ASTM F485 Standard Practice for Effects of Cleaners on Unpainted Aircraft Surfaces

The standard "ASTM F485 Standard Practice for Effects of Cleaners on Unpainted Aircraft Surfaces," published by the American Society for Testing and Materials (ASTM), describes a procedure for determining the effect of cleaners on unpainted aircraft surfaces. This procedure is used by visual inspection to identify scratches or permanent stains that require polishing. This standard is used to ensure that candidate aircraft surface cleaners do not leave a residue that, when dried, would leave a permanent stain and require polishing to remove.

ASTM's aerospace material standards are primarily instrumental in evaluating materials, components, and devices used in the aerospace and aircraft industries. Aerospace material standards allow various companies worldwide to test these materials to evaluate their thermal, optical, mechanical, chemical, and electrical properties. These materials can be in solid, liquid, or gas phases. Components and devices are also tested to determine their performance and safe operation. Aerospace material standards also address the design and safe operation of various engines used in unmanned aircraft systems and aircraft. These standards also help define procedures for visual range flight operations, airworthiness, maintenance manuals, and aviation regulations for unmanned aircraft systems.

The effects of cleaners on unpainted aircraft surfaces can be significant and can affect both the structural integrity and appearance of the aircraft. Unpainted surfaces (usually aluminum or aluminum alloys) require special care during cleaning to prevent corrosion, pitting, or other types of damage.

Unpainted aircraft surface types are generally as follows:

• Bare aluminum or alclad (a corrosion-resistant aluminum sheet composed of high-purity aluminum surface layers)
• Titanium or stainless steel in high temperature areas

Unpainted surfaces are preferred on military and some commercial aircraft for weight savings or ease of inspection.

The effects of some cleaning materials on unpainted surfaces are as follows:

• Alkaline cleaners are effective on oils and greases. They are safe at the correct pH. However, if they are too strong or not rinsed properly, they can cause corrosion or erosion.
• Solvent cleaners remove adhesives and grease and evaporate quickly. However, they have drawbacks such as surface drying, cracking of sealants, toxic fumes, and potential metal fatigue.
• Acid-based cleaners are used for deoxidation and polishing, but can pit aluminum, cause hydrogen embrittlement, or corrosion.
• Enzymatic/biological cleaners are environmentally friendly and low-toxic, but they are not as effective and require longer dwell times.

Possible surface deterioration risks of unpainted surfaces are:

• Corrosion: The most common and serious risk. It is accelerated by residues and improper rinsing.
• Pitting: Caused by strong acids or alkalis, especially those with high pH values.
• Discoloration: A dull or streaky appearance caused by incompatible cleaners.
• Loss of protective oxide layer: Critical to corrosion resistance in aluminum.

Cleaners are essential for maintaining unpainted aircraft surfaces, but misuse can lead to corrosion, structural deterioration, and costly repairs. Therefore, adhering to industry standards, selecting the right cleaner for the material, and implementing proper cleaning protocols are critical to maintaining aircraft airworthiness and longevity.

Aircraft maintenance requires regular cleaning to ensure both performance and safety. While painted surfaces are often protected by coatings, unpainted aircraft surfaces, such as bare aluminum or composite materials, are more vulnerable to damage from chemical cleaners. Understanding how different cleaners affect these surfaces is important to maintain structural integrity and prevent corrosion.

Unpainted aircraft surfaces, especially on military and commercial aircraft, are often left exposed for the following reasons:

• Weight reduction
• Heat dissipation
• Inspection visibility
• Aesthetic or functional design

These surfaces accumulate contaminants such as hydraulic fluid, fuel residue, insect residue, salt, and atmospheric pollutants. While cleaning is necessary, improper chemical use can lead to deterioration.

Common types of cleaners used on airplanes include:

• Alkaline cleaners: Used to remove oil, grease, and carbon. Can be corrosive to aluminum alloys if not properly diluted or rinsed. May cause surface etching or discoloration.
• Acidic cleaners: Effective in removing oxidation or mineral deposits. Risk of pitting corrosion on bare metal surfaces. Often used in conjunction with inhibitors to reduce corrosive effects.
• Solvent-based cleaners: Used for degreasing or removing sealants. They are less likely to cause corrosion but may affect adhesives and sealant integrity. If used improperly, they can pose a health and environmental hazard.
• Enzyme or biodegradable cleaners: Designed to be environmentally friendly and gentle on surfaces, they're a good alternative for light cleaning without the harsh chemicals.

The possible effects on unpainted surfaces can be summarized as follows:

• Pitting corrosion: This condition is caused by acidic or improperly neutralized alkaline cleaners. The materials affected are aluminum and magnesium. This leads to structural weakening and the initiation of cracks.
• Staining and discoloration: This is caused by alkaline residue or solvent reaction. Affected materials include bare metal and composites. This results in cosmetic issues and the need for repolishing.
• Etching: This condition is caused by high-pH alkaline cleaners. The materials affected are aluminum alloys. This results in a rough surface texture and high friction.
• Sealant degradation: This is caused by solvent-based cleaners. Affected materials include gaskets, rubber, and composite adhesives. This results in loss of integrity and fluid leakage.
• Surface fatigue: This condition is caused by repeated, aggressive cleaning. All materials are affected. This leads to microcracks and increased inspection frequency.

Ultimately, while cleaning is critical for unpainted aircraft surfaces, care must be taken to prevent chemical damage. Selecting the right cleaner and applying it correctly helps preserve the aircraft's structural integrity, appearance, and airworthiness. Maintenance personnel should always follow industry standards and original equipment manufacturer recommendations to ensure safe and effective cleaning practices.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, boasts a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with ASTM F485 Standard Application for the Effects of Cleaners on Unpainted Aircraft Surfaces.