SAE AS598A-2024
Aerospace Microscopic Sizing and Counting of Particulate Contamination for Fluid Power Systems

Standard No.

SAE AS598A-2024

Release Date

2024

Published By

Society of Automotive Engineers (SAE)

Status

Be replaced

Replace By

SAE AS598A-2081

Latest

SAE AS598A-2081

Introduction

Standard Framework and Technological Evolution

AS598A, as a technical specification reconfirmed under the SAE Five-Year Review policy, focuses on achieving precise quantification of particles larger than 5μm in hydraulic fluids through membrane filtration devices and microscopic counting systems. Compared with the previous version, the main additions are:

Technical Elements	New Contents of AS598A	Technical Significance
Calibration Factor Calculation	New Formula F=Ae/(H×L×N)	Improve the Mathematical Precision of Statistical Counting
Blank Analysis Procedure	Section 9.1 Critical Cleanliness Application Requirements	Reducing Background Contamination Interference
Dispute Resolution Clause	Chapter 14 Laboratory Proficiency Testing	Standardized Quality Control Procedure

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Key Instrument Specifications

The standard sets clear requirements for filtration devices and counting devices:

• Membrane filter: 47mm diameter, grid accuracy 3.10±0.02mm, petroleum-based fluids require white cellulose ester membrane
• Microscope system: Stereo microscopes are prohibited, and the objective lens combination must provide 50× and 100× magnification
• Vacuum system: Minimum vacuum degree 457mmHg (18 inches of mercury)

Application Case: Aviation Hydraulic Oil Testing

A certain aircraft uses MIL-PRF-83282 synthetic hydrocarbon-based hydraulic oil. When tested according to AS598A standard:

Sample Preparation Using Ultrasonic Bath Treatment to Sediment Contaminants Insufficient Mixing Leads to Counting Deviations Microscope Calibration Recalibration is Required Every Time an Operator Changes Uncorrected magnification for interpupillary distance adjustment Boundary determination Only counting upper/left boundary particles Incorrectly counting right/bottom boundary particles

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Correlation with other standards

AS598A should be used in conjunction with the following standards:

• ARP4285: Basic method for membrane filtration procedures
• AS4059: Classification of contamination levels for hydraulic fluids
• MIL-PRF-83282: Specification for synthetic hydrocarbon-based hydraulic fluids