Ferritic Stainless Steel Fuel Pipe Crevice Coating
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Solution Overview
Problem
Fuel pipes made from lower-grade materials than SUS436L face challenges in achieving sufficient corrosion resistance, particularly in crevice structures exposed to salt spray environments, as existing coating methods are either costly or ineffective in covering internal crevice areas.
Innovation Solution
The use of cationic electrodeposition coating with a crevice opening amount of 0.2 mm or more, ensuring a coating film forms inside crevices, combined with a ferritic stainless steel composition that balances cost and corrosion resistance, and employing projections on metal fittings to enhance coating penetration and coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If lower-grade material (Mo-free AISI439 steel) is used to reduce material costs, then material cost is reduced, but corrosion resistance deteriorates
Solution Approach 1:
The patent uses a composite structure combining Mo-free AISI439 steel (lower-grade material) with a cationic electrodeposition coating layer. This composite approach allows the base material to provide structural integrity while the coating layer provides the corrosion resistance that would otherwise require expensive alloying elements like Mo, thus resolving the contradiction between material cost and corrosion resistance
Solution Approach 2:
The patent changes the chemical composition parameters of the steel by eliminating Mo while adjusting Cr content (13-18%) and adding specific elements (Ti: 0.03-0.30%, Nb: 0.03-0.30%). This parameter optimization allows the lower-grade material to achieve sufficient corrosion resistance when combined with the electrodeposition coating, enabling cost reduction without sacrificing reliability
2Reliability
If conventional coating methods are used to improve corrosion resistance, then corrosion proofing is improved, but coating cost increases
Solution Approach 1:
The patent replaces conventional mechanical coating methods (such as spray coating or dip coating) with cationic electrodeposition, which uses electrochemical principles to deposit the coating. This substitution enables the coating to be drawn into crevice structures by electrochemical attraction, providing superior corrosion protection at lower cost compared to conventional coating methods that cannot effectively coat internal crevice surfaces
3Manufacturing precision
If crevice opening amount is increased to allow coating penetration, then coating coverage is improved, but structural integrity may be compromised
Solution Approach 1:
The patent optimizes the crevice opening amount to a specific parameter range (0.05-0.50 mm) that allows sufficient electrodeposition coating penetration while maintaining structural integrity. This precise parameter control enables the coating to reach internal crevice surfaces for complete corrosion protection without compromising the strength or structural function of the fuel pipe assembly
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 stabilizes salt spray corrosion resistance while providing an inexpensive fuel pipe solution, with improved corrosion protection even with lower-grade materials, as demonstrated by cyclic corrosion tests.
Implementation Method 1
coating by cationic electrodeposition
Implementation Method 2
coating by cationic electrodeposition
Implementation Method 3
placing sacrificial positive electrodes of zinc at the locations where passivation films are damaged and making use of sacrificial corrosion
Data Source
AI summary
A fuel pipe which is inexpensive and is excellent in salt spray corrosion resistance, characterized by being comprised of a steel pipe member having as a material a ferritic stainless steel which contains, by mass %, C: 0.015% or less, Si: 0.01 to 0.50%, Mn: 0.01 to 0.50%, P: 0.050% or less, S: 0.010% or less, N: 0.015% or less, Al: 0.010 to 0.100%, and Cr: 13.0 to 18.0% and further, one or both of Ti: 0.03 to 0.30% and Nb: 0.03 to 0.30% and a metal fitting part, the metal fitting part and the steel pipe member having between them a crevice structure at the surface which the structure is exposed to a salt spray environment, an opening amount at a crevice part of the crevice structure being 0.2 mm or more, and an inside of the crevice part being coated by electrodeposition.