ASTM D923 standard practices for sampling electrical insulating liquids
SAMPLING OF CANS, DRUMS, TANK CARS, TANK TRUCKS, AND SMALL ELECTRICAL EQUIPMENT
13. Using the Dip-Type or Drum Thief Device (Fig. 1)
13.1 Cleaning the Device - Clean the device by rinsing the inside and outside surfaces with Stoddard solvent, or other suitable solvent. Place a small funnel in one end of the tube, place the forefinger of one hand over the other opening, and partially fill the device with solvent. Remove the funnel, cover the opening with the forefinger of the other hand and flush the tube by agitating the solvent back and forth. Empty the tube, flush the outside surface with solvent, and take care after rinsing not to touch any portion of the tube that will be immersed in the liquid when the sample is being taken.

13.2 Sampling Procedure - Close the top hole of the device with the thumb and introduce the lower end into the liquid to be sampled to a depth of approximately 300 mm. Remove the thumb, allowing the liquid to flow into the device. Again, close the upper end with the thumb and withdraw the device, holding it in a nearly horizontal position. Shift the position of the device so that the liquid will flow back and forth in the tube, rinsing the inside surface. During this operation, take care to avoid handling any portion of the device that will be immersed in the liquid to be sampled. Discard the liquid used for rinsing. With the thumb again covering the top hole of the device, insert the lower end into the liquid at an angle so that it will come to rest on the bottom of the container at the center. Raise the device approximately 3 mm off the bottom and then release the thumb (Caution: see Note 2). When the device is filled, replace the thumb quickly, withdraw the device, and, placing the tip inside the neck close to the side of the sample container, release the thumb and allow the contents to fill the container. The free hand may be placed at a point above the liquid level to guide the tip of the device to its position on the sample container. When the container is filled, stop the flow of liquid by returning the thumb to the top hole. Do not close the bottom hole with the use of the other hand. Quickly close the sample container and attach an identifying tag. Where provided, replace the stopper in the container that was sampled.

NOTE 2 - Caution: The standard 55 gal (208 L) oil drum is so designed that when full and standing on end the bottom will bulge, thereby becoming concave on the inside so that at the center it is about 10 mm below that portion which is directly below the bung opening. It is essential when sampling liquid in this type of container that the dip-type device be inserted at an angle so that the bottom sample is obtained from that portion of the liquid in the center. The use of disposable polyethylene gloves would be appropriate when using this device.

14. Using the Pressure-Type Device (Fig. 2 and Fig. 3)
14.1 Apparatus - The following apparatus is required for the functioning of the pressure-type device:
14.1.1 Nitrogen Gas Cylinder - A tank of dry nitrogen gas for supplying the necessary nitrogen pressure to the liquid in the drum to be sampled. The nitrogen gas must meet the requirements prescribed in Table 1 of Specification D1933.

14.1.2 Pressure Regulator, to reduce the gas pressure to the desired value.

14.1.3 Safety Valve - A relief valve set to operate when the nitrogen pressure reaches 69 kPa (10 psi).

14.2 Cleaning the Device - Invert the device, hold it in a perpendicular position, and place the U-bend in a pail or similar container. Insert a small funnel into the top end of the tubing, and thoroughly rinse the inside surface of the tubing by flushing it several times with Stoddard solvent or other suitable solvent. Drain the solvent from the tubing and pour more solvent over the outside surface of those parts of the tubing that will be immersed in the liquid while the sample is being taken. When this operation is completed, exercise care not to touch any part of the sampling tube that will be immersed in the liquid when obtaining a sample. Precaution - Before proceeding to use this method, inspect the area in which the drums to be sampled are located to be positive there is adequate ventilation, preventing a concentration of the nitrogen gas which is dissipated during the sampling operation. Comply with OSHA regulations concerning confined space.

14.3 Sampling Procedure - Screw a sample bottle into the brass cap and adjust the bung on the tube so that when the bung is screwed into the drum the sampling tube will extend into the liquid to a depth of about 300 mm. With the hose from the nitrogen tank clipped on the check valve, set the three-way plug cock to permit nitrogen to flow into the drum. Adjust the regulator so that the pressure is gradually increased to 34 kPa (5 psi). This will purge air from sample bottle and subsequently start the liquid to fill the bottle. When the bottle is approximately 7/8 full, shut off the nitrogen supply and at the same time, vent the drum to the atmosphere by means of the three-way plug cock. Immediately vent the release valve in the top of the tube by means of the push-button valve. Unscrew the bottle and collect the drainage liquid from the tube. Discard this sample. Screw a clean sample bottle into the brass cap, push the tubing to the bottom of the drum, and set the three-way plug cock to permit nitrogen to flow into the drum. Restore 34 kPa (5 psi) pressure to the drum by means of the pressure regulator. This will purge the air from the sample bottle and subsequently start the liquid to fill the bottle. When the bottle is full, shut off the nitrogen supply and vent the drum to the atmosphere. Vent the release valve by means of the push-button valve, remove the sample bottle, and immediately screw the cover on tightly. Attach an identifying tag to the bottle. Withdraw the tube from the liquid and allow to drain. In sampling a shipment of new liquid in drums, the device may be inserted into the next drum and the sample taken without further cleaning or rinsing of the device, provided the previous sample showed no evidence of moisture or foreign particles.

15. Using the Tank Car-Type Device (Fig. 4)
15.1 Cleaning the Device - Holding the device suspended by its handle, thoroughly rinse the inside surface and then the outside surface with Stoddard solvent or other suitable solvent. When the liquid to be sampled is askarel, the solvent used for rinsing the device must not be from a petroleum base.

15.2 Procedure for Sampling Oil - When sampling a tank car, tank truck, or a large storage tank of oil not provided with a sampling-test nipple, it is desirable that bottom samples as defined in Practice D4057, be taken in the area around the drain pipe. Prior to obtaining any sample, rinse the device by lowering it into the tank of oil approximately 300 mm beneath the surface, and with a cord attached to the plunger raise it so that liquid will fill the reservoir. When filled, release the plunger, withdraw the device, and discard the contents; then lower the device gently until it rests on the bottom of the tank, taking care that it is held in an upright position. The plunger will have recessed, and filling of the device will be evidenced by bubbles of air rising to the surface of the oil. When the bubbles cease to rise, the device is filled. Withdraw the device. In emptying the device into the sample container, allow the oil to flow against the side of the container. Repeat the operation at points on an imaginary circle around the drain pipe until the desired number of samples have been obtained. When it is desired to obtain samples at some specified depth, raise the plunger by means of the attached cord and when filled, as indicated by the cessation of air bubbles rising to the surface, withdraw the device. Empty the device into the sample container, observing the precautions previously mentioned. It is suggested that twice the number of samples or test specimens to be subjected to the desired tests be taken and half the number held in abeyance pending the possibility of additional tests being necessary, in which case a revisit to the location for resampling would be avoided. Attach an identifying tag to each sample bottle as soon as it has been filled.

15.3 Procedure for Sampling Askarel - When sampling a tank car, tank truck, or large storage tank of askarel not provided with a sampling-test nipple, take the samples from the surface layer of the liquid unless otherwise specified. Remove the plug in the top of the device and lock the plunger in its lowest or closed position. Gradually lower the device into the liquid so that the hole in the top is just below the liquid level, thereby filling the reservoir; withdraw the device from the liquid and discard its contents in accordance with current applicable government regulations; then refill the device by repeating the operation. In emptying the device into the sample container, allow the askarel to flow down the side of the container; do not allow the askarel to flow in a stream that splashes to the bottom of the container. The number of samples to be taken depends on the number of tests required. Attach an identifying tag to each sample container as soon as it is filled.

16. General Considerations
16.1 When taking samples of liquid from large storage tanks, transformers, oil-circuit breakers, gravity-feed reservoirs on oil-filled cable feeders, and other electrical equipment, the electrical equipment drain valve is usually adequate. However, when high relative humidity conditions exist and it is desired to obtain samples through a closed system, the manifold in Fig. 5 is recommended.

16.2 Unrepresentative samples are often obtained when sampling electrical apparatus using the sampling ports mounted on drain valves without appropriate preparation. The flow allowed by these ports is not adequate to properly flush the drain valve and drain valve extension of the electrical apparatus. Since the fluid in the drain valve and extension remain quite dormant during the normal operation of the electrical apparatus, contamination with stem packing and moisture must be thoroughly flushed prior to the collection of a sample.

17. Mandatory Conditions
17.1 When it is necessary to obtain a sample from a piece of energized equipment not hermetically sealed, under no circumstances take the sample by any other means than from an external sampling valve.

17.2 All non-hermetically sealed equipment in this category, filled with insulating fluid having a relative density (specific gravity) less than 1, should be provided with the sampling outlet located at the bottom of the tank so that bottom samples of the oil may be obtained.

17.3 All non-hermetically sealed equipment in this category, filled with insulating fluid having a relative density (specific gravity) greater than 1, should be provided with the sampling outlet located at the top of the tank at the 25°C (77°F) liquid level so that a top sample of the liquid may be obtained.

17.4 Hazards of Sampling Electrical Apparatus:
17.4.1 Do not draw samples from any energized electrical equipment with a small volume of oil, especially those that require the addition of oil to maintain the electric strength of the insulation system.

17.4.2 Energized electrical apparatus being sampled must have a positive pressure at the sampling outlet, so as not to introduce an air bubble into the apparatus during the sampling process. Refer to 18.1.

17.4.3 Do not sample electrical apparatus if only a drain plug is provided, as it would be difficult to control the flow.

17.4.4 Do not draw samples from energized instrument transformer (C.T.s and P.T.s).

18. Using Electrical Equipment Sampling Outlet
18.1 Check for positive pressure at a sampling outlet by placing a slug of insulating fluid in a piece of clear plastic tubing and attaching it to the sampling outlet. While observing the slug of insulating fluid, slowly crack the sampling outlet valve open. If the slug moves towards the electrical apparatus, a negative pressure exists, and sampling should be discontinued. If the slug moves away from the electrical apparatus, a positive pressure exists, and samples can be obtained safely. Take extreme care in performing this procedure.

18.2 Place a flush-oil container under the main drain valve and remove the security pipe plug from the drain valve. Wipe the inside of the valve and threads with a clean lint-free cloth. Drain at least 2 qt of fluid into the flush-oil container to flush the drain valve and drain valve extension. One of two procedures may then be used to prepare the sample outlet.

18.2.1 Procedure A - Install a sample adapter on the drain valve (suitable thread size bushing adapter IPS to 3/8 in. bayonet) with a piece of oil-resistant tubing attached. Flush the valve and installed sample adapter by flushing at least 1 qt of fluid into the flush-oil container before collecting sample.

18.2.2 Procedure B - Install the drain valve security plug. Attach oil resistant tubing to the sample port on the drain valve and flush at least 1 qt of fluid into the flush oil container before collecting the fluid in the sample container.

18.3 When collecting the sample in a glass jar, bottle or tin-plated steel can, hold the sample container so that the fluid will run down the sides and limit aeration of the fluid. Partially fill the sample container several times and slosh the fluid around to warm the container in order to prevent condensation. Discard the fluid after each rinse. The flow of fluid should be gentle but not interrupted from the start of the flushing of the valve and container to the completion of the final filling of the sample container.

18.4 Obtain the sample for evaluation by allowing the fluid to flow down the sides of the container or from the bottom up, filling the container to overflowing. Once the container is full install the cap immediately.

18.4.1 If glass sample containers are used, adequate space should remain in the container to allow for expansion of the fluid during warming of the sample. This applies to samples that are collected at temperatures below the temperature of the sample storage area.

18.5 Close the drain valve, remove the sample adapter, if used, and install the drain valve security plug with a non-hardening thread sealant. Do not reuse the tubing. Clean the sample adapter before reusing on other oil-filled compartments or apparatus.