06Ni7DR is a high-performance alloy structural steel plate specifically designed for ultra-low-temperature applications. The designation carries clear technical significance: "06" indicates an average carbon content of approximately 0.06%, classifying it as a low-carbon steel, which enhances weldability and toughness; "Ni7D" denotes a nickel (Ni) content of about 7%, where "D" stands for "low temperature" use, emphasizing its excellent low-temperature toughness; and "R" stands for "Rongqi" (vessel), indicating its dedicated use in pressure vessel manufacturing. Therefore, 06Ni7DR refers to a 7% nickel-containing steel plate designed for ultra-low-temperature pressure vessel applications.
This steel plate is primarily used in the fabrication of large welded pressure vessels operating at extremely low temperatures (down to -120°C or lower). Typical applications include inner tanks of liquefied natural gas (LNG) storage tanks, storage and transportation equipment for cryogenic liquids (such as liquid oxygen, nitrogen, and argon), deep cryogenic separation units, and aerospace propellant storage tanks. Under such extreme conditions, conventional steels lose ductility and toughness and are prone to brittle fracture. In contrast, 06Ni7DR, with its high nickel content, significantly lowers the ductile-to-brittle transition temperature, maintaining excellent impact resistance and fracture toughness in ultra-low-temperature environments, ensuring safe and reliable operation.
Key characteristics of 06Ni7DR include outstanding low-temperature impact toughness (retaining high impact energy values even at -115°C or -120°C), good weldability, excellent cold-forming capability, and moderate strength. Nickel, as the key alloying element, refines grain structure, stabilizes austenite, and effectively inhibits crack propagation. The steel is typically supplied in a normalized or normalized-and-tempered condition to achieve uniform microstructure and stable mechanical properties. Additionally, its clean steelmaking process and strict control of impurities ensure high material reliability.
The current national standard for 06Ni7DR is GB/T 3531-2023 "Steel Plates for Low-Temperature Pressure Vessels", released in 2023, replacing the previous GB/T 3531-2014 edition. This updated standard systematically includes advanced low-temperature steels like 06Ni7DR, specifying clear requirements for chemical composition, mechanical properties (especially impact toughness at -115°C), ultrasonic testing, and inspection rules. Its implementation provides a reliable technical basis for the design and manufacture of ultra-low-temperature pressure vessels, meeting the high standards of safety and durability required in modern energy and chemical industries.
Ultrasonic Testing (UT)
A key non-destructive testing technique that uses high-frequency sound waves to detect internal flaws in steel plates. The probe emits sound waves, which reflect when encountering defects such as cracks or inclusions. The receiver captures the echoes, enabling precise determination of defect location and size. With high sensitivity, strong penetration, and fast inspection speed, UT effectively ensures internal quality, widely used in the production of heavy plates, pressure vessel plates, and other high-end products to guarantee safety and reliability.
Magnetic Particle Testing (MT)
A common surface inspection method that magnetizes the workpiece, causing leakage magnetic fields at surface or near-surface defects like cracks or inclusions, which attract magnetic particles to form visible indications. Simple to operate and highly sensitive, MT is suitable for rapid inspection of surface and near-surface flaws in ferromagnetic materials, widely used for online or offline inspection of plate edges, ends, and welds, ensuring product quality and safety.
Penetrant Testing (PT)
A non-destructive method for detecting surface-breaking flaws. A penetrant liquid is applied to the cleaned steel surface, allowing it to seep into defects such as cracks or pores. After removing excess penetrant, a developer is applied, causing the trapped penetrant to bleed out and form visible indications. Simple and cost-effective, PT is suitable for inspecting surface defects in various non-porous materials, commonly used for welds, castings, and complex components, effectively ensuring surface quality of steel plates.
