High-pressure high-temperature (HPHT) well bore conditions present a unique challenge for the equipment and materials exposed to them. The subsea environment further exacerbates the HPHT challenge due to corrosive seawater, weight restrictions, variable external loads, and lack of immediate accessibility. From a materials perspective, a comprehensive understanding of the material physical properties and robust analysis of the potential failure mechanisms active in HPHT and subsea conditions is necessary for satisfactory equipment design validation and verification. This paper will discuss the challenges in HPHT materials selection and qualification, and the process by which acceptable design practices, safety margins, and prototype testing will be established. Environmentally assisted cracking and fatigue cracks are the dominant failure mechanisms in HPHT designs. Due to the elevated pressure and temperature, elastic-plastic material design models are applied. Dependable physical performance under extreme conditions is the primary objective. Metallic materials are generally subject to tensile tests at elevated temperatures, fracture toughness tests in simulated environments (including the drilling, production, and saltwater with corrosion protection environments). Fatigue crack growth testing is performed in order to determine the relevant material properties in anticipated environments. Elastomeric and metallic seals in HPHT design must be operable for across wide temperature range in corrosive environments and must be tested accordingly. Presently, standards specific to HPHT drilling equipment designs are still under development, and designs are evaluated from first principles due to the lack of field data. Functional production, inspection, and quality standards must also be developed. ABS is currently addressing these challenges at a design level with OEMs and is assisting in contributing to safety by verifying and validating that designs for HPHT equipment will follow the guidelines per all applicable API and ASME codes and standards. This paper will discuss the challenges associated with the material selection. This paper aims to help to establish a baseline for on-going efforts in standardizing the certification process of HPHT materials and their manufacturing processes for global applications. The knowledge gained by the development projects will be instrumental for the classification society certifying materials for HPHT equipment, to develop certification requirements aimed at improving safety on deep-water drilling units and preventing pollution of the environment.
Tandem SAW (Submerged Arc Welding) is one welding process that has been applied to maximize the welding productivity at the panel stage in ship building field. The weld bead profiles produced by Tandem SA welding exceed the acceptance criteria specified in some international regulations, such as AWS D1.1, ISO 5817 and NORSOK M-101. These regulations limit the applicable weld bead profiles, especially weld bead height, regardless of any consideration of design category. The fundamental reason for the limitation of weld bead profiles is related to the weldment fatigue properties. In this regard, we have investigated the effect of weld profiles on fatigue properties. The effect of weld bead profiles on fatigue properties has been experimentally verified and statistically analyzed, and new criteria for weld bead profiles which satisfy E curve as the design S-N curve are proposed for tandem SA welding.
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