Fatigue Performance of High Strength Riser Materials Subjected to Sour Environments

07121-DW1403

Primary Performer
Southwest Research Institute, San Antonio, TX 78238

Additional Participants
BP, Inc. (cost share contributor)

Abstract

Objectives:
New offshore reserves have exhausted the design margin available with conventional materials requiring a new generation of high strength, corrosion resistant alloys suitable for sour conditions. Although some of these materials likely already exist, the testing has not been performed to identify them. Given this, the overall objective of this program is to develop fatigue performance data for high strength materials for deepwater, high pressure, high temperature and sour/corrosive reservoir fluid risers. The focus of this program is to explore several different materials and systems (titanium, steel, forgings and nickel alloys) and determine which of these various materials exhibits the best properties. Both fatigue crack initiation (S-N) and fatigue crack growth (FCG) behavior will be assessed during this program in a variety of different environmental conditions.

Description and Methods:
This program is a material screening program designed to quantify and understand performance of high strength alloys in primarily sour conditions. Fatigue testing (both stress-life and fatigue crack growth) will be performed on candidate steel, titanium and nickel-rich alloys. A variety of test environments will be utilized during testing including: lab air, seawater, seawater with cathodic protection, sour brine and sour brine with InsulGel on the specimen (InsulGel is a heat transfer insulation). Existing facilities at SwRI will be used for testing in the highly aggressive environments. Some limited fatigue testing examining the impact of test duration (frequency effects) and variable amplitude loading will also be performed on selected materials to assist in optimizing test conditions for replicating in-service behavior. In addition to the fatigue testing, the fracture properties will also be assessed by measuring tensile properties as well as fracture toughness (JIc-based). The total program duration is 15 months with over 200 tests planned.

Impact:
Upon completion of this program, the most promising materials for the next generation of reserve developments will be identified. Once identified, these candidate materials can be further developed to enhance their properties for the given design considerations. These materials will also be subject to further investigation for different properties and behavior during subsequent phases of this program.

Principal Investigator: Steve Hudak