Structural integrity monitoring of subsea systems: steel catenary riser case study

Risers are a critical part of a subsea system in terms hydrocarbon containment. After they have been designed, built, installed and in operation, it is impossible to predict their hydrodynamic response to the elements of the sea and operation. This is witnessed particularly in the Gulf of Mexico where it is impossible to predict hurricanes and other weather occurrences for the lifetime of a subsea system. Installing online monitoring equipment on the riser can help to fully understand the hydrodynamic response. A recent Steel Catenary Riser (SCR) installed on a production field in the Gulf of Mexico follows this principle. This monitoring system is one of the most comprehensive subsea structural monitoring systems to date. It utilises prestigious award winning strain measurement and state-of-the-art motion devices. These are optimally placed along the SCR to continuously measure and store real-time full scale riser response. The main objectives of the monitoring equipment are as follows: 1. To help in the understanding of basic hydrodynamic behaviour of SCRs. This includes vortex induced vibrations, riser behaviour at the pull tube exit region and riser soil interaction at the touch down region. The information generated will be used in future riser designs. Impact of vessel induced motion (VIM) to transferred acceleration onto the riser, particularly heave acceleration translated into bending dominated fatigue in touch down zone (TDZ). 2. The data collected will be used to validate the riser systems robustness and calculate fatigue damage to the critical risers, particularly after significant environmental or operational events.