In 1989 a series of study work carried out by Conoco (UK) Limited identified that a number of gas risers could be susceptible to fatigue decay in the region of the riser elbow.
It was considered at that time that further analytical analysis would not add greatly to the confidence in the methods of assessing the long term integrity of these riser elbows.
A decision was made to undertake a work programme that involved detailed underwater NDE inspection of the riser transition welds in question, combined with an offshore programme of stress monitoring. This would provide accurate information on the exact level of wave induced stressing which could then be processed into weld fatigue data.
The offshore work programme was carried out in 1989 and 1990 and the resulting data was used to assess the likelihood of fatigue failure of the risers using probabilistic techniques.
This paper outlines the riser inspection and monitoring programme together with the results and subsequent conclusions.