Where failure analysis and electrochemistry meet

By combining ENDURES’s expertise in materials science and electrochemistry, we were able to determine the root cause of failure and to optimise future design and operational conditions.

Joost van Dam

A significant reduction in cooling performance was observed in an e-drive cooling system. Thanks to ENDURES’s unique testing facilities, the corrosion expert team was able to perform an in-depth failure investigation as well as to study the internal corrosion behaviour and corrosion kinetics through electrochemical analysis. This enabled the customer to optimise their design and operational conditions.

DAMAGE INVESTIGATION

A reduced performance of the e-drive cooling system was observed in a vessel. Closer examination of the e-drives (electric fan cooling system) revealed corrosion in the cooling block of the e-drives, resulting in loss of cooling capability. ENDURES investigated the cause of the corrosion, taking into account the materials used and e-drives design, the composition of the cooling water system and additives used (corrosion inhibitors). An extensive damage investigation consisting of visual inspection, optical microscopy, 3D-microscopy and scanning electron microscopy (SEM) coupled with EDS was performed on the dysfunctional cooling block to determine the root cause of failure. Active dissolution and redeposition of aluminium were blocking the ducts of the cooling device. Corrosion was most severe at contact regions between stainless steel turbulators and the aluminium duct wall. An additional cooling block was used to electrochemically study the role of the different materials and additives on the corrosion rate. Using zero resistance amperometry, it was shown that galvanic coupling between stainless steel and aluminium caused corrosion rates to sixfold multiply. In addition to that, it was proven that the dissolution rate of the aluminium was intensified by not using demineralised water.

RECOMMENDATIONS

For future designs, the use of stainless steel turbulators was strongly discouraged. Alternatively, they can be coated to prevent galvanic coupling. In addition to this, it was highlighted that all systems should be operating with demineralised water and appropriate concentrations of additives.