We can do a failure analysis of failure to ascertain the reason for failure. This is the recommended route even before plugging tubes on a shell & tube heat exchanger. We have plugged tubes before only to have an adjoining tube leaking after a short period of time, reason for failure was baffle plate wear.
Main reasons for failure:
Due to insufficient protection against freeze-ups, ice forms in the heat exchanger and the huge mechanical force of the ice formation damages the tubes or the plates/welding in a heat exchanger. Multi methods of protection is required in refrigerated heat exchangers and should include the following:-
- Electrical inter lock on pump failures or trips.
- Flow switch in water pipe line.
- Differential pressure switch on water in/out on heat exchanger.
- Manual reset anti freeze stat mounted correctly on heat exchanger.
- Low suction protection on refrigeration circuit.
Too high flow in the heat exchanger can lead to baffle plate wear, the baffle plate just vibrates through the tube of the heat exchanger.
Without proper water treatment water systems are prone to growth of ie Sulfate Reducing Bacteria. The bacteria starts propagating under a self-built barnacle and turns anaerobic, then starts generation sulfuric acid that can chew through any metal.
Sulphate reducing bacteria attack as seen when barnacle is removed and damaged area is cleaned up.
The holes in a tube seen from the inside.
In this case inferior quality copper tubing was used for manufacture and this led to electrolytic corrosion.
Frequent failures and below design performance of chill and hot water systems is a real problem due to dirt in the system. A common result of failure is that the maintenance staff removes strainers “because they block too easily”. This then leads to blockages further downstream in the system as well as heat exchangers, control valves and cooling cools are also prone to blockages.
Plate heat exchangers are even more susceptible to blocking as their specification for particles are 500micron or smaller depending on the type and brand of heat exchanger.