A350 grade LF1 forgings API Std 650 mechanically-anchored flat-bottom tanks

Large Low-Pressure Tanks Corrosion Allowance
In cases in which the rate of corrosion is closely predictable, additional metal thickness over and above that required for the initial operating conditions shall be provided and shall be at least equal to the expected corrosion loss during the desired life of the tank.
When corrosion effects are indeterminate before the tank is designed (although they are known to be inherent to some degree in the service for which the tank is to be used), and when corrosion is incidental, localized, or variable in rate and extent, the best judgement of the API Std 650 mechanically-anchored flat-bottom tanks designer must be exercised in establishing reasonable maximum excess tank wall thicknesses. For all tanks that come under this classification, a minimum corrosion allowance of 1/16 in. shall be provided.

Lateral braces between outer bay rafters must be provided if asymmetrical structural shapes are used for rafters and if the API Std 650 mechanically-anchored flat-bottom tanks API 650 tanks are located in areas subject to earthquakes. The bracing must be adequately sized for the seismic zone specified.

Generally, external environment corrosion should be considered before design and construction of API Std 650 mechanically-anchored flat-bottom tanks and so on storage tanks. The corrosion on the outer surface of storage tank is often worse than that on the inner surface. Especially in the chemical industry area, there are often acid fog, alkali or salt dust in the atmosphere. These impurities form an active corrosive medium with dew or steam and oxygen in the atmosphere. The corrosion of the external environment of the storage tank shortens the maintenance period of the storage tank, even causes the storage tank to be scrapped in advance, which affects the normal operation of the storage and transportation.