Aviation Chemical Cleaning and Solvent Degreasing Guide

This guide outlines the shop-floor procedures, solvent compatibility matrices, and quality control standards for aviation component degreasing. It covers approved chemical selection, step-by-step cleaning methods, and post-clean inspection requirements.

1. Pre-Cleaning & Setup (On the Floor)

Step 0: Gross De-Mucking

Never apply solvent rags directly to a component caked in heavy runway grit, thick hydraulic fluid (Skydrol), or baked-on turbine soot. Wiping a gritty part with a solvent rag creates an abrasive grinding paste that will scratch and score the metal substrate.

• Action: Scrape off heavy sludge using approved plastic scrapers or wipe down with coarse, dry shop rags before initiating the chemical solvent wash.

Solvent Container Management

• Plunger Cans: Apply fluid cleaners to wiping cloths via closed pressure dispensers or plunger cans. Never dip dirty wiping media directly into bulk chemical reservoirs.
• Pre-Saturated Wipe Tubs: Keep container lids tightly sealed between individual wipes. Leaving tubs open on your tool cart will cause the solvent to evaporate within hours, rendering the remaining wipes completely useless.

2. Approved Solvents & Substrate Matrix

All organic fluid solvents must be stored, managed, and applied strictly at ambient temperature.

CRITICAL TITANIUM PROHIBITION (FAA AC 43.13-1B): Components fabricated entirely or partially of titanium or titanium alloys must never come into contact with halogenated or chlorinated solvents (e.g., trichloroethylene, methylene chloride). Residual chlorine ions cause severe, accelerated stress corrosion cracking once the component reaches operational temperatures.

Note on Organic Solvents: While pure organic solvents (such as Acetone or MEK) do not violate the FAA’s halogenated restriction, they are not universally authorized. Always cross-reference the specific component’s OEM manual. Many OEM specifications strictly prohibit ketones on titanium assemblies that are permanently mated to composite structures, advanced elastomeric seals, or specialized acoustic coatings, as these solvents will rapidly degrade non-metallic elements.

Substrate Authorization Table

• A (Authorized): Approved for use.
• NA (Not Authorized): Prohibited unless explicitly approved by the OEM for that specific part number.

A* = Authorized with restrictions. See the mandatory OEM and configuration constraints detailed below.

3. Solvent Technical Profiles (Quick Reference)

Standard Organic Solvents

• Acetone: Ultra-fast evaporation. Cuts heavy oils and un-cured resins rapidly. High fire risk (flashpoint -20°C). Can cause “flash condensation” (moisture buildup) on cold metal. Attacks plastics, rubber seals, and paint.
• Methyl Ethyl Ketone (MEK): Fast evaporation. Excellent for removing stubborn grease, sealants, and adhesive residues. Grants slightly more working time than acetone. Highly toxic; requires dedicated vapor ventilation. Destroys standard nitrile and neoprene gloves/seals.
• Isopropyl Alcohol (IPA): Medium evaporation. Used at 99% purity for electrical parts, instrumentation, and final pre-inspection wipe-downs. Safe on almost all plastics, rubbers, and cured coatings.
• White Spirit: Slow evaporation. Petroleum-distillate fluid excellent for cutting heavy protective storage waxes and thick oils over large metal areas. Must be mechanically dry-wiped immediately to prevent leaving a light hydrocarbon film.

Engineered Specialty Fluids

• Ardrox 552: Rapid-to-medium evaporation. High-flashpoint (65°C), low-odor aliphatic hydrocarbon. Used for general degreasing and surface prep before Non-Destructive Testing (NDT).
• Diestone DLS: Controlled evaporation. A safer, low-VOC replacement for MEK. Optimized for cleaning and activating polyurethane primers before structural bonding or painting.
• Supersolve AS: Fast evaporation. Ultra-pure aerosol spray with high dielectric strength. Designed to clean avionics, circuit boards, and electrical blocks without leaving any residue.
• Lotoxane: Slow, controlled evaporation. Ultra-low hazard, highly refined hydrocarbon fluid. Safest option for sensitive light alloys on the line.
• Dyna 200: Slow evaporation. Completely VOC-free heavy degreasing fluid. Highly compatible with structural metals and rubbers, but strictly prohibited on high-strength steels.

Immersion Bath Agents

• Stoddard Solvent: Industry-standard bulk cold tank immersion fluid. Ideal for stripping cutting oils and storage greases from raw machined parts.
• Turco IND 79 / Degreasol 99 R: Heavy-duty emulsifiable bath cleaners. Used to strip baked-on carbonized oils and synthetic engine lubricants.
• Mag-Chem Tecksol / Skysol: Eco-friendly solvent alternatives. Skysol is specifically tailored to clean engine nacelle structures without degrading surrounding structural sealants.
• Bioact 105: Natural ester/terpene blend with an exceptionally high flashpoint. Used in deep soak tanks to dissolve heavy high-temperature waxes and preservative greases.

4. Step-by-Step Degreasing Procedures

Method A: Hand-Wipe (The Two-Cloth Method)

Aggressive dry-wiping with highly volatile ketones can generate static sparks. Ensure the component is electrically grounded or bonded to the aircraft or stand before using these solvents in enclosed zones.

• Solvent Application: Immediate Execution. Soak an approved lint-free, non-woven aerospace wiping cloth (conforming to AMS 3819 specifications) with an approved solvent. Wipe the component thoroughly to dissolve the oil, grease, or soil layer.
• Mechanical Lift: Before Solvent Evaporates. Immediately follow behind with a second clean, dry, lint-free cloth to wipe the dissolved contaminants off the surface before the solvent flashes off. If the solvent dries on its own, the contaminants are simply re-deposited onto the metal as an invisible film.
• Forced Drying: Final Step. Blow-dry the component completely using a clean, filtered, dry compressed air source to clear out any remaining moisture or solvent pockets.

Method B: Tank Immersion

1. Lower Solution: Lower the components slowly into the degreasing tank to prevent splashing.
2. Agitate: Use mechanical stirring, ultrasonic systems, or approved fiber bristle brushes to accelerate soil breakdown.
3. Drip Cycle: Smoothly pull the component from the bath and hold it directly above the liquid level, letting all excess fluid drip completely back into the tank.
4. Air Dry: Blast out all blind holes, fluid traps, and recesses with a filtered, dry compressed air source.

PROHIBITED PRACTICE: Cleaning with highly acidic or alkaline chemical solutions is strictly prohibited on components featuring intricate lap joints, permanent mechanical interfaces, or blind cavities. If these chemicals get trapped in tight spaces, standard rinsing cannot remove them, causing severe localized structural corrosion over time.

5. Water Quality Standards & Rinse Controls

Dirty rinse water leaves mineral deposits and corrosive salts on dried parts. Prior to processing any components, water quality parameters must be strictly monitored.

The Titanium Rinse Mandate

If a titanium engine part is scheduled for welding, heat treatment, or FPI inspection directly after washing, the final rinse must be executed with high-purity deionized water meeting these strict parameters:

• Conductivity Ceiling: Maximum conductivity of 1 to 10 µS/cm.
• Halogen Limit: Total combined concentration of dissolved chlorine and chloride ions must be less than 50 ppm (tested via ASTM D1253 or ASTM D512).

Rinse Tank Gauge Monitoring & Quality Controls

When utilizing shop-floor rinse tanks or hand-pressure sprayers, adhere to these strict limits:

• Critical Final Rinses (<1–10 µS/cm): Final rinses for flight-critical, engine, or NDT-bound components must utilize high-purity Deionized (DI) water with a strict conductivity ceiling of 1 to 10 µS/cm (or a minimum resistivity of 100,000 to 1,000,000 Ohm·cm).
• Bulk Pre-Wash Supply Check: Incoming fresh water used exclusively for initial bulk washing or gross de-mucking stages must read below 50 µS/cm.
• The 100 µS/cm Absolute Redline: For general bulk rinse tanks, stop washing parts immediately if the tank conductivity monitor climbs above 100 µS/cm. The rinse bath must be completely drained, flushed, and refreshed with pure DI water before work can resume.
• Hand Spray Pressures: Keep hand-pressure rinse sprayers regulated strictly below 2.0 psi (0.14 bar) to prevent forcing residual surface contaminants deeper into permanent mechanical joints or lap seams.

6. Post-Clean Controls, Baking, & Handling

Component Drying Temperature Ceilings

When drying components using thermal ovens, forced air, or heat lamps, adhere strictly to alloy- and structure-specific temperature windows:

• Composite & Sensitive Assemblies (70°C / 158°F Max): Component surface temperatures must not exceed 70°C when handling composite structures, elastomeric seals, or specialized surface coatings to prevent thermal degradation or delamination.
• Heavy Structural Metals (100°C – 120°C / 212°F – 248°F): For robust components fabricated from high-strength steels, titanium, or nickel-cobalt alloys, OEM manuals routinely authorize controlled drying oven temperatures up to 120°C. This higher range is preferred for heavy metal parts to guarantee rapid, total moisture evacuation from deep blind holes and intricate lap joints without metallurgical risk.

Hydrogen Embrittlement Furnace Clock (SAE AMS2759/11)

High-strength structural steels with a tensile strength greater than 180 ksi (or Rm greater than 1150 MPa), such as landing gear cylinders or major pylon attach bolts, can crack and fail catastrophically if they absorb atomic hydrogen during cleaning.

• The Relief Trigger: While pure organic solvents (Acetone, MEK, IPA) do not inherently liberate the atomic hydrogen required to cause hydrogen embrittlement, process contamination remains a critical risk. If a solvent bath becomes cross-contaminated with water, drag-in acids, or halogenated solvent residues, galvanic interactions can occur that introduce an embrittlement hazard. True hydrogen risks are heavily driven by aqueous chemical washes, acid/alkaline stripping solutions, or unapproved specialty fluids (like Dyna 200). Never assume a solvent wash is completely risk-free if fluid bath purity standards are compromised.
• The Mandatory Bake: If an unapproved chemical contact event occurs, the component must be placed into a calibrated furnace and baked at 190°C ± 10°C (375°F ± 25°F) for a minimum of 3 to 24 hours to drive out the trapped hydrogen.
• The 4-Hour Deadline: The baking sequence must begin within 4 hours maximum of the chemical exposure. If you miss this window, permanent micro-cracking will initiate, and the part may be permanently scrapped.

Post-Clean Glove Rule (Handling Protocol)

The moment a component exits its final drying cycle, bare-hand contact is strictly prohibited.

• Why: Skin constantly secretes natural oils, sweat, and salts. Touching reactive, freshly degreased metal transfers these contaminants instantly. During subsequent engine operation, high-temperature welding, or painting, these baked-on skin impurities trigger rapid pitting corrosion, weld contamination, or complete paint adhesion failure.
• The Lint Hazard: The use of traditional white cotton gloves is strictly prohibited. Cotton fibers inherently shed and snag on machined edges or thread roots. During Fluorescent Penetrant Inspection (FPI), these trapped fibers absorb dye and create false defect indications—or worse, mask actual micro-cracks. During structural bonding prep, trapped cotton lint acts as a surface contaminant that compromises the adhesive matrix.
• Action: Technicians must wear clean, dry, powder-free, cleanroom-grade nitrile gloves during all post-clean transport, assembly, and inspection phases to guarantee zero skin-oil transfer and zero fiber contamination.

7. Quality Assurance (QA) Inspection & Disposal

Cleanliness Check: The Water-Break Test (ASTM F22)

Before moving a rinsed component into an oven or hitting it with compressed air, execute this quick empirical cleanliness check:

• PASS: The water spreads out and clings to the entire metal surface in a smooth, continuous, unbroken sheet. This confirms all invisible oil films are gone.
• FAIL: The water breaks apart, beads up, or pulls away from specific zones within 10 to 30 seconds. This proves a monomolecular layer of oil, grease, or a fingerprint is still on the part. Reject the part and return to Step 1.

Visual Inspection Checklist

Once dry, confirm the part meets all visual criteria:

• Surface Uniformity: The part looks identical across all profiles.
• Zero Stains: No chemical fluid run lines, streak patterns, or white evaporation rings.
• Zero Residues: 100% free of dry chemical residues, dust, or lint fibers. Pay close attention to rough material edges, lap joints, and thread roots where lint-free cloth fibers frequently snag and tear away, which can mask critical defects during NDT.

Hazardous Waste Disposal

• Rags and Wipes: Never throw solvent-soaked cotton cloths, cheesecloths, or used pre-saturated wipes into standard plastic trash bins. This creates an immediate shop fire hazard and triggers environmental fines.
• Action: Dispose of all spent wiping mediums immediately into designated, self-closing, fire-safe Hazardous Waste / Flammable Liquid metal bins.