B41oa oil and Gas Processing Section a flow Assurance Heriot-Watt University

3.4.2 Wax Appearance Temperature (WAT) 
In order to design wax prevention strategies, the temperature below which wax 
will freeze out is required. The cloud point, i.e., Wax Appearance Temperature 
(WAT), is traditionally measured by detecting the temperature at which wax 
crystals first becomes visible upon cooling. The experimental methods 
commonly used for measuring WAT are as follows: 
Standard Test Method for Cloud Point: ASTM 
This method detects WAT visually. However, when using this test method, the 
sample fluid is cooled non-uniformly and the cooling rate is irregular. 
Other Visual Techniques: non-ASTM Method 
One example is using microscopy. This method has a high sensitivity, since it 
detects WAT during the early stages of crystal nucleation. The visual 
technique is, however, limited to the clear fluid and not dark crude oil. 
Differential Scanning Calorimetry (DSC) 
DSC is based on latent heat measurement. The DSC signal is the time 
derivative of the heat flow into the sample – its sensitivity is reduced with a 
slow temperature-change rate. 

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TOPIC 3: Wax Deposition 
 
 
 
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When ta DSC is used to measure WAT, the sample is commonly cooled at a 
high temperature-change rate, such as 10 K/min (Ronningsen et al., 1991; 
Elsharkawy et al., 2000). 
Thus, the main weak point of this method is the need for relatively high 
temperature-change rates – this, together with continuous temperature 
changes, makes it basically impossible to ensure equilibrium. 
Viscometry 
Viscometry is based on monitoring the fluid viscosity as a function of 
temperature. WAT is detected by finding an inflection point in the viscosity 
change curve as temperature is reduced – the method depends on the amount 
of wax required to cause a detectable change in the sample viscosity.