Cloud and Pour Point

Cloud and Pour Point

Cloud and Pour Point

Pour Point

The pour point of a liquid is the temperature at which it becomes semi solid and loses its flow characteristics. In crude oil a high pour point is generally associated with a high paraffin content, typically found in crude deriving from a larger proportion of plant material.

Two pour points can be derived which can give an approximate temperature window depending on its thermal history. Within this temperature range, the sample may appear liquid or solid. This peculiarity happens because wax crystals form more readily when it has been heated within the past 24 hrs and contributes to the lower pour point.

The upper pour point is measured by pouring the test sample directly into a test jar. The sample is then cooled and then inspected for pour point as per the usual pour point method.

The lower pour point is measured by first pouring the sample into a stainless steel pressure vessel. The vessel is then screwed tight and heated to above 100 °C in an oil bath. After a specified time, the vessel is removed and cooled for a short while. The sample is then poured into a test jar and immediately closed with a cork carrying the thermometer. The sample is then cooled and then inspected for pour point as per the usual pour point method.

 

Automatic Method

ASTM D5949, Standard Test Method for Pour Point of Petroleum Products (Automatic Pressure Pulsing Method) is an alternative to the manual test procedure. It uses automatic apparatus and yields pour point results in a format similar to the manual method (ASTM D97) when reporting at a 3°C.[1]

The D5949 test method determines the pour point in a shorter period of time than manual method D97. Less operator time is required to run the test using this automatic method. Additionally, no external chiller bath or refrigeration unit is needed. D5949 is capable of determining pour point within a temperature range of -57°C to +51°C. Results can be reported at 1°C or 3°C testing intervals. This test method has better repeatability and reproducibility than manual method D97.

Under ASTM D5949, the test sample is heated and then cooled by a Peltier device at a rate of 1.5 +/- 0.1°C/min. At either 1°C or 3°C intervals, a pressurized pulse of compressed gas is imparted onto the surface of the sample. Multiple optical detectors continuously monitor the sample for movement. The lowest temperature at which movement is detected on the sample surface is determined to be the pour point.

 

Why we need to know?

  • Pour point is the temperature above which a lubricant or fluid will move freely under normal conditions
  • Oil and gas companies pay close attention to pour point because it has an impact on drilling and transport. If a petroleum deposit has a high pour point, usually reflecting a high paraffin content, it may be difficult to extract. Drilling teams need the oil to flow so they can pull it up with drilling rigs. Transport can also become a problem; in some cases, oil pipelines need to be heated to keep the oil at pour point and ensure it moves smoothly from oil fields to shipping terminals and other destinations
  • Manufacturers of lubricants also have concerns in this area. For products like motor oil, the lubricant may need to operate at a range of temperatures. Technicians don’t want oil that flows too readily at low temperatures because it might thin too much at high temperatures and cause problems with the engine. They also need to consider issues like handling engines in extreme cold, where it is sometimes necessary to heat lubricants or entire engine blocks to keep the equipment operational

 

Pour Point of Lubricating Oil and Base Oil

 

Type of Oil

Deg C (°)

Base Oil SN 150

-8

New Engine Oil

-8

Diesel

-1

 

Cloud Point

The cloud point of a fluid is the temperature at which dissolved solids are no longer completely soluble, precipitating as a second phase giving the fluid a cloudy appearance. This term is relevant to several applications with different consequences.

In the petroleum industry, cloud point refers to the temperature below which wax in diesel or biowax in biodiesels form a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines. The wax also accumulates on cold surfaces (e.g. pipeline or heat exchanger fouling) and forms an emulsion with water. Therefore, cloud point indicates the tendency of the oil to plug filters or small orifices at cold operating temperatures.

In crude or heavy oils, cloud point is synonymous with wax appearance temperature (WAT) and wax precipitation temperature (WPT).

The cloud point of a nonionic surfactant or glycol solution is the temperature where the mixture starts to phase separate and two phases appear, thus becoming cloudy. This behavior is characteristic of non-ionic surfactants containing polyoxyethylene chains, which exhibit reverse solubility versus temperature behavior in water and therefore “cloud out” at some point as the temperature is raised. Glycols demonstrating this behavior are known as “cloud-point glycols” and are used as shale inhibitors (see Talk). The cloud point is affected by salinity, being generally lower in more saline fluidsthe cloud point of a solution, whereas builders or other salts will depress the cloud point temperature.

 

Automatic Method

ASTM D5773, Standard Test Method of Cloud Point of Petroleum Products (Constant Cooling Rate Method) is an alternative to the manual test procedure. It uses automatic apparatus and has been found to be equivalent to test method D2500.

The D5773 test method determines the cloud point in a shorter period of time than manual method D2500. Less operator time is required to run the test using this automatic method. Additionally, no external chiller bath or refrigeration unit is needed. D5773 is capable of determining cloud point within a temperature range of -60°C to +49°C. Results are reported with a temperature resolution of 0.1°C.

Under ASTM D5773, the test sample is cooled by a Peltier device at a constant rate of 1.5 +/- 0.1°C/min. During this period, the sample is continuously illuminated by a light source. An array of optical detectors continuously monitor the sample for the first appearance of a cloud of wax crystals. The temperature at which the first appearance of wax crystals is detected in the sample is determined to be the cloud point.

 

Why we need to know?

  • The cloud point of petroleum products and biodiesel fuels is an index of the lowest temperature of their utility for certain applications. Wax crystals of sufficient quantity can plug filters used in some fuel systems.

 

Cloud Point of Lubricating Oil

 

Type of Oil

Deg C (°)

New Engine Oil

-15

Petroleum

-43

Diesel

6