In the field of marine engineering and high-end equipment manufacturing, ENiCu-7 nickel-copper alloy welding rods, as classic materials in the AWS A5.11 standard, continue to play an irreplaceable role. This welding material complies with the ISO 14172:2016 international standard, and its registered composition range is Ni≥62%, Cu 28%-32%, and Fe≤2.5%. With its unique corrosion resistance, it has become an important medium for connecting key equipment.
■ Material properties are authoritatively certified
According to the technical documents of the American Welding Society (AWS), the ENiCu-7 welding material deposited metal exhibits a corrosion rate of ≤25mdd (mg/square decimeter/day) in a 6% ferric chloride solution at 50°C in the ASTM G48 standard test, which is significantly better than the 150mdd level of conventional 304 stainless steel welding materials. This characteristic is due to the synergistic effect of its nickel matrix and copper elements, which can form a stable passivation film in a chloride ion environment.
A comparative study published in 2021 by the Department of Marine Engineering at the Norwegian University of Science and Technology (NTNU) showed that in a simulated seawater circulation system, the crevice corrosion depth of ENiCu-7 welds was only 40% of that of ERNi-1 nickel-based welding materials, verifying its long-term reliability in the marine environment.
■ Industrial application is steadily advancing
In the field of shipbuilding, public information from Hudong-Zhonghua Shipbuilding, a subsidiary of China Shipbuilding Group, shows that ENiCu-7 welding rods account for 35% of the welding of the secondary shielding layer of the liquid cargo tank of the 174,000 cubic meters LNG carrier it built, mainly used for dissimilar steel connections. The technical white paper of Hyundai Heavy Industries of South Korea revealed that the material can stabilize the impact energy of welds at -50°C at more than 54J in polar ship construction.
In the field of nuclear power, France's Framatome obtained ASME III nuclear power certification in 2020, approving the use of ENiCu-7 for the maintenance welding of pipelines in the secondary circuit auxiliary system of pressurized water reactors. my country General Nuclear Power Engineering Company has also successfully applied this material in the maintenance of the seawater circulation system of Yangjiang Nuclear Power Station.
■ Technology upgrade continues to deepen
Current industry research and development focuses on process optimization. Harbin Welding Research Institute's 2023 experiment showed that by adding 0.6%-0.8% niobium, the corrosion resistance of ENiCu-7 welding materials in 10% sulfuric acid solution can be increased by 22%. Sandvik Group's latest ENiCu-7-G welding wire product has achieved stable production of 1.2mm fine-diameter welding wire, which meets the needs of robot automated welding.
■ The standard system is gradually improved
The National Welding Standardization Technical Committee (SAC/TC55) issued the "Technical Guide for the Application of Nickel-Based Welding Rods" in 2023, clarifying the welding process parameter range of ENiCu-7 in marine environment: it is recommended to control the heat input to 8-25kJ/cm, maintain the interlayer temperature at 80-150℃, and no heat treatment is required after welding. The draft DIS 24597 standard being developed by the International Organization for Standardization (ISO) has added a test method for this material in a hydrogen environment.
■ Market prospects and challenges
According to statistics from the China Welding Association, my country's consumption of nickel-based welding materials will reach 18,000 tons in 2022, of which the ENiCu-7 series accounts for about 15%. With the advancement of national key projects such as the development of deepwater gas fields in the South China Sea and the construction of coastal wind power installation ships, the annual demand growth rate of this material is expected to remain at 8%-10%. However, it is still facing industrial bottlenecks such as the high price of imported welding wire (about 380 yuan/kg) and the long training cycle of welding process personnel.
Industry insiders pointed out that the continued development of ENiCu-7 requires in-depth collaboration among material manufacturers, scientific research institutes and end users. Recently, the "Marine Materials Welding Joint Laboratory" jointly built by Baosteel Special Steel and Jiangnan Shipyard is focusing on the hydrogen-induced crack prevention technology of this material in multi-layer welding of ultra-thick plates (more than 50mm), and the relevant results are expected to be transformed into engineering within the year.