Surface preparation and initial corrosion protection

VOC = volatile organic compound HAP = Hazardous air pollutant Sec 313 of the Emergency Right-to-know Act (EPCRA), also known as Title 111 of the Superfund Amendments and Reauthorization Act of 1986 (40 CFR Part 372). Use of strong acid process, no supplier notification. Ligroine (light naphtha), VM P naphtha, Stoddard solvent, and certain paint thinners are also commonly referred to as mineral spirits. These distillation fractions contain less than 10 % by mass HAPs (see Table 14.26.4). 

SfH ying thinner solvent cleaner (fast) Epoxy MIBK, 24 % 8.58 1.7 28 116 23.3 0.796 0.54 

Lacquer retarder (thinner) cleaner (slow) Lacquer EGBE, 51% 10.2 0.072 0.6 169 26.9 0.899 3.0 

Spray gun cleaning procedures may be a once-through type with collection of spent solvent in a container for disposal or reuse. Some facilities use commercial gun washers. Because gun washers are enclosed and recirculate solvent, they can reduce the amount of solvent lost by evaporation. In either case, the emissions are calculated as the difference between the amount used and the amount recovered. 

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The British Standard Code of Practice for protecting iron and steelwork from corrosion, BS 5493 1977 contains a section on inspection which may be helpful. This type of inspection is entirely unnecessary for very simple painting schemes. In such situations an occasional visit by an inspector may be sufficient to ensure acceptable results once initial standards of surface preparation and paint application have been established. 

We can define pretreatment as the initial conditioning period whereby a corrosion inhibitor is applied to the metal surfaces of the cooling system. Pretreatment conditions must be conducive to the rapid formation of the protective barrier. The conditioning procedure should involve (1) the cleaning and preparation of metal surfaces, and (2) the actual application of higher than normal inhibitor concentrations. 

The most popular method involves deposition initially of a layer of electroless copper up to 2 /an thick. The excellent conductivity of the copper ensures that this gives good results for attenuation (that is, for shielding). The copper layer is followed by electroless nickel up to 1 /an thick, which protects against abrasion and corrosion. Obviously it is important that the nickel not be porous and with this in view an activation stage may be interposed, with chemical deposition of palladium on the surface of the copper in preparation for the nickel. 

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