This trust is essential to make the blending process straightforward, so that blenders dont have to tweak formulations significantly, either through viscometrics (grade balance) or, worse, additive treat. In this way, a blender can ensure consistency in its performance and marketing claims.

Remember, there is no hiding behind previously obtained API or ACEA qualifications for crankcase oil performance with a given base stock slate. This is true even if the base stock is formally in-specification but has shifted significantly in terms of typical inspection properties. Both industry organizations explicitly state that the ultimate responsibility for the performance of the blended lubricant lies with the blender/marketer.

When buying base stocks from a third-party supplier, it makes sense for the blender to check samples of each grade of the suppliers slate in detail and, indeed, to check regularly so that finished lube customers have assurances on performance. This may seem like stating the obvious, but all too often, it does not happen.

Frequent checks pay dividends. Not only should the blending laboratory be satisfied about initial performance, but it also should provide feedback to purchasing managers in the supply chain on any typical value drift that raises concerns about the purchase of subsequent batches.

When setting up a base stock supply agreement, the contract usually references a set of specification values for each performance parameter as well as typical values. The specification controls the purchasing agreement, not the typical value; therefore, it is wise to ensure that the delta between the specification and the typical value is reasonable but not excessive. There should not be an inherent assumption that typical values will be representative for the term of the contract.

Sometimes, manufacturers or sellers will exploit a large delta between specifications and typicals to significantly lower the quality of the base stock later in the supply agreement – for example, to increase throughput rates – while still formally being within contractual specification. An example could be the saturates levels in API Group II or III base stocks, where a higher throughput at the saturation stage can result in better plant utilization but lower saturates.

Formally, a Group II base stock must have greater than 90 percent by weight of saturates (on a molecular basis), and this is often the offered specification. But a Group II at 92 percent saturates is little better than a Group I at 88 percent saturates in terms of performance. And it will not match the performance of a severely hydrotreated Group II at a typical saturates level of more than 98 percent in a number of areas.

In addition, the lower saturates base stock may well have a significantly different response to antioxidants or ashless dispersants in the additive package. This change in additive response can result in performance issues, especially for lubricants with low treat rates such as hydraulic fluids or industrial turbine oils.

To some extent, it does not matter what the typical value of a given specification parameter is as long as it is consistent because the blender will have formulated accordingly. And the additive treat rate will reflect the quality of the base stock being used.

Of course, this cant be pushed too far because there will always be some base stocks on the market where the quality shift is too great to be compensated for with additives. Indeed, some parameters (such as air release) cannot be compensated by additives at all, even if allowed by industry bodies or original equipment manufacturers.

Therefore, the base stock should be assessed in the laboratory and a reasonable delta between a given specification and its typical value agreed upon. And a blender ultimately has to be prepared to walk away if a reasonable agreement cannot be reached. This approach will avoid the issue of having to exclude a given base stock slate from blending certain products in a blenders portfolio and all the associated logistical issues.

Another issue relative to specifications is to ensure that both laboratory personnel and procurement managers fully understand which specifications are necessary and which are not. Ive seen specification sheets where a given parameter is present for largely historic reasons, inserted without proper understanding of a base oils composition/performance relationships. This can lead to unnecessary specification checks that cloud more relevant quality issues and do not guarantee finished lube performance. Indeed, in some cases, excess specifications are often coupled anyway, meaning that one specification is already effectively controlled by another in the list and is not independently variable – and thus pointless.

Ideally, base oil specification and typicals sheets for purchase contracts should be concise, with independently variable specifications. They should cover safety (e.g., flash point) and performance (e.g., viscosity index, saturates), and the sheets author should understand what every specification represents. The sheet should include a specification/typical delta set that will ensure unhindered blending operations, consistent quality lubricants and minimal disputes between manufacturer/supplier and blender.