Submarine Power Cable Sheath Welding Without Embrittlement Cracks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Submarine power cables face challenges with traditional lead sheaths, such as lead-free alternatives like copper and stainless steel, which can lead to welding defects and water infiltration due to hydrogen embrittlement and solidification issues, compromising the integrity of the insulation system.
Innovation Solution
A method involving autogenous welding of a copper sheath with very low oxygen content or specific stainless steel compositions within defined chromium and nickel equivalent ranges, ensuring a high-quality, crack-free water-blocking layer without filler materials, and using protective shielding gases to prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper material with normal oxygen content is used for the metal sheath, then the water barrier function is provided, but hydrogen embrittlement and cracking occur in the weld due to oxygen reaction with hydrogen forming water vapour
Solution Approach 1:
The patent changes the oxygen content parameter of the copper material from normal levels to very low levels (at most 0.1 wt.% oxygen). This parameter change prevents the chemical reaction between oxygen and hydrogen during welding, eliminating water vapour formation and subsequent cracking, while maintaining the water barrier function
Solution Approach 2:
The patent creates an inert welding environment by using autogenous welding without filler material and by controlling the copper composition to be inherently resistant to hydrogen embrittlement. This inert approach prevents harmful chemical reactions during the welding process
2Reliability
If stainless steel with high chromium and nickel equivalents is used for the metal sheath, then the corrosion resistance and ductility are improved, but the welding complexity and material cost increase
Solution Approach 1:
The patent specifies precise parameter ranges for chromium (16-25%) and nickel (11-22%) equivalents in the stainless steel composition. These parameter changes optimize the material properties for welding performance, corrosion resistance, and ductility while avoiding excessive complexity in the welding process
Solution Approach 2:
The patent uses stainless steel as a composite material system combining specific proportions of chromium, nickel, and other alloying elements. This composite approach achieves the desired balance of properties without requiring complex welding procedures
3Ease of manufacture
If filler material is used in the welding process, then the weld filling and bonding are facilitated, but weld defects and geometry deviations occur due to intermittent feed and contamination
Solution Approach 1:
The patent extracts and eliminates the filler material from the welding process, using only autogenous welding of the metal sheath edges. This removal of filler material eliminates the sources of contamination and intermittent feed problems, resulting in superior weld geometry precision and continuity
Solution Approach 2:
The patent employs self-service welding where the metal sheath itself provides all necessary material for the weld without external filler addition. The edges are melted and joined directly, allowing the material to self-regulate the welding process and achieve precise geometry
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces hydrogen embrittlement risks, prevents water infiltration, and ensures a smooth, circularly symmetrical geometry for the water-blocking layer, enhancing the durability and reliability of submarine power cables.
Implementation Method 1
When welding oxygen containing copper, hydrogen from the atmosphere may diffuse into the weld melt and react with the cuprous oxide, forming water vapour. This leads to a considerable volume expansion. Small vapour bubbles form at mainly the grain boundaries and risk to cause cracking along the grain boundaries.
Implementation Method 2
c) welding opposing edges of the metal sheath longitudinally by autogenous welding to form a metallic water-blocking layer around the insulation system
Implementation Method 3
using protective shielding gases to prevent oxidation
Implementation Method 4
some stainless steels that are welded autogenously will have weld defects such as cracks that are formed due to an unfavourable solidification process, phase transformations, and/or give an unfavourable weld microstructure
Implementation Method 5
they also solidify not fully austenitic but with a delta ferrite phase which is very beneficial for avoiding solidification cracks
Data Source
Figure 1~2
Figure 3
AI summary
A method of manufacturing a submarine power cable, comprising: a) providing an insulation system around a conductor, the insulation system including an inner semiconducting layer arranged around the conductor, an insulation layer arranged around the inner semiconducting layer, and an outer semiconducting layer arranged around the insulation layer, b) arranging a metal sheath around the insulation system, and c) welding opposing edges of the metal sheath longitudinally by autogenous welding to form a metallic water-blocking layer around the insulation system, wherein the metal sheath consists of a copper material comprising at least 99 wt.% copper and at most 0.1 wt.% oxygen, or wherein the metal sheath consists of a stainless steel which has a chromium equivalent in a range of 16-25 and a nickel equivalent in a range of 11-22 according to a Schaeffler-DeLong constitutional diagram for which the chromium equivalent is calculated according to the formula %Cr + %Mo + 1.5 × %Si + 0.5 × %Nb and the nickel equivalent is calculated according to the formula %Ni + 0.5 × %Mn + 30 × (%C + %N).