MTS Water Quality Guide - Manual (Page 10)

Heat Exchanger Care and Water Quality Guide 10 Heat Exchanger Care
What is the life expectancy of my heat exchanger?
All heat exchangers have a finite life and must be considered an expendable
component, subject to failure at some point in time. Properly used and
maintained, your heat exchanger could last up to 20 years.
What causes heat exchanger failure?
Heat exchangers usually provide a long service life with little maintenance other
than a routine inspection and cleaning. Fouling and corrosion are the main causes
of degraded performance or failure. A very expensive failure occurs when a leak
develops, allowing the cooling water to mix with the hydraulic fluid,
contaminating both the hydraulic system and the cooling water system.
Other heat exchanger failures can be caused by silting, scaling or other forms of
obstructing the cooling water passageways. These types of failures are not as
disastrous as corrosion failures, but can occur over time.
Fouling
Fouling is the accretion of deposits that decrease the thermal transfer of a surface
and increase the system's flow resistance. The result is that due to reduced heat
transfer coefficients, the cooling water volumetric flow rate has to increase to
keep the system at the same temperature.
Corrosion
Corrosion is the degradation of a metal due to chemical reactions with the
environment.
Shell and tube hydraulic fluid-to-water heat exchangers are usually constructed
with copper or copper alloy tubes. Copper and its alloys are normally resistive to
corrosion, but the corrosion rate will vary depending on the concentration of one
or more corrosive elements present in the hot hydraulic fluid or cooling water. A
normal corrosion rate is 5–25 µm per year. This implies an operating life of 20
years for your heat exchanger. Higher than expected corrosion rates will
drastically reduce this operating life.
Over a period of time, this slow dissolving of the metal will result in component
failure:
• Corrosion products may settle in the heat exchanger tubing, causing the
fluid flow to be blocked.
• Corrosion can eventually cause leaks between the water and hydraulic fluid
supplies.
– Water contamination in the hydraulic fluid can seriously shorten the
life of the hydraulic components of your HPU and test system.
– Hydraulic fluid in the water can result in a costly cleanup supervised by
your local environmental protection agency.
Which type of contamination occurs is dependent on the extent of the corrosion
and the pressure in the hydraulic fluid and water supplies. Since fluid tends to
flow from a high pressure area to one of low pressure, the lower pressure fluid
will become contaminated. Eventually, however, both the water and the supplies
may be contaminated as more leakage occurs.