Corrosion

The causes of corrosion are clear. As soon as water enters a heating system, the process of corrosion begins. This is because different metals within the system, usually copper, steel and brass, are exposed and react chemically in water which acts as an electrolyte. Oxygen entering the water supply also begins the corrosion process. As do impurities in radiators and pipes such as flux residues and copper swarf. In pressed steel radiators, crevices or stressed areas such as corners, are particularly vulnerable to corrosion.

The consequences of corrosion, sludge and scale, are the two chief culprits. Black oxide sludge develops in unprotected heating systems once corrosion starts. The sludge forms dense sediment deposits in all quiet areas of a central heating system and causes the majority of problems in radiators, pipes and boilers. Scale, on the other hand, is formed by hardened deposits of lime that are attracted to the hottest surfaces - radiators, pipes and boiler. Like black and red sludge (red sludge is caused by excessive air/oxygen entering the system), scale causes loss of efficiency, heat loss and mechanical failure.

SYMPTOMS OF CORROSION

1. FREQUENT VENTING
When the top of a radiator is cold during operation, either air or hydrogen is to blame.
Hydrogen gas builds up as a by product of electrolytic corrosion and is flammable - due caution is required!
Action: cleanse and protect the system.
Micro air leaks allow air into the system (but not water out) causing a build up of red sludge.
Action: clean all jointing materials and remake if necessary on the suction side of the pump.
Closed system pressure top ups may be required.
2. BOILER FAILURE
If deposits of black and red sludge and limescale build up to a point where heat transfer is severely restricted, the boiler can overheat and fracture.
Action: the entire installation must be cleansed and protected, especially when commissioning a replacement boiler.
3. BOILER NOISE
This increases in frequency and intensity as deposits of sludge and scale build up in an unprotected boiler.
Action: cleanse and protect the boiler. If insoluble objects such as sand or flux enter the boiler, then hard flushing may be required.
4. RADIATOR FAILURE
Like any working part of the system, radiators are prone to corrosion from installation debris and can fail within a few years.
Action: in particular, new systems must be pre-commission cleansed and protected and existing systems cleansed and protected.
5. PUMP SEIZURE AND FAILURE
The abrasive and magnetic properties of black oxide sludge increase shaft and bearing wear in pumps and valve actuators, causing them to either stick or fail. Action: cleanse and protect the system.
6. FUEL WASTAGE
Without treatment, corrosion debris will accumulate in the boiler causing increasing limescale deposits, reduced heat transfer and up to a third of a fuel bill going to complete waste.
Action: cleanse and protect an existing system; new systems should be pre-commission cleansed to maintain design efficiency and protected for long term maintenance.
7. COLD SPOTS
The familiar cool low central area of a radiator indicates a built up of a black sludge sediment that restricts flow and reduces heat.
Action: cleanse and protect the entire system.
8. LEAKING VALVES
A combination of loose gland nuts, failed or failing 'O' rings and poor packing around the stem of the radiator are usually to blame.
Action: replace the valve and protect the system.