Flux-Cored Wire Composition for Cryogenic LNG Tank Welding
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Solution Overview
Problem
Existing welding materials for structural steel in liquefied gas environments are limited in their applicability across different materials, leading to confusion and economic disadvantages, and they do not provide excellent cryogenic toughness.
Innovation Solution
A stainless-steel flux-cored wire with adjustable contents of Mn, Cr, and Mo, designed to produce a weld metal with excellent strength and cryogenic impact toughness, capable of welding 9% nickel steel, high manganese steel, and stainless steel without restrictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional welding materials are used for different structural steel materials (9% Ni steel, high manganese steel, stainless alloy), then the strength and impact resistance requirements can be met for each specific material, but the application is limited and causes confusion in the work process and economic disadvantages
Solution Approach 1:
The patent develops a universal welding wire composition that can be applied to multiple types of structural steel materials including 9% Ni steel, high manganese steel, and stainless alloy without requiring material-specific wire formulations. This single wire composition achieves the required strength and impact resistance for all these materials, eliminating the need for multiple specialized wire types and simplifying the welding material selection process.
2Strength
If Cr—Ni-based stainless steel or 9% Ni steel is used for cryogenic storage structures, then the strength at low temperature is improved compared to aluminum alloy, but the manufacturing cost increases due to the inclusion of expensive nickel
Solution Approach 1:
The patent modifies the chemical composition parameters of the welding wire by optimizing the content ranges of Cr (13-25%), Ni (6-15%), Mn (1-10%), and Mo (0-5%), along with specific flux composition ratios. These parameter changes enable the weld metal to achieve the required cryogenic toughness and strength while controlling nickel content to reduce manufacturing costs compared to conventional Cr—Ni-based stainless steel structures.
3Quantity of substance
If nickel-free high-manganese steel is used for structural steel in liquefied gases, then the cost increases and load to heat treatment facility increases due to an increase in the number of heat treatment cycles, but it is completely free of nickel
Solution Approach 1:
The patent employs a welding wire composition that produces weld metal with austenite as the main tissue structure, which inherently provides cryogenic toughness without requiring extensive heat treatment cycles. This approach uses the metallurgical properties of the weld metal itself to achieve the desired performance, eliminating the need for multiple heat treatment operations and reducing facility load while maintaining complete freedom from nickel.
4Reliability
If the content of Cr and Mo is increased to improve cryogenic toughness, then the impact resistance at low temperature is improved, but the manufacturing cost increases
Solution Approach 1:
The patent optimizes the content parameters of Cr (13-25%) and Mo (0-5%) within specific ranges, along with their ratio relationship, to achieve the required cryogenic toughness. By carefully controlling these composition parameters and their interactions with Ni and Mn content, the patent attains excellent impact resistance at -196°C while avoiding excessive chromium and molybdenum addition that would significantly increase manufacturing costs.
Data Source
AI summary
Provided is a stainless steel flux-cored wire for manufacturing an LNG tank. From the stainless steel flux-cored wire, it is possible to obtain a weld metal having excellent tensile strength and impact value by adjusting the contents of Mn, Mo, and Cr. The stainless steel flux-cored wire is applicable to welding of 9% nickel steel, high manganese steel, and stainless steel materials and can provide a weld metal having excellent cryogenic toughness in a weld zone because the contents of Mn, Mo, and Cr are adjusted.