Vapour phase inhibitors

The testing of vapour phase inhibitors, usually referred to as volatile corrosion inhibitors, is essentially a matter of placing a test specimen in the vapour space of a closed vessel containing an aggressive atmosphere — frequently water vapour, perhaps with SO2 present—and a quantity of the inhibitor. Variations on the basic technique include provision for circulation of the vapour, the use of paper impregnated with inhibitor, provision for temperature cycling, etc. 

If a spare rotor or element is purchased, it shall be prepared for unheated indoor storage of 3 years. Storage preparation shall include treatment with a rust preventive and enclosure in a vapour barrier envelope with slow release vapour phase inhibitor. The rotor or element shall be boxed for the type of shipment specified. A rotor shall have a resilient material (but not lead, TFE or PTFE), at least 3 mm (0,12 in) thick, between the rotor and its support cradle support shall not be at the rotor s Journals. An element shall have its rotor secured to prevent movement within the stator. 

Humidity chambers Used in testing vapour phase inhibitors using wet-dry cycles. Tropical, marine and industrial atmospheres are simulated. Percentage of surface area rusted in the case of ferrous metals is measured. Changes in surface properties such as color in the case of nonferrous metals are assessed [10, 11]... 

Kunzelmann, U., Jacobasch, H.J., and Reinhard. G., Investigations of the influence of vapour phase inhibitors on the surface charge of iron oxide particles by zeta-potential measurements, Werkstoffe Korrosion. 40, 723, 1989. 

Other field tests with proprietary vapour-phase inhibitors [17] in a parking garage with chloride-contaminated precast slabs did not show encouraging results. Corrosion-rate measurements showed a reduction of 60% in areas with initially intense corrosion but also an increase of corrosion rate in areas with low corrosion rates. On structures from 1960 with an admixed-chloride content higher than 1% by mass of cement, already featuring patch repairs, a three-year corrosion rate survey showed lower corrosion rates in the treated areas compared to untreated ones, but cracking and spalling increased also in the treated areas [18]. 

Vapour phase inhibitors can also be considered as adsorption inhibitors. These are used for protection of wrapped components temporarily. The inhibitor is placed together with the component(s) and acts due to its suitable low saturation pressure, leading to a sufficiently durable inhibitor condensate on the metal surface. By this the effect of water and oxygen is prevented. It should be emphasized that these inhibitors may accelerate corrosion on some non-ferrous metals and alloys. Examples of vapour phase inhibitors are bicyclohexyl-ammonium nitrite and cyclohexyl-amine carbonate. 

Other methods include use of intelligent pigging as well as corrosion prediction models developed by C. De Waard and some other modifications that have been published and commercialized by several other investigators. However, after prediction and/or detection of corrosion incidents inside the pipelines, the most cost-effective method of control is the use of corrosion inhibitors. These are usually amine based and are thus water dispersible. They are usually blended with vapour phase inhibitors and probably some flow enhancers. 

Vapour phase inhibitors or migrating corrosion inhibitors have been used to impregnate packaging, greases and waxes for many years to protect steel machinery and components, particularly before use. An American company... 

Vapour phase inhibitors (VPIs) are volatile compounds that can be incorporated into a number of carriers such as waxes, gels and oils. They will diffuse through the air, or the concrete pores, to the steel surface. In principle their ability to diffuse as a vapour gives them an advantage over liquid inhibitors. However, they can also diffuse out of the concrete unless trapped in place. They may diffuse poorly through saturated concrete. 

Fiaud C. Theory and practice of vapour phase inhibitors. In TrabaneUi, G. Corrosion Inhibitors. The Institute of Materials, 1994 1-11. 

Type of carrier paper or film for the vapour phase inhibitors. 

Piaud, C., Theory and Practice of Vapour Phase Inhibitors, in A Working Party Report on Corrosion Inhibitors, London, U.K., The Institute of Materials, 1994, pp. 1-11. 

When flow velocities are lower, the flow is partly annular, with a higher concentration of liquids in the bottom half of the pipe, i.e. the film of liquids is thicker. Lower flow velocities allow some free liquid to collect in the bottom of the line, and slug flow predominates. As the flow rate declines, stratified flow predominates and the stream has separate gas and hquid phases. The top portion may not be regularly contacted at aU by liquid, except that condensed from the gas. A vapour-phase inhibitor or some means of introducing a periodic batch that contacts the top of the fine should be considered. In stratified flow, partitioning of the inhibitor between oil and water layers is important Slug flow increases requirements for the ability to withstand shear stress. 

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