TREATMENTS AND FLUIDS
Fluid thinking: two ways to encourage failure
There are two ways to encourage your cooling system to fail – using a fluid that contains no or limited corrosion inhibitors, and not preparing the system correctly to allow the fluid to work to its full potential. Jerry Lewis, chief technical officer at Kilfrost elaborates.
W
ater is commonly used in cooling as a thermal conductor. The molecules are small, but bond strongly in all direction to give a dense and
compact structure. This density and strong bonding means that water can carry a lot of energy without boiling at low temperatures. In addition, as the molecules are small, water has a low viscosity and is easy to pump. The potential failures with water are its problems of metallic corrosion and freezing. Almost all industrial systems contain components in piping or heat exchangers that can corrode in the presence of water, particularly if oxygen is also available. You could add glycol to the water to offer some freeze protection and some corrosion inhibition will clearly help. On the other hand, to discourage corrosion-based failure and to improve the longevity of cooling system hardware, fluid evaluation and selection is crucial.
Expert fluid manufacturers are committed to providing, research and development intelligent fluids that provide accredited corrosion protection. This is achieved using a combination of ASTM international standards, usually the testing method ASTM D1384 and the standards specification ASTM D3306. This accreditation can offer reassurance that hardware is adequately protected by the fluid used.
ASTM D1384 This standard defines the protocol for setting up glass 30 May 2021
laboratory equipment for the corrosion testing of six specific metal coupons in a mixture of 33% of the heat transfer fluid to be tested, diluted with standard corrosive water, 67%.
The metal coupons are immersed in the solution, the mixture aerated at 100ml/min air, and the entire test carried out at 88°C for 336 hours (two weeks). This is clearly a tough test versus the conditions to which most heat transfer fluids (HTF) would be subjected, however, it is the standard of testing that HTF customers expect. The ASTM D1384 methodology describes the way in which the coupons are arranged in the test fluid to allow some interaction to take place. The test pieces are separated by one insulator in the centre of the spindle holding the six coupons together, although the three soft metal coupons and the three iron-based coupons are in galvanic contact through metal spacers. The testing should be done in triplicate and the average of the three test coupon corrosion results should be reported.
ASTM D3306 The measurement of coupon corrosion allowed in the ASTM D1384 test depends upon the method used as further described in ASTM D3306. The simulated service test is used primarily for automotive applications. For heat transfer fluids, the glassware limits described in this standard are used, and any test run that gives weight loss
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