ASTM D4310 Method for Sludging and Corrosion Tendencies of Inhibited Mineral Oils
10. Procedure for Oxidizing the Oil
10.1 Adjust the heating bath to a temperature high enough to maintain the oil in the oxidation test cell at the required temperature of 95 ± 0.2°C.

10.2 Fill the empty oxidation test tube with 300 mL of the oil sample to the graduation mark. Slide the catalyst coil over the inlet of the oxygen delivery tube. If the wires are uneven at one end of the coil, position the coil so that this end is down. Place the oxygen delivery tube with the coil into the test tube. Place the condenser over the oxygen delivery tube and test tube. Immerse the test tube in the heating bath. Adjust the heating bath liquid level so that the tube is immersed in the liquid to a depth of 355 ± 10 mm. Connect the condenser to the cooling water. The temperature of the outlet water should not exceed 32°C at any time during the test.

10.3 Connect the oxygen delivery tube to the oxygen supply (see 7.10) through the flowmeter using new poly vinyl chloride flexible tubing no more than 600 mm in length. Before using, the interior of the new tubing should be rinsed with n-heptane and blown dry with air. Adjust the rate of flow to 3 ± 0.1 L and continue flow for 30 min.

10.4 Raise the condenser unit from the oxidation cell and add 60 mL of reagent water through the opening thus provided. The test is considered to start at this point.

10.5 Throughout the duration of the test, maintain the temperature of the oil-water mixture (sample temperature) at 95 ± 0.2°C in each test cell with oxygen flowing. Accomplish this by maintaining the bath at the temperature that is found necessary to give the required 95°C sample temperature. The temperature of the bath is always higher than the sample temperature due to the cooling effect of the oxygen gas flow, and depends on heating bath medium, capacity, circulation, and on the number of tests cells in the bath. Measure the sample temperature by a thermometer positioned in the oxidation cell by a thermometer bracket, as in Fig. 4 (see Note 6). Make temperature measurements only with new oil samples, and preferably with dummy cells used specifically for temperature measurement. When an actual test sample is used, remove the thermometer immediately after temperature measurement is complete. Check the temperature in this way in various parts of a multiple-cell bath to verify uniformity of temperature control. Once the required bath temperature is found, maintain at that temperature ± 0.2°C.

NOTE 6 - With the arrangement shown in Fig. 4, the 76-mm immersion point of the thermometer is positioned at the oil surface. To allow for heating of the stem portion of the thermometer above the immersion point in the upper portion of the test cell, subtract 0.10°C from the thermometer reading to obtain the true test temperature.

10.6 Add additional reagent water to the oxidation cell as required (see Note 7), at least every 2 weeks during the test, to restore the water level to the shoulder of the oxygen delivery tube. Add the water using the sampling tube and the 50-mL capacity syringe.

NOTE 7 - Under some circumstances, the level of water cannot be observed because of deposits or emulsion formation. Marking the upper oil level of the filled oxidation tube by some suitable means and maintaining this level by periodic water additions will keep the proper amount of water in the cell. The correct level for water additions may, if desired, be indicated by a movable metal strip (see Fig. 5) that is clamped to the outside of the oxidation test tube by, for example, an adjustable ring-type hose clamp. To use this indicator, the lower end of the strip is set at the upper oil level when the test is started. As the test proceeds and water evaporates to cause the oil level to fall, sufficient makeup water is added, particularly just before oil samples are taken, to return the oil level to the level marked by the indicator strip.

11. Procedure for Handling End of Test Oil
11.1 Upon completion of 1000 h of test time, remove the oxidation apparatus from the heating bath and remove the condenser.

11.2 If an end of test acid number measurement is required, remove the sample as follows:
11.2.1 While the oxidation apparatus and the oil are still hot, raise and support the oxygen delivery tube together with the catalyst coil just clear of the oil in the oxidation tube and allow to drain for 5-10 min. Lower the oxygen delivery tube together with the catalyst coil so that the end of the oxygen delivery tube is about in the middle of the oil layer. Raise and support the oxygen delivery tube together with the catalyst coil just clear of the oil in the oxidation tube and allow to drain for about 5 min. Carefully lift the oxygen delivery tube out of the oxidation tube and using a pipette bulb, remove a 3 mL aliquot of sample into an appropriate vial. Quickly replace the delivery tube over the oil to continue draining for an additional 25 to 30 min.

11.2.2 If using a syringe sampling tube to remove a specimen for acid number measurement, insert the sampling tube down through the center hole in the condenser and submerge to approximately the middle of the oil layer. Withdraw 6 mL of oil into the syringe then let the sampling tube rest on the bottom of the oxidation tube for 5 min to allow water to settle to the bottom of the syringe. At the end of 5 min, adjust the sample volume to 3 mL and remove the sampling tube from the oxidation cell. This method allows most of the water withdrawn with the test oil to be returned to the test cell. The 3 mL sample is dispensed into a sample vial for acid number analysis by Test Methods D664 or D3339. Shake the test oil sample thoroughly before taking a sample from the vial for titration.

11.3 If an end of test acid number measurement is not required, raise and support the oxygen delivery tube together with the catalyst coil just clear of the oil in the oxidation tube and allow to drain about 30 min. Suspend the oxygen delivery tube/catalyst coil assembly over a 1000-mL beaker. Pour the contents of the oxidation tube into the beaker. Place a thermometer in the beaker and wait for the sample temperature to drop to 50°C (122°F) before proceeding further. Use 250 mL of n-heptane from a wash bottle in portions to rinse the catalyst coil and walls of the oxidation tube into the beaker. Care should be taken to remove all traces of oil from the coil. Continue rinsing the oxidation tube with 100 mL of water from a wash bottle. Add the water washing to the same beaker containing the heptane washings (see Note 8). Briefly stir the oil-heptane-water mixture, cover with a watch glass, and allow to stand away from light for a period of 16 to 20 h (see Note 9).

NOTE 8 - Occasionally solid material may adhere to the walls of the oxidation tube, the catalyst coil, the oxygen tube, or condenser and resist displacement by heptane or water. This material is recovered by manual scraping using a rubber policeman and heptane washes. The additional material and heptane washes are added to the oil-heptane water mixture.

NOTE 9 - The purpose of the 16 to 20-h waiting period is to allow sufficient time for equilibration of insoluble material with the oil-heptane and water phases. This procedure also improves the ease of filtration of the sludge by allowing time for coalescence of the material into a more filterable form.

12. Procedure for Determination of Sludge Weight
12.1 Prior to filtering the oil-water mixture, weigh two filter membranes to the nearest mg in weighing vessels (A1 mg and B1 mg) (see Note 10, Note 11). Mount two filter holders on 1000-mL filter flasks. Assemble the two filter holders with the two membranes. Handle the membranes only with forceps having unserrated tips. Apply vacuum 13.3 ± 0.7 kPa (100 ± 5 mm Hg) absolute pressure and carefully decant approximately equal portions of the oil-heptane layer into the two filter funnels without adding any of the water layer (Note 12). After the oil layer is filtered through, rinse the filter funnels with n-heptane, allow air to pass through the filter briefly, and begin addition of the water layer to the two filters. After the contents of the beaker have been divided approximately equally between the two filter funnels, thoroughly rinse the walls of the beaker and of the funnel with portions of water and then with portions of n-heptane. A rubber policeman may be used to scrape the walls of the beaker. Do not use less than 50 mL of water and 250 mL of n-heptane for each filter in this first rinsing procedure. Then, in a second rinsing operation, rinse each filter with an additional 100 mL of n-heptane. The final rinses of n-heptane from this second operation should be completely colorless after passing through the filters.

NOTE 10 - Weighing bottles, watchglasses (one as receptacle, one as a cover), glass petri dishes or aluminum foil dishes have been used for this purpose.

NOTE 11 - More than two filter membranes may be used if a large amount of sludge is present.

NOTE 12 - Filtration of the oil-heptane layer will proceed at an optimum rate if no water is introduced into the filter during the filtration. A suitable technique employs the use of a separatory funnel to separate the water from the oil layer before beginning the filtration. Occasionally, because of the nature of the deposits, filtration proceeds at a very slow rate despite precautions in avoiding simultaneous filtration of oil and water layers. In such cases prolonged (overnight) filtration times may be considered. However, unless the filtration is being directly attended, filtration should be stopped, that is, filter equipment brought to atmospheric pressure. Then leave solvent on the filter and cover the filter holder with a tight cover until the filtration at specified vacuum conditions is resumed the next day.

NOTE 13 - The use of microwave-digestion method is an acceptable alternative to ashing.

12.2 With the vacuum applied, remove the clamp and funnel from the filter membrane and funnel base. Rinse the surface of the membrane with a gentle stream of n-heptane, directing the stream from the edge towards the center so as to remove final traces of oil from the membrane. Maintain the vacuum for a short time to remove final traces of n-heptane. Transfer the membranes to the identical weighing vessels used in the initial weighing and dry for at least 1 h in the oven at 105°C. Allow the weighing vessels to cool in the cooling vessel in the vicinity of the balance for at least 2 h. Weigh the filters (in the weighing vessels) to the nearest mg. Return the weighing vessels with the filter membranes to the oven and dry, cool, and reweigh. When the difference in the weight of the insoluble material before and after successive drying/weighing operations is less than either 2 mg or 5 %, report the last weighing as the final weight (A2 mg and B2 mg).

13. Procedure for Determination of Copper in Oil, Water, and Sludge for Procedure A
13.1 Preparation of Oil and Water Layers for Copper Determination - After completion of the filtration proceedings (see 12.2), transfer the oil-heptane and the water filtrates from the two 1000 mL filter flasks to 1000-mL separatory funnels. Separate the oil-heptane and water layers. Weigh two beakers of the proper size to the nearest gram. Weigh into one of the beakers the total amount of oil-heptane mixture from the separatory funnel to the nearest gram (WO-H g) and weigh into the second beaker the total amount of water from the separatory funnel to the nearest gram (Ww g).

13.2 Analysis for Copper:
13.2.1 Direct Method (homogeneous sample) - Determine the copper content on the oil-heptane mixture and on the water solution according to any suitable method, such as atomic absorption (AA), direct current plasma (DCP), inductively coupled plasma (ICP) or X-ray fluorescence (XRF) (P1O-H% or P2O-H ppm; P1W% or P 2W ppm). If the results are below 1000 ppm, report in ppm; if the results are 0.100 % or more, report in percent.

13.2.2 Ash Method (non-homogeneous sample) - For the insoluble material (sludge) and in case the oil-heptane mixture and the water solution are not homogeneous, use the ash method. After the last weighing of the filters (see 12.2), ash the two filters with the insoluble material using the sulfated ash procedure of Test Method D874.

13.2.3 If the ash method is used for the oil-heptane mixture or the water solution, evaporate the solvent or the water and ash the residue using the sulfated ash procedure of Test Method D874. Weighing and calculating the ash content are not necessary. Dissolve the ash by washing down the walls of the vessel with 5 mL concentrated hydrochloric acid. Digest on a steam bath for 15 min to effect the solution of all copper present. Cool the samples to room temperature and transfer the acid solution to a 50-mL volumetric flask and dilute to volume with distilled water. Determine the copper content on the water solution according to any suitable method, such as AA, DCP, ICP or XRF. (P3I%, P4I ppm; P3O-H%, P4O-H ppm; P 3W%, P4W ppm).