GB/T 17283.2-2026 Natural gas—Determination of moisture—Part 2：Determination of water content by oscillation frequency difference method English, Anglais, Englisch, Inglés, えいご
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ICS 13.220.10
CCS H 57
National Standard of the People's Republic of China
GB/T 17283.2-2026
Natural gas - Determination of moisture - Part 2: Determination of water content by oscillation frequency difference method
天然气 水分的测定 第2部分：用振荡频差法测定水含量
Issue date: 2026-01-28 Implementation date: 2027-02-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
Introduction
1 Scope
2 Normative References
3 Terms and Definitions
4 Principle
5 Apparatus and Equipment
6 Instrument Measurement
7 Instrument Calibration
8 Processing of Result Data
9 Repeatability
10 Test Report
Determination of Water in Natural Gas — Part 2: Determination of Water Content by Oscillation Frequency Difference Method
WARNING: This document does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this document to establish appropriate safety and health practices and ensure compliance with any national regulatory conditions.
1 Scope
This document describes the principle, apparatus and equipment, measurement procedure, instrument calibration, processing of result data, repeatability, and test report for the determination of water content in natural gas by the oscillation frequency difference method.
This document is applicable for the on-line determination of water content (volume fraction) in pipeline natural gas, within the measurement range of 5 × 10⁻⁶ to 2000 × 10⁻⁶.
2 Normative References
The following documents contain provisions which, through normative reference in this text, constitute essential provisions of this document. For dated references, only the edition cited applies. For undated references, the latest edition (including any amendments) applies.
GB/T 13609 Guidelines for Sampling of Natural Gas
GB/T 20604 Natural Gas — Vocabulary
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 20604 and the following apply.
3.1
oscillator
A thin wafer, operated under a constant voltage, capable of oscillating at a specific frequency, where its oscillation frequency changes with variations in the wafer's mass.
NOTE: Oscillators are generally classified as measurement oscillators and reference oscillators. The measurement oscillator is enclosed within the measurement cell and can contact the sample gas; it is used to measure the mass of water adsorbed on its wafer. The reference oscillator is completely sealed within a closed reference cell, not connected to the outside atmosphere. When supplied with a constant voltage, it generates a constant oscillation frequency, used to calibrate the measurement oscillator, whose performance may change over time.
4 Principle
A thin wafer within the detection chamber is coated with a layer of sensitive hygroscopic material. Under certain temperature conditions, when a constant voltage is applied, it generates an oscillation frequency. When a natural gas sample flows over the wafer, the hygroscopic material on its surface adsorbs water from the natural gas. The change in mass on the wafer's surface alters its natural oscillation frequency, and the oscillation frequency changes proportionally to the change in mass of the adsorbed water on the coating. The water mass is determined by measuring the difference in the oscillation frequency of the wafer. Through conversion, the corresponding water volume is obtained. Combining this with the injection volume of the sample gas yields the water content expressed as volume fraction. The relationship between water mass and oscillation frequency is shown in Formula (1):
The working principle of determining water content by the oscillation frequency difference method is illustrated in Figure 1.
During the reference phase, the sample gas flows through a dryer to remove water before entering the measurement cell. The oscillation frequency of the wafer at this time is f₁. The dry gas oscillation frequency fᴅ is the difference between the measurement cell frequency at this time and the oscillation frequency of the reference cell. During the measurement phase, the moist sample gas (containing water) enters the measurement cell directly without passing through the dryer. The oscillation frequency of the wafer at this time is f'₁. The wet gas oscillation frequency fₛ is the difference between the measurement cell frequency at this time and the oscillation frequency of the reference cell. This yields the oscillation frequency difference Δf of the wafer under the same gas background conditions, differing only in water content. Combining this with Formula (1) gives the mass of water adsorbed on the wafer.
5 Apparatus and Equipment
5.1 Composition of the Analysis System
An on-line moisture analysis system using the oscillation frequency difference method shall consist of a sampling unit, a sample conditioning unit, an on-line moisture analyzer using the oscillation frequency difference method (hereinafter referred to as the analyzer), a sample vent line, and a signal transmission unit.
A schematic diagram of the workflow for the on-line moisture analysis system using the oscillation frequency difference method is shown in Figure 2.
5.2 Sampling Unit
The sampling unit includes the sample transfer line, sampling probe, and associated pressure regulators. It must be capable of obtaining a representative and stable sample gas flow from the pipeline, minimizing the time delay of the sample within the line. During the sampling and pressure reduction process, condensation of water shall be prevented. During sample transfer, the sample transfer line and pressure regulators shall have insulation and heat tracing capabilities. The heat tracing temperature shall be higher than the gas dew point temperature to avoid water condensation in the sample gas due to low ambient temperature during transport.
The installation of the sampling probe shall comply with the requirements of GB/T 13609.
5.3 Sample Conditioning Unit
The sample conditioning unit shall be installed upstream of the analyzer. It includes pressure regulating devices, flow meters, and filters capable of removing particulates and liquid hydrocarbons. The pressure regulating device should preferably have insulation and heat tracing measures to ensure the sample gas entering the instrument is in a gaseous state. Additionally, the sample conditioning unit shall be connected to a bypass line, allowing rapid venting of gas from the line to ensure a fast flow of sample gas to the analyzer.
5.4 Analyzer
The analyzer shall be capable of stably measuring water content. It mainly consists of a sample measurement oscillator, a reference oscillator, a piezoelectric measuring device, a dryer, a moisture generator, a thermostatic enclosure, and a temperature controller. The piezoelectric measuring device acquires oscillation signals from the measurement and reference oscillators, enabling alternating measurement of the oscillation frequencies of dry gas and sample gas. The dryer can reduce the water content (volume fraction) in the sample gas to below 0.025 × 10⁻⁶, producing a reference gas. The moisture generator can produce a humid gas with a known water content for parameter correction of the instrument's measurement status. The thermostatic enclosure and temperature controller can maintain the entire instrument enclosure temperature within the required range for the instrument.
5.5 Signal Transmission Unit
Transmits the test results to the station control computer using a specific communication protocol.
5.6 Sample Vent Line
A line for venting the sample gas after it has passed through the analyzer, connected to the analyzer's measurement outlet. The vent line shall have provisions for draining liquid and preventing backflow.
6 Instrument Measurement
6.1 Preparations
6.1.1 Install the sampling unit, sample conditioning unit, analyzer, vent line, and signal transmission unit as shown in Figure 2, and verify that the pressure ratings of all components are suitable for the field process conditions.
6.1.2 Check and verify that components such as the sample transfer line, sampling probe, and flow meters are clean and dry. If necessary, all pipelines and devices upstream of the analyzer should be purged.
6.1.3 Check and verify that all pipelines and components through which the gas flows are free from leaks.
6.2 Sample Testing
6.2.1 Adjust the flow rate and pressure of the sample gas according to the analyzer's requirements, and power on the analyzer.
6.2.2 Adjust the bypass valve. The flow rate should preferably be controlled between 0.5 L/min and 1 L/min to reduce the residence time of the sample gas in the pipeline and avoid excessive pressure drop that could cause water condensation. Thoroughly purge and replace the gas in the entire pipeline system with the sample gas.
6.2.3 Set various parameters according to the analyzer's requirements and measure the sample gas.
6.2.4 When the analyzer reading stabilizes, record the water content (volume fraction) value.
NOTE: If needed, the water content value can be combined with parameters such as the gas source pressure, using specific conversion relationships, to calculate the water dew point temperature of the natural gas.
7 Instrument Calibration
The analyzer should be calibrated using certified reference materials for water or a water content measuring instrument with a higher accuracy level.
Calibration should be performed annually or whenever the analyzer undergoes major maintenance.
