Introduction
Steel tubes used in automotive fuel systems should be fit for their intended purpose. Depending on the application, they may be subject to pressure, vibration, moisture, temperature variation, and other service conditions. Surface condition and corrosion protection are therefore integral considerations when making selections.
CNG steel tubes and fuel-system tubing need to conform to the material, dimensional, pressure, and safety requirements appropriate to their intended use. Surface protection is an important part of this evaluation, but it cannot substitute for the requirements for tube material or system design.
Why Is Surface Protection Important for Steel Tubes?
Steel can corrode through reaction with moisture, oxygen, salts, or other environmental substances. Corrosion can impact surface condition, and can reduce the thickness of the tube wall if left unaddressed.
A treatment or protective coating at the surface can help to limit exposure of the underlying steel to the environment. The method should be appropriate to the base material, service conditions, and the requirements for the finished component.
What Factors Influence Corrosion?
The behaviour of the steel in terms of corrosion resistance can depend on several factors, including:
- The steel grade and surface condition.
- Exposure to moisture, road salts, and other contaminants.
- Temperature and operating environment.
- Presence and condition of protective coatings.
- Handling, forming, and installation practices.
- Inspection and maintenance requirements.
The system should be evaluated in terms of the conditions to which it will be subjected.
What Should Be Considered for Passivated Tubes for CNG Applications?
Passivated tubes for CNG applications are only considered appropriate in cases where the base material and specified treatment are fit for the system to which they are applied. Passivation is generally associated with suitable corrosion resistant alloys, and should not be expected to offer the same protection as a metallic coating on ordinary carbon steel.
For CNG service, buyers must make sure that the tube conforms to the applicable requirements for the system’s pressure, materials, dimensions, connections, and service conditions. A surface treatment cannot make a tube suitable for high pressure gas service if it was found to be unsuitable.
What Are the Requirements for CNG Steel Tubes?
CNG steel tubes need to be selected on the basis of the requirements of the compressed natural gas system to which they will be applied. This may involve the tube having a specific pressure capability, material properties, dimensional tolerances, connection compatibility, and relevant inspection or testing requirements.
A suitable tube should be supported by the documentation required by the applicable standard or system specification. Surface protection should be evaluated separately as part of the overall design process.
How Does Surface Protection Relate to Fuel Injection Tubing?
Fuel injection tubing carries fuel between components in a system which has been engineered for particular operating conditions. Material selection, the wall thickness, dimensional accuracy, and connection design are therefore all integral to the functionality of the tube.
Surface protection may be required to address external corrosion, depending on the environment and component specifications. However, the suitability of a coating depends on its compatibility with the tube material, forming processes, and intended service.
Not every coating is suitable for every fuel system. The applicable product and system requirements should dictate which form of treatment is appropriate.
What Is a Protective Coating for Steel Tubes?
A protective coating for steel tubes is a layer applied to the surface to reduce exposure to corrosive environments, or provide another particular surface property.
Depending on the material and application, protection may take the form of metallic coatings, conversion treatments, or other approved systems. The applicability of a coating should be evaluated on the basis of its coverage, adhesion where applicable, compatibility with subsequent operations, and performance under the intended service conditions.
Coatings can be damaged during bending, assembly, and handling. Inspection therefore needs to consider the finish of the final component, rather than just assessing the coating as it was applied.
What Should Buyers Check Before Selecting Tubes for Automotive Fuel Systems?
Automotive fuel system tubes should be evaluated against the technical and regulatory requirements of the system. Buyers should therefore consider:
- Material grade and specified mechanical properties.
- Required dimensions and tolerances.
- Operating pressure and temperature.
- Compatibility with the fuel and fittings.
- Required corrosion protection and surface finish.
- Inspection, testing, and documentation requirements.
Automotive fuel system tubes should meet the technical and regulatory requirements specified for their intended application.
For high pressure applications such as CNG, only use tubing which has been specified and approved for the intended system. General purpose steel tubing should not be expected to be suitable.
How Does Sainest Tubes Support Automotive Tube Requirements?
Sainest Tubes Pvt. Ltd. lists fuel injection tubes, bright annealed tubes, and passivated tubes among its product offerings. The appropriate product should be selected on the basis of the required material, dimensions, surface treatment, and specification for the application.
Conclusion
Surface protection provides assistance in managing corrosion risks, but its effectiveness depends on the material, treatment, environment, and the condition of the finished tube. For CNG and automotive fuel systems, the tube must first meet the applicable pressure, material, dimensional, and system requirements. Protective treatments should then be selected as part of the complete engineering specification rather than as a substitute for suitability testing.