by Cade Gulledge, Industrial Solutions Engineer | Lard Oil Company
For many, oil analysis is a “checking the box” activity — pulling a sample from wherever is easiest to get oil into a bottle, and checking the report when there’s an “alert”, if at all. But major financial decisions are often made from these results, so it pays to make sure you’re doing it right.
Here are 3 keys to ensuring quality insights from Oil Analysis:
1.) Select the right sample point.
The first question to ask yourself is: “what insights am I trying to gain from this?” This is an important question that’s often overlooked. No matter your answer, the data you view on your Oil Analysis report is dependent on the quality of the sample you pull. Whether the asset is 12 gallons or 12,000 gallons, you only have ~4oz / 125ml to gain insight from – so you’ll want to make the sample count.
Whether the asset is 12 gallons or 12,000 gallons, you only have ~4oz / 125ml to gain insight from – so you’ll want to make the sample count
If you want to check the cleanliness of the oil on its way to the bearing, then you should pull the sample on the supply line downstream of the filter:
If you want to check for signs of varnish or deposits, the oil drain port on the cooler is a great spot to pull from:
For routine oil sampling, most of the time you’re looking for signs of wear and impending failure. In this case, you should collect the sample from the closest point as possible to what it just lubricated. My hierarchy of sample points are as follows:
Routine Sample Points for Circulating Systems
1st: Common Return Line
This is where you’re most likely to get the most “representative” sample — getting all of the relevant constituents of the oil you’d hope to see on the results into a 4oz bottle. If there’s wear occurring, oil reaching the end of its life, or any other alarming phenomena, you’ll catch it here.
“Points” to look for:
- Unused Ports on the return line. Turbulence is what you’re looking for — a uniform mixture of any contents suspended in the oil.
- P/T Gauges (w/o thermowells) to tee off of. Many sample valves on the market allow you to bend and cut rigid tubing into turbulent zones. Even if a port is occupied, you can usually “tee” off of it with one of these sample tubes.
- Drain lines or “doglegs”. All large circulating systems have these somewhere. You’re looking for one that’s on the common line — downstream of where individual lines feed, which not all systems have. These are usually within a few feet of the reservoir. Just be sure and “flush” the volume of stagnant oil before taking the actual sample.
2nd: On Reservoir Near Return Outlet
When there’s no where to pull the sample on the common return, this is your next best option. Following the logic above, you’re looking for a place to pull the sample that’s near the outlet of the return into the reservoir. To do this, drawings or pictures showing the internal piping of the reservoir may be necessary.
“Points” to look for:
- Unused ports on the top or side of the reservoir where rigid tubing can be bent near the return outlet.
- Breather ports or gauges to adapt with rigid tubing to extend to the active zone.
3rd: Supply Line Upstream of Filters
The next best option (by no means bad) is on the supply line before suspended components are filtered out. While you may not be getting the oil as it just left the load zone, spectroscopy is measuring materials smaller than around 10 microns, making it likely that some are still suspended as they circulate back through the lube oil pump. This is especially true if the reservoir is smaller than 500 gal or so.
“Points” to look for:
- Unused ports upstream of filters. Even if occupied by a gauge, you can tee off of it as before. Depending on your design, the heat exchanger typically has available ports if there are none on the supply piping itself.
- Supply line or kidney-loop filter housing. Just be sure of the port you’re selecting — check drawings or bypass and drop the filter to inspect which port is upstream.
Routine Sample Points for Gearboxes
1st: Dipstick or Other Unused Port
If your gearbox is critical enough to warrant sampling, then it is critical enough to outfit it with a proper sight glass and throw the dipstick away. The dipstick port is typically a great location since you can get close to the gears without chewing up the tubing as you drop it in.
- Utilize a sight glass to check oil level and condition
- Replace dipstick port with rigid tubing sample valve bent close to the mating gears
2nd: Drain Port with Tubing Bent Close to Gears
- Use a sample valve that incorporates a swivel feature to ensure the end of the tube stays put while tightening
- Tee off of the main drain or utilize a secondary drain port so you can still drain the oil when needed
Sampling Past Machine Guarding
2.) Be Consistent
The value of oil analysis typically isn’t recognized overnight. That’s because quality insights don’t come from single data points, they come from trends.
Quality insights don’t come from single data points, they come from trends.
Uphold the following practices consistently to ensure your trends are accurate:
- Identify your sample point, label it, and always pull from that point. This can be taken a step further by incorporating technology such as QR codes to submit the sample from the field and view previous sample results:
- Try to pull samples at consistent time intervals when the equipment is running.
- Always flush any “trash” that has accumulated at the point. A good practice is to flush at least the volume of the sample that you’re about to collect. A better practice is to flush the volume of stagnant “zones” to make sure the oil you send off is representative of the oil circulating through the lines.
- Replace tubing when necessary. Some say to replace the tubing between each sample. If you’re properly flushing, you may only need to replace the tubing between sampling different oils or if the prior sample was heavily contaminated.
- Only take the cap off when you’re ready to pull the sample, and put it back on as soon as the bottle is full. Don’t let anything that didn’t come from the stream of oil end up in the bottle.
- Utilize valves that are meant for sampling lube oil. Traditional ball valves or opening existing lines can make a mess and lead to oil spills, and oil sampling valves are usually cheaper than a DIY valve. Using the right valve can help to eliminate misleading results.
3.) Optimize Frequencies
The overall goal of oil analysis is to mitigate failures. You do this by capturing the data between a problem and the onset of failure. While sampling more frequently increases the likelihood of capturing that event, the costs of testing and labor have to be accounted for. Consider the following factors and industry standards to optimize your sample interval:
- Criticality – If this asset fails and causes a shut down, it warrants sampling more frequently.
- Bad actors – Assets deemed problematic should be sampled according to how often that problem occurs and what you plan to do about it. For example, if an asset is known to have misalignment or undergo abnormal loading, it makes sense to sample it more often to estimate the failure timeline and see if it can make it to the next planned outage. Conversely, if an asset is known to have continual water ingression and you aren’t removing it with a dehydrator or other means, there is little value to gain by sampling it more frequently.
- “Replaceablility” – How available are those parts? Do you have extras on the shelf, or is this the only one like it in the world?
When in doubt, the following standards are a safe guideline:
The bottom line is that you should understand why you’re doing oil analysis before gathering and sending off samples. This usually requires going into the field to survey and understand the nuances of each asset.
Of course [sales plug], time is money and we have a ton of experience conducting Oil Analysis Surveys as a service, among other on site services in our portfolio.
So if you have any questions about concepts, products shown in this article, or are interested in an Oil Analysis Survey or other on site service, feel free to message me directly via LinkedIn or email at firstname.lastname@example.org.