Heavy Wall UOE SAWL Pipes for Ultradeepwater and Sour Service Application
Authors: Moreira F. Arroyo , Stachelberger Christian , Silva Ronaldo Cristiano da , Gauss Christian 
Published: June 2014

The necessity of oil and gas exploration to attend the worldwide demand led to new challenges for engineering and materials development. The reserves of Pre-Salt in Brazilian coast is an example of such challenge, since it combines fields that are located at approximately 250 km off the coast, up to 3,000 meters deep water and corrosive environments. All these factors are detrimental to the pipeline making it necessary to develop new products that are capable to comply with demanding requirements for hostile environments, considering corrosion resistance in the presence of H2S, high strength, high toughness and heavy wall thickness to resist the external collapse pressure and good weldability for field installation. The UOE-SAWL process for pipe production enables the transportation of large amounts of oil and gas using large diameter pipes in safe conditions. In order to attend the main Brazilian projects, special requirements including DNV-OS-F101 have to be fulfilled by the pipe manufactures taking into account the as mentioned challenges to be overcome. The desired steel properties can be achieved by high end technologies in steelmaking, such as optimum rigorous alloying design, vacuum degassing and dynamic soft reduction, followed by Thermomechanical Control Process plus accelerated cooling (TMCP+ACC). The cleanness of the obtained steel associated with the accelerated cooled microstructure have an important role in the sour service resistance, weldability and mechanical properties. This paper presents the evaluation of mechanical properties and corrosive resistance of OD 24 in, WT 38.1 mm grade DNV 450 SFD produced according to DNV-OS-F101, supplementary requirements and corrosive tests carried out in conformance with NACE MR0175 and NACE TM0177. Good results were obtained in Charpy V-Notch tests of Base Metal, Heat Affect Zone and Weld, DWTT, CTOD and all the others required mechanical tests. Satisfactory results were also obtained in the HIC and SSC corrosive tests. The combination of all the obtained results make this pipe capable to face the challenges of the new exploration fields in Brazil.

Introduction

Nowadays long-distance offshore deepwater and ultra-deepwater pipelines have been and are still being built for the transportation of large quantities of oil and gas. The Brazilian offshore province began to attract the attention of the oil industry a couple of decades ago. The exploration of deepwater fields in the Presalt province and hence the necessity of oil and gas transportation, requires demanding material properties, leading pipe manufactures to seek for products excellence [1].

The pipes used for this application are commonly produced using the " UOE" process. This method provides many advantages in terms of product capacity, productivity, material properties and dimensional control. These applications require high strength, low D/t ratio in order to have good collapse resistance, high impact toughness, good weldability and sour resistance. In order to achieve the desired properties, the steel has been produced using the state of the art technology in steelmaking, such as optimum rigorous alloying design, vacuum degassing, dynamic soft reduction, etc. The effects of this technique, associated with the Thermomechanical Control Process plus the Accelerated Cooling (TMCP+ACC) resulted in enhanced material properties.