Materials of Construction - Protective Coatings
April 29, 2002

Introduction Concrete         Surface Preparation         Environmental Conditions         Products Structural Steel

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Introduction

Protective caotings are used throughout an acid plant to protect equipment, structures, piping, etc. from the corrosive elements present in the atmosphere and from direct contact with liquid cause by spills.   Protective coatings serve two main purposes:

• Prolong the life of equipment, structures, piping, etc.
• Improve the visual appearance of the plant

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Concrete

Concrete foundations and structures in an acid plant are subject to attack from concentrated sulphuric acid.  Some of the attack occurs underground which can go undetected for many years. 

Concrete surfaces in containment areas must be protected from acid spills and wash downs.  The concrete must withstand attack from hot concectrated sulphuric acid as well as weak acid.  Special sulphur concretes can be used which are resistant to attack but even they should be protected by a coating applied to the surface.

Protective coatings for concrete must have the following characteristics:

• Resist attack from sulphuric acid in all concentrations
• Resist attack from hot sulphuric acid
• Impermeable
• Resist alkalies and solvents
• Easy to apply
• Excellent adhesion
• Can be used indoors and outdoors
• Resist exposure to the elements when used outdoors
• Resist mechanical abuse from personnel and vehicular traffic

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Surface Preparation

Coating performance is proportional to the degree of surface preparation.  Prior to coating, all surfaces must be clean, dry and free of all contaminants, including oil, dust dirt, grease, oil, salt deposits, etc.

The concrete must be allowed to cure a minimum period (generally 14 days) and attain a minimum of 80% of its final physical properties prior to applying any protective coating. 

The surface of the concrete is generally primed with the manufacturer's recommended primer prior to applying the final protective coating.

Specific instructions for the preparation of the concrete surface will be provided by the manufacturer and should be strictly adhered to obtain the maximum performance.

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Environmental Conditions

The environmental conditions at the time of application and during the curing period will greatly affect the performance of the protective coating.   The ambient temperature must be within an acceptable range, generally, between 10 to 38ºC (50 to 100ºF).  The surface temperature of the concrete must also fall within an acceptable range, generally, between 16 to 32ºC (60 to 90ºF).  Surface temperatures must be at least 3ºC (5ºF) above the dew point to prevent condensation during application and initial dry through period.

The coating must not be applied when it is precipitating or there is a chance of precipitation during the initial drying through period. 

The environmental conditions will affect the working time for the product.  Generally, in colder temepratures the user has more time to work with product before it begins to set.  Initial setting, maximum recoat, and curing times all increase with decreasing temeprature.

Instructions outlining the most suitable environmental conditions for successful application of the coating will be provided by the manufacturer and should be strictly adhered to obtain the maximum performance.

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Products

The following product(s) have been used successfully for protecting concrete surfaces which are exposed periodically to sulphuric acid spills, leaks, wash down, etc.  The ability of the coating to protect the concrete is dependent on many factors, some of which have been mentioned above, as well as handling of the product, method of application, maintenance of the coating, etc.

Product	PSX™ 756 Formerly Amercoat 3343
Type	Engineered Siloxane™ Surfacer
Color	Medium Grey
Components	3
Curing Mechanism	Chemical Reaction
Coats	1 or 2
Dry Film Thickness	40 to 100 mils per coat
Manufacturer	Ameron Protective Coatings Group
Location	201 North Berry Street Brea, California USA 92622-1200

or

Product	Primer Dimetcote 9 Inorganic Zinc Primer	Topcoat Amrcoat 741 Self-Cure Inorganic High Heat Coating
Dry Film Thickness	75 microns	125 microns

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Structural Steel

Alkyd based paints are not suitable for an acid plant environment.  Epoxy based paints are recommended.

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