Steel Catenary Risers (SCRs) have been a preferred riser solution for many deepwater field developments since the last decade, which encompass different floater solutions, water depths, geographical areas and environmental conditions. Due to the importance and complexity of deepwater SCR systems, different levels of independent design verification, from document review to independent analysis, are usually performed by an Independent Verification Agency (IVA). DNV has been involved in independent design verification of SCRs installed on TLPs, Spars and Semi-submersibles in different deepwater fields around the world.
DNV uses a risk differentiated approach for riser verifications. The different levels of verification and the associated activities are first described. Different methods used in SCR design analysis are then reviewed and discussed. Various strategies for time domain riser analysis and guidelines on how to efficiently perform verification analysis are presented. An example of efficient SCR verification is also given. The paper finally discusses the verification of wave-induced and VIV fatigue responses with focus on fatigue sensitivities to a range of design input and analysis parameters.
Since the first use of Steel Catenary Risers (SCRs) in 1994 for the Auger TLP for oil and gas export in a water depth of 872 m, SCRs have become a preferred riser concept in almost every new deepwater field development and have been designed and installed on various host floater types including TLP, Spar, semi-submersible and FPSO. Compared to other riser concepts for deepwater oil exploration and transportation, SCR systems have several advantages such as, they can meet greater load requirement and more hostile operating environments; the system is relatively simple in comparison to top-tensioned or hybrid riser systems; they are also less costly than other types of risers such as flexible risers.
Due to the importance and complexity of deepwater SCR systems, it is commonly required that design verifications are performed by an Independent Verification Agency to examine the assumptions, methods and results of the design process and to ensure that the specified requirements of the riser system are satisfied. Independent design verification should be complementary to routine design activities and should be developed and implemented in such a way as to minimize additional work and cost, but to maximize its effectiveness.
DNV has been involved in independent design verification of SCRs installed on TLPs, Spars and Semi-submersibles in different deepwater fields around the world. The DNV risk differentiated approach for riser verifications and the different levels of verification and the associated activities are described in this paper. Different methods used in SCR design analysis are then reviewed and discussed. Various strategies for time domain (TD) riser analysis and guidelines on how to efficiently perform verification are presented. A SCR verification example is also given to demonstrate how computational efficiency can be achieved for TD analysis. Verification of SCR fatigue response (wave-induced and VIVinduced) is an essential activity and is discussed with focus on fatigue sensitivities to a wide range of design input and analysis parameters.
