Caustic corrosion boiling

Caustic Corrosion. Concentration of caustic (NaOH) can occur either as a result of steam blanketing (which allows salts to concentrate on boiler metal surfaces) or by localized boiling beneath porous deposits on tube surfaces. 

In tests lasting for 14 days, Copson found that the susceptibility of steel to stress-corrosion cracking in hot caustic soda solutions increased with increase in nickel content up to at least 8-5%. Alloys containing 28% and more of nickel did not fail in this period. In boiling 42% magnesium chloride the 9% nickel-iron alloy was the most susceptible of those tested to cracking (Table 3.38). Alloys containing 28 and 42% nickel did not fail within 7 days. 

Hydrazine hydrate is actually used. It is an expensive reagent procured by distilling hydrazine sulfate with caustic soda in a silver retort. It is poisonous, corrosive, strongly basic, and attacks glass, cork, and rubber. Pure hydrazine hydrate is a white crystalline solid which melts at 40° and boils at 118°, but the usual commercial material is an 85% solution of the hydrate in water. 

Violent boiling spewed several tons of caustic soda droplets from an open manway on the roof of the tank. These droplets rained down in the vicinity of the tank and traveled downwind inside the plant. A light wind carried the caustic soda over rail cars tm a nearby in-plant railroad spur and further to employee automobiles in the several acre chemical plant s main parking lot. Corrosive chemical fallout was detected over 1-1/4-miles (2 km) away. The Plant Emergency Brigade used fire hoses to wash down the affected areas. 

AEROTEX GLYOXAL 40 (107-22-2) Flammable solid, but normally sold as an inhibited 40% solution. A highly reactive reducing agent. Violent reaction with water causes polymerization. Temperatures above boiling point of 122°F/50°C can cause polymerization. Reacts, possibly violently, with strong acids, caustics, ammonia, amines, amides, aldehydes, chlorosulfonic acid, ethylene amine, hydroxyl-containing materials. Corrosive to metals aluminum, copper, tin, steel, zinc. 

An example is the SCC of stainless steel at 200 °C in a caustic solution or in aerated chloride solution where no traces of dissolution are visible on the crack face. The three conditions, namely, tensile stress, susceptible sample material, and a corrosive environment are the conditions necessary for stress corrosion to take place (73, 90). For instance, SCC of metals has been by far the most prevalent cause of failure of steam generator components in pressurized water reactors (PWRs) to an extent of 69% of all cases, piping in boiling water reactors (59.7%) and PWRs (23.7%). More than 60% of inspected steam turbines in nuclear power plants have disks with stress corrosion cracks (91). 

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