issia Yamal LNG / Arctic LNG 2

1 Project Background and Extreme Environment

The Yamal LNG/Arctic LNG 2 project is one of the world’s largest polar liquefied natural gas projects, located on the Yamal Peninsula in Russia, within the Arctic Circle. This large-scale energy project integrates natural gas exploration, development, liquefaction, transportation, and sales. Upon full completion, the project will produce 16.5 million tons of liquefied natural gas and 1 million tons of condensate annually, with approximately 4 million tons of LNG destined for the Chinese market. The environmental conditions of the Yamal LNG/Arctic LNG 2 project are extremely harsh, with minimum temperatures in the Arctic Circle reaching -52°C. This extreme environment presents unprecedented challenges for equipment materials:

• Low-Temperature Brittleness Challenge: Ordinary steel is prone to brittle fracture in ultra-low temperature environments, leading to equipment failure.

• Thermal Expansion and Contraction Effects: Significant temperature variations cause substantial thermal expansion and contraction in materials, posing severe challenges to the sealing of connection points.

• Transportation and Installation Difficulties: The polar environment is unsuitable for on-site construction. The project adopts a modular construction approach, with modules prefabricated in China and transported to the Arctic site for assembly.

Facing these challenges, butt-welded pipe fittings and forged flanges have demonstrated significant technical advantages, ensuring the safe and stable operation of the entire liquefied natural gas plant under extreme conditions. The table below summarizes the main environmental requirements of the Yamal LNG/Arctic LNG 2 project and the corresponding solutions provided by flange technology:

*Table: Environmental Requirements of the Yamal LNG/Arctic LNG 2 Project and Flange Technology Solutions*

2 Core Advantages of Butt-Welded Forged Flanges

2.1 Advantages in Low-Temperature Toughness Under Extreme Conditions

One of the core advantages demonstrated by butt-welded forged flanges in the Yamal LNG/Arctic LNG 2 project is their exceptional low-temperature toughness. In the extreme low-temperature environment of the Arctic, ordinary carbon steel materials undergo brittle transition, with impact toughness sharply declining, Very easy causing sudden fracture accidents. The specialized stainless steel flanges used in the Yamal LNG/Arctic LNG 2 project, through special formula design and manufacturing processes, can maintain excellent mechanical properties under ultra-low temperature conditions of -196°C.

These flanges typically adhere to material standards such as ASTM A420 Gr.WPL6, A403 Gr.WP304/304L, ASTM A350 Gr.LF2 Cl.1, and A182 Gr.F304/304L. These materials, through appropriate heat treatment processes and chemical composition control, offer good low-temperature impact toughness. The special stainless steel pipes developed specifically for the Yamal LNG/Arctic LNG 2 project employ a formula design that emphasizes “high corrosion resistance, good low-temperature impact toughness, and excellent welding performance,” achieving stable performance and ease of construction under harsh climate conditions. This material grade ensures safe operation in extremely cold environments, preventing leaks or fractures caused by material brittleness.

2.2 Structural Integrity and Sealing Reliability

Another significant advantage of butt-welded forged flanges is their unparalleled structural integrity and sealing reliability. The forging process ensures continuous and dense metal grain flow, eliminating defects commonly found in cast flanges such as pores, shrinkage cavities, and inclusions, thereby providing higher structural strength and integrity. In the Yamal LNG/Arctic LNG 2 project, the transportation pressure of liquefied natural gas is extremely high, and the medium is flammable and explosive, placing extremely demanding requirements on the sealing of connection points.

The butt-welding connection method provides uniform stress distribution, reducing stress concentration at the joints. The extended neck design of the Long Weld Neck (LWN) flange offers better reinforcement, support, and alignment for the piping system, which is particularly beneficial when combined with equipment such as pressure vessels and pumps. This design is especially important in the modular construction of the Yamal project, as the modules must withstand significant vibration and impact during transportation, requiring flange connections with superior fatigue resistance.

Table: Performance Comparison Between Butt-Welded Forged Flanges and Traditional Flanges in the Yamal Project

2.3 Ease of Maintenance

In terms of safety and maintainability, butt-welded forged flanges also demonstrate significant advantages. Due to the bad environment of the Arctic region, equipment maintenance and repair operations are extremely difficult and costly, thus placing very high demands on the reliability and maintenance-free nature of equipment. Butt-welded forged flanges achieve this goal through their optimized design and precise manufacturing processes.

3 Modular Construction and Flange System Integration

The Yamal LNG/Arctic LNG 2 project has adopted a revolutionary modular construction approach, representing a major breakthrough from traditional factory construction models. Due to the harsh Arctic conditions being unsuitable for on-site construction, the project innovatively employed a “factory-built” strategy, dividing the plant into multiple modules that were manufactured in China and then transported to the destination for assembly. This construction method placed special requirements on the flange system, and butt-welded forged flanges, with their unique advantages, became the ideal choice for modular construction.

The precise dimensions and excellent performance of butt-welded forged flanges played a key role in this process. Through precision machining and strict quality control, these flanges ensured perfect matching and connections between modules. All welding procedure qualifications for the modules used in the project passed in one attempt, with excellent performance test results, achieving industry-leading standards. The structural ultrasonic testing weld rework rate was only 0.79%, and the pipeline radiographic testing weld rework rate was only 0.96%. This high-quality standard ensured that the modules could be quickly assembled upon arrival at the Arctic site, significantly reducing on-site construction time and costs.

Modular construction also requires the flange system to possess good adaptability and flexibility. The butt-welded forged flanges used in the project incorporate various piping flange standards and sealing face types, catering to diverse engineering needs. This combination of standardization and diversity optimizes module layout design, improves space utilization, and maintains structural stability and safety during transportation.

4 Conclusion and Outlook

The Yamal LNG project, as the world’s largest polar LNG project, presents unprecedented challenges for equipment materials. Butt-welded pipe fittings and forged flanges, with their exceptional low-temperature toughness, excellent structural integrity, reliable sealing performance, and good maintainability, played a vital role in the project, ensuring the safe and stable operation of the entire system under extreme conditions.

Looking ahead, with the deepening of Arctic energy development and the growth of liquefied natural gas demand, butt-welded pipe fittings and forged flange technology will continue to evolve and develop. New material applications, intelligent manufacturing, and digital twin technology will become the development directions for the next generation of flange products.