Submarine Power Cable Sheath Welding Against Embrittlement Cracks
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Solution Overview
Problem
Submarine power cables face challenges with traditional lead sheaths, such as lead-free alternatives like copper and stainless steel, which can suffer from welding defects and hydrogen embrittlement, leading to water infiltration and potential damage to 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, to form a metallic water-blocking layer, reducing hydrogen embrittlement and weld defects, and ensuring a high-quality, smooth weld geometry.
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 and Heat Affected Zone during autogenous welding
Solution Approach 1:
The patent changes the oxygen content parameter of the copper material from normal levels to very low levels (≤0.1 wt.% oxygen). This parameter change prevents hydrogen embrittlement and cracking during autogenous welding while maintaining the water barrier function, as the low oxygen content eliminates the formation of cuprous oxide that would otherwise react with hydrogen to form water vapor bubbles.
Solution Approach 2:
The patent applies local quality by ensuring the copper material has uniformly low oxygen content specifically in the regions that will be welded and the heat affected zone. This localized material property optimization prevents cracking in critical areas while maintaining the overall water barrier function of the sheath.
2Ease of manufacture
If filler material is used during welding of the metal sheath, then the welding process can proceed, but weld defects and geometry deviations occur
Solution Approach 1:
The patent extracts and eliminates the filler material from the welding process, performing autogenous welding instead. This removal of filler material prevents weld defects and geometry deviations caused by intermittent feeding and contamination, while the welding process remains feasible due to the optimized copper material composition that is easier to weld.
Solution Approach 2:
The patent applies self-service by using the base copper material itself as the welding material without adding external filler. The copper material's own properties (low oxygen content) enable successful autogenous welding, making the material self-sufficient for the welding process and eliminating the need for separate filler materials.
3Reliability
If stainless steel with unfavourable composition is used for the metal sheath, then the water barrier function is provided, but solidification cracks and unfavourable weld microstructure occur during autogenous welding
Solution Approach 1:
The patent changes the compositional parameters of the stainless steel, specifically optimizing the chromium equivalent (16-25) and nickel equivalent (11-22) ranges. These parameter changes ensure favourable solidification behavior and microstructure formation during autogenous welding, preventing solidification cracks while maintaining the water barrier function.
Solution Approach 2:
The patent uses composite material principles by carefully balancing multiple alloying elements (chromium, nickel, and other elements) in the stainless steel composition. This composite approach creates a material with optimized properties that resist solidification cracking and form favourable weld microstructures while providing the required water barrier protection.
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 enhances the quality and reliability of the water-blocking layer, reducing the risk of cracking and water infiltration, thereby protecting the insulation system and maintaining the integrity of the submarine power cable.
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
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
Data Source
AI summary
A method of manufacturing a submarine power cable, including: 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).