LIFE CYCLE ASSESSMENT AND PERFORMANCE
TESTING OF ALTERNATIVE CARC PAINTING SYSTEMS

 

Duane A. Tolle1, Kenneth R. Stone2, and S. Kevin Taylor3
1,3Battelle, 505 King Avenue, Columbus, OH 43201-4693, USA
1Corresponding Author’s Telephone 614-424-7591
2National Risk Management Research Laboratory, U.S. Environmental Protection
Agency, 26 W. Martin Luther King Drive, Cincinnati, OH 45268, USA

 

Objectives of LCA and Performance Testing

The Department of Defense (DoD) and the U.S. Environmental Protection Agency (EPA) jointly sponsored this project, with funding from EPA and DoD’s Strategic Environmental Research and Development Program (SERDP). The objective was to demonstrate the use of the Life-Cycle Assessment (LCA) approach, modified to include the additional Life-Cycle Design principles of cost and performance (EPA, 1995), for optimizing the process of painting military vehicles with chemical agent resistant coatings (CARC). The study was designed to take advantage of a streamlined Life-Cycle Inventory (LCI) conducted previously by Pacific Environmental Services (PES) (Hendricks et al., 1995), which focused on CARC stripping and painting operations at the Army’s Transportation Center in Fort Eustis, VA. CARC is a paint system used by DoD, because it is resistant to penetration by chemical agents. The approach includes all three of the following components of LCA as defined in documents by EPA (1993) and the Society of Environmental Toxicology and Chemistry (SETAC, 1991 and 1993): LCI, Life-Cycle Impact Assessment (LCIA), and Life-Cycle Improvement Assessment (LCImA).

The LCA demonstration objective was met by a report which identified the environmental impacts of five alternative CARC systems involving different combinations of primer, thinner, topcoat, and application equipment (EPA, 1996; Stone and Tolle, 1997). The recommended alternative involved changing the existing primer and application equipment, but retaining the baseline thinner and topcoat. Thus, the objectives for the follow-on technical evaluation were to confirm the performance of the preferred CARC alternative recommended by the LCA against the baseline system by criteria specified in standard test procedures or military specifications, ease of operation and clean up, and evaluation on two substrates (steel and aluminum). This evaluation involved spraying test panels at two Army bases and laboratory evaluation.

 

CARC System Components

CARC is a system consisting of a primer and topcoat formulated with a variety of pigments, heavy metals, and solvents. It cures rapidly after application forming a durable finish. The one-component topcoat used at Fort Eustis meets MIL-C-53039A. Prior to applying the CARC topcoat, the vehicle is cleaned and primed. Since aluminum oxide is used as the blasting medium at Fort Eustis to remove CARC and has high efficiency with low cost, it was chosen for the baseline evaluation. The painting technique selected for the baseline was high-volume, low-pressure (HVLP) spray painting using the Binks Mach 1. The most commonly used primer, which was selected for the baseline CARC system, is a solvent-thinned, two-part epoxy that meets MIL-P-53022. The thinner selected for the baseline meets MIL-T-81772B and is used to dilute the primer for ease of application and to control the primer’s drying rate.

 

Alternative CARC Systems

Five alternative CARC systems were evaluated against the baseline system described above. These alternative systems differed from the baseline in the use of primer, thinner, and/or paint spray gun, but used the same topcoat and blasting media. The alternative primer was a water-thinned, two-part epoxy that meets MIL-P-53030. The alternative thinner meets Federal Standard A-A-857B and was used at Fort Eustis. The alternative spray gun was a turbine HVLP, which reduces the amount of turbulence relative to the conventional HVLP gun, and thus, decreases the amount of overspray. The preferred alternative, which was identified by the LCImA and compared to the baseline in the performance evaluation, involved the alternative primer and the turbine HVLP spray gun.

 

Life-Cycle Impact Assessment (LCIA) Description

 

The LCIA is based on data from the streamlined LCI prepared by PES (Hendricks et al., 1995). The LCI involved collection of secondary environmental and utility data that describe the generic production of components for the CARC painting/depainting system and their raw materials. Site-specific LCI data were collected from Fort Eustis on paint application, depainting, and disposal of spent CARC and blast media. These data include the raw materials used, water and energy requirements, air emissions, water effluents, and solid waste streams. The functional unit used was 1,000 ft2 of painted surface, because the important requirement for any type of paint is the amount of materials required for producing a good finish over a specific area.

An LCIA involves the examination of potential and actual environmental and human health effects related to the use of resources (energy and materials) and environmental releases (SETAC, 1993). An LCIA is divided into the following three phases: Classification, Characterization, and Valuation. The characterization phase may include normalization, which compares the contributed potential impact of the system under investigation to the overall environmental problem magnitude, in order to place the system-level results in perspective. In this study, the normalization factor was the impact quantity for the stressor creating the greatest impact potential in the baseline for a given impact category.

Classification was conducted after scoping and is the process of linking or assigning data from the LCI to individual stressor categories within the three major stressor categories of human health, ecological health, and resource depletion. Based on the stressor/impact chains developed during classification, the following nine impact categories were selected for impact characterization: smog formation potential, ozone depletion potential, acid deposition potential, global warming potential, human health inhalation toxicity potential, terrestrial (wildlife) toxicity potential, aquatic (fish) toxicity potential, land use potential (for solid waste disposal), and natural resource depletion potential (including fossil fuels and minerals).

Characterization involved the analysis and estimation of the magnitude of impacts for each of the stressor categories by using the SETAC (1993) Level 2/3 approach of multiplying equivalency factors times the quantity of a resource or pollutant associated with a functional unit of CARC. For the Level 2 evaluation, a limited subset of the chemicals identified during the LCI had already been assigned impact equivalency units in published documents (Heijungs, 1992; Nordic Council, 1992). Impact equivalency units were created for some chemicals identified in the baseline or alternative LCIs, by using the SETAC (1993) Level 3 Toxicity, Persistence, and Bioaccumulation Potential Approach. New toxicity equivalency factors were developed based on a modification of a hazard ranking approach (EPA, 1994; Swanson et al., 1997).

Valuation involved assigning relative values or weights to different impacts, so they can be integrated across impact categories for use by decision-makers. The same approach was used for cost and performance measures so that a total score for all decision criteria could be determined. The Analytical Hierarchy Process (AHP) valuation method used in this study is a methodology for supporting decisions based on relative preferences (importance) of pertinent factors (Saaty, 1990). Preferences were expressed pair-wise in a structured manner by using Expert Choice™ software in connection with a four-member team that included one cost engineer, one paints/coatings specialist, a civil engineer, and an ecologist.

 

Economic Parameters for LCA

The annualized costs estimated in this LCA were restricted to direct and indirect internal costs (i.e., costs associated with the Army's depainting and painting operations). Direct costs are closely associated with the depainting and painting operations and include expenses related to capital expenditures for building, equipment, renovations, etc., and operating costs such as operating labor, materials, utilities, maintenance, and waste disposal. Indirect costs are costs which are incurred, but might be spread across several facilities on base, and included in labor overhead. External costs were not included in the analysis. The advantage of this approach is that information on internal costs was readily available from the Army, suppliers, and private industry.

The annualized cost to depaint and paint Army vehicles was estimated using a factored estimate costing procedure (Peters and Timmerhaus, 1991), which provides a candid approach to preparing cost estimates with a medium level of accuracy. Capital costs are accurate within ±40 percent, and operating costs within ±30 percent. A base case and five alternative cases were evaluated. Fort Eustis was selected as the baseline site, so its plant capacity; staffing; and paint-, primer-, thinner-, and abrasive media-usage rates were used to estimate typical costs. The preferred alternative selected for evaluation was determined to have an annual cost saving of more than $230,000, based on paint usage at Fort Eustis.

 

Performance Parameters for LCA

Performance assessment parameters for the LCA were developed for the three CARC system components (application equipment, primers, and thinners) that were varied in the five alternatives. The two evaluation parameters selected for application equipment included surface quality and transfer efficiency (ability of the application equipment to minimize overspray and bounceback. The ability of the application equipment to effectively apply CARC was ranked according to the surface quality of the applied coating. An acceptable finish is one with no visible application-induced surface blemishes (e.g., orange peel, blistering).

The major performance issues of primers are corrosion inhibition, adhesion, and cure rate. Since the primers under evaluation in this study are all pre-approved to meet military specifications, they are assumed to provide sufficient corrosion inhibition. Adhesion was evaluated with respect to impacts resulting from changes in environmental conditions, such as temperature and humidity. Cure rate and ease of cleanup of the primer were evaluated with respect to the impact on the painting schedule and the level of effort required.

The thinner evaluation parameters included thinning ratio (thinning effectiveness) and film characteristics. Thinners were evaluated based on the percentage of thinner needed to dilute CARC to within sprayable viscosity limits. Thinners were also ranked according to the ability of the thinner to provide an acceptable finish. Thinners that evaporate too slowly or too quickly can cause undesirable surface defects.

 

Improvement Assessment (LCImA)

The potential environmental impact significance of each impact category for the baseline and the five alternatives was characterized using the same set of nine equivalency factors listed above. The importance of each individual resource or chemical within an impact category was determined by multiplying the equivalency factor times the inventory value in pounds per functional unit. The total potential impact for a given impact category was then determined by normalizing each individual item (chemical or resource) score against the highest item score for the baseline in a particular impact category and adding all of the normalized scores for each item within that particular impact category.

The preferred alternative that included both the alternative primer (water-thinned) and the alternative spray gun (turbine HVLP) had the lowest normalized environmental impact scores (least impact potential) for seven of the nine impact categories. These seven categories were global warming, ozone depletion, resource use, acid deposition, smog, human inhalation toxicity, and terrestrial toxicity. The remaining two impact categories (aquatic toxicity and land use) were lowest for the alternative that included only the alternative spray gun.

The overall scores for improvement potential were determined for each alternative by application of the AHP valuation weights to the normalized impact category scores, as well as to scores for the cost and performance criteria. These overall scores in decreasing order (lowest score is best) for each alternative are: Baseline (1.191), Alternative Thinner (1.134), Alternative Primer (1.019), Alternative Thinner plus Primer (1.016), Alternative Gun (1.006), and Alternative Primer plus Gun (0.898). These results indicate that the use of the alternative gun makes the largest potential improvement for an alternative that changes only a single factor and combining this with the alternative primer results in the best CARC option.

 

Performance Testing of Alternatives in Field and Laboratory

Steel and aluminum coupons (4 x 6 in panels) were used to compare the performance of the baseline and preferred alternative at each of two sites. In order to get a sense of how the alternative might perform at sites with different climatic conditions, Fort Eustis and Fort Campbell were selected to participate in the technical evaluation. Fort Eustis exhibits higher humidity and temperature and the vehicles it paints are often forward deployed in salt-laden environments. Fort Campbell is located in the Midwest and most of its vehicles do not get deployed to such hostile environments. At the conclusion of the test, each site was also asked to paint a full-sized vehicle: a Humvee at Fort Campbell and a forklift at Fort Eustis.

One area of concern was the use of a water-based primer in a high humidity environment. Fort Eustis did encounter repeated difficulties with the primer running on the test coupons, but the painters indicated that they believed the problem could be controlled after more experience with the product and a better understanding of its characteristics. Fort Campbell did not encounter problems with the primer.

The turbine HVLP system performed extremely well at both sites, even though it was decided not to thin the thick CARC topcoat. Painters at both sites commented on the simplicity of design and ease of cleanup, resulting in reduced cleanup time and solvent use. The high level of transfer efficiency for the turbine HVLP, resulted in a 40% decrease in paint usage.

Test panel drying time in the field was based on three measures in ASTM D 1640: "set-to-touch", "dry-hard", and "dry- through". These tests indicated that the materials are within military specifications, although some of the drying times for the topcoat slightly exceeded the 30-minute maximum. Both primers had similar "set-to-touch" times, but the alternate primer had shorter "dry-hard", and "dry-through" times. Coating thickness differences caused varying rates of drying, even at different places on the same test panel.

Laboratory tests on the painted test panels (paint film for quartz spring test) consisted of six methods: (1) Tape adhesion test using cross-hatch method (ASTM D 3359-95), (2) Visual appearance test for surface imperfections (MIL-C-53072B sec. 4.3.3.8), (3) Conical mandrel test of flexibility (ASTM D 522-93a), (4) Immersion test of water resistance (ASTM D 870-87), (5) Taber abrasion test of wear resistance (ASTM D 4060), and (6) Colorimeter test of hiding efficiency (ASTM D 2244).

 

Results of Test Panel Analysis

Adhesion testing was conducted on all CARC systems on both substrates. Only one system from one site failed the adhesion test (alternative primer and spray gun used to paint aluminum), but this was probably an anomaly, because it did not occur for the same system and substrate at the other site. Since the test is somewhat subjective, the slightly better rating for systems using the alternative primer was not significant enough to rate one system as the superior system.

Visual inspection of test panels for surface imperfections did not detect any significant differences between the alternatives.

Results of the flex test, which involved bending a test panel over a conical mandrel, can be summarized as follows: (1) All aluminum panels with topcoat and primer applied failed the flex test at both sites, (2) Most carbon steel panels with topcoat and primer applied at Fort Eustis failed the flex test, (3) All carbon steel panels painted at Fort Campbell passed the flex test, and (4) All panels (both substrates, both sites) painted with primer only passed the flex test. Although some flex failures did occur, particularly for aluminum panels, the paint systems performed relatively equally in terms of flex characteristics.

Three test panels from each "primer" only system were partially submerged in a water bath and then evaluated for water-related damage both visually and with a tape adhesion test. All of the panels at Fort Campbell painted with the baseline primer on both substrates exhibited evidence of blistering and seven of the 12 panels also failed the adhesion portion of the test. It appears that the blistering may have been caused by solvent entrapment, where solvent is trapped in a first layer of the paint by the immediate application of a second layer. Many of the panels at Fort Campbell were sprayed with two layers of primer. There was visual evidence that the panels at Fort Eustis were "dry sprayed", where solvent leaves the paint before it hits the target. This would avoid solvent entrapment and may explain why the panels at Fort Eustis did not show water-related damage.

Wear resistance was measured at three locations on each panel before and after subjecting coatings to 1000 wear cycles with the Taber Abraser. The average change in coating thickness was reported by panel and for all replicates of the same system. There was no difference in wear resistance in the panels painted at Fort Campbell, but panels for some systems at Fort Eustis did show wear. This difference at Fort Eustis appeared to be caused by overspray contributing to the initial thickness or spraying the topcoat too thin, but did not appear to be due to differences in the paint systems.

Hiding efficiency was determined using a colorimeter to measure the difference for each site and substrate between the test panels painted with topcoat and primer and a standard painted with only the topcoat. Since there were no substantial differences between the test panels and the standard, and all system differences were less than 1 unit (with 3-4 being humanly observable), the four systems were considered to perform equally in hiding efficiency.

 

Overall Conclusions

The results of this study indicate that the combined LCA and life cycle design approach is viable and greatly improves the tradeoff analysis between different decision elements. The use of valuation weighting, although not essential, makes it easier to identify the preferred alternative. Limitations of the LCA approach are the need for refinement in the normalization step and data gaps in the LCI and LCIA.

Of the five CARC alternatives considered, two of them (alternative gun and a combination of alternative gun and primer) clearly showed the potential for environmental improvement over the baseline without significant change in cost or performance.

The performance evaluation, which compared the baseline with the preferred alternative, showed that the alternative painting materials (primer and thinner) were generally equal to the baseline and the alternative spray gun (turbine HVLP) was superior to the baseline gun. The high level of transfer efficiency for the turbine HVLP, required about 60% as much paint to cover a full-sized vehicle as the conventional HVLP. This could result in a potential annual cost saving, for a base with paint consumption like Fort Eustis, of more than $230,000.

 

References

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Hendricks, D., R. Purcell, M. Tedijanto, and D. Russell. 1995. Life Cycle Inventory for Chemical Agent Resistant Coating. Draft Report. Prepared by Pacific Environmental Services, Incorporated for the U. S. Environmental Protection Agency, Risk Reduction Engineering Laboratory, Office of Research and Development, Cincinnati, OH.

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