Effect of Sea-water on the Corrosion Performance and Thread Engagement of Coated Fasteners for Offshore Applications.

Abstract

Collaboration between A60N and Doxsteel Fasteners was carried out to investigate the performance of coated bolts for offshore applications.

 

Cd, HDG, Ni-Co, PTFE, TSA, and Zn-Ni coatings were applied to high strength steel fasteners for subsea applications. All the materials were subject to total immersion in natural seawater conditions in the costs of West Australia during six months.

 

Ni-Co coating was the only material that did not allow marine adhesion and growth, and did not show signs of corrosion in studs and nuts; Ni-Co coating was free of marine growth and red rust, opposite to the other coatings that showed the presence of both. In the disassembling test, Ni-Co coating was the only material that did not suffer seizing when applying an equivalent amount of the original tightening torque. After electrochemical testing, Ni-Co coating was the material that offered the highest corrosion protection. The testing facilities showed to be the best suited and state-of-the-art facilities for subsea corrosion testing.