Whenever a new component is about to be commissioned, the first thing we need to address is the lubricant. A typical original equipment manufacturer’s (OEM) recommendation will usually state something like “use a high-quality turbine oil with a viscosity of ISO VG 32.” This leaves a lot to the imagination.
The OEM has not indicated what types of additive the lubricant should have, what base oil should be used and how to adjust the viscosity requirement based on the ambient conditions of your facility verses the test facility conditions the OEM used to determine these values.
However, imagination aside, a keen technician can recognize some of the requirements specified by the OEM and select the proper lubricant to get the job done.
We first need to read between the lines of the OEM’s general lubrication recommendation. The OEM has told us to use a high-quality turbine oil with a viscosity of ISO VG 32. If we pull this statement apart, we arrive at three distinct specifications.
First, the OEM states that the lubricant must be of high quality. You may guess that the OEM is simply saying to buy a product with which you have had previous success with regard to its quality.
This could include the quality of service from your local distributor, quality delivery times, quality selection of products, quality sales representatives, etc. These items are all important. But the trained lube tech may recognize this description as an indication to which American Petroleum Institute (API) base oil category must be used in this component.
In this case, high quality may mean a higher API category. As we look at the description of the most common API base oil categories in Figure 1, we can tell that as the group number increases, the price per gallon increases as well. T
here are several reasons for this, including the refining used to process the base oil and the amount of impurities they can separate out of the oil during that particular refining process.
Looking at the comparison of Group I base oils to Groups II and III, it is plain to see the difference in how effective the refining process is at separating these unwanted impurities (Figure 1).
|
API Base Oil Categories
|
||||
| Base Oil Category |
Sulfur (%)
|
|
Saturates (%)
|
Viscosity Index
|
| Group I ($1.12/gal) |
>0.03
|
and/or
|
<90
|
80 to 120
|
| Group II ($1.20/gal) |
<0.03
|
and
|
>90
|
80 to 120
|
| Group III ($3.35/gal) |
<0.03
|
and
|
>90
|
120
|
| Group IV ($5.00/gal) | PAO synthetic lubricants | |||
| Group V ($8.00/gal) | All other base oils not included in Group I, II, III, IV | |||
| Unofficial Category: | Severe Hydroprocessed Base Oils | |||
| Group II Plus ($1.50/gal) |
0.03
|
and
|
90
|
90 to 120
|
| Test |
Solvent-refined Base Oil (Group 1)
|
Typical Hydrocracked Base Oil Properties (Group II and III)
|
| Saturates % by wt. |
85 to 90%
|
>99%
|
| Aromatics % by wt. |
9 to 15%
|
<1%
|
| Polars % by wt. |
0 to 1%
|
0.0%
|
| Sulphur % by wt. |
0.05 to 0.11%
|
0.001%
|
| Nitrogen ppm |
20 to 50
|
<2
|
| Color D1500 |
0.5 to 1.0
|
<0.5
|
So how does this relate to the OEM guidelines for lubricating a component? The OEM recommends high quality, and did not specifically mention to use a synthetic. It’s likely a push to use a lubricant produced to meet Group II or III criteria, and not a synthetic.
The second hint the component OEM provides in its generic lube spec is to use a turbine oil. There are several turbine oils on the market today that are commonly made from either Group II or Group III base oils.
But the generic term “turbine oil” is usually synonymous with a premium-quality lubricant with excellent oxidation stability, one that has been fortified with rust and foam inhibitors. This is enough information to start searching for the component’s required lubricant.
There are many categories of oils with these properties, but the turbine oil group of lubricants tends to have just the said oxidation, foam and rust inhibiting additives and not much else. In other instances, other rust and oxidation-inhibited oils (hydraulic oils for instance) may also include additives not required for this application.
Thirdly, the component OEM gives us the most crucial piece of information yet. This component requires a lubricant with a viscosity of ISO VG 32 at 40°C. This is not a hint. This is a specific requirement laid out in black and white.
But beware, the OEM has not provided information on the operating environment of the component when using this recommended viscosity. It is also likely that this component will end up in several climates around the world and be subjected to temperature extremes requiring lubricants outside of the ISO VG 32 recommendation.
It is important to recognize that OEM recommendations do not cover the broad application of their components around the world. As I mentioned, in this case the OEM likely developed this requirement based on favorable conditions.
It is the task of the trained lube tech to recognize and adjust to an extreme condition, based on the ambient environment and the demands of the component.
So where does this leave us? We require a premium-quality lubricant, made from Group II or Group III base stock, with excellent oxidation stability and rust and foam inhibitors, and it needs to have a viscosity of ISO VG 32 at 40°C. With this type of information, we can now procure the required lubricant confident that it is the correct lubricant.
Somehow it seems there are questions left unanswered. Questions like, “Why doesn’t the OEM make a specific product recommendation instead of using generic descriptors I need to decipher?”
And maybe more importantly, “Why is there absolutely no mention of required fluid cleanliness provided in the OEM specification?” Look in upcoming issues for my perspective on these issues and more.