New Code for the Design of Dynamic Risers for Floating Production Installations
Authors: Stanton Paul N. , Kavanagh William Kieran , Garrett David L. , Mork Kim J. 
Published: July 2010

API RP 2RD was published in 1998, API RP 1111, Third Edition was published in 1999, and DNV-OS-F201 was published in 2001. Both 2RD and F201 are dynamic riser codes while RP 1111 is a pipeline code that includes dynamic pipeline risers. This paper describes a new code for the design of dynamic risers for floating production installations. This new code is scheduled to become ISO 13628-12 and also to be adopted by API as a replacement for API RP 2RD. A JIP formed in 2008 expedited the development of the new code, which is currently scheduled for ISO ballot in 2010 as a draft international standard (DIS).

The new code has both mandatory (normative) and recommended (informative) practices. This paper will show the new Table of Contents and highlight the major differences between the new code and API RP 2RD. A significant difference is the way combined loads are checked. The new code allows designers to use any one of four methods:Method 1 based on the current API RP 2RDMethod 2 based on ISO 13628-7 (for completion and workover risers)Method 3 from DNV-OS-F201Method 4 from API 1111

Annexes illustrate the use of the new code for top-tensioned and steel catenary risers.

Background

A task group was formed to write a new recommended practice for floating production system risers in the fourth quarter of 1992. API RP 2RD Design of Risers for Floating Production Systems (FPSs) and Tension-Leg Platforms (TLPs) was finally published in June of 1998, almost six years later. In 1992 there were only three TLPs installed and no Spars. The only free-hanging compliant risers were made of flexible pipe. The first steel catenary riser was being designed for the Auger TLP, but was not installed until 1994. Five more TLPs with top-tensioned risers (TTRs) and a few more SCRs were installed before 2RD was published. The first Spar was installed in 1997. It used TTRs for production and catenary flexible pipe risers for export. Thus at the time 2RD was being written, industry experience was based mainly on top-tensioned risers for floating drilling vessels and TLPs.

In January 2001, Det Norske Veritas (DNV) published Offshore Standard DNV-OS-F201, Dynamic Risers. There are major differences between the 1998 API RP 2RD and DNV-OS-F201. Consequently, in 2003 a small API task group was formed to write a " bridging document?? between the two codes. At the summer 2003 API Standardization Conference, this plan was scrapped in favor of writing a new code based on 2RD and F201. A new task group for this task met for the first time in early 2004. In keeping with API goals at the time, the new code was to be written as an ISO document and adopted back by API. At the first task group meetings, another API document was introduced into the mix, API RP 1111, Third Edition, July 1999, Design, Construction, Operation, and Maintenance of Offshore Hydrocarbon Pipelines (Limit State Design). As its names implies, RP 1111 is a pipeline recommended practice. However, it also gives guidance on how to design SCRs, which in essence are a continuation of pipelines and flowlines.