SCR Riser CMT Welding for Stress Corrosion Resistant Joints
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Solution Overview
Problem
Existing welding methods for steel catenary risers (SCR) in marine environments fail to adequately address high hardness and high stress corrosion sensitivity, leading to potential cracking and reduced service life due to the formation of coarse grain heat affected zones and martensitic structures.
Innovation Solution
A welding method using CMT technology with an 80% Ar+20% CO2 shielding gas, optimized welding parameters, and U-shaped narrow gap bevels to reduce hardness and improve stress corrosion resistance, including specific current, voltage, and speed settings, along with preheating and gas timing adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CMT welding technology with low heat input is used, then welding efficiency and forming quality are improved, but hardness of coarse grain heat affected zone increases and stress corrosion resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing welding current (180-200A for root/filler passes, 130-150A for cap pass), voltage (20-23V for root/filler passes, 13-15V for cap pass), and welding speed (400-500mm/min for root/filler passes, 245-255mm/min for cap pass) to control heat input. This resolves the contradiction by finding the optimal parameter range that maintains high welding efficiency while preventing excessive hardness and improving stress corrosion resistance through controlled thermal cycles
2Strength
If welding is performed to connect pipelines, then pipeline connectivity is achieved, but coarse grain heat affected zone forms with high hardness and brittleness
Solution Approach 1:
The patent uses periodic action through multi-pass welding sequence (root pass, filler passes, cap pass) with specific parameter settings for each pass. This periodic welding approach allows controlled heat accumulation and dissipation, preventing excessive coarse grain formation while ensuring strong joint connectivity. The interpass cooling periods enable microstructure refinement between passes
3Strength
If welding parameters are optimized for anti-fatigue performance, then stress corrosion sensitivity increases due to high hydrogen diffusion coefficient
Solution Approach 1:
The patent applies local quality by using different welding parameters for different passes (root pass, filler passes, cap pass) and different regions of the weld. The root pass uses higher current (180-200A) to ensure penetration and reduce stress concentration, while cap pass uses lower current (130-150A) to control hardness. This localized parameter optimization balances anti-fatigue performance with reduced stress corrosion sensitivity in critical areas
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
The method results in stable arcs, reduced coarse grain zone hardness, enhanced anti-stress corrosion cracking ability, and extended service life of SCR risers by minimizing martensitic structure effects and optimizing welding efficiency.
Implementation Method 1
Cold Metal Transfer technology (CMT) adopts welding withdrawal technology to avoid the heating effect of short circuit current on the weld pool
Implementation Method 2
under the protective gas of 80% Ar+20% CO2
Implementation Method 3
the heating effect of short circuit current on the weld pool
Data Source
AI summary
This disclosure relates to a welding method for improving the stress corrosion resistance of a welded joints of a riser pipe and a product thereof. The welding method including: using CMT to weld SCR riser pipe under a shielding gas of 80% Ar+20% CO2. The welding current for the root pass and fill pass is 180 A to 200 A, and the welding voltage is 20 V to 23 V, and the welding speed is 400 mm/min to 500 mm/min; the welding current of the cover pass is 130-150 A, the welding voltage is 13-15 V, and the welding speed is 245 mm/min to 255 mm/min.