The construction of large-scale projects often comes with various challenges, some of which include the first-time implementation of new ISO 17781 requirements along with new company specification requirements on hot tensile tests and SCC tests on field girth welds. One of the main challenges that arise when dealing with larger diameters is maintaining oxygen content below 500ppm to avoid oxidation at the root. Stress corrosion cracking test (SCC): Strict technical requirements were specified, including four-point bend test as per NACME TM0316 for autogenous welding. SCC tests were conducted on the 16” line pipe production weldment in a third-party lab accredited by ISO 17025. The same SCC test requirements were subjected on the girth welding produced in the field, even though all passes were welded with filler metal, to evaluate the heat affected zone (HAZ) of the line pipe with autogenous weld. As the girth weld is not subjected to solution annealing, the welding parameters were tuned to ensure the girth weld and its HAZ meets the SCC test criteria of no pits.
Elevated tensile test: Performed at the design temperature, this is an important property for this line and shall meet room temperature mechanical strength requirements.
Charpy impact test: Was conducted to meet ISO 17781 Quality Level 1 requirements even though Quality level 2 is accepted for oil and gas environments. Also test temperature applied in line with ISO 17781 -46deg C, in spite of the minimum design temperature being warmer than 5deg C.
Pitting corrosion test: ASTM G48 test was conducted on the weldment in the as-welded condition without altering the root condition. No pickling was performed to simulate the production weld, and the entire thickness was subjected to test method A. The test was successful and weight loss was lesser than 4gm/m2.
Overcoming project schedule challenges
The project faced technical challenges in meeting yield strength, hot tensile, corrosion, and impact tests. COVID-19 restrictions affected raw material and product shipments, but effective remote inspections and frequent communication with suppliers and manufacturers helped maintain manufacturing quality. Deviations from specification requirements were managed through technical authority approvals. Qualifying submerged arc welding posed challenges, but optimising welding parameters improved toughness and corrosion test requirements. Double welding before transferring to the site improved productivity and helped meet project schedules.
To ensure manufacturing quality, technical alignment and pre-inspection meetings were held in the mill, and close monitoring and collaboration with vendors were established to mitigate COVID-19 restrictions. A third-party inspector was mobilised to the mill for effective monitoring and quick resolution.
Construction of this larger diameter DSS pipeline required special equipment including internal clamps, purge monitors, flow meters, boroscope inspection equipment and highly-skilled welders. The COVID-19 pandemic posed significant challenges in mobilising high-skilled welders, equipment, and tools to the construction site.
In conclusion, the successful fabrication and installation of a large diameter DSS pipeline underlines the resilience of the oil and gas industry in the
face of unexpected challenges like the COVID-19 pandemic. Despite disruptions and logistical hurdles, the project was completed before the deadline, meeting all requirements, and demonstrating the benefits of innovative practices and effective collaboration between pipe mills, contractors, and end users. The use of digital tools for remote inspections and close monitoring of vendors helped ensure compliance with project requirements, while technical authority approvals managed any deviations. The project’s success is a testament to the dedication and technical expertise of the team involved, who overcame all odds and obstacles to deliver a high-quality and reliable pipeline. This project serves as an excellent example of how best practices, technical alignment, and innovation can help organisations overcome challenges and achieve their goals.
The authors would like to express their gratitude to Petroleum Development Oman, as well as the individuals, contractors, and suppliers, associated with this project. Their contributions and support have been invaluable in making this project a success.