ABSTRACT

Since oil discoveries are moving towards ultra-deepwater areas, such as Pre-Salt in Brazil, collapse resistance is a key factor in the design of the pipelines. Large diameter UOE pipes are being increasingly used for the construction of such pipelines.

It is known that the cold forming, and the final expansion in the UOE linepipe manufacturing process, reduces the compression resistance for elastic collapse. Due to this, the DNV collapse formula includes a fabrication factor that de-rates by a 15% the yield strength of UOE Pipes. However, DNV also recognizes the effect of thermal treatments and the code allows for improvement of the fabrication factor when heat treatment is applied.

This paper presents the qualification of UOE pipes with enhanced collapse capacity focusing the use of a fabrication factor (alpha fab, afab) equal to 1. TenarisConfab has performed a technology qualification process according to DNV-RP-A203 " Qualification Procedures for New Technology" and the main aspects of the qualification process are presented in this paper which included significant material and full scale testing, including combine load testing, compression testing and a final analysis.

The qualification process achieved successful results and this will allow TenarisConfab use of a fabrication factor equal to 1 directly in deepwater and ultra-deepwater offshore pipeline projects with a possible reduction in material and offshore installation costs and also potentially enhancing the feasibility of many challenging offshore projects.

INTRODUCTION

The exploration of oil and gas reserves at distant points from coast is bringing significant challenges to Oil & Gas industry. Some fields are located at hundreds of kilometers from the coast and are placed at water depths up to 3,000 meters. Deepwater pipelines will be subject to a large net external pressure and collapse capacity may be governing for the wall thickness design. In this condition, the pipe resistance becomes an important challenge due to present installation methods and due to the considerable loads caused by the pipe weight due to the heavy wall thickness necessary to resist the external collapse pressure. The need to produce and transport large volumes of gas in safe conditions demands the use of large diameter steel pipes produced by UOE-SAWL process which is a confident alternative and has already been applied in some important projects. Considering this harsh environment, it is necessary to study and develop a pipe with enhanced collapse resistance capable to resist ultradeep water pressures and also reduce installation loads by optimizing wall thickness.

The great majority of the pipelines worldwide are designed following DNV-OS-F101 [2]. The collapse resistance of the pipe is significantly influenced by a number of factors related to pipe properties and hence pipe manufacturing process. Furthermore, through a proper control of the pipe making process and understanding of linepipe properties, improvements in the collapse resistance of UOE linepipe are possible. [5]

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