How to decide the corrosion allowance while designing a vessel

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Could anyone tell me how to select the corrosion allowance required to be assumed while designing a vessel, in particular for a high pressure ammonia storage receiver used in a refrigeration plant.

Pl help. Thanks in advance

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[metengr]

The typical anhydrous ammonia storage tanks are constructed of stress relieved, carbon steel in accordance with ASME Section VIII, Div 1 requirements. From my experience with our power plant SCR's that use ammonia injection, our design specification for ammonia storage tanks required a 1/8" corrosion allowance. The 1/8" is a common value used in pressure vessel design. I would see no difference for your application. Remember, the corrosion allowance is not taken credit for in calculating minimum vessel wall thickness.

 

[stanweld]

Corrosion allowances are determined from established corrosion rates of a material exposed to a corrosive media, concentration and temperature of exposure and then deciding the desired service life of the vessel. There are a number of resource books available to provide corrosion rates.

 

[Metalguy]

You must determine the amount of moisture in the ammonia. A little moisture will greatly reduce the corrosion rate.

 

[metengr]

Metalguy;
The moisture content can vary from 0.2 to as much as 0.5 percent, but must remain above a minimum threshold of 0.2 percent by weight to prevent SCC of carbon steel by liquid ammonia with any entrapped air in the vessel.

 

[grnblr]

Thanks metengr

the details will help

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