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9. Selection of stainless steels for handling citric acid (C3H4OH(COOH)3)

Introduction

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

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

Corrosion resistance of stainless steels

The iso-corrosion diagram 0.1mm/year lines show that either the 304 (blue) or 316 (red) types can be selected for normal storage & handling applications.
(The chain line represents the solubility and the broken line the boiling point)

 

See Corrosion Handbook for source data.

The 304 types should be adequate for most applications.

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

At temperatures above 80 degC the 316, or preferably the 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.

Uses for citric acid with stainless steels

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

Passivation of stainless steels

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