Strategic Oil Analysis: Systems, tools and tactics

Tribology & Lubrication Technology, Apr 2009 by Johnson, Mike, Spurlock, Matt

First of a five-part series on oil analysis (April, May, July, November, December)

A properly developed, scheduled and executed program can help you keep 'normal' machine wear to a minimum.

This is the first in a five-part series addressing oil analysis, (hereafter referred to as OA). OA is the control tool that the reliability engineer uses to grade the effectiveness of machine lubrication practices and activities.

I am pleased to join forces with Matt Spurlock for this series. Matt is the machine lubricant subject matter expert at Allied Reliability, Inc., in Indianapolis, Ind., and possesses strong practical knowledge in both machine lubrication and oil analysis principles. He has proven to be quite effective pulling meaningful diagnoses from data sets for all types of machines.

This article provides a brief history of oil analysis as a machine care function, an overview of the purpose for oil analysis and introduces the tactics associated with establishing an effective analysis program.

USED OIL ANALYSIS: A HISTORY

Systematic used oil analysis began just after World Ware Il in the railroad industry in the western United States. During the early years, wear metals were identified by several wet chemistry methods. It wasn't until the development of the spectrograph that used oil analysis truly began to show promise as a value-added predictive technology.

In the mid-1950s, the U.S. Navy began using oil analysis to monitor jet engines. This program became the basis for the military's Joint Oil Analysis Program. Over the years, this program has partnered with several civilian companies to develop useful technologies and instruments for use in both laboratory bench-top testing and plant floor screening.

The first independent commercial oil analysis laboratory was opened in 1960. Since then more than 250 used oil analysis laboratories have opened in North America alone. While many of these laboratories are considered private interest labs, there are a handful of commercial providers that process several thousand samples per day

USED OIL ANALYSIS: THE OBJECTIVE

It has been stated many times by machine lubrication professionals and lubricant developers that machine surfaces experience normal wear. While it is true that surfaces do bump, rub and wear, this condition shouldn't be viewed as normal. Machine wear may be common, but machine owners spend many thousands of dollars, roughly 5% of the annual cost of maintenance, trying to avoid wear.

Modern lubricants are a product of exceptional research and development and generally are robust and durable. If those product capabilities are applied properly, following accepted engineering principles for product selection, application and contamination control, then the prospect of normal wear should be very low.

Nonetheless, lubricated machine surfaces do wear, degrade and fail. Accordingly, a properly developed, scheduled and executed OA condition monitoring practice is useful to monitor the conditions that create downtime and production losses related to all lubricated mechanical components, including both oil and grease applications.

Lubrication practices provide insight into machine operation by focusing on lubricant health, sump/lubricant contamination conditions and changing machine health. The progressions to failure of many lubricated components follow degraded lubricant health and contaminated sumps. Additionally, as the contaminant loads increase, lubricant health declines, further supporting this three-pronged approach.

MACHINE CONDITION ANALYSIS

As shown in Figure 1, the predominant threat to long-term performance is surface wear' . Wear is caused by a handful of repeating problems. One of the most common applications for oil analysis is machine condition assessment by wear debris measurement. This is commonly performed through spectrographic analysis, which reports metals in parts per million. Spectrographic analysis generally is performed in one of two ways, ICP (inductively coupled plasma) and RTD (rotating disc spectroscopy), also known collectively as atomic emission spectroscopy (AES).

While both ICP and RTD are standard components of most oil sample test slates, both have weaknesses when it comes to identifying wear debris from components in moderate to advanced stages of failure, characterized by high concentrations of large particles.

The weakness is due to the overall detection limits of the instruments. The ICP has a high accuracy level to particles less than 5 microns in size. The level of accuracy is reduced significantly between 5 and 8 microns, and detection effectiveness is lost for particles above 8 microns. RTD has similar detection parameters for wear particles up to 10 microns. To combat the limiting effects of atomic emission spectroscopy, additional tests should be included in the default test slate, including:

Particle Quantifier (PQ). The PQ gives an index value that is not size dependant. This trendable value can assist in identifying large ferrous wear particles. Used in conjunction with AES, the PQ helps confirm growing normal wear, the onset of aggressive wear or the prospect of eminent catastrophic failure. Due to the very limited sample prep, the PQ test is both inexpensive and highly repeatable.