By Thomas Dalsgaard, Head of Sales, SILHORKO-EUROWATER A/S
Demineralization and deaeration of district heating make- up water have for many years been a privilege for only a few major district heating companies. Lately it has become possible for smaller and middle-sized district heating companies to benefit from new technologies to produce salt and oxygen free district heating water. WHY IS IT IMPORTANT TO REMOVE SALTS AND OXYGEN IN DISTRICT HEATING MAKE-UP WATER? Often smaller district heating (DH) companies argue that “we have always used softened make-up water. We add chemicals for alkalizing the water, scavenging oxygen and then take care of hard water that eventually breaks into our system”. Another common statement is that “when we cut our pipes we see no corrosion. If we see corrosion it must be coming from outside the pipes”. The last postulate might very well be the first impression you get when you look on a corroded pipe, but it is not always the reality.
WHAT CAUSES CORROSION AND CAN CHEMICALS AVOID CORROSION? There are four main factors promoting corrosion; • Aggressive ions (salts) causing increased conductivity in the water • Oxygen • Incorrect pH • Biological activity The corrosion process has started from the inside of the pipe and penetrated the steel. Water will leak to the outside of the pipe, and the corrosion process will proceed and accelerate continuously as long as the conditions for corrosion exist. Corrosion products will continue to form outside the pipe, growing bigger and bigger corrosion products. The corrosion products shown on the picture have grown so big that it has lifted the insulating layer of polyethylene (PUR), creating an air gap between the steel pipe and the insulation.
Example of corrosion in a district heating pipe. At first it might look like the corrosion is coming from the outside penetrating to the inside but typically it’s not the case.
The photos show corrosion on a DH pipe due to poor DH water quality. High content of salts, and the presence of oxygen has started the corrosion process inside the DH pipe.
D I S T R I CT ENERGY - SUS TA I NAB L E C I T Y T RANS FORMAT I ON
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