Performance of Galvalume� Sheet in Animal Confinement Applications Background:Galvalume sheet continues to enjoy significant growth in the construction market due ainly to its outstanding corrosion resistance in a wide variety of environments, including those in rural, industrial, marine and severe marine regions of the country. Atmospheric corrosion testing, now on-going for more than 25 years, has clearly demonstrated that Galvalume sheet is at least 2-4 times more durable in these environments than G90 galvanized sheet1. Field inspections of buildings constructed more than a dozen years ago with commercial Galvalume sheet confirm the long-term durability of the product also extends to regions of the country exposed to acid rain2. In certain applications, however, even the best of materials can be challenged by severely aggressive environments. One of these applications is the animal confinement building, where pigs, cattle or poultry are intensively housed. This Technical Bulletin is aimed primarily at distributing information on the performance of Galvalume sheet in these animal confinement applications in efforts to assist in materials selection decisions. Animal Confinement Housing:An increasing percentage of pigs, cattle, turkeys and chickens are being raised on farms in buildings where the animals are confined for all or most of their lives. While this practice affords certain benefits in regulating the environment for optimizing productivity, the resulting animal waste and waste decomposition by-products can create significant corrosion problems for materials used in the construction of those buildings. Although it almost goes without saying that direct contact with animal wastes should be avoided, even materials which do not come in contact with the wastes themselves are subject to extremely corrosive conditions. Building design factors which impact on the corrosivity of these environments include insulation and ventilation practices, as well as the nature of the animal waste disposal system. Insulation: Corrosion in confinement buildings has been observed to occur on both the topside and the underside of roofing panels. Waste decomposition gases such as methane, hydrogen sulfide and ammonia can combine with water vapor to form a very corrosive solution which then condenses on the underside of metal roofing panels, resulting in severe corrosive attack. To protect the roofing panels, many confinement buildings are constructed with rigid board or batt insulation. Galvalume is a registered trademark of BIEC International, Inc. Well sealed joints and vapor barriers help maintain moisture tightness so aggressive condensates cannot form between the insulation and the roofing panels. Since some structures exhaust corrosive fumes under the eaves, extending the rigid board insulation out to the drip edge helps protect the underside of the eaves from accelerated attack. Ventilation: Since the corrosive fumes are generated within the animal confinement building, any efforts to improve ventilation will tend to reduce the severity of general corrosion due to decreased concentration of the noxious gases. Natural and power ventilation through ridge caps and sidewalls can be used, but attention should be given to the areas where the fumes are discharged; i.e., the concentrated gases can increase the corrosive attack of materials in the proximity of the discharge area. Waste Disposal Systems: Removal of animal wastes impacts upon the corrosivity of the environment, not only by the method of removal, but also by the frequency. The most aggressive systems involve water mixtures, or slurries, used many times in pig confinement to flush the wastes away from the building. In some pig and cattle confinement buildings, a mechanical blade is used to periodically drag the wastes to one end of the building for subsequent removal. The natural moisture associated with pig and cattle wastes, together with these waste removal systems, make pig and cattle confinement buildings extremely corrosive environments. In poultry broiler or breeder houses, animal wastes are often collected in a dry litter of wood chips or sawdust. The litter is replenished or replaced several times a year. In many egg-laying operations, chickens are kept in tiered cages from which the wastes fall to a "basement" level below. The piles of waste are removed once or twice a year. The dryer nature of poultry waste, together with the methods for removal, make poultry houses somewhat less corrosive in nature than pig and cattle confinement buildings. This is borne out by building inspection results described later. Cattle and Pig Confinement:Due to the corrosive factors noted above, attack of Galvalume sheet in cattle and pig confinement buildings is particularly severe. Pinpoint surface and edge rusting has been observed within one year and, in some cases, perforation of the roofing panels in three to four years. Areas of the buildings exhibiting the most severe attack including the underside of uninsulated roofs, crevices between roof panels and purlins where condensate was trapped and the topside of roof panels near ventilators. Neighboring buildings have not been adversely affected by their proximity to cattle and pig confinement buildings, presumably due to effective dispersion of fumes once they are exhausted. While the durability of all metallic sheets is reduced in these types of environments, the use of aluminum sheet or galvanized sheet with heavy zinc coatings (preferably G185 or heavier) will prevent or forestall the onset of red rust. Galvalume sheet (bare or prepainted) is not recommended for cattle and pig confinement buildings. Poultry Confinement:Field inspections have shown that poultry confinement buildings are significantly less corrosive environments than cattle and pig confinement buildings, but still more aggressive than non-confinement agricultural and rural environments. A recent survey of more than 40 chicken and turkey confinement buildings indicated that hot dip galvanized sheet roofing panels with G90-G125 coatings performed well for about 15 years before the onset of significant amounts of red rust. (Typical one-side coating thicknesses for these coating weight designations are 0.77-1.07 mils, or 19.6-27.2 microns.) The degree of red rust observed in the sixteenth year for these buildings ranged from light to very heavy, affecting 5-40% of the roofing panels. Such performance is typical of galvanized sheet materials where good galvanic protection is provided initially, followed by rapid corrosion of the base steel once the galvanized coating is consumed. The field performance of AZ55 Galvalume sheet (typical one-side coating thickness of 0.88 mils, or 22.4 microns) in these buildings reflects a different corrosion mechanism. Corrosion usually begins as cosmetic pinpoint rust staining of panel faces. The degree of rusting is light for the first one to five years. The rust stain becomes darker and light edge rusting begins to appear after about 10 years. Thus, while the initial attack on Galvalume sheet begins earlier than on galvanized sheet, the ensuing corrosion progresses more slowly with time. While it is difficult to predict long-term corrosion performance in aggressive environments, the corrosion behavior observed in the field suggests that the practical service life of AZ55 Galvalume sheet is anticipated to be equivalent to that of G90 galvanized sheet in poultry confinement buildings. Non-Confinement Agricultural and Rural Environments:While animal confinement building applications certainly push the corrosion resistance properties of metallic-coated sheet materials to their limits, there are large numbers of other agricultural and rural construction applications in which Galvalume sheet has been performing successfully for upwards of 15 years. In addition, long-term atmospheric corrosion tests in progress for over 25 years demonstrate the excellent corrosion resistance of Galvalume sheet in these and other environments. For example, Galvalume sheet is commonly used in structures for hay and farm equipment storage, grain bins and silos, vegetable processing, etc. Recent field inspections of several silos and sweet potato curing and packing buildings in use for 8-16 years revealed that Galvalume sheet roofing panels were providing excellent corrosion resistance with no rust on panel faces, rollformed ribs or edges. For structures that are used sporadically to shelter animals, where occupancy is infrequent, generally not intensive, and building housekeeping procedures are improved compared to intensive animal confinement buildings, Galvalume sheet can be expected to perform in much the same manner as in non-confinement buildings. Some examples of these types of structures would include livestock exhibit buildings and equestrian training rings. In carefully monitored outdoor corrosion tests, now on-going for more than 25 years, Galvalume sheet is continuing to demonstrate that it provides the optimum combination of long-term durability, edge protection and resistance to crevice corrosion in rural, industrial, marine and severe marine environments3. The superior performance of Galvalume sheet in the rural environment is clearly demonstrated by the fact that the Galvalume sheet panels continued to be free of rust, while the galvanized G90 sheet panels exhibited first rust after 14 years. (For additional updated information on these tests, refer to Bethlehem brochure 4065, "Galvalume Sheet - A Superior Material for Building and Architectural Applications".) SummaryBased on closely monitored outdoor corrosion tests in progress for over 25 years and actual field inspections of animal confinement and agricultural non-confinement buildings up to 20 years old, the following conclusions and recommendations can be made:
References1. J.C. Zoccola, H.E. Townsend, A.R. Borzillo and J.B. Horton, "Atmospheric Corrosion Behavior of Aluminum-Zinc Alloy-Coated Steel", Atmospheric Factors Affecting the Corrosion of Engineering Metals � STP 646, S.K. Coburn, Ed., ASTM, pp 165-184 (1978). 2. W.D. Barker and A.R. Borzillo, "Field Study: Standing Seam Holding Up Well", RSI, pp 30-32 (December 1988). 3. H.E. Townsend, A.R. Borzillo and W.D. Barker, "Performance of Al-Zn Alloy-Coated Steel Sheet After 22 Years of Atmospheric Corrosion Testing", Intergalva, Rome, Italy (June 1988) |
