Ferritic Stainless Steel Oil Filler Pipe with Aluminized Fitting
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Solution Overview
Problem
Existing oil filler pipes made of stainless steel SUS436L face challenges in salt corrosion resistance, particularly in gap structures exposed to chloride environments, where crevice corrosion can lead to fuel leakage and safety issues, and current coatings and sacrificial protection methods are either costly or ineffective in preventing corrosion.
Innovation Solution
A ferritic stainless steel oil filler pipe with an aluminized stainless steel metal fitting and a cation electrodeposition coating film, where the metal fitting has an Al-plating weight per unit area of 20 g/m² to 150 g/m² and the coating film thickness is 5 μm to 35 μm, ensuring corrosion resistance regardless of gap opening size, and the metal fitting is attached to the pipe's outer surface to prevent Al invasion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SUS436L stainless steel is used for the oil filler pipe, then salt corrosion resistance is improved, but cost increases due to resource prices
Solution Approach 1:
The invention uses a composite structure combining SUS436L stainless steel pipe with an aluminized stainless steel sheet (sacrificial anode material) attached to its outer surface. This composite design leverages the excellent salt corrosion resistance of SUS436L while using the more cost-effective aluminized steel for sacrificial protection, reducing overall material costs while maintaining or enhancing corrosion resistance performance.
Solution Approach 2:
The aluminized stainless steel sheet serves as a sacrificial anode that is intentionally designed to corrode preferentially and consume itself to protect the more expensive SUS436L pipe. This disposable protective layer provides economical corrosion protection by sacrificing a cheaper material to preserve the structural integrity of the main pipe component.
2Ease of manufacture
If a metal fitting is directly attached to the inlet pipe to reduce components, then manufacturing simplicity is improved, but crevice corrosion risk increases due to gap formation
Solution Approach 1:
The aluminized stainless steel sheet acts as an intermediary sacrificial anode placed between the metal fitting and the SUS436L pipe. This intermediary layer preferentially corrodes in the gap region, providing electrochemical protection to the pipe and fitting interface, thereby preventing crevice corrosion while allowing the simple direct-attachment manufacturing approach to continue.
Solution Approach 2:
The invention converts the potentially harmful gap structure into a beneficial configuration by placing the sacrificial anode in the gap area. The gap now serves to position the sacrificial protection material where it is most needed - at the corrosion-prone interface - transforming the structural weakness into an opportunity for enhanced protective functionality.
3Reliability
If cation electrodeposition coating is applied to improve salt corrosion resistance, then corrosion protection is improved, but coating application difficulty increases in gap structures
Solution Approach 1:
The sacrificial anode serves as an intermediary corrosion protection mechanism that does not require complex coating application processes in difficult-to-reach gap areas. Instead of relying on electrodeposition coating to penetrate and protect the gap interior, the sacrificial anode provides electrochemical protection that works effectively in the gap environment regardless of coating accessibility.
Solution Approach 2:
The invention replaces the mechanical/coating-based protection approach (electrodeposition coating) with an electrochemical protection mechanism (sacrificial anode). This substitution eliminates the manufacturing difficulty of applying coatings to gap structures by using a different protection principle that does not require physical coating access to the gap interior.
4Reliability
If zinc sacrificial anode is used for corrosion protection, then sacrificial protection is improved, but zinc consumption is excessive in chloride environment
Solution Approach 1:
The invention changes the material parameter of the sacrificial anode from zinc to aluminized stainless steel. Aluminum has a more favorable electrochemical potential and forms a protective oxide layer in chloride environments, resulting in slower consumption rates compared to zinc. This parameter change maintains effective sacrificial protection while significantly reducing the rate of material loss.
5Reliability
If galvanized steel plate is used for inlet pipe to eliminate gap, then gap corrosion is prevented, but melted zinc invades the inlet pipe causing clogging
Solution Approach 1:
The aluminized stainless steel sheet serves as a disposable sacrificial anode that is intentionally placed on the exterior of the pipe. This design prevents the sacrificial material from melting and invading the fuel system, as the aluminum corrodes in a controlled manner on the pipe surface rather than melting and flowing into the inlet pipe like galvanized zinc would.
Solution Approach 2:
The invention converts the potential harm of sacrificial material invasion into a benefit by using aluminum instead of zinc. Aluminum forms a stable protective oxide layer during corrosion that prevents it from melting and flowing into the fuel system, thereby eliminating the clogging problem while maintaining the sacrificial protection function.
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 solution provides reliable salt corrosion resistance for oil filler pipes, preventing crevice corrosion and fuel leakage, while maintaining cost-effectiveness by reducing Al consumption and avoiding clogging in fuel injection systems.
Implementation Method 1
a surface of the steel pipe member and a surface of the metal fitting other than the gap are covered with a cation electrodeposition coating film
Implementation Method 2
the metal fitting made of an aluminized stainless steel sheet having an Al-plating weight per unit area ranging from 20 g/m² to 150 g/m²... preventing crevice corrosion
Data Source
AI summary
An automotive member or oil filler pipe includes: a member of ferritic stainless steel containing, in mass %, at most 0.015% of C, at most 0.015% of N, 10.5 to 18.0% of Cr, 0.01 to 0.80% of Si, 0.01 to 0.80% of Mn, at most 0.050% of P, at most 0.010% of S, 0.010 to 0.100% of Al, more than 0.3 to 1.5% of Mo, and one or both of 0.03 to 0.30% of Ti and Nb; and a metal fitting of an aluminized stainless steel sheet, which is attached to the member to define therebetween a gap structure to be exposed to a chloride environment, and has an Al-plating weight per unit area ranging from 20 to 150 g/m2 in the gap structure. Surfaces of the metal fitting and member not facing the gap are coated with a cation electrodeposition coating film having a thickness of 5 to 35 μm.