Charles L. Baker Jr., with ExxonMobil Research & Engineering Co. in Paulsboro, N.J., spoke about the need for a new definition of base stock slate at the ICIS Middle Eastern Base Oils & Lubricants Conference in Dubai in October, and in a follow-up interview with LubesnGreases. Baker chairs the American Petroleum Institutes Base Oil Interchange/Viscosity Grade Read-Across Task Force.

A key concept in engine oil approvals, included in both APIs Engine Oil Licensing and Certification System (codified in API Publication 1509) and in Europes ATIEL Code of Practice, is the capability of a manufacturers base stocks offering, that is, its base stock slate, said Baker.

APIs slate definition dates from the early 1990s, when it was included in the earliest version of API 1509. Appendix E of 1509 states: A base stock slate is a product line of base stocks that have different viscosities but are in the same base stock grouping and from the same manufacturer.

This definition is inadequate because it did not fully anticipate future base stock complexity, said Baker, and API 1509 does not explain what problems can occur if a slate contains different base stocks at the same viscosity.

Since the 1990s, what has happened is an increase in manufacturing complexity. Many companies have more plants, joint ventures, multiple sites.

All About Capability

The importance of slate is increasing, Baker contended.

The oil marketer is responsible for the [engine] oil being sold. Only the lubricant marketer can view the entire chain as it affects the final product. But the base stock manufacturer is responsible for declaring a slate and supplying capable base stocks with respect to base oil interchange and viscosity grade read-across. (When base stocks are blended for a lubricant, they become base oil under APIs definitions.)

A base stock manufacturer declares a slate which, with a range of mainstream market-general additives, should be capable of achieving the category performance for the targeted engine oil category. Being capable is not a guarantee that all additive technologies will work or work equally well, said Baker.

Approved base oil interchange within the slate allows the use of different base stock viscosity grades to blend the base oil for a given formulation. For example, an SAE 10W-30 could use a 5 centiStoke stock, or a combined 4.5 and 6 cSt, or a combined 4.5 and an 11 cSt base stock, all from the same slate, with no further engine testing required. But, Baker cautioned, the properties of the base oils must be similar enough to enable this blending.

Alternately, Baker continued, approved viscosity grade read-across within the slate allows blending a range of viscosity grades. For example, the 4.5, 6 and 11 cSt base stocks could be used to blend 5W-30 or 10W-30 or 15W-40 or 20W-50 oils with essentially similar additive technology with no further engine testing. But again, the base oils must be similar enough to enable this blending.

Base stock slates preserve the diversity of commercial offerings, and they provide value, said Baker. That value is both money saved and time saved in testing. A single light-duty engine test, for example, can cost $20,000 to $40,000, while heavy-duty diesel engine tests can easily run $100,000.

Every base stock slate is manufacturer-dependent, Baker continued. A slate requires a single manufacturer to maintain proper control of base stock quality. Base stock specifications are not sufficient predictors of performance in finished engine oils. In addition to physical and chemical tests and known base stock compositional parameters, feedstock, refining parameters and quality assurance system also influence the capability of a base stock slate to formulate engine oils. This is the fundamental reason why base oil interchange requires pertinent test data, not just technical judgment.

Demand for Discipline

Virtually all lubricants need more than one viscosity of base stock to achieve the required finished product properties, Baker continued. A slate provides significant value by allowing greater flexibility and faster qualification across many products while maintaining product integrity.

But value is delivered only if there is a clear understanding and disciplined usage of slate, Baker asserted. Formulation qualification must use the most severe base stocks – that is, you must test with the most challenging, the poorest quality, generally the highest-volatility base stock in the slate, not the best.

In properly designing a slate, the base oil manufacturer must consider parameters such as Noack volatility, saturates, sulfur and low temperature properties.

Different slates in the same API base stock groups are often distinguished by significant differences in volatility and low-temperature properties, noted Baker, and engine oils depend strongly on base stock properties in these areas. Blended base oils can have significant Noack differences, and slates should carefully consider this. In the Sequence IIIG engine test for wear and oil thickening, for example, base oils in the same slate can pass or fail based on volatility differences.

Europes Approach

In the latest edition of its Code of Practice guidelines on base stock quality assurance and base oil interchange, Europes Association Technique de lIndustrie Europeenne des Lubrifiants (ATIEL) includes its own definition of base stock slate. In its Appendix B, the Code of Practice states:

A base stock slate is a product line of base stocks that:

1. Are produced by the same manufacturer.

2. Meet the ATIEL definition of base stock.

3. Are in the same ATIEL Base Stock Group.

4. May have different specified viscosities and other properties.

5. Have been demonstrated, in lubricants for which compliance with ACEA Oil Sequences is claimed, to be technically substitutable by other appropriate base stocks on the same slate.

The Code goes on to note that a manufacturer may have more than one base stock slate, and it allows for linked slates that are interchangeable without the need for further engine testing.

The original definitions were only for Group I; Groups II and III were not available originally, Hans Thomassen, managing director of Kuwait Petroleum Research & Technology in Rozenburg, Netherlands, told LubesnGreases.

Producers who developed the original definitions had a long history of base oil production. Now we have many new producers. When these people work first with pilot plants and then go to full production, they may find it difficult to always hit the right specs.

Contrary to API 1509, the ATIEL Code contains guidelines on how to control manufacturing.

Base oil buyers must be able to rely on test data from previous production, Thomassen continued, noting that he was expressing his personal views and not speaking for ATIEL.

A key element of the ATIEL Code was adoption of the most severe base stock principle, he continued. You must look at the lowest-quality, worst base stock [in the slate]. If you prove the quality level with the worst-performing stock, youll know the higher-performing stock will pass.

The goal of the ATIEL definition, said Thomassen, is to make everyone aware of the steps to take to ensure that data will not be questioned. Discussions are ongoing within ATIEL on base oil interchange and engine testing in particular.

The focus on base oil slates, he said, is not just buyer beware. Its manufacturer beware. Variations in product quality must be acceptable, although what is acceptable will vary.

API: Tough New Guidelines

In December, APIs Base Stock Slate Definition working group (consisting of ExxonMobils Charles Baker, Christopher Cornish of Infineum and Thom Smith from Valvoline) submitted a proposed new definition of slate, with guidelines for implementation, to the API Lubricants Group. As this issue of LubesnGreases goes to press, the working group is reviewing comments, in hopes of submitting a final document in May that will, with Lubricants Group approval, amend Publication 1509.

APIs proposed new definition is quite more involved than the ATIEL proposal, Baker said in January. In slate definition, weve proposed a system that relies on test performance, not group or grouping.

There was a lot of debate and a lot of disagreement within the API Lubricants Group, Thom Smith, Valvoline technical director in Lexington, Ky., told LubesnGreases. We made the definition of slate liberal, but added restrictions on how you can interchange within a slate. Its a philosophical change. If base stocks are different, you need to test. You need to be assured the interchange wont impact performance of the oil.

Under the December proposal, the new definition will adhere to a set of base stock slate principles. These are:

a) No change in base stocks from those defined in the ACC Candidate Data Package can compromise the quality of the engine oil being sold.

b) Properties of the base oil blend determine whether interchange is allowed within a single manufacturers slate or between different slates.

c) Oil marketer is responsible for oil being sold must appear high up in Publication 1509, in addition to its current placement in Appendices E and F which address base oil interchange and viscosity grade read-across.

d) Appropriate levels of base stock flexibility from tested formulations should be available.

e) The concept of the base oil manufacturer determining what constitutes his slate will be part of the definition.

f) The base stock slate definition will be a result of and dependent on the application of all of these principles.

The working group then proposed a new definition of slate, a new definition of slate manufacturer, and three new sets of interchange guidelines (for interchange of base stocks within a slate for passenger car motor oils, for heavy-duty engine oils, and for bench tests).

The new definition of slate that API is considering states: A base stock slate is a product line of base stocks from a manufacturer that can be substituted in a finished oil with no performance penalty. Base stocks within a slate can be substituted to formulate different viscosity grades without performance penalty when applying Viscosity Grade Read-Across Guidelines.

The new definitions alone are inadequate to assure finished oil quality if widely different base stocks are included in the same slate, the working group wrote, so the additional flexibility in defining base stock slates is balanced by new additional guidelines for changing stocks within a slate.

Slates have good economic value and really help the industry. They allow engine oil categories to come in faster. But you have to have discipline about what you put in your slate, Baker concluded. The industry needs to think more about these issues.

Is Harmony in the Forecast?

Base stock slate definition is a critical element of both APIs and ATIELs base oil interchange programs, but their definitions differ at a time when base stock supply is an increasingly global business.

Our customers must comply with whichever licensing or approval requirements are mandated by the code relevant to their product claims, said Mike Brown, technical manager in Flemington, N.J., for SK Lubricants Americas.

For API and ATIEL, these definitions were developed by their respective consensus processes. The engine performance requirements in these codes reflect different engine designs, different fuel qualities, different emission systems and oil drain intervals. So it is not surprising that the ATIEL Code of Practice and API 1509 guidelines have different base stock slate definitions, since they evolve from different starting points.

Nonetheless, said Brown – whose company is one of many around the world today that manufacture a single slate of base stocks at multiple sites – We support harmonization of slate definitions if these industry bodies want to accomplish this task.

A global slate definition would provide more clarity for additive companies in setting their strategies to gain API licenses and/or ATIEL approvals in globally available base stocks, Brown continued. A global slate definition provides more clarity for blenders and marketers in deciding their supply-chain strategies. There is less chance of misinterpretation among the users of these codes if the definitions are more closely harmonized.