MTS Water Quality Guide - Manual (Page 15)

Heat Exchanger Care and Water Quality Guide Heat Exchanger Care 15
How can I improve the life of my heat exchanger?
Routine inspections and maintenance enable you to slow the degradation effects
in heat exchangers. The effects will always be present, however, and will sooner
or later result in the necessity of replacing the degraded components.
Choose the right
material for your water
conditions
Although you cannot prevent corrosion from ever occurring in your heat
exchanger, the corrosion rate can be reduced by selecting the appropriate
materials for your heat exchanger. MTS can assist its customers in selecting the
proper material for heat exchangers (copper, copper-nickel alloy or stainless
steel) based on an analysis of the water supply.
Plate design heat
exchangers
The plate design heat exchanges use stainless steel plate because if it general
resistance to most of the cause for corrosion making it suitable for use with most
sources of fresh water: city water, pond water or cooling towers. The city water
should have a chloride content of <5 ppm. Pond water should be filtered or
screened and cooling towers must be properly maintained to prevent fouling. The
cooling water can have a ph of 7 to 8.5
MTS does not recommend using stainless steel plates if your cooling water is
saltwater or sea water.
Tube and shell design
heat exchangers
The standard material used in heat exchanger tubes is 99.9% pure soft copper.
Copper-nickel (CuNi), an alloy of copper that has 10% nickel, offers a high
resistance to corrosion caused by many common pollutants. A 90-10 copper alloy
tube has a corrosion rate that is typically one-half to one-third that of pure copper,
and adds 20–25% to the cost of the heat exchanger. This alloy is a good solution
to the problem of mildly corrosive water, such as ground water supplies. But it is
not a solution to severe corrosion problems that may occur when cooling towers
are used.
Another measure that can be taken to enhance heat exchanger life is to add zinc
anodes to the heat exchanger bonnet. Most copper-nickel heat exchangers can be
furnished with zinc anodes. These anodes screw into a threaded opening added to
the bonnet, and protect the tube sheet and bonnet metal against dezincification
corrosion. The zinc anodes will corrode before the copper alloy tubes in most
cases. Zinc protection from the zinc anodes will decrease with time because of
metal loss, so the zinc anodes should be inspected regularly and replaced as
required.
MTS recommends that if your cooling water supply is saltwater or sea water, heat
exchangers with 90-10 copper-nickel tubes and tube sheets, bronze bonnets and
zinc anodes should be used to reduce the corrosion rate.
Keep your water
supply clean
Contaminants in the cooling water supply can partially or completely block the
heat exchanger chambers. Blocked chambers will decrease the efficiency of the
heat exchanger and may result in damaging erosion or corrosion. Dirt or small
objects, such as organic material may coat the chambers and lead to corrosion.
You can prevent sediment buildup in the chambers by installing a filter or strainer
in the cooling water inlet to prevent large particles from entering the chambers.
MTS recommends that water strainers be installed ahead of the heat exchanger if
the source of cooling water contains large amounts of particles or sediment.
Note Because most corrosives are dissolved solids, strainers usually provide
only minimal corrosion protection. A strainer will be useful in preventing
corrosion damage only in those instances where a suspended solid is
corrosive.