It is highly recommended
that the shell & tube heat exchanger, along with the control head, be cleaned/serviced periodically according to manufacturer’s recommendations and local water conditions/usage.
Due to local water conditions, [excessive hardness-minerals], the heating package may need solution cleaning and control head inspection yearly, or after 1 full year of being in service, with water flowing through the tube side. 
Some areas have better water conditions than others, obviously.
Where the local city/municipal water conditions are favorable, water side cleaning and control head inspection can be delayed, perhaps up to 24-36 months, or more. Water usage also directly affects cleaning/service intervals.
A water analysis and flow usage can help determine your schedule for cleaning/servicing, which analysis is often available from your chemical/water treatment provider. 
A clean and efficient  heat exchanger package helps save recources by conserving steam, lowering condensate discharge, and helps minimize the use of chemicals used to condition the steam/condensate. This also extends the life of the tube bundle, by keeping solids off the heat transfer surfaces.
For a Standard Service Breakdown, see link to the left.
Oftentimes where local water conditions show heavy hardness and other contaminants, and the heat exchanger is not serviced regularly, internal components are attacked, and the metal damaged, see pics. [see 'Resources' for some additional reading on this]
One of my favorite old sayings is: "an ounce of prevention is worth a pound of cure", Benjamin Franklin I believe. In the case of these heat exchangers, in the application typically being utilized [heating municipal water], this saying holds very true.
Another area of concern regarding the condition of the shell & tube heat exchanger which uses steam on the shell side is condensate management, local water conditions, and condensate removal. Please see RESOURCES tab for more information about local water conditions and related water based corrosion.
Most of these units have inverted bucket traps, which cycle according to load. Typically it is recommended that a strainer be installed before the trap, to help protect the trap from contaminants, and it can also act as a troubleshooting mechanism, to help determine if the trap is working.
When these traps fail, or fail to operate properly, or there is excessive back pressure in the condensate discharge lines, the condensate can back up and sit inside the shell. If the quantity of condensate is great enough, the tube bundles will come in contact with the condensate.
Many facilities do not manage condensate control for their steam supply or returns, or use amines, etc., in an effort to combat carbonic acid, oxygen pitting, etc.
Therefore, if left unchecked over time, the condensate can attack the metal of the tubes, causing degradation/corrosion of the metals.
It is good maintenance practice to test and maintain your traps in proper operating condition, and make sure that your condensate removal system is not subject to excessive back pressure, blow by, etc.
Flow Engineering will test your traps and check your entire system while servicing the heat exchanger package, and any issues noted will be recorded in the inspection report for your reference.
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