In many companies, it's common practice to review and re-tender MRO contracts on a three- to seven-year cycle. Lubricants are no exception, particularly in today's economy where lubricant prices, like those for every other crude oil-based commodity product, are rising to unprecedented levels. While this practice is not inherently "bad," there are certain pitfalls which can occur when switching lubricant suppliers. Beyond the business aspects of a change in supplier - such as price, distribution network, service and support - perhaps the single-biggest problem companies face when working with a new supplier is the issue of lubricant incompatibility.

This is not a trivial issue. There are definite performance differences between products from different suppliers. But in a general sense, it is fair to say that for commonly used lubricants - where the application or environment is not particularly severe - each supplier will have an equivalent product which to a first degree will provide adequate performance characteristics for any given application.

But buyers beware: equivalent or comparable is not the same as compatible.

When comparing two lubricants, comparable simply means that based on physical and chemical performance properties (viscosity, viscosity index, pour point, demulsibility, oxidation resistance, wear prevention, etc.), the two products should perform similarly and appropriately, assuming the lubricant is selected with the correct performance properties for the given application. Compatible, on the other hand, defines how products, when mixed at certain ratios, interact either physically (e.g. Do they mix homogeneously or do they separate?) or chemically (Does the base oil or additive package of the first lubricant chemically react with those of the second lubricant?).

The issue of incompatibility should be a real concern to anyone switching lubricant suppliers. The reason is simple. Given that on the first day of the new lubricant contract it is highly unlikely that each oil sump, greased bearing, hydraulic system or circulating system is going to be drained, flushed and refilled, or packed with the new product, it's almost inevitable that cross-contamination will occur. The question is not if mixing will occur, but what, if anything, will cross-contamination and potential incompatibility of different lubricants do to the equipment?

Lubricant incompatibility is not a surprise to any lubricant supplier. What is surprising is the often casual approach taken by some vendors, or end-users. It's not uncommon to hear nebulous comments such as "it should be OK" and "I don't foresee any problems" when the issue of compatibility is raised. Of course, such comments would hold no weight in any litigation or dispute resolution in the event that millions of dollars of repairs or lost production occur as the result of a lubricant incompatibility-related failure.

When it comes to insuring compatibility, the onus should really be on the end-user. That's not to say that end-users need to become lubrication engineers, formulation experts or chemists. Rather, as the benefactor of a well-engineered supplier transition, end-users should be demanding of their new supplier to demonstrate compatibility, not with platitudes such as "it should be OK" but with cold, hard data.

Most suppliers have already conducted cross-compatibility studies between their own lubricants and those of their competitors. Where such data doesn't exist, it's strongly recommended that either the supplier, or an independent third-party organization, develop a series of compatibility studies and tests. The process is relatively straightforward.

For oils, it's common practice to create test samples by blending the two products in the ratios 10:90, 50:50 and 90:10, along with samples of each new oil. For each sample, data for key performance tests known to be impacted by incompatibility - including oxidation resistance, air release, demulsibility, filterability and storage stability - are compared for each blended sample with the new oil samples. For the blends to be considered compatible, the performance properties must fall in the range bracketed by the two new oil samples. Otherwise, further testing may be required to ascertain the degree to which incompatibility may have occurred.

It's important to understand that even if two oils pass these compatibility tests, there's no guarantee that the two oils will be compatible in service. Other factors, not taken into account by lab tests - such as different blend ratios, elevated (or lower) temperatures or certain process chemical contaminants - can all impact in-service compatibility. However, one thing is clear: If two oils pass the lab-based compatibility tests, the probability of in-service compatibility is far higher than if the decision to mix two oils is based on supposition or hearsay.

For greases, the process is similar, though there is one added complexity: the thickener type. In fact, thickener incompatibility is far and away the leading cause of grease incompatibility. As such, grease compatibility testing, typically conducted with blend ratios of 25:75, 50:50 and 75:25, focuses more on changes to the thickener properties - such as worked penetration (a measure of the in-service consistency of the grease) and bleed rate (the rate at which the oil wicks from the thickener) - in addition to the chemical and wear prevention characteristics of each grease.

Just like oils, compatibility in the lab offers no cast-iron guarantee of in-service compatibility. But again, it's far more likely if they have first passed the lab-based tests.

For many companies, changing lubricant suppliers is a fact of life. So, don't take a chance. If you're faced with the prospect of introducing new lubricants to the plant, make sure you protect your valuable assets by performing due diligence with compatibility testing before it's too late.