4.3 Liquid in Glass Thermometer
4.1 Introduction 12 We have learned from the previous section that tank gauging will provide us with liquid level measurements that can be converted into volumes at actual or observed temperature. We have also learned that volumes at observed temperature are converted to volumes at standard temperature, 15 ° C or 60 ° F, by use of volume correction factors. To obtain a volume correction factor, it is necessary to know the temperature and density of the liquid being measured; therefore, accurate temperature measurement is as important to the determination of accurate volumes as is accurate gauging. Accurate and representative temperature determination is one of the "key critical" elements of any custody transfer, because volumes of petroleum products are bought and sold at standard temperature, usually 60 ° F or 15 ° C. An error in temperature will result in an error in volume; for example, a 5 ° F error on the closing temperature of a 500,000-barrel tank of medium density, 35.0 API crude oil will result in a 700-barrel error; which at prices of $90 /bbl is worth around $63,000.00. Even a 1 ° F error in this situation would cost someone $12,600.00.
4.2 Types of Thermometer There are two basic types of thermometer used to determine the temperature of petroleum: Liquid in Glass Thermometer. Portable Electronic Thermometer, commonly referred to as a "Thermoprobe". The API MPMS standard which covers these thermometers, and their use is Chapter 7.1 and 7.2. While these two types of thermometers differ considerably in construction, they have a number of areas of application in common. Regardless of the type of thermometer used, both have requirements for: Accuracy specifications. Bench inspection calibration or verification. Field inspection. Immersion time required to reach temperature equilibrium.
There are a number of different types of liquid in glass thermometer assemblies for measuring petroleum. The most common is the "cup case assembly," which is also known as a "wood back." The cup case assembly consists of a hardwood housing, with a cup attached to it. The stem of the thermometer sits in the housing and the bulb of the thermometer is located in the cup. See figure on the following page.
Clamp
11/8”
ASTM thermometer
Hard wood
100ml cup (corrosion resistant metal)
Clamp
3/4”
30°
3/8” 1” ± 3/16”
Closed bottom
13/4”– 2”
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