Toughness properties of a friction hydro pillar processed offshore mooring chain steel

Abstract

In the past few years, solid-state welding has been a great alternative in comparison to the conventional fusion welding technologies. Solid-state welds are usually processed in lower temperatures than the other common fusion joints, tending to avoid problems such as hydrogen embrittlement, brittle microstructures and porosity. Therefore, these advantages can be useful to industrial applications which do not allow fusion welding. Offshore mooring components, which are fabricated under restricted standard requirements to ensure the floating marine integrity, is one of these applications. Thus, defects in links of mooring chains cannot be repaired by traditional welding, resulting in high operational costs. In this context, this study aims to characterize the Friction Hydro-Pillar Processing (FHPP) application to a mooring chain steel IACS UR W22 grade R4. The main process parameter studied was an axial force ranging from 30 to 60 kN. The welded joints were evaluated by metallography (macro and microstructure) and microhardness mapping. Furthermore, the toughness properties were assessed by Charpy and Crack Tip Opening Displacement (CTOD) tests, and the fractures were afterwards observed by scanning electron microscopy (SEM). The results showed that an increase in the axial force enhances the Charpy and CTOD values. Keywords: Toughness properties, Mooring steel grade R4, Friction hydro-pillar processing, Microstructure, Microhardness