallon by the coverage rate, you’ll divide the VOCs lbs per gallon (as stated on the product data sheet) by the coverage rate in order to get the VOC emissions per square foot.

The result will be a very small figure. For example, if a coating has 3 lbs VOCs per gallon with a 250 ft² coverage rate, the VOC emissions per square foot is 0.012 lbs. When the VOCs per gallon are multiplied by the square footage of the coated item—or average annual square feet coated in a maintenance program—we can then see the impact.

For instance, a project with 10,000 ft² coated with the above sample product at 0.012 lbs would have 120 lbs VOC emissions per 10,000 ft2, as shown below. It adds up quick!

A Solvent Based System Versus a Waterborne System

Now, let’s compare two coating systems and their estimated annual VOC emissions. The below illustration is based on a petrochemical facility that decided to only permit waterborne coatings on site in order to reduce VOC emissions and eliminate the need to store paint thinners.

On an aggressive year for maintenance painting, we’ll assume this facility could paint 500,000 ft² with its standard maintenance coating system. Let’s estimate the forecasted VOCs using the standard epoxy-urethane system, compared to the proposed water-based, epoxy-acrylic finish system.

The Epoxy-Urethane System

The above illustration depicts the VOCs and volume solids of a solvent-borne coating system by volume. The volume solids remain after solvents—in this instance, VOCs—evaporate out of the coatings.

The Waterborne System

Many waterborne coatings also have VOCs that contain solvents, in addition to the water. The above illustration depicts the amount of VOCs, water and volume solids of a coating by volume.

The Importance of Solids by Volume

While the VOCs per gallon on the product data sheet for waterborne coatings may be lower, the question is—will those lower VOCs lbs per gallon translate to lower overall emissions for the customer?

Let’s round off the values of each product to an industry average, using generic coatings to compare a solvent-borne maintenance system to one that is waterborne.

System A: Solvent-Borne Maintenance System
Epoxy Mastic: 75% Volume Solids 1.8 lbs VOCs Per Gallon
Polyurethane: 65% Volume Solids 2.7 lbs VOCs Per Gallon
System B: Waterborne Maintenance System
Water-Based Epoxy: 50% Volume Solids 2.0 lbs VOCs Per Gallon
Acrylic Finish: 50% Volume Solids 1.5 lbs VOCs Per Gallon

The initial comparison shows the water-based epoxy as slightly higher in VOCs per gallon than the solvent-borne epoxy. However, the acrylic finish in the waterborne system is significantly lower in VOCs per gallon than the polyurethane finish. That said, what really jumps out is volume solids percentage of the coatings in each of the two systems.

The owner specified the same dft for each system. How, then, will the lower volume solids affect the coverage rate, total quantities used and resulting VOC emissions?

On average, this facility coated approximately 500,000 ft² per year in maintenance paint. The most common system was a “spot, full, full” system for atmospheric service.

Spot Primer: Epoxy @ 4-6 mils dft
Intermediate: Epoxy @ 4-6 mils dft
Finish: Polyurethane @ 2-3 mils dft

The coating applicator would first wash the structure to be painted, perform spot surface preparation on the degraded areas and spot prime with epoxy mastic. Then, the applicator would apply a full intermediate/tie coat of epoxy mastic, followed by a full coat of polyurethane.

For spot repair systems, the estimators found that 30% of the total square footage to be coated was the ideal figure for estimating square footage of the spot primer. With that in mind, this is how we would calculate the total annual paint usage:

Spot Prime: 500,000 ft² x 30% = 150,000 ft²
Full Intermediate: 500,000 ft²
Full Finish: 500,000 ft²

From this data, we can estimate the total gallons needed for the two maintenance systems based on various coating types, assuming a 20% loss factor:

Total Gallons Needed for System A (With 20% Loss Factor):
Epoxy Mastic 75% Volume Solids 650,000 ft² @ 5 mils dft = 3,380 gal
Polyurethane 65% Volume Solids 500,000 ft² @ 2 mils dft = 1,200 gal
Total Gallons Needed for System B (With 20% Loss Factor):
Water-Based Epoxy 50% Volume Solids 650,000 ft² @ 5 mils dft = 5,065 gal
Acrylic Finish 40% Volume Solids 500,000 ft² @ 2 mils dft = 1,950 gal

Next, let’s take a look at the total estimated VOCs for each maintenance system:

System A: Solvent-Borne
3,380 gal x 1.8 lbs VOCs per gal 6,084 lbs VOCs
1,200 gal x 2.7 lbs VOCs per gal 3,240 lbs VOCs
Total: 9,324 lbs VOCs
System B: Waterborne
5,065 gal x 2.0 lbs VOCs per gal 10,130 lbs VOCS
1,950 gal x 1.5 lbs VOCs per gal 5,715 lbs VOCs
Total: 15,845 lbs VOCs

The Addition of Thinners

When looking at the “environmentally friendly” waterborne system, the total VOCs are significantly higher than those of the solvent-borne system. However, there is a critical component missing from this calculation—the paint thinners required for solvent-borne systems. Because thinners for solvent-borne coatings are typically 100% VOCs, this can significantly add to the total.

Though required solvent use is lower for many of today’s coatings, we will use the estimators’ old rule of thumb for this example—that there should be approximately 10% more gallons of paint thinners than the total paint gallons purchased. So, if 100 gallons of solvent-borne paint are needed, that will add 10 gallons of paint thinners to the order.

But how does the addition of solvents change the comparison between the solvent-borne and waterborne maintenance systems? Most solvents are about 7.1 lbs VOCs per gallon. Based on this, below are the total estimated VOCs for each system with solvents added:

System A: Solvent-Borne
3,380 gal x 1.8 lbs VOCs per gal 6,084 lbs VOCs
1,200 gal x 2.7 lbs VOCs per gal 3,240 lbs VOCs
4,580 gal x 10% x 7.1 lbs VOCs per gal 3,252 lbs VOCs
Total with Solvents: 12,576 lbs VOCs
System B: Waterborne
5,065 gal x 2.0 lbs VOCs per gal 10,130 lbs VOCS
1,950 gal x 1.5 lbs VOCs per gal 5,715 lbs VOCs
Total: 15,845 lbs VOCs

With the addition of paint thinners used to reduce the solvent-borne coatings, the totals of the two systems are much closer. However, in this case, the solvent-borne system is still about 20% lower in VOC emissions than the waterborne system—a significant difference.

The point of this explanation is that VOCs should be treated like a cost by coating professionals to help customers properly plan and budget. All key stakeholders—especially HS&E personnel—should have the information and tools needed to make informed decisions. Our responsibility goes beyond simply manufacturing a coating that meets the allowed VOCs per gallon in a specific region.

In part five of this blog post series, we will explore the impact of the “human factor” and the life cycle of an industrial coating system on lowering VOC emissions.

Need Help Selecting the Right Coating for Your Project?

Contact a local sales representative from Carboline’s Technical Service team.

Part 3 of 6: How to Choose Industrial Coatings with Low VOC Emissions

6-Part Blog Series: The Role of High-Performance Coatings in Shrinking the Carbon Footprint

In part two of this blog post series, we explored how the prevention of steel corrosion can reduce environmental impact by improving the overall carbon footprint. In this next blog post, we will discuss how to evaluate the volatile organic compounds (VOCs) produced by high-performance industrial coatings, as well as which data points to use when choosing a coating system with lower VOC emissions.

When I talk with asset owners about changing their coating specifications to lower VOC emissions, the topic of waterborne coatings inevitably pops up. The lines from a classic poem, The Rime of the Ancient Mariner, come to mind: “Water, water, everywhere… and all the boards did shrink. Water, water, everywhere… nor any drop to drink.” Will waterborne coatings be the answer for achieving zero, or near zero, VOC emissions in industrial coating applications? Or will they remain tantalizingly close, but just out of reach—like the sea of water surrounding the ancient mariner who was dying of thirst?

My personal experience is that waterborne coatings apply and cure well, as long as the environmental conditions during application fall in what I call the “Goldilocks Zone”—just right. Temperature and humidity changes affect the drying and curing times of all coatings—but have a greater impact on waterborne coatings as compared to those that are solvent borne.

Because there is a narrow range of acceptable environmental conditions for optimal coating application, this reduces the number of days that waterborne coatings can be applied outside of climate-controlled facilities. In addition, most high-performance waterborne coatings used in industrial settings still contain VOCs with co-solvents. Although water can be used to clean equipment and reduce waterborne coatings for application, many of these coatings are not free of VOCs.

When choosing an industrial coating system, the pounds per gallon and grams per litre are the data points most often referenced on a product data sheet, as they are government defined. The EPA Test Method 24 is the standard in the U.S. for measuring and recording VOC values—though these values, as well as the acceptable levels of VOCs, can vary by legislative region. Oftentimes, the stated VOCs per gallon in waterborne coatings are much lower than those found in solvent-borne coatings. However, there are other factors that should be considered when evaluating their impact on emissions.

A 100% solids, zero VOCs coating system is another viable path to achieving zero VOC emissions. In fact, I’m confident that 100% solids, catalyzed epoxy coatings will be the future default technology for tank linings. The industrial coatings industry is getting closer to that end every year, as chemists innovate all phases of this technology for tank linings.

Although tank linings with zero VOCs from catalyzed, 100% solids products are already commonly used in the industrial setting, some big questions still remain a mystery. For instance, will chemists in research and development be able to develop 100% solids coating technology for atmospheric exposure use? Can these 100% solids coatings be made surface tolerant? Will they be suitable for application via airless spray, conventional spray, or roll and brush? Only time will tell.

While we don’t know what technical breakthroughs will be made by chemists and coating formulators in the future, we can still make informed decisions now on how to lower VOCs. In part four of this blog post series, we will explore the data points that should be understood by specifiers and environmental, health and safety personnel who select and approve coatings in order to forecast VOC emissions.

Need Help Selecting the Right Coating for Your Project?

Contact a local sales representative from Carboline’s Technical Service team.

Part 2 of 6: Save the Steel, Save the Planet!

Protecting steel bridges like this one is just one way protective coatings help the environment.

6 Part Blog Series: The Role of High-Performance Coatings in Shrinking the Carbon Footprint

In part one of this blog post series, we began to explore the role that high-performance industrial coatings play in helping to shrink emissions and the overall carbon footprint. Though the title for part two of this series may be a little hyperbolic… it’s not by much.

Steel is the cornerstone of modern civilization—it’s strong, relatively inexpensive and lacks any viable alternatives. Some form of steel is used in virtually every modern structure, piece of equipment and vehicle. It’s the most essential material used in construction.

However, it takes a significant amount of energy to produce steel. Most of the energy used to make iron, and in turn steel, comes from fossil fuels. These energy sources produce a lot of carbon dioxide, as well as volatile organic compounds (VOCs), that are ultimately released back into the atmosphere.

In addition, steel that is left unprotected will begin to corrode, losing all the properties that make it an essential construction material. The protection of steel assets from corrosion—in turn preventing the need for asset replacement—is by far one of the most environmentally friendly actions that a facility or asset owner can implement. This is especially true when considering the environmental impact of protecting those steel assets.

How Steel Protection Reduces Environmental Impact

For example, a 6-inch schedule 40 steel pipe weighs about 19 lbs per foot. A 105-foot run of this 6-inch pipe would weigh close to 1 ton. If this steel pipe had to be replaced due to corrosion, the environmental cost is high. In fact, for every ton of steel that is produced by steel mills, approximately 2 tons of CO2 are released back into the atmosphere!

To protect that same 105-foot run of 6-inch steel pipe with a standard three-coat, high-performance coating system would generate less than 10 lbs of VOCs emissions. Though 2 tons of CO2 versus 10 lbs of VOCs is a dramatic difference, it’s a common occurrence.

In addition to the 2 tons of CO2 produced from steel, the VOCs generated by the transportation of steel from the mill to the jobsite exceed those produced by high-performance industrial coatings that could be used to prevent asset replacement in the first place.

Using High-Performance Coatings to Mitigate Steel Corrosion

In order for legislative bodies and companies to reduce the overall carbon footprint from made-made activities, the importance of protecting steel from preventable replacement due to corrosion cannot be understated. The use of high-performance industrial coatings to mitigate corrosion should be strongly encouraged—and even demanded.

Although minimizing VOCs in high-performance industrial coatings—plus carbon emissions from all sources—should be the ultimate goal for companies, the prevention of steel corrosion can have a significant impact on improving the overall carbon footprint.

In part three of this blog post series, we will discuss how to measure the VOCs produced from high-performance coatings, as well as why it’s important to understand what the numbers listed on a coatings manufacturer’s product data sheet mean for VOCs emissions.

Need Help Selecting the Right Coating for Your Project?

Contact a local sales representative from Carboline’s Technical Sales team.

How Polarity & Molecular Size Impact Tank Lining Selection

Water, crude oil, sulfuric acid, caustic soda, ammonia, dimethylformamide, sodium acetate, gasoline, jet fuel, bleach, nitric acid, beer, toluene and brine—this is quite an extensive spread, but it’s only a fraction of the chemicals for which industrial coatings manufacturers develop and maintain tank lining systems.

With that in mind, what properties of these chemicals lead to a choice of one lining solution over another? How is crude oil different from water on a functional level, and what impact does that have on our lining options?

The relevant variables here are polarity, molecular shape and molecular size. The size and shape are pretty intuitive—that is, how big is the molecule, and what is its shape? Those weird drawings on your high school chemistry chalkboard were not merely abstractions. They more or less represent the actual shapes and relative sizes of various molecules.

Cross-Link Density in Chemical Resistance

Our recent blog post on cross-link density in polymer tank linings discussed the chemistry behind polymers and how cross-link density impacts their chemical resistance. That is relevant here. The smaller a molecule is, the tighter the crosslinking must be to prevent that molecule from penetrating the film. A helpful analogy is to compare chicken wire to mosquito screen. In addition to keeping chickens in, the chicken wire allows flies and mosquitos to enter. The mosquito screen also keeps chickens in, but is small enough that it prevents flies and mosquitos from entering as well.

This point leads to a general rule of thumb that lining selection is typically more challenging when it comes to smaller molecules, with water being a notable exception. Molecules that generally fall on the smaller end of the size range—such as methanol, dichloromethane, hydrogen sulfide, chloroform, formic acid and ammonia—usually require lining materials with higher cross-link density to protect the steel tank in which they will be stored.

The Chemistry Behind Polarity

The concept of polarity, on the other hand, is a bit trickier. In simple terms, polarity is a measure of how polar a given molecule is. When you hear the word “pole” in everyday context, you might imagine an object that has two opposite extremities, such as a north and south pole on a globe, or N and S poles on a common house magnet. Likewise, when two people have strongly differing opinions, they are said to be polarized. In chemistry, the term “polarity” is used in an analogous way—but with electric charge.

All atoms and molecules have positively charged protons and negatively charged electrons that constitue them. That distribution of charge is often lopsided and, as a result, many molecules have a distinctly “+ end” and a distinctly “- end.” This is precisely what polarity is—a measure of how pronounced and distinct these positive and negative ends are. Molecules can range in polarity from a little to a lot, while some completely lack polarity altogether. Examples of the latter include methane, carbon tetrachloride and hexane (a main component of gasoline).

For reasons that are a bit beyond the scope of a blog post, it is this middle-ground—the molecules that have some polarity, but not too much—that tend to be lining killers. This is because these types of molecules are polar enough to be soluble in water, but non-polar enough to wiggle through a mostly non-polar polymer film. In other words, there is a sweet spot between totally non-polar and highly polar that usually creates the most aggressive lining commodities.

Impact of Polarity & Cross-Link Density on Polymer Tank Linings

Going back to the variables of polarity, molecular shape and molecular size, the commodities that typically require the most robust cross-linked linings tend to be small and somewhat polar. These include methanol, ethanol, dichloromethane (methylene chloride), ammonia, hydrochloric acid, formic acid and acetic acid. Considering our rule of thumb discussed above, all of these commodities usually require either high-baked epoxy phenolics, thick-film epoxy novolacs or thick-film vinyl esters.

Some commodities, like hydrofluoric acid, are very polar and absolutely smash this rule—along with most tank linings. However, given the vast number of chemicals out there and all the variables at play, we are bound to see chaotic behavior in some instances that would have been difficult to predict from first principles. This is why it’s so critical to conduct physical tests, instead of relying on theories.

Although you won’t need to know the polarity or size of the molecules in a commodity the next time you consult with an industrial coatings manufacturer, it is helpful to have a basic understanding of these concepts and how they impact the selection of polymer tank linings.

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