Standard passivation by nitric acid attacks iron at the surface this only partly solves the problem. The remaining iron under the skin will now corrode both inwardly and outwardly. The inward corrosion is known as I.G.A. or intergranular attack. The results are metal fatigue and surface corrosion, the latter being disastrous to any food, medical, or surgical application. The photograph on the side of the page indicates how passivation by nitric acid actually raises the micro finish of a surface because it leaves pits where iron had existed. Any high purity application such as a gas or liquid valves and pumps, bearings vacuum systems or fuel supplies would be subject to detrimental effects with out through passivation.