ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils
ASTM D4378 Standard Practice for In-Service Monitoring of Mineral Turbine Oils for Steam and Gas Turbines
6. Sampling
6.1 General - When taking oil samples from storage tanks or equipment in service, it is important that the extracted sample will be representative and be taken from a specified location(s) to monitor the properties of the lubricant. Correct sampling techniques are vital to achieve this. The following are some suggested guidelines for proper sampling technique and sampling handling techniques (see Practice D4057).

6.2 Representative Sampling - A sampling location that supports repeatable and representative sampling to monitor the health of the equipment and the properties of the lubricant. To be representative, a sample must be obtained either from an agitated tank or a free-flowing line.
6.2.1 The primary sampling port is the location where routine oil samples are taken for monitoring oil contamination, wear debris and the chemical and physical properties of the oil and is as follows:
6.2.1.1 Dipping from the Tank - Oil samples should be taken by dipping from the tank. Lubricant should be thoroughly circulated before the sample is taken.

6.2.1.2 Oil Return Line Sampling Port - For circulating systems, the preferred location for oil samples should be taken on a single return line prior to entering the sump or reservoir.

6.2.2 The secondary sampling methods are to be used for measuring contamination and wear debris contributed by individual components, and can be located anywhere on the system to isolate upstream components. This is where contamination and wear debris contributed by individual components will be found:
6.2.2.1 Sampling from a Line - The line should contain lubricating oil which is free flowing and not deadheaded. For instance, the lines in a bearing header, an active filter, and active heat exchanger are free flowing; the lines to a gage cabinet are deadheaded. In equipment with dual filters or heat exchangers, the inactive filters or heat exchangers do not have flowing fluid and are not suitable sampling points. When using a sampling line, it is necessary that the line has been thoroughly flushed before taking a sample. Adequate amount of flushing will depend on sampling line dimensions, length, and diameter.

NOTE 1 - Test values obtained will differ depending on the sample locations. Use caution when comparing sample results from different sample points.

6.2.2.2 Tapping from a Reservoir - As previously described, the lubricating oil must be thoroughly agitated in the reservoir and the tap line flushed before a sample can be taken.

6.2.3 An oil sample is probably not representative if: (1) the system oil is hot while the sample is cold, (2) the oil in the system is one color or clarity in a sight glass while the sample is a different color or clarity, and (3) the viscosity of the reservoir oil is different from that of the sample when both are at the same temperature.

6.2.4 It should be noted that on occasion a sample may be requested which will not be representative. At that time, sampling instructions, as specified by the requestor, must be followed. For example, a sample might be taken off the top or the bottom of a tank to check for contamination. In all cases the sample point should be marked on the sample bottle.

6.3 Oil Sample Bottles - Samples should be taken in a suitable sample bottle. To be suitable the bottle should be:
6.3.1 Clean - If in doubt about its cleanliness, use another bottle; if this is not possible, flush it out with the oil to be sampled.

6.3.2 Resistant to the Material Being Sampled - To verify the bottle's resistance, if time permits, allow the sample to stand in the bottle and observe its effects. Aluminum foil makes a good, resistant cap liner.

6.3.3 Appropriate for Whatever Handling is Required - Bottles with leaking tops and glass bottles improperly protected are not suitable for shipment. Appropriate regulations for handling and shipment of samples must be observed.

6.3.4 Appropriate for the Analyses Required - An extensive chemical analysis, if that is why a sample is required, cannot be done on the contents of a bottle which is too small.

NOTE 2 - Some lubricant suppliers and commercial laboratories provide sample bottles which meet all these requirements. These should be used whenever possible. If frequent samples are taken, an adequate supply of containers should be kept.

6.4 Sample Markings - A sample should be properly marked. Markings should include at least the following information:
6.4.1 Customer name (if appropriate),

6.4.2 Site or plant name,

6.4.3 Location (unit number, tank number, compartment number, and so forth),

6.4.4 Turbine serial number (or other ID),

6.4.5 Turbine service hours,

6.4.6 Oil service hours,

6.4.7 Date sample taken,

6.4.8 Type of oil sampled (lubricant ID),

6.4.9 Sampling point/port ID,

6.4.10 Type of purification system (filters/centrifuge, and so forth), and

6.4.11 Makeup (volume) since last sample was taken.

6.5 Sampling of New Oil Deliveries:
6.5.1 A sample of the new lubricant is required to provide a base line for the physical and chemical properties of the lubricant. Also samples taken should be representative of the oil being examined but obtained from the point(s) most indicative of gross contamination by debris and water, that is, just above the bottom of the drum or tanker compartment bottom.

6.5.2 When consignments of oil are in drums, sample them in accordance with Practice D4057.

6.5.3 For bulk consignments, sample each tanker compartment. If these are clear of debris and water, then the samples can be combined for subsequent laboratory analysis of the consignment.

6.5.4 In cases where the product is suspected of being nonuniform, sample a larger number of drums. Where contamination is suspected there is no alternative to sampling every drum.

6.5.5 From tanker deliveries, in addition to sampling individual tanker compartments, further sample(s) should be taken preferably from the outlet of the flexible pipework or at least from the tanker bottom valve manifold. This further sampling is necessary because the tanker contents can become contaminated by residual material left in the bottom valve manifold. This can occur particularly when different products are being carried in separate compartments or previous deliveries of a different product have been made to other locations without subsequent adequate cleaning and flushing.

6.5.6 Bottom samples must be collected by either a tube or thief sampler (for example, Bacon bomb). These samplers permit collection of settlings on the bottom of the container without introducing false contamination by scraping the container lining or wall.

6.5.7 Take the sample(s) from the outlet of the flexible pipework or the tanker bottom valve manifold while maintaining a good flow after flushing the line.

6.6 Preservation of Sample - If tests are not run immediately, store the sample(s) away from strong light or excessive heat.