Selection of Stainless Steel for Handling Citric Acid C3H4OH (COOH)3

Citric acid is a weak organic acid, found in fruits such as lemons (citrus)

Either the stainless steel 304 or stainless steel 316 types can be considered for most storage and handling applications. Citric acid is also be used forcleaning stainless steel and passivating stainless steel.

The low carbon types (304L stainless steel or 316L stainless steel) may be needed for temperature above around 60 degC to avoid any risk of intergranular attack in weld heat affected zones.

The iso-corrosion diagram 0.1mm/year lines show that either the stainless steel 304 (blue) or stainless steel 316 (red) types can be selected for normal storage & handling applications. 

(The chain line represents the solubility and the broken line the boiling point)

The stainless steel 304 types should be adequate for most applications.

At temperatures above 80 degC the stainless steel 316, or preferably the stainless steel 316L types, should be considered.

In common with most acid handling applications, chloride contamination may be a cause of pitting corrosion and so in these cases more pitting resistant grades may need to be considered.

Citric acid can be used for cleaning & passivating stainless steel, as an alternative to nitric acid. Solution strengths of 5-10% citric acid are used for passivation treatments.

Source: Yaang Pipe Industry Co., Limited (www.yaang.com)