May 4, 2009
ABS approves Petrobras MPSO design
In a slew of OTC 2009 announcements, ABS reported that it has provided its basic design approval for Petrobras' Mono-Column Floater, Production, Storage and Offloading Unit (MPSO) intended for ultra deepwater operation in the Gulf of Mexico (GOM). The approval is significant as it consolidates the MPSO design concept as one viable option for the next phase of the Cascade Chinook field in the GOM. The MPSO is a short cylindrical mono-column floater that is also being considered for sites offshore Brazil.
ABS provided an early conceptual stage review of the design and issued its "approval in principle" or AIP in 2005.
The MPSO concept is a non ship-shaped floating production storage and offloading facility (FPSO). The intent is for offloading to be carried out using DP2 class shuttle tankers. It is designed to be permanently moored to the seabed, remaining on station for its operational life. This offers an advantage over the traditional ship-shaped FPSO which would require a disconnectable turret due to the environmental characteristics of the Gulf of Mexico.
Since the unit is slated for Gulf of Mexico operations, ABS has provided regulatory compliance assistance to Petrobras. "Our extensive experience in the Gulf of Mexico and our ability to work closely with the U.S. Coast Guard as well as the Minerals Management Service has been a valuable contribution to the project," says Luiz Feijo, ABS Project Manager for the MPSO.
Though the MPSO breaks with the tradition of converting existing tankers into FPSOs, those conversions remain a strong market and, in another of today's OTC announcements, ABS said that it has adopted new structural requirements for the evaluation of converted FPSO units. The criteria are contained in a revised version of the society's ABS Guide for Building and Classing Floating Production Installations.
The society also provided a preview of its soon-to-be released standards for newbuild FPSOs during an OTC press conference.
ABS has been working with industry for the past year in a two-phase approach toward revising the FPSO structural criteria: phase one relates to conversions and phase two relates to newbuilds.
"The methodology and practices for the new FPSO conversion criteria are offshore-centered," says Xiaozhi (Christina) Wang, Senior Managing Principal Engineer, ABS Corporate Technology. "The new requirements apply FPSO-specific loading conditions and prescribed strength assessment procedures that are to be followed."
ABS says the criteria allows for better prediction of environmental loads using more realistic load cases.
Ms. Wang says the revised fatigue assessment approach takes account of actual FPSO operations, including the variations in tank loadings due to the many loading and offloading cycles, as well as sea waves and swell.
FPSOs are intended to operate at a specific site for years without drydocking. Normal maintenance, inspections and repair are carried out on-site. To reflect this, the new standards do not require port down time for repairs as is the case for trading tankers.
With much heavier and larger topside production facilities being developed for FPSOs, the new requirements outline a topside and hull interaction analysis procedure requiring finite element analysis.
The upcoming newbuild criteria include all the features developed for conversions such as more realistic loading cases, high cycle and low cycle fatigue strength assessment, hull girder ultimate strength assessment and hull interaction analysis with topside structure.
In other OTC announcements, ABS said that it has been been selected to class the first newbuild jackups for Petrobras in 25 years. The two LeTourneau Technologies Inc. (LTI) Super S116E jackups will be built at Sao Roque do Paraguaću, Bahia, Brazil, by Consorcio Rio Paraguacu. This consortium is composed by three major Brazilian contractors, Oderbrecht, Queiroz Galvao and UTC. They are scheduled for delivery in 2011.
ABS also chose OTC to unveil its ABS Eagle Offshore Structure Assessment Program (OSAP) Version 2.0. The software now allows designers of tension leg platforms (TLPs) and spars to check the compliance of their designs with ABS class requirements. Initially it was applicable only to semisubmersibles.