Ferrography

Run From Failure with Ferrography Testing

Venequip offers ferrography, an analytical test that allows analysis of wear particles present in a lubricant sample in order to identify the source of component wear. Ferrography is an excellent method for determining the size distribution and type of wear particles and is typically used if conventional oil analysis shows an abnormal wear pattern. It can also be used to routinely monitor condition and wear on high-risk components.

Save Time, Avoid Costly Breakdowns and Repairs

Reduce unscheduled downtime, create more effective maintenance scheduling, shrink maintenance costs, and improve equipment reliability and safety: In many cases, ferrography is able to identify catastrophic wear modes, when typical ppm wear metals do not show any sign of wear condition. Ferrography can actually pinpoint specific component failure modes to alert to catastrophic equipment failures.

When used in conjunction with a regular SOS™ oil analysis program, ferrography can provide the necessary information to make accurate and decisive maintenance decisions that can mean the difference between scheduled repairs versus costly repair after failure.

How Ferrography Works

An extremely sensitive test, ferrography detects wear and contaminant particles from 1 to 250 microns in size and can capture contaminant particles that normally don't show up on standard tests. Ferrography can also quantify the specific type of wear mechanism that generated the particles such as rubbing wear, abrasive wear or corrosive wear.

Ferrography magnetically separates wear metals and contaminant particles from a lubricant. The process starts with an oil sample passing over a glass slide that sits on a magnetic plate. Metallic wear particles in the sample are attracted to the magnetic plate and line up in rows with the largest particles at the top of the ferrogram. The non-metallic particles will deposit randomly across the slide. A trained analyst then uses a high magnification microscope to visually determine the type and severity of particles produced through wear and contamination. Particles can be classified according to size, shape and metallurgy. A trend of wear particle concentration typically presents the opportunity for proactive maintenance programs.

Wear Particles

The most common wear particle types generated through the wear process include metallic particles from normal rubbing wear, cutting wear, severe sliding wear, bearing wear and gear wear. Dirt particles are also responsible for wear.

The particles are classified to determine the type of wear and the source.

White nonferrous particles, often aluminum or chromium, appear as bright white particles. They are deposited randomly across the slide surface with larger particles getting collected against the chains of ferrous particles. The chains of ferrous particles typically act as a filter that collects contaminants.

Copper particles usually appear as bright yellow particles but the surface may change after heat treatment. These also will be randomly deposited across the slide surface with larger particles resting at the entry point of the slide and gradually getting smaller towards the exit point of the slide.

Babbitt particles consisting of tin and lead appear gray, sometimes with speckling before the heat treatment. After heat treatment of the slide, these particles still appear mostly gray, but with spots of blue and red.

Contaminants are usually dirt (silica) and appear as white crystals and are identified since they are somewhat transparent.

Fibers

Fibers typically from filters or outside contamination, are long strings that allow the transmitted light to shine through. They can appear anywhere on the ferrogram, however they tend to be washed towards the exit end.

Ferrous particles can be broken down to five different categories, high alloy, low alloy, dark metallic oxides, cast iron and red oxides. Ferrous particles are identified using the reflected light source on the microscope. Transmitted light will be totally blocked by the particle.

High Alloy Steel: particles are found in chains on the slide and appear gray-white. The distinguishing factor in the identification between high alloy and white nonferrous is position on the slide. If it is white and appears in a chain, it’s deemed to be high alloy. Otherwise, it’s considered white nonferrous.

Low Alloy Steel: particles are also found in chains and appear gray-white but they change color after heat treatment. After heat treatment they usually appear as blue particles but can also appear pink or red.

Dark Metallic Oxides: deposit in chains and appear dark gray to black. The degree of darkness is indicative of the amount of oxidation.

Cast Iron: particles appear gray before heat treatment and a straw yellow after the heat treatment. They are incorporated in chains amongst the other ferrous particles.

Red Oxides (Rust): polarized light readily identifies red oxides. Sometimes they can be found in chains with the other ferrous particles and sometimes they are randomly deposited on the slide surface. A large amount of small red oxides on the exit end of the slide is generally considered to be a sign of corrosive wear. It usually appears to the analyst as a "beach" of red sand.