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  • Vol. 60, No. 6 June 2004

    Founded 1945

    CORROSION SCIENCE

    515523538548561

    2004 F.N. Speller Award Lecture: Efficacy of Vapor Phase Corrosion InhibitorTechnology in ManufacturingB. Miksic, R. Boyle, and B. Wuertz

    Corrosion Mechanism of Nickel-Containing Stainless Steels in ConcentratedAqueous Solutions of Sulfuric AcidJ.R. Kish, M.B. Ives, andJ.R. Rodda

    Detecting External Failures in Coated, Buried Pipelines: Theoretical Modeland Experimental VerificationH. Castaneda and M. Urquidi-Macdonald

    Corrosion Evaluation of Alloy 800 in Sulfate/Vanadate Molten SaltsC. Cuevas-Arteaga, J. Uruchurtu-Chavan'n, J. Gonzalez, G. Izquierdo-Montalvo,J. Porcayo-Calderon, and U. Cano-Castillo

    Electrochemical Study of UNS S32550 Super Duplex Stainless Steel Corrosionin Turbulent Seawater Using the Rotating Cylinder ElectrodeG. Kear, B.D. Barker, and F.C. Walsh

    CORROSION ENGINEERING

    573

    584594

    Microstructural Characterization and Pitting Corrosion Behavior of UNS S30466Borated Stainless SteelD.A. Moreno, B. Molina, C. Ranninger, F. Montero, and J. Izquierdo

    Effect of Climatic Parameters on Filiform Corrosion of Coated Aluminum AlloysN. LeBozec, D. Persson, D. Thierry, and S.B. Axelsen

    Development of an Artificial Saliva Solution for Studying the Corrosion Behaviorof Dental AlloysG.S. Duff6 and E. Quezada Castillo

  • CORROSION SCIENCE SECTION

    2004 F.N. Speller Award Lecture:Efficacy of Vapor Phase Corrosion InhibitorTechnology in Manufacturing

    R. Boyle, * and B. Wuertz*

    ABSTRACT

    Corrosion is a plight that faces everyone who works withmetals. Its impact on the U.S. economy has been documentedto be about 4% of the gross national product. It was esti-mated that about one third of the corrosion damage could beavoided. The avoidable costs were related to the failure touse the best practices available. There are several ways ofcombating corrosion. One way that is gaining wider accep-tance is to use vapor phase corrosion inhibitors. Volatile cor-rosion inhibitors were originally developed to protect boilersand piping systems of ships to be mothballed. Their effective-ness and ease of application attracted early users. Over theyears, the field of usage has increased to cover electronics,packaging, process industries, reinforced concrete, coatings,and metalworking fluids.

    KEY WORDS: vapor phase corrosion inhibitors, manufactur-ing, metals

    INTRODUCTION

    A 2002 NACE International study estimated that theannual cost of corrosion in the United States alonenears 3.1% of the gross domestic product (GDP)astaggering $340 billion. The real-world implication tometal manufacturing and processing is the addedcost of doing business. Aside from the most visibleeffects, such as product failure and rejection, arethose "hidden" costs that are part of the everyday

    Presented as the F.N. Speller Award Lecture at CORROSION/2004, March 2004, New Orleans, LA.Corresponding author.Cortec Corporation, 4119 White Bear Parkway, St. Paul, MN55110.

    manufacturing process. Expenditures on cleaning,blasting, reworking, and disposal combined withlabor-intensive additional processing steps greatlyaffect the bottom line.

    To combat the devastating effects of corrosionand in an attempt to preserve valuable militaryequipment, the U.S. Navy tested the first volatile cor-rosion inhibitor (VCI) chemistry for the mothballingof boilers and similar structures on war ships in thelate 1940s. The core chemistry at that time was atoxic amine nitrite solution applied to the inside ofinaccessible spaces. Although a similar nitrite-basedchemistry is still widely used today, there is an effec-tive, environmentally sound, and safer alternative.(Figure 1).

    A new generation of corrosion inhibitors emergedin the late 1970s called vapor phase corrosion inhibi-tors (VCIs). These new chemistries were developed toutilize state-of-the-art, nontoxic organic inhibitors ina wide variety of forms. The VCI technology, as de-scribed below, protects metals from corrosion duringmanufacturing, processing, shipping, storage, andwhile in use without any residual contamination tothe protected metal. The result is a vast line of prod-ucts all designed to take the cost of corrosion out ofthe metalworking and manufacturing process.

    CORROSION AND VCIs

    Simply defined, corrosion is the natural processof a material, usually a metal, returning to its origi-nal state through an electrochemical process due toa reaction with the surrounding environment. Al-

    Vol. 60, No. 60010-9312/04/000083/$5.00+$0.50/0

    2004, NACE International 515

    B. Miksic,

  • CORROSION SCIENCE SECTION

    Toxicity DataChemical LD50 (mg/kg-rat)

    Table salt 3,000(sodium chloride)

    Food preservative/corrosion inhibitor 85(sodium nitrite)

    Nitrite-based VCI powder 284

    Non-nitrite-based VCI powder 2,100

    FIGURE 1. Toxicity data for some common corrosion inhibitors.

    Molecules ofVCt in gaseous phase

    FIGURE 2. VCI molecules vaporize, condense on all metal surfaces,and re-heal and self-replenish through further condensation of thevapor.

    though corrosion is a natural process, certain atmo-spheric conditions that a metal is exposed to duringits manufacture, processing, storage, or shipmentcan aggressively accelerate the degradation. Mostnotable of these factors are sulfur dioxide (typicallyassociated with the burning of coil, oil, and gas),acids in packaging materials, and temperature andhumidity fluctuations during transit.

    VCIs are organic compounds that have sufficientvapor pressure under ambient atmospheric condi-tions to travel essentially to the surface of the metalby diffusion and to adsorb physically onto the sur-face. In the presence of moisture, the VCI moleculebecomes polarized and attracted to the anode andcathode of the metal. Once the VCI protective ionsare adsorbed onto the surface, the electrochemicalprocess of corrosion is interrupted as the ions createa protective barrier to contaminants such as oxygen,

    water, chlorides, and other corrosion accelerators.With the protective barrier in place, the corrosion cellcannot form and corrosion is halted. (Figure 2).

    Unlike nitrite inhibitors, which do not havesufficient vapor pressure under ambient conditions,VCI products can actually protect yellow and ferrousmetals as well as soldered parts and alloys. Whereaswater-displacing, water-absorbing, dehumidification,and barrier products try to alter an ever-changingenvironment surrounding the metal, VCI technologypassivates the metal's surface. In fact, VCI moleculesactually use the same mechanism that acceleratescorrosion to accelerate the release of protection mol-eculesa built-in defense mechanism (Figure 3).

    MANUFACTURING WITH VCI PRODUCTS

    During the typical manufacture of a metal prod-uct, the material is cleaned, oiled, blasted, machined,finished, assembled, painted, and packagedin somecases, numerous times before it is sent to the cus-tomer. By effectively utilizing the benefits of VCItechnology, many of these in-process steps can becompleted eliminated (Figure 4). Other cost savingsresult when the disposal and cleanup costs are cal-culated. Imagine a manufacturing process where thestarting metal structure is processed without needfor secondary oil rust preventatives, rework, rustremoval, blasting, or cleaning.

    VCIs in their pure form are usually off-whitepowders and can be used in this form for protectionof large void spaces (such as the heat recovery steamgenerators [HSRGs], boilers, turbines, and pipespreviously coated with amine nitrite inhibitors). Addi-tionally, VCIs can be incorporated into coatings,greases, functional fluids, cleaning systems, hydro-testing solutions, even concrete and plastics. Theresult for a manufacturer utilizing VCI product isstreamlined processes, improved product quality andacceptance, and overall cost reduction.

    But how do VCI molecules affect the metal sur-face? The VCI molecules are designed specifically toprevent reactions on the metal surface. Whereasmany methods of corrosion protection alter the metal(i.e., stainless vs carbon steel, cathodic protection,and treatment of metal), VCIs do not alter the surfaceas the protective ions are adsorbed to the surfacerather than becoming permanently attached.

    A study was conducted on VCI products todetermine how the protective molecules affected theexposed ends of fiber optics cables. Three productswere tested, including VCI-treated anti-stat polyeth-ylene film, polyurethane foam impregnated with VCI,and VCI powder contained in high-density vapor per-meable polyethylene film pouches. The testingshowed that there was no indication of attenuationchange caused by the corrosion inhibitors. The re-sults of this study are included in Figure 5.

    516 JUNE 2004

  • CORROSION SCIENCE SECTION

    Corrosion Prevention Methods Used by Military OrganizationsCorrosionPrevention

    Method Product Type Benefits Disadvantages

    Water-displacing products Petroleum-based(light oils or thixotropicgreases)

    Water-absorption products Silica gel (dessicants)

    Dehumidification Dehumidifier Vapor barrier bags

    VCIs Anodic inhibitors (e.g.,sodium nitrite [NaNO2],dicyclohexylamine nitrite,sodium benzoate)

    Cathodic inhibitors Mixed inhibitors

    Relatively inexpensive Water displacement Create a barrier coating on

    metal surfaces Excellent permanent protection

    Economical alternatives fortemporary protection

    Effective for storage andshipping

    Effective in electronic andelectrical operations

    Can be successful if air flow tothe metal is totally restricted

    Vapor barrier bags areexcellent for one-time use (offera sturdy multilayer film)

    Good way to protect electronics

    Anodic inhibitors> Prevent metal cor