The permissible repair parameters are the critical instrument for the health monitoring of the heat exchangers and the operator should be well versed with the prescribed limits. However, degradation in performance due to fouling/corrosion is bound to happen and following maintenance routine is what AIC heat exchangers recommend. It should be undertaken as and when required or as per OEM’s schedule:
(a) Manual Cleaning. Scaling is a common phenomenon which reduces the performance of the heat exchanger. It is a layer which gets deposited on the tube and acts as a insulator. Therefore, the end plate of the heat exchanger must be opened and each tube should be cleaned using an elongated wire brush.
(b) Chemical Cleaning. If manual cleaning cannot be done at regular interval or has been missed due to any reason, there is a very high chance of solidification of these layers on the tubes which cannot be cleaned using manual wire brush. Therefore, chemical cleaning using caustic soda or suitable chemical as prescribed by OEM depending upon the material of the tube should be passed through the tubes. These chemicals react with the layers deposited on the tube and breaks them. However, a lot of precaution is required while carrying out chemical cleaning as it involves a separate system to be rigged up, hence it should only be done in the presence of an expert.
(c) Thermostat. The initial starting of any system from cold condition does not require heat exchanger; therefore a thermostat operating valve should be installed at the inlet of the fluid being cooled. The valve will bypass the fluid till certain temperature and will open only when the temperature of the fluid has increased sufficiently to be required to be cooled.
(d) Regular Repairs If there are indications that heat exchanger is not working at its optimum capacity then inspection of the entire heat exchanger should be done. If any faulty or leaky tubes are detected then they can either be plugged or welded. Plugging means that the damaged tubes are put out of use and is usually done when less than 10% of the tubes are found to be damaged. If the product is under warranty then it is strongly recommended that OEM (original equipment manufacturer) be brought to undertake repairs and inspection.
(D) Pressure Testing on site Pressure testing is an important part of maintenance or post maintenance routine because heat exchangers work with high temperatures and pressures. Testing is usually done at 110% of the operating pressure. This is done to ensure performance beyond any doubt. If the pressure remains stable then it implies that your heat exchanger is working just fine.
The above mentioned aspects are very basic but important in ensuring the high efficiency of the heat exchangers. Further, the operator involved should be professional enough to know the prescribed limits of the heat exchanger and should operate only at those limits. No aspect of heat exchanger should be presumed, it is highly recommended that specification guide must be referred to before doing any maintenance routine.