TR3 Guidelines for Minimizing Water Staining of …

1 Guidelines forMinimizing WaterStaining of AluminumGuidelines for MinimizingWater Staining of AluminumTR3 FIFTH EDITION, MAY use of any information contained herein by any member ornon-member of The Aluminum Association is entirely Aluminum Association has used its best efforts in compilingthe information contained in this book. While the Associationbelieves that its compilation procedures are reliable, it does notwarrant, either expressly or implied, the accuracy or completenessof this Aluminum Association assumes noresponsibility or liability for the use of the information Aluminum Association published standards, data,specifications and other technical materials are reviewed andrevised, reaffirmed or withdrawn.

2 Users are advised to contact TheAluminum Association to ascertain whether the information in thispublication has been superseded in the interim betweenpublication and proposed The Aluminum AssociationThe Aluminum Association, Inc. is the trade association for producers of primary aluminum, recyclers and semi-fabricated aluminum products, as well as suppliers to the in Arlington, Virginia, with offices in Detroit, Michigan, the Association provides leadership to the industry through its programs and services which aim to enhance aluminum sposition in a world of proliferating materials, increase its use asthe material of choice, remove impediments to its fullest use,and assist in achieving the industry s environmental, societal.

3 And economic companies operate about200 plants in the and many conduct business ASSOCIATION SHEET AND PLATEDIVISION COMPANIESA lcoa Rolled ProductsAMAG Rolling GmbHARCO Aluminum Aluminum, Aluminum AluminumCorporationJW Aluminum CompanyKaiser AluminumCorporationNichols AluminumNovelis Tinto AlcanUnited AluminumCorporationWise Metals GroupThe 2009, fifth edition has been revised through the support of the Technology Committee of the Sheet and Plate Wilson Blvd., Suite 600 Arlington, VA 22209 Guidelines for Minimizing Water Staining of AluminumContents1. Introduction ..42. Causes of Water Stain ..4A. External Sources ..4B. Moisture Condensation ..43. Packaging ..74. Inspection Procedures.

4 75. Prevention ..86. Conclusion ..9 Appendices1. Aluminum Water Stain Prevention .. Instrument Suppliers .. Suppliers of Water Indicator Labels .. Suppliers of Water Stain Preventatives ..1031. IntroductionAluminum is naturally attractive and resistant tocorrosion. Unlike most other metals, it takes care ofitself. When exposed to dry or moist air it combineswith oxygen to form a tough, transparent,protective oxide coating. In the presence ofmoisture, aluminum will not rust as will steel, butunder certain conditions aluminum will stain. Suchstains are usually found objectionable for estheticreasons; they have no significant effect on strengthbut may cause processing problems whereadditional surface finishing or fabrication is to beperformed.

5 Virtually all Staining problems occurduring shipping, handling, or storage. Some of theincorrect practices that result in Water Staining andways to minimize or avoid the Staining arediscussed in this pamphlet. A summary of themeasures to minimize Water Staining is provided in Appendix 1 and is reproduced as a handy wallchart, which is included with this pamphlet. Copies of the chart may be obtained from The Aluminum Causes of Water StainAluminum and other metals can stain when Water istrapped between wraps, sheets or other matingsurfaces. If there is no air flow to remove the Water ,prolonged contact between the Water and the metalcauses a reaction between the two which results inwater stain.

6 Figures 1 and 2 show examples of waterstaining on aluminum coiled and flat sheet,respectively. There are two main sources of this SourcesObvious sources are rain, snow and Water coming in contact with the surface of thealuminum from sources such as a leaking tarp on atruck or a leaking roof in a storage area has thepotential for causing Water CondensationThis is the more complex of the two sources andtherefore harder to understand and control. Airnormally contains moisture in the form of invisiblewater vapor. Relative humidity, expressed as apercentage, provides a measure of the amount ofwater vapor actually in the air compared to the totalamount of Water vapor that the air can hold. As thetemperature of air increases, its capacity to hold watervapor point is the temperature at which watervapor from the air begins to condense and is affectedby the relative humidity and temperature of the dew point can be determined from a chart (seeTable 1), based on simple measurements of airtemperature and relative humidity.

7 The type ofinstrument used to measure (and log) temperature andrelative humidity is shown in Figure 3. The older styleof thermometers containing mercury should not beused because mercury from broken thermometers cancorrode aluminum and other metals. Some suppliersof these instruments are listed in Appendix 1 Water Stain on CoilFigure 2 Water Stain on Sheet Water vapor condenses on the surface of a metal ifthe temperature of the metal drops below the dewpoint of the surrounding air. Afamiliar example ofcondensation is the fogging of one s eyeglassesupon entering a warm room after being in the coldoutdoors. Another common example is condensationon a cold beverage can as shown in Figure 4. As mentioned before, when the temperature ofaluminum drops below the dew point of air, watercomes out of the air and deposits on the surface ofthe aluminum.

8 The temperature of the aluminumcan drop below the dew point of the air under thefollowing Storage:When storing metal, it is not recommended toleave warehouse doors open especially duringthe spring and fall months, when there may beextreme differences in temperature between dayand night. During the night, cold air enters andstarts cooling the metal. During the day, if thetemperature and humidity of the air increaserapidly, the dew point rises quickly. But, thetemperature of the aluminum increases at a muchslower rate; this sets up the condition wherewater begins to condense on the surface of this process is not limited to falland spring months but may occur wheneverthere are large enough fluctuations intemperature and Loading:Loading metal removed from a cool or coldstorage area into a warm trailer or railroad car,on a humid day, can result in condensation onthe aluminum.

9 This can occur during any seasonof the year; however, for some areas it may bemore pronounced in Unloading-Moving Cold Metal IntoWarm Storage:Condensation at the unloading point is morelikely to occur during the cooler months. Thefollowing example may help to clarify this point:Metal at 16 C (60 F) in a warehouse isloaded into a trailer and shipped.

10 The metal is intransit for about two days. The outsidetemperature is - 1 C (30 F). Within a two-daytransit period, the temperature of the metalgradually decreases to -1 C (30 F). When thealuminum reaches its destination, it is unloadedand moved directly into a warehouse where thetemperature is 16 C (60 F) and the relativehumidity is 50%. From Table 1, the dew point ofthe air is 5 C (41 F). Since the temperature ofthe aluminum is now lower than the dew pointof the air, conditions are ideal for Water tocondense on the surfaces such as the edges ofstacked sheet or coils. The condensed moisturecan enter between the sheets and wraps bycapillary action and may produce Water 3 Digital Instrument for MeasuringTemperature & HumidityFigure 4 Condensation on Cold Aluminum Cans Table 1.