Napthenic acid attack

Most crude oils contain some napthenic acid. These acids tend to concentrate in those crude oil components that boil between kerosene and heavy gas oil. Naphthenic acid corrosion is characterized by a general thinning of stainless steel vessels and tower internals at temperatures between 450 to 750°F. Rates of corrosion are greatly accelerated in areas of high velocities. 

My experience indicates that stainless steels that have high chrome and nickel content are not very resistant to naphthenic acid attack. What is required is molybdenum. 304 stainless steel is unsuitable due to its low moly content. Even 316 stainless steel, which has about 2 percent moly, offers only marginal protection. 1 usually specify 317 stainless steel, which has about 3 percent moly, when designing for naphthenic acid services. 

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A few acid woods, such as oak, chestnut and Western red cedar, accelerate surface weathering of aluminium, but do not usually give rise to serious attack . Timber preservatives containing soluble copper compounds should be avoided creosote and zinc napthenate are satisfactory preservatives for wood in contact with aluminium. 

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