Nathan Hardy , associate research scientist , and Jim Lukanich , director of applied technology - CWT , at Kurita America , introduce an alternative corrosion inhibitor
Filming amine use in multi-metal hot water systems
Nathan Hardy , associate research scientist , and Jim Lukanich , director of applied technology - CWT , at Kurita America , introduce an alternative corrosion inhibitor
Corrosion in industrial and commercial water treatment continues to be a major concern as companies strive to reduce costs while maintaining their assets . The need to protect heat exchange equipment and associated piping is vital in minimising operational costs and preventing downtime . Traditionally , copper and carbon steel have been the metals of choice .
Aluminium is becoming an increasingly attractive option for heat transfer as it has high thermal conductivity relative to its initial capital cost . 1 However , aluminium also brings challenges . It is a much more anodic metal than either iron or copper , increasing its potential for galvanic corrosion , which can lead to devastating effects . It is also an amphoteric metal , whose protective oxide film is soluble at both low and high pH .
Because of this , aluminium boiler manufacturers often recommend a lower pH range ( 8-8.5 ) for optimal protection . This creates another problem because it raises the corrosion potential for carbon steel , which prefers a higher pH (> 9.0 ). For systems containing aluminium heat exchangers , the need to provide corrosion inhibition for all metal surfaces has never been greater .
Filming amines
Filming amines have been around for decades and , in the water treatment space , are most often used in steam
Figure 1- Monoamines & diamines preventing water & dissolved gases reaching metal surface
boiler applications . Whilst their use as primary corrosion inhibitors has been limited , they are receiving increasing attention in heating and cooling water applications .
Film-forming amines ( FFAs ) are being considered for application in both closed and open cooling water systems as they are biodegradable and leave no hazardous by-products . FFAs have a strong affinity for metal surfaces , probably due to the partial positive charge on the nitrogen atom as the amine comes into contact with metal surfaces . This attraction is increased by the hydrophobic tail , further pushing the amine away from water and toward the metal surface , leaving a tightly packed film with hydrophobic tails protruding outward . 2
Polyamines , which inhibit corrosion in a similar mechanism to monoamines ( Figure 1 ), are often preferred as they can form a more resilient film . Film formation is a dynamic process , where constant attachment and detachment is taking place ; the additional secondary amine provides an extra binding site between the FFA and the metal surface .
The de-wetting of the metal surface inhibits corrosion by preventing
28 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981