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Knowledge for the Sulphuric Acid Industry

Introduction
General
Definitions
Instrumentation
Plant Safety
Metallurgial Processes
Metallurgical
Sulphur Burning
Acid Regeneration
Lead Chamber
Technology
Gas Cleaning
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Strong Acid
Acid Storage
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Liquid SO₂
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Materials of Construction
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Materials of Construction - Storage Tanks
November 11, 2002

Introduction

The material selected for sulphuric acid storage tanks will depend on a number of factors such as:

• Tank size
• Desired acid quality
• Costs
• Acid concentration
• Storage temperature

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Shell

The materials of construction will depend on the acid concentration, temperature and composition.  The table under the heading Recommended Materials lists the options for materials of construction.  By far the most common material of construction is carbon steel.

Where iron pickup needs to be minimized stainless steel can be used for the shell although at considerably higher costs.  An alternative to stainless steel is anodically protecting the tank.

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Linings

Linings can serve to minimize or eliminate corrosion of the tank and reduce contamination of the acid.

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Phenolic Coatings

Baked phenolic coatings are use to minimize iron pickup and corrosion in tanks storing 93% H2SO4.  The life of this type of coating is severely limited in 98% to 99% service.  Phenolic coatings should never be exposed to alkaline neutralizations because alkali attacks phenolic coatings even in dilute concentrations.

The integrity of the lining is dependent on the quality of the surface preparation and the actual application of the lining.  All internal surfaces must be inspected, degreased and sandblasted.  A thermally cured phenolic coating #P403 of 0.178 mm to 0.254 mm (0.007 to 0.010 in.) thick is applied using a multi-coat procedure immediately following sandblasting. 

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Glass-lined

Glass-lined storage tanks are used where the acid is extremely pure and no contamination of the acid is permitted.  The storage requirements for high quality acid are generally small so storage tanks are generally small.

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Recommended Materials

The following materials are recommended for sulphuric acid service.

When specified, plate material shall be:

• Impact tested required where ambient temperatures are low such as in northern climates.
• Fully killed as per API 650.
• Fine grain practice as per API 650.

Some investigators claim that copper bearing steels such as ASTM A285 Gr. C, S57 provide lower corrosion rates and resistance to hydrogen grooving but others feel that there is no advantage and the added cost of the steel is not warranted.

The following steels are not recommended for use in sulphuric acid storage tanks:

• Carbon steel to ASTM A36, A283, A285, A515
• High strength steels and low alloy steels

When carbon steel to ASTM A36 or A285 is specified, it shall be made using other than rimmed or capped steel practices.

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