GB/T 21451.5-2019Petroleum and liquid petroleum products -- Measurement of level and temperature in storage tanks by automatic methods -- Part 5: Measurement of temperature in marine vessels (English PDF)

3.1 Automatic Tank Thermometer; ATT

Automatic tank thermometer refers to an instrument which continuously measures temperature in storage (or cargo) tanks.

NOTE: a type of marine ATT, also known as automatic tank temperature measurement

4.2.2 All the marine ATTs shall be designed, selected and installed in accordance with

corresponding national and/or international (IMO, IEC, CENELEC, ISGOTT, ISO, etc.)

vessel electronic safety standards. ATT shall have certified documents that are consistent with the classification of dangerous zones that it is applied to.

4.2.3 In terms of ATT installed on vessels, all the exposed metal components shall be

firmly grounded, namely, connected to the vessel body.

4.2.4 All the ATT equipment shall be maintained under safe operating conditions.

Equipment maintenance shall be conducted in accordance with the manufacturer’s requirements.

4.3 General Requirements

4.3.1 General requirements provided in 4.3.2 ~ 4.3.6 are applicable to various types of

ATT.

4.3.2 Temperature and liquid level in marine vessels shall be simultaneously measured.

4.3.3 When temperature measurement is conducted on bulk cargo transportation, the

data shall be immediately recorded, unless long-distance digital display equipment can regularly and automatically record the temperature.

4.3.4 During the loading and/or unloading at multiple ports, before the transportation

of products (front reading) and after the transportation of products (rear reading), the same standard procedure shall be adopted to measure the temperature in marine vessels.

4.3.5 In order to prevent unauthorized adjustment or intervention, safety guarantee

shall be provided to ATT. When ATT is applied to custody transfer metering, certain conditions shall be provided to the sealing of the calibration adjustment device.

NOTE 1: this kind of protection might need to install ATT sensor in a temperature casing.

NOTE 2: ATT sensor may be integrated in the combination (for example, float, belt or rod)

of automatic level gauge (ALG). When some designs (float and belt) are not in service, the combination of liquid level/temperature sensor might be raised to the location of “retention”. During the tank-washing period, ATT cannot be used.

4.3.6 When ATT is applied to special occasions, its design and installation might need

to obtain type approval from relevant national institutions. After conducting a series of specific tests on ATT and complying with the authorized installation mode, type approval will generally be released.

5.1 Overview

circumstances are exceptions here:

---Cargo tank capacity is less than 159 m3, or, liquid level is lower than 3 m;

---The maximum variation of vertical temperature is less than 1 °C;

---The manually measured average temperature is used for custody transfer metering.

NOTE: when liquid temperature in the vessels is uniform, or, when temperature stratification in the vessels is relatively small and acceptable (see GB/T 8927), single-point temperature measurement may be adopted.

7 ATT Equipment - Instruction of Electronic Temperature Sensing Element

7.1 Resistance Temperature Detector In terms of generally used automatic temperature measurement equipment, its basic operating principle is that the resistance of metal (for example, copper or platinum)

varies with the temperature.

Generally speaking, copper or platinum RTD is used for temperature measurement in custody transfer metering, because it has extremely high accuracy and stability. The resistance of RTD may be measured through Wheatstone bridge circuit or other suitable electronic components. RTD may be resistance wires intertwined on non-conductor support core, or, thin-film type or other types. This component shall be correctly installed in a stainless-steel shell. If necessary, circuit shall be intrinsically safe. Temperature sensing element shall be installed in a suitable temperature casing.

The length of the sensing part of point-type temperature sensing element shall not exceed 100 mm.

7.2 Other Temperature Sensing Element Other temperature sensing elements (such as thermocouple, thermistor, semiconductor and optical fiber, etc.) may also be adopted. However, they shall be calibrated and comply with the inspection tolerance provided in this Part, otherwise, it shall not be deemed that their accuracy is applicable to custody transfer metering.

8 Installation of Marine ATT

8.1 Overview The installation of marine ATT shall comply with the requirements in the instructions provided by ATT and ALG manufacturer.

applied for temperature measurement in custody transfer metering, the calibration tolerance provided in this Part shall be satisfied. The reference standard of ATT calibration shall be traceable to corresponding national standards.

NOTE 1: precise electronic temperature element and on-site transmitter used for fixed automatic tank thermometer need to be calibrated before installation. Generally speaking, on-site calibration adjustment device for transmitter will not be provided.

NOTE 2: the objective of 9.2 ~ 9.4 is to inspect the calibration adequacy and accuracy of ATT (including temperature element, transmitter and on-site/long-distance digital display device) after its installation.

When manual temperature measurement is adopted to inspect or calibrate ATT, manual temperature measurement shall be conducted in accordance with GB/T 8927.

The uncertainty of the reference standard for on-site calibration shall not exceed 0.1 °C (necessary calibration correction value shall be adopted).

ATT may be calibrated/inspected in accordance with system or component.

9.2 Calibration and Inspection of Single-point ATT for Custody Transfer Metering

9.2.1 Calibration before installation The reference standard of ATT calibration shall be traceable to corresponding national primary standards. Before installation, single-point ATT shall be calibrated under controllable conditions (namely, factory or laboratory) in accordance with one of the two methods below:

a) In three or more temperature points within ATT’s operating range, through thermostatic bath and use standard thermometer to measure its temperature.

Conduct overall calibration of ATT (including temperature sensor, temperature transmitter/converter and digital display device); the requirement of accuracy is shown in 5.3.2.

b) Or, independently calibrate ATT components. Measure the resistance of temperature element in thermostatic bath; use accurate resistor or thermal calibrator (recently calibrated by a national metering institution). Respectively simulate the input temperature of ATT temperature transmitter and digital display device; the requirement of accuracy is shown in 5.3.3.

9.2.2 Initial inspection in shipyard or sea trial

9.2.2.1 Overview In shipyard or sea trial, in accordance with ATT manufacturer’s instruction, conduct a relatively low accuracy of temperature measurement of shipping cargos.

9.3 Calibration and Inspection of Multiple-point ATT for Custody Transfer Metering

9.3.1 Calibration before installation In accordance with the calibration procedure of single-point ATT provided in 9.2.1, inspect every temperature sensing element of ATT. Please refer to 5.3.4 for the requirement of accuracy.

9.3.2 Initial on-site inspection in shipyard or sea trial

9.3.2.1 Overview In shipyard or sea trial, in accordance with ATT manufacturer’s instruction, conduct initial inspection and debugging. When it is feasible, a method provided in 9.3.2.2 and

9.3.2.3 shall be adopted.

9.3.2.2 Component-based inspection

9.3.2.2.1 Temperature sensing element Use a recently calibrated PET to inspect temperature sensing element’s measurement data. When cargo hold approaches fully-loaded state, lower PET temperature measuring probe to the depth of placement of the temperature sensing element; move the temperature sensing probe up and down (within the range of around 300 mm), till the temperature becomes stable. The difference between the temperature measured by each temperature sensor of multiple-point ATT and the temperature measured by PET shall be within 0.75 °C.

9.3.2.2.2 Temperature transmitter Use temperature calibrator (for example, precise resistor or thermal calibrator) to simulate the input of three or more temperatures within the expected operating range of the vessels. Conduct inspection of ATT, excluding the temperature element. In each temperature point, the difference between ATT digital display temperature and resistor’s equivalent temperature shall be within 0.25 °C.

9.3.2.3 System-based inspection As an alternative method for independent calibration and inspection of temperature sensing element and transmitter, PET, which is calibrated before the inspection, may be adopted to conduct overall inspection of ATT; it would be better if the storage tank approaches fully-loaded state, and all the temperature sensing elements are completely immersed. Measure the liquid temperature in the depth of the temperature sensing element. In each measurement location, move PET temperature measuring probe up and down (within the range of around 300 mm), till the temperature becomes