Weld procedure qualification methodologies for ExxonMobil high strain pipelines are presented. ExxonMobil has been involved in the design and construction of high strain pipelines for both onshore and offshore applications. These projects have included onshore applications involving potential seismic activity (fault displacement and soil liquefaction) as well as arctic applications that may involve displacements associated with frost heave and thaw settlement. Recent offshore installations have been designed and constructed to accommodate potential displacement caused by ice scour. Some of these installations have been designed to accommodate in excess of 3% longitudinal tensile strain demand. A critical element of the overall pipeline design is the qualification and validation of acceptable strain capacity for the pipeline girth welds. A girth weld qualification test program, based on large scale proof testing (i.e., curved wide plates) has been developed and executed.
Pipeline applications that are subject to global plastic strains require specific testing and qualification programs intended to verify the strain capacity of the girth welds. Such strain demands are generally beyond the limits of standard ECA applicability which normally cover demands up to 0.5% strain. Therefore, qualification of welding procedures for high strain environments require significantly more testing than weld procedures intended for stress-based designs. The plastic strain capacity of girth welds is a function of the pipe and weld metal properties, as well as the maximum flaw size allowable in the girth weld. Specific weld metal/heat affected zone properties, based on small scale testing, should be combined with full scale curved wide plate testing of girth welds that include artificial flaws.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Erha and Erha North field development in deepwater Nigeria consists of multiple subsea wells connected to a floating production, storage, and offloading vessel (FPSO) via flowlines and steel catenary risers (SCRs). Processed crude oil is exported through an oil offloading system (OLS), consisting of a catenary anchor leg mooring (CALM) buoy and dynamic offloading lines (OLLs).The SCRs were identified as a key technical issue due to high-fatigue performance requirements, especially under potential sour service conditions. In addition, the associated flexible joint performance in a relatively high-temperature environment also extended the design envelope for this critical component. Innovative clad overlay and clad welding technologies were developed within the Project timeframe and efficiently executed both onshore and offshore. A rigorous design and qualification effort, including the development of novel sour environment fatigue testing and ultrasonic inspection technologies, ensured system integrity.The OLS was also identified as a key technical challenge early in the Project. The innovative, U-shaped OLL design is a first in the industry. The OLLs presented performance challenges similar to those of the SCRs, but in addition, the complicated coupled buoy/mooring/OLL motion behavior posed a unique challenge for OLL fatigue design. A dedicated qualification and validation program was devised to confirm system integrity. The design and execution teams utilized new technology and lessons learned from past projects to ensure that the installed system would meet challenging acceptance criteria.This paper discusses challenging issues and resolutions for the SCR and OLL designs. The extensive qualification programs, including CALM buoy model tests, SCR cladding and welding qualification tests, and the flexible joint qualification, are also discussed.
To facilitate development of future deeper water assets, riser and pipeline designs using current X65 carbon steel requires increased wall thicknesses to manage the demand from large tensile loads. This increase in wall thickness is due to the weight of the pipe body and the fatigue performance at the hang-off and the touch-down point for steel catenary risers (SCR) and steel lazy wave risers (SLWR). The increased wall thickness poses challenges for fabrication, design, installation and project execution due to the single side welding of thick pipe. Increasing the steel grade from the current X65 to X80 or higher strength grade could reduce the pipe wall thickness and provide potential cost savings from total tonnage and is therefore considered as a potential alternative for deeper water steel riser applications. However, it is challenging to meet the hardness acceptance criteria (i.e. 250 HV10) as per DNV-ST-F101 for the higher strength steel weldment, particularly for sour service. The objective of this study was to understand the effect of hardness on sulfide stress cracking (SSC) resistance of X80 line pipe base material and weldment in sour service environments. A 323.9 mm OD × 25.4 mm WT seamless quenched and tempered X80 line pipe was used for this study. Coupons were extracted from the pipe and then heat-treated by welding simulator (Gleeble™). Implementing controlled cooling, hardness values ranging from 270 to 350 HV10 were achieved, and representing the heat affected zone (HAZ) hardness. Four point bend SSC test were performed on coupon halves as per NACE TM-0316, loaded to 80% actual yield strength (AYS) and tested for 30 days in selected NACE Region 2 and 3 environments as specified in NACE MR0175/ISO 15156-2. Coupons showed no indication of SSC cracking for the samples with measured hardness values of ∼320 HV10 in the selected NACE Region 2 and 3 environments.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Erha and Erha North Project utilizes a steel catenary riser (SCR) system to connect the floating production, storage, and offloading vessel (FPSO) to the subsea infrastructure. The system is a hybrid, composed of both steel and clad corrosionresistant alloy (CRA) pipe, with the CRA clad pipes located in the touch-down and hang-off areas of the SCRs. The CRA clad pipe sections are required to obtain satisfactory fatigue life due to the presence of CO 2 and potential H 2 S in the production stream. In total, four production and two test lines were required, with a total of 1,120 m of CRA clad pipe installed.Ultrasonic inspection of the welds joining the CRA clad pipes proved to be technically challenging due to the bimetallic features of the weldment and the small flaw size allowable for this fatigue-dominant application. Further complicating this effort was the need for reliable flaw detection on a real-time basis to maintain the pipelay rate. To meet these challenges, Shaw Pipeline Services (SPS) was enlisted to develop an automatic ultrasonic testing (AUT) system capable of reliable inspection of the weldments. This paper discusses the AUT system qualification program, product implementation, and lessons learned. Included in these discussions are technological challenges and respective approaches for metallurgically bonded and weld overlaid clad girth weld ultrasonic inspection, as well as detailed sizing accuracy data on seeded (i.e., intentionally planted) defects during the qualification stage and sizing accuracy data on production welds with naturally occurring flaws.
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