ABSTRACT
Available fracture toughness (FT) test methodologies are reviewed in this publication to compare their details. Accurate characterization is crucial to obtain the material properties utilized in new technology development projects such as high pressure high temperature (HPHT) equipment in sour service. While fracture mechanics was utilized only for fitness for service activities in the industry, the new HPHT design guideline requires fracture mechanics analysis for a pressure containing primary barrier equipment. Therefore, FT becomes a critical parameter to be obtained and utilized in design verification. Selection of a test method (standard) for sour service condition is based on the application of the equipment since each method has its own limitations.
In this work, a comprehensive study was performed to better understand the FT testing in a corrosive environment. Seven common standards, ASTM E399, ASTM E1820, ASTM E1681, ASTM F1624, ISO 12135, BS7448 and NACE TM0177 for FT testing of Metals were scrutinized in details. These standards were reviewed; pros and cons are tabulated and discussed. Recommendations that could be used in decision making process to select the right standard for the appropriate purposes are noted. Additionally, future research work that would help to obtain more accurate test data is recommended.
INTRODUCTION
Offshore exploration has trended to wells of higher pressure and higher temperature over time. Currently, an increasing number of discovered fields have pressures higher than 15000 psi (103.4 MPa) and temperature above 350 °F (177 °C), defined as high pressure high temperature (HPHT) or ultra HPHT fields. Additionally, a majority of these fields are located in offshore deep water or ultra-deep water which adds to the complexity of the field development. Material selection for this condition has become a challenge as higher strength materials are required for the harsh deep water offshore conditions. As material strength increase hydrogen embrittlement becomes more pronounced as a majority of the HPHT fields contains H2S in the production fluid or need protection by cathodic protection.
