GB/T 21246-2007 in English

《GB/T 21246-2007埋地钢质管道阴极保护参数测量方法》由TC355（全国石油天然气标准化技术委员会）归口，主管部门为国家标准化管理委员会。
本标准规定了埋地钢质管道阴极保护参数的现场测量方法。本标准适用于埋地钢质管道阴极保护参数的现场测量。钢质储罐外底板、滩海钢质管道和结构的阴极保护参数测量可参照采用。

1 Scope

This standard specifies site measurement method for cathodic protection parameters of buried steel pipeline.
This standard is applicable to site measurement for cathodic protection parameters of buried steel pipeline. Measurement for external bottom plate of steel storage tank, steel pipeline in beach and cathodic protection parameters of structure may be adopted by reference.

2 Normative References

The following normative documents contain provisions which, through reference in this standard, constitute provisions of this standard. For dated reference, subsequent amendments to (excluding correction to), or revisions of, any of these publications do not apply. However, the parties whose enter into agreement according to these specifications are encouraged to research whether the latest editions of these labels are applied or not. For undated references, the latest edition of the normative document is applicable.
JJG 123 Verification Regulation of D.C. Potentiometers
JJG 124 Verification Regulation of Amperemeters Voltmeters Wattmeters and Ohmmeters
JJG 123 Verification Regulation of DC Digital Voltmeter
JJG 123 Verification Regulation of Earth Resistance Meter
JJG 123 Verification Regulation of DC Digital Amperemetor
JJG 622 Verification Regulation of Megohmmeter

3 Terms and Definitions

For the purpose of this standard, the following terms and definitions apply.
3.1
The pipe-to-soil potential
It refers to potential difference between pipeline and its adjacent electrolyte (soil).
3.2
On potential
It refers to potential of measured structure on the electrolyte (soil) where the cathodic protection system is persistently operated.
3.3
IR drop
It refers to voltage drop produced within electrolyte (soil) between reference electrode and metal pipeline due to current flow according to Ohm's law.
3.4
Off potential
It refers to potential of measured structure on the electrolyte (soil) at the instant power failure.
Note: Generally, measurement shall be immediately carried out after cathodic protection current is cut off and before polarization potential has attenuated.
3.5
Voltage spiking
It refers to transient potential fluctuation on pipeline caused by transient process at the interrupted or applied instant of cathodic protection current.
3.6
Close-interval potential survey (CIPS)
It refers to such a kind of method that the reference electrode is moved in close-interval (generally 1m~3m) along ground surface at the top of pipe to measure the pipe-to-soil potential.
3.7
Intensive measurement technique
It refers to the technique that the pipe-to-soil potential and soil potential gradient in vertical direction are measured simultaneously.
Note: intensive measurement technique may identify defect in anti-corrosion coating and can calculate the potential after all the IR drops are eliminated at the defect area.
3.8
Equalising current
It is also referred to as "secondary current" and refers to current between polarization difference positions of structure after protection current is interrupted; equalising current may be the error source of IR drop potential.
3.9
Reference electrode method remote from pipeline
It refers to such method that the reference electrode is placed in soil relatively remote measured pipeline (ground potential is nulling) to measure the pipe-to-soil potential.
3.10
Remote earth
It refers to such area where any measurable voltage drop caused by current flow is absent between any two points.
3.11
Coating resistivity
It refers to product of coating resistance and coating surface area.
3.12
Coating resistance

1 Scope
2 Normative References
3 Terms and Definitions
4 General Requirement
5 Potential Measurement
6 Output Current of Sacrificial Anode
7 In-line Current
8 Resistivity of External Coating on Pipeline
9 Insulation Property of Insulated Joint (Flange)
10 Grounding Resistance
11 Soil Resistivity
12 Ground Leak Detection of External Coating on Pipeline