Strong Acid System - Piping - Acid Line Maintenance
March 15, 2005

Introduction Safety Precautions Equipment and Supplies Procedure

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Introduction

Maintenance on acid lines will be required to replace worn components, repair leaks, install new equipment or instruments, etc.  This type of work requires special precautions due to the hazardous nature of the contents.  The ‘normal’ hazards of sulphuric acid burns will be present as well as the additional hazard of explosions due to hydrogen gas formation.

Sulphuric acid in contact with metal can generate explosive mixtures of hydrogen gas, particularly in storage tanks, vessels and pipelines. 

Safety Precautions

When maintenance is done on acid lines the utmost caution must be exercised in order to prevent injury from acid burns as well as guarding against the possibility of explosions.  The most important basic rule to follow when breaking into any pipeline is to treat every line as though it were full and under pressure.

Equipment and Supplies

Non-sparking tools

Test equipment for the presence of explosive gas mixtures

Procedure

Isolate the line to be worked on by closing the appropriate valves and locking out the pumps.  Remember that even though an isolation valve is closed it may still leak.

Open all drain valves and vent valves and allow the contents of the line to drain to a safe location.   Opening high point vent valves will allow any hydrogen to escape.

Access to the area to be worked on should be provided so that the workers are positioned above the line.  This will prevent acid from draining down on the workers when the line is broken into.

Working above the line, slowly and cautiously loosen the flange bolts at the bottom and on the farthest side away from you so that any leaks will be away from you.  If the line has not been isolated or drained properly acid may leak or stream out when the connection is broken.  As well, hydrogen pressure in the line can force acid out in a stream.   The line may not have been isolated or drain properly if acid continues to leak or stream out of the broken connection.  Check that the line has been drained and isolated properly.

Once all the acid is removed from the line, isolate the portion of line by installing blind flanges as required.

Flush out the section of line being worked on thoroughly with water or soda ash solution to neutralize acidity and continue flushing until the line is clean and the water leaving the line has a pH of 6.5 to 7.0.

Drain all water from the line and blow the line clear and dry with compressed air.

Test the gas in the line for the presence of explosive mixtures before using open flames, cutting torches or welding on the line.  If explosive conditions are present re-flush the line until it is clean and re-test.

Work can now be safely performed on the line.  Re-testing for the presence of an explosive mixture should be performed again throughout the work to ensure it is safe to continue working on the line.