Materials of Construction - Acid Resistant Linings
May 9, 2003

Introduction Pecora Mastic and Acid Resistant Brick Pecora Mastic, PTFE and Acid Resistant Brick PTFE and Acid Resistant Brick Ceramic Paper

Associated Links Acid Brick Mortar Installation Specification Installation Details Lining Installation Pecora Mastic Rhepanol ORG

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Introduction

Sulphuric acid is a highly corrosive and equipment design to handle sulphuric must be corrosion resistant.  Exotic alloys are available which provide excellent corrosion resistance and long service life.  The disadvantages of these alloys are their high costs.  Acid resistant linings have been used since the early days of sulphuric acid manufacture.  They provide excellent resistance to sulphuric acid at a reasonable cost since less expensive materials such as carbon steel can be used for the walls of the vessel or tank.

Traditional lining materials are:

• Acid Resistant Brick
• Pecora Mastic
• Rhepanol ORG
• PTFE
• Ceramic Paper

These materials are commonly used in combination with each other to provide the total acid resistant lining for protection of carbon steel vessels.

Pecora Mastic and Acid Resistant Brick

Description	This lining system consist of a thin layer (3 mm) of pecora mastic which is trowelled on to the steel surface.  The steel surface must be free of mill scale, rust, dirt, etc.  Generally, the surface of the steel is sandblasted or wire brushed.  A layer of mortar (5 mm) is applied directly over the pecora mastic and the first layer of acid resistant brick is set into the mortar.
Advantages	Relatively low first cost Ease of application Effective unless damaged by excessive temperatures Life expectancy of approximately 20 years
Disadvantages	Low threshold temperature Ineffective if not applied over the entire surface of the steel being bricklined

Pecora Mastic, PTFE and Acid Resistant Brick

Description	This lining system consist of a thin layer (3 mm) of pecora mastic which is trowelled on to the steel surface.  The steel surface must be free of mill scale, rust, dirt, etc.  Generally, the surface of the steel is sandblasted or wire brushed.  10 mil PTFE sheets are laid on top of the pecora mastic while it is still tacky.  The pecora mastic is used to hold the PTFE sheet in place as well as providing an added layer of protection.  The PTFE sheets are overlapped a minimum of 150 mm (6”).  A layer of mortar (5 mm) is applied directly over the PTFE sheet and the first layer of acid resistant brick is set into the mortar.
Advantages	PTFE sheets are impervious to sulphuric acid Life expectancy of more than 20 years
Disadvantages	Higher incremental cost than pecora mastic and acid resistant brick PTFE sheets to not stick well to the pecora mastic Higher cost for installation Longer to install If PTFE sheet is punctured, acid may pool behind the PTFE sheet

PTFE and Acid Resistant Brick

Description	This lining system consists of 10 mil PTFE sheets applied to the steel sheel using an epoxy.  The steel surface must be free of mill scale, rust, dirt, etc.  Generally, the surface of the steel is sandblasted.  The PTFE sheets are overlapped a minimum of 150 mm (6”).  A layer of mortar (5 mm) is applied directly over the PTFE sheet and the first layer of acid resistant brick is set into the mortar.
Advantages	PTFE sheets are impervious to sulphuric acid
Disadvantages	Requires an excellent surface preparation to ensure complete adhesion of the PTFE sheets The epoxy has a low temperature limit and will fail over time

Ceramic Paper

Ceramic paper soaked in potassium silicate is generally used in 'dry' service only.  It is therefore not suitable as a lining for towers or pumptanks.   However, ceramic paper soak in potassium silicate is used in areas that are normally hot and there is the risk that the acid dew point is reached during normal operation or during shutdowns.  Areas of application are sulphur furnaces where the ceramic paper is installed between the refractory lining and carbon steel shell or on refractory lined hot gas ducts.

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