Beware of surface damage to electroless nickel plated components
Choose the right coating for the job - flaws in electroless plated nickel coatings can cause failure of the underlying component.
Electroless Nickel Plating (ENP) is often the coating of choice for bolts and other components as it i) provides good resistance to corrosion and wear, ii) covers metal surfaces uniformly, iii) can be varied to achieve specific hardness requirements, and iv) is aesthetically pleasing.
However, ENP coatings are only effective in service if the coating is not damaged during transportation and installation and its thickness is within the recommended thickness range for the service conditions (refer ASTM B733-97). Damage or reduced coating thickness can result in reduced corrosion resistance and premature failure of the component. Other factors which may influence premature failure of ENP coated components include i) flaking, ii) pitting, iii) delamination and iv) contamination of the coated surfaces - all of which would expose the base material of the component and promote premature failure by corrosion mechanisms.
It should be noted that in steel components such ‘holidays’ (areas where the underlying material is exposed) cause the underlying material to i) become anodic to the coating, and ii) pit rapidly (the underlying steel tries to protect the coating from corroding - unlike galvanising where the coating protects the exposed region). Owing to potentially large differences in surface area (between the holiday and coated region) this pitting can be very rapid and have severe consequences.
Although there are many applications where ENP coatings are adequately suited, they should not be employed in corrosive environments where the integrity of the coating cannot be ensured.
Published in Technical Tips by Origen Engineering Solutions on 1 July 2015