A fresh initiative on the use of daylight magnetic particle inspection for the inspection of underwater steel structures

Abstract

Underwater magnetic particle inspection (MPI) was a common non-destructive testing (NDT) method in the early days of North Sea oil and gas development (in the 1970s/early 1980s). It was primarily used to find cracks in nodal welds on offshore structures. Underwater MPI was carried out using fluorescent inks, which were visible under ultraviolet (UV) light and had to be carried out in the hours of darkness. This led to lengthy and costly inspection programmes, as the inspection work was generally done during the summer months, with perhaps only 4 h of darkness in the northern North Sea. The use of underwater MPI declined from the late 1980s for about 25 years but is now making a comeback. As offshore structures age and exceed their original design lives, the spectre of fatigue cracks has led to the need for detailed node weld inspection. During the last 25 years, MPI inks have changed. Although they conform to the relevant international standards, these standards are for topsides use and thus not necessarily applicable to underwater conditions. Recent trials have been conducted to determine the suitability of available inks to increasing white light levels underwater. This paper presents the work and discusses the findings, which have application worldwide.