Indentation and erosion behavior of electroless Ni-P coating on pipeline steel

Electroless Ni-P coating has a potential use in oil and gas pipeline industry due to its good corrosion and wear resistance. However, the erosion and indentation behavior of the coating have not been fully explored yet. The objective of this study is to investigate the suitability of utilizing electroless Ni-P coating in the oil and gas industry by characterizing its mechanical damage under erosive and denting conditions. In this study, electroless Ni-P coating with different thicknesses were deposited on API X100 pipeline steel and characterized using XRD, SEM and EDS. Structural characterization indicates that as-deposited Ni-P coating has an amorphous structure with 9-11 wt% phosphorus content. Hertzian-type indentation and solid particle erosion tests were performed in order to investigate the extent of the mechanical damage in the coatings. Optical microscopy and SEM observations of the indentation impressions show the presence of Hertzian, radial and bend cracks. It is found that the indentation behaviour of electroless Ni-P coating is significantly influenced by coating thickness. Eroded surfaces were examined and operative erosion mechanisms were identified. It was found that the erosion rate of electroless Ni-P coating is higher than the substrate.The suitability of utilizing electroless Ni-P coatings in the oil industry was assessed.