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