What to do when Your Heat Exchanger is fail?
A lack of effective cooling due to heat exchanger failure can cause production losses and unplanned downtime. Fortunately, two common causes of exchanger loss — mechanical failures and chemically induced corrosion — can be prevented.
Heat exchangers are used in many critical processes to protect other valuable manufacturing equipment, optimise energy consumption and reduce associated operating costs. A properly selected, installed and maintained heat exchanger can help enhance the reliability and efficiency of a fluid system. When a heat exchanger fails, however, it can lead to costly downtime.
Two common types of heat exchanger failure — both of which can be prevented — are:
- Mechanical failures, including steam or water hammer, thermal fatigue and freeze up.
- Chemically induced corrosion, resulting from a chemical interaction with circulating fluids.
This article will review the operational problems that can develop in a shell-and-tube type heat exchanger and describe the corrective actions that can be taken in order to prevent such problems.
Causes for Mechanical Failures
Mechanical failures in industrial shell-and-tube heat exchangers can take seven different forms:
- Metal erosion.
- Steam or water hammer.
- Thermal fatigue.
- Freeze Up.
- Thermal expansion.
- Loss of cooling water.
Excessive fluid velocity on either the shell or tube side of the heat exchanger can cause damaging erosion as the tubing metal wears. If corrosion is already present, it can be accelerated. Erosion has the potential to remove the tube material’s protective film, exposing fresh metal to further attack.
Areas most prone to erosion are the U-bend of U-type heat exchangers and the tube entrances of all shell-and-tube heat exchangers. Tube-entrance areas can experience material loss when excessive, high velocity fluid from a nozzle is divided into many smaller streams as it enters the heat exchanger. When excessive velocity occurs at the entrance area of tubes, it typically produces a horseshoe-shaped erosion pattern.
Several steps can be taken to minimise the risk of metal erosion. The maximum recommended velocity in the tubes and entrance nozzle is a function of many variables, including tube material, fluid handling and temperature. Materials such as steel, stainless steel, and copper-nickel withstand higher tube velocities than copper (table 1). Where practical, staying below these velocities will help minimise metal erosion.
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