STREAM JIP – Insights into Steel Catenary Riser Response Using Measured Data

Abstract

The objective of the STREAM (Steel Riser Enhanced Analytics using Measurements) JIP is to provide a measurement based foundation for SCR and lazy wave riser modelling to ensure that the fatigue response is assessed with adequate but not overly conservative parameters. To achieve this objective, the JIP utilizes field measurements from 4 in-service SCRs and 1 SLWR in water depths from 3,000 ft to 5,000 ft. The field measurements correspond to a range of environments including hurricanes and loop currents, riser functions, sizes, VIV suppression coverages and host vessels. The processing commences with data QA, error assessment and data filtration. Riser response is categorized into wave dominated events, VIV events and others such as MIV events. As-built finite element riser models are developed and simulations are conducted using measured motions. The resulting analytical responses are compared with the measured motion and strain data to determine the level of conservatism or otherwise in typical riser wave fatigue analysis. SHEAR7 models driven by measured current profiles are used to compare predicted VIV response to observed VIV amplitudes and frequencies. Analysis results indicate that industry standard fatigue assessment is indeed conservative. Sensitivities are conducted and presented on key design parameters that are known to be conservatively used in design such as hydrodynamic coefficients and SHEAR7 inputs. A set of parameters is derived that not only reduces fatigue damage bias but also improves the reliability in predictions. Recommendations are made with regards to further refinement of analysis parameters and understanding of atypical riser responses. Measured riser response that does not conform to typical wave and VIV spectra are presented and discussed. The combined assessment of full scale field data from multiple catenary risers is an industry first. The results from this JIP offer valuable insight into riser response characterization with potential applications for SCR/SLWR life extension and more efficient new designs. Note that in this paper, the term SCR is often used a generic term to describe both the regular SCR as well as the lazy wave implementation of it, the SLWR.