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Shell and tube heat exchanger servicing and repair

Posted by Esther Akers on Feb 19, 2014 9:12:00 AM


    
U-tube_heat_exchanger

Shell and tube heat exchangers are the most common types of heat exchanger found in oil refineries and other chemical processing plants. They're design makes them ideal for high pressure applications. As is the way with high pressure lines, preventing leakage is critical to plant performance but preventing leakages where temperatures and line contents can be volatile make this an ongoing process.

Fouling

The most common problem to occur with heat exchangers is fouling. This is when there is a build up of materials on the inside of the tubes within a heat exchanger. Any build up of material on the inside of tubes will restrict the flow of the line contents within the tube and decrease the heat exchanger due to the increased wall thickness in the tube.

There are many types of fouling, each presenting a different set of challenges, but the most common causes are:

  • Crystallization
  • Polymerization and or oxidation
  • Settlement of sludge, rust or dust particles
  • Biological deposits
  • Corrosion

Repairing tubes with severe fouling can require the complete replacement of the tube bundle. This is a costly job that requires the whole heat exchanger to be stripped down.

Fouling within tubes can also be corrected using high pressure cleaning systems. These systems use a high pressure lance to inject fluids into the tubes and blast away the material build up. This can also be costly as specialist company will take the heat exchangers to a workshop, thus removing it from the plant altogether, where the operation can be performed.

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Heat exchanger flange repair

Within a shell and tube heat exchanger you will commonly find three types of flange.

Girth flanges -These are used in the shell and channel barrels.

Internal flanges - Used in the floating head exchanger. They allow the internals of the tube bundle to be disassembled and removed.

Nozzle flanges - Used to connect the heat exchanger to the line. The flange and gasket size, pressure rating and standards are determined by the line specification.

In the same way that fouling of the tubes within the heat exchanger impacts its efficiency, well maintained heat exchanger flanges similarly play an important role. In the diagram above, we would expect division plate (located at the tube sheet) to become corroded over time. This can be avoid with regular maintenance.

Using a standard Mirage flange facing machine range with our heat exchanger mounting kit you can resurface heat exchanger flanges, including the face of the tube sheet, on-site without incurring costly transportation costs. You can achieve workshop quality tolerances with on-site machining.

Download Mirage Machiones Flange Facing Case Study Pack

Topics: On-site machining

   

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