Thomas Maier explains how the right choice of materials prevents damage from corrosion by cooling water
Cooling water circuits place special requirements on the connections and lines used. Which materials and versions are needed depends on the particular application and the conveyed media. To design a reliable and long-lasting solution requires very close examination of the application conditions. It pays to get some expert advice.
One such expert is Eisele, which offers a product range called Liquidline for cooling water applications. Depending on the particular application, metal cooling water connections can be manufactured from brass, stainless steel or aluminium. The brass connections of the Liquidline feature dezincification-resistant elements for contact with media. This provides a high level of protection against corrosion in most standard applications. They were designed for applications where the use of expensive acid-resistant stainless steel is not yet required. Cooling water, with a pH value in the range of 5 to 6, is only slightly acidic.
The pharmaceutical industry or paint shops, for example, process substances with higher acidity, in which case stainless steel connections are better suited. In circuits equipped with aluminium heat sinks, on the other hand, aluminium connections are also needed to prevent electrolytic corrosion of the aluminium cooler. Liquid coolers are often made of aluminium due to the high thermal conductivity of the material and are designed for several years of service. To guarantee reliable connection technology throughout the entire life cycle, compatible materials have to be used.
The time-proven design principles of the solid metal push-in connectors such as those of the Liquidline 2500 series were applied to corrosion-proof aluminium for these applications. For this purpose Eisele uses the special material EN AW-AlSi1MgMn. Conventional aluminium alloys do not have the necessary water resistance, which is why the manufacturers of liquid coolers are increasingly using this material.
The problem of dezincification
Dezincification is a long-known process that can lead to corrosion damage on cooling water fittings. In rare cases it is observed on brass components that are in constant contact with water. The colour of the corroded area changes to reddish copper, indicating that it no longer has any inherent strength. Explained simply, the main alloy components of the brass dissolve: copper and zinc are oxidised into water-soluble salts. The zinc is carried away by the cooling water, while the copper accumulates as a sponge-like mass. This process generally occurs only in soft water with a high chloride content and low carbonate hardness.
Dezincification can be prevented by the right choice of materials and proper handling of the components – for example through compliance with specified tightening torques. The flow-optimised connections of the Liquidline are therefore manufactured from a special dezincification-resistant material. The danger of dezincification corrosion due to high chloride content and low carbonate hardness is effectively eliminated. The solution is highly resistant in industrial water, steam, various saline solutions and many organic liquids.
For the toughest cases; stainless steel
In some cases, stainless steel coolant connections should be used instead. Wherever standard materials such as plastic, brass and aluminium reach their limits in connection technology, the Eisele Inoxline provides an economical stainless steel solution. Stainless steel features excellent protection against corrosion even with aggressive media and at high temperatures. It is especially resistant to acidic media and aggressive cleaners. In choosing the right materials one needs to consider not only the media used, but also the ambient conditions such as temperature and atmosphere. Stainless steel connections are necessary especially in case of pH values below 5. The same applies if ammonia or very high nitrate and chloride content is present in the medium itself, in any cleaners that are used or in the installation environment. Nitrate can be a problem especially in areas with intensive agricultural production.
The problem of electrolytic corrosion
Electrolytic corrosion can cause cooling water connections to literally disintegrate within a short time, for no apparent reason at first glance. In electrolytic corrosion, direct currents or direct current components in alternating voltages can cause damage to fittings.
If two identical metal elements are connected by an external current to form one galvanic element, the metal element functioning as an anode breaks down. The disintegration starts with the base element of the alloy. The reason for electrolytic corrosion is often the presence of undetected neutral or residual currents. If the cause of such problems cannot be easily eliminated, stainless steel should be used here as well.
Before choosing the material for cooling water connections, it is always necessary to examine the specific conditions at the installation site. In this respect one needs to consider not only the media used, but also ambient conditions such as temperature and atmosphere.
For more information, visit www.engineerlive.com/design
Thomas Maier is managing director of Eisele.
