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Sulphuric Acid on the WebTM Technical Manual DKL Engineering, Inc.

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Maintenance and Inspection - Gas-to-Gas Heat Exchangers
September 8, 2003

Introduction
Maintenance and Inspection Schedule		 Associated Links

Introduction

All gas-to-gas heat exchangers in an acid plant should receive regular maintenance and inspection in order to minimize the amount of downtime experienced due to problems with the exchangers.  The units that will require the most maintenance are the unit in 'cold' service such as the Cold, Cold Interpass/Reheat and SO3 Coolers.

Maintenance and Inspection Schedule

Daily At least once a day the shell and tube side drains of the gas-to-gas heat exchangers should be checked by briefly opening the isolation valve to see if any liquid has collected in the heat exchanger.  This requirement applies mainly to the Cold and Cold Interpass Exchangers due to their operating conditions.  The Hot and Hot Interpass Exchangers operate at a high enough temperature that condensation of liquid will not occur.
Monthly At least once a month a complete plant pressure profile and temperature survey should be performed.  This will include collecting the relevant operating data for the heat exchangers as well.  Analysis of the data will indicate the degree of fouling and pressure drop increase.  This information can be used to plan any work required on the heat exchangers during a plant shutdown.
Shutdown During the annual plant shutdown all gas-to-gas heat exchangers should be inspected internally.  The tube side is typically fully accessible for inspection while limited access is generally available to the shell side.  Items to consider during the inspection are:
  • Degree of corrosion and scaling
  • Condition of any metallized surface or interal lining
  • Tube-to-tubesheet joints
  • Flatness of the tubesheet
  • Degree of sulphate build up
  • Perform metal thickness measurements
  • Condition of the tubes
  • Condition of equipment expansion joints
  • Condition of all welds
  • General condition of the shell

If a leak is suspected in the heat exchanger, test will need to be carried out to determine which tubes are leaking and repairs done.  A tubesheet map should  be maintained identifying which tubes have been plugged. 

All problems that have been identified during the inspection should be rectified and the exchanger completely cleaned out prior to placing it back in service.