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5 Warning Signs Your Glycol System Needs Attention

Updated: Oct 27, 2022

By Ben Feeney | October 22, 2021

1) Glycol percentage is too high

Most plant managers know glycol is used for pipe freeze and burst protection, but what happens when glycol percentage is too high or low? Is there a “Goldilocks Zone”

for Propylene or Ethylene glycol percentages?

Most systems operate best when glycol is maintained at around 1/3rd or 33% of system volume. This percentage should protect most systems below freezing. It is important to always follow equipment manufacturer guidelines for recommended glycol percentages.

Glycol should rarely be above 40% by volume. Overfilling a system with glycol causes a steep decline in heat transfer, leading to higher energy bills. This chart represents the heat transfer loss based on glycol percentage. Notice a system filled with 60% glycol may lose almost 25f% heat transfer!

2) Low corrosion inhibitors

Glycol may be purchased with or without corrosion inhibitors. It is important that the water is tested to determine if additional corrosion inhibitors are needed to protect system metals.

3) Glycol breakdown

Glycol breaks down over time and use. As glycol is exposed to heat or oxygen, it will break down into three different organic acids. When a breakdown occurs, severe damage may develop on system metals leading to corrosion. Regular testing should be done every year to ensure glycol is in good health. Often, a low reserve alkalinity and pH indicate glycol breakdown. Boland has chemicals in the form of pH adjustment and borate buffers that will boost the alkalinity and pH back to desired ranges.

4) Low glycol percentage

When system glycol is below 20% it is no longer poisonous to bacteria and may become a nutrient source. This can cause the potential accumulation of biofilm and other harmful bacteria in the system. Biofilm impedes heat transfer and leads to biological induced corrosion (BIC).

5) High iron levels

Iron levels should be tested to determine if corrosion of mild steel is a concern. Ideally, iron levels should be below 1ppm. Higher levels may be seen if the system does not have filtration as part of the protection package. Inhibitors such as molybdate and nitrite may be used to reduce the level of mild steel corrosion.

Before the weather dips down to freezing levels, let's check your glycol levels and prevent severe damage.


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