CS220487B1 - Method for determining the average insulation conductivity in a ground-laid insulated pipe - Google Patents

Abstract

The invention solves the problem of measuring the average insulation conductivity of buried pipelines, even in areas with stray currents. The essence of the invention is a method of determining the average insulation conductivity by calculating from the measured attenuation of the pipeline, considered together with the surrounding soil as a coaxial line, where the pipeline is the inner conductor and the surrounding soil is the outer conductor. For the pipeline, the primary parameters are first calculated from the known dimensions and the dependence of the attenuation on the primary parameters is used to calculate the pipeline run per 1 km and then the average insulation conductivity per 1 m2. The invention can be used in the gas industry, water industry, petrochemicals and related fields.

Description

The invention solves the problem of measuring the average conductivity of insulation in buried pipes as well as in stray current areas. The subject of the invention is a method of determining the average conductivity of an insulation by calculating from the measured attenuation of a pipe taken together with the surrounding soil for coaxial conduction, where the pipe represents the inner conductor and the surrounding soil the outer. For pipelines, the primary parameters are calculated from the known dimensions and the piping leakage per 1 km is calculated from the attenuation on the primary parameters and then the average insulation conductivity per 1 m ² is calculated. The invention can be used in the gas, water, petrochemical and related fields.

The present invention relates to a method for determining the average conductivity of a ground insulated pipe.

So far, the average conductivity of insulation of buried pipes has been measured by DC methods based on the principle of direct current and line voltage measurement.

These methods are vastly inaccurate in stray current areas and therefore often unusable. Another disadvantage is the need to use special current outlets, which are not built on many piping systems and therefore the average insulation quality cannot be determined at all.

When using DC methods, it is also necessary to interrupt the DC current of up to several tens of amperes at several-second intervals, which places considerable demands on the equipment used, which must be specially designed for this measurement. The direct current that is fed into the pipeline must usually have several tens of amperes. In order to push a current of this magnitude into the pipeline, a special grounding with low ground resistance around one ohm must be used.

Such grounding is very difficult to build and in practice only anode grounding fulfills these requirements. Up to 50 amperes can also be forced into the pipeline by connecting the rectifier with anode ground. These facts limit the applicability of DC methods only where cathodic protection is already in place and the quality of insulation by DC methods cannot be checked for new, freshly included pipes.

These disadvantages, i.e. the measurement of insulation quality only in areas without stray currents and in pipelines where cathodic protection has already been installed, are eliminated by the method of determining the average conductivity of the insulated ground pipeline according to the invention, which consists in dividing the pipeline into Sections whose length is chosen according to the power of the low-frequency signal source and the attenuation of the low-frequency signal passing through the pipeline is measured on each section by connecting the low-frequency signal source approximately 2 km before the measured section. the end of this section measured signal level of the selective voltmeter tuned to the frequency of the low frequency signal source, the average conductivity of the insulation of the section [/ rS / m ^2] is calculated according to well ⁶

G ™ -. - _- f

21T> r _of 2B who. A = 4 A ^ f1AlTfjZLC-fStrfRoZ B ^ (2JrrL) ^z f D = (2a) ^From R + 8 (Kf) ² RLC, and is the measured attenuation per 1 km of pipeline in [dB] at fv [Hz], which is calculated by the relationship

1o _&

Lh where U _x is the low-frequency signal at the beginning of the section in [V], U ₂ is the low-frequency signal in [V] at the end of the measured section of 1 in [km], R, L and C are pipe parameters calculated according to = £ · J 'ιο ^ εν c --- r- j

19 ^ -¾

V * t * ⁴ »

where η is internal pipe radius in [mm], s is pipe wall thickness in [mm], v is pipe insulation thickness in [mm], p _v is pipe resistivity in [fm ² / m], pz is soil resistivity v [ifímm ² / m], f is the frequency in [Hz] at which attenuation measurements are taken a, ε, is the relative permittivity of the pipe insulation, μΓ is the relative permeability of the steel from which it is made is calculated as the arithmetic mean of the values calculated for each section.

The main advantage of the invention is the possibility of measuring the average conductivity of the insulation even in areas with stray currents due to the use of a low-frequency signal which is not affected by stray currents in any way. Another advantage is that any galvanic connection to the pipe is sufficient to measure the low-frequency signal level on the pipe.

The average conductivity of the pipe insulation shall be calculated as the arithmetic mean of the values determined for the sections of that pipe. The length of the sections on which the pipeline whose average conductivity is to be determined is divided is selected with respect to the power of the low-frequency signal source, the sensitivity and selectivity of the selective voltmeter, and the interfering signals. The attenuation of the low-frequency signal is measured in the individual sections in the manner shown in the drawing.

A portable low-frequency signal source 2 is connected between line 1 and anode ground 4. The portable selective nano-meter 3 is connected to the measurement terminal 6 and the ground 5. On the line 1, there is another measuring terminal 7 at a distance of 5 km. is the measured average conductivity of the insulation. The distance between the test lead 6 and the connection point 8 of the low-frequency signal source is 2 km.

The attenuation of the low-frequency signal is calculated for the individual segments according to the relation where U! is the signal level measured by the selective voltmeter between the measurement terminal 6 and ground and U ₃ is the signal level measured between the measurement terminal 7 and the ground and 1 is the distance between the measurement terminals.

The attenuation measurement is performed at a frequency ranging from 10 [Hz] to 1 [kHz] with respect to interference and desired range, as the frequency increases, the attenuation of the low frequency signal increases and the range of the low frequency signal source decreases.

In order to calculate the average conductivity of the insulation, the following parameters must be known: inner pipe radius r _b pipe wall thickness s, pipe insulation thickness v, pipe resistivity p _v , soil resistivity p _z , relative permeability of the steel from which pipe μ _Γ is made relative permittivity of pipe insulation e _r .

The inner pipe radius r _x can be calculated from the known nominal pipe size. Soil resistivity is the average value of several measurements taken along a measured section. The average conductivity of the pipe insulation is calculated according to ¹ ° ⁶ -P + ^ D ^Z + 4AB ”2ΊΓ ^ 28

A = 4 «? + (4aVf) * LC- (2ffC) ^z 8 = (2 ^^,

D = (2a) ^From R + 8 (fff) ^From RLC, = * ^Δ

The quantity a is the attenuation per 1 km of pipe measured and calculated as above, f is the frequency in [Hz] at which the attenuation was measured. R, L and C are the parameters you pipe reckoned of relations ^{Λ (10} · V / ^{L "2ίΓ ΐ} (Γ ★ ^{2 '10 (1 +} y £) / _ ~ ¹⁰ ^ ⁶ 18 ^ ^C

The quantity r ₃ is the outer radius of the pipe with insulation and can be calculated according to the relation r ₃ = r ₂ + v

The quantities r ₍ , s and c) must be represented in formulas in [mmj, distance 1 between the measuring leads at the beginning and the end of the measured section in [km], the soil resistivity p _z and the pipe resistivity p _v v [QmmVm],

To check the correctness of the calculation or measurement, it is appropriate to measure and calculate the average insulation conductivity for several frequencies. At frequencies from 10 [Hzj to one [kHz] the average insulation conductivity must always be the same. In case that different insulation conductivity is measured at different frequencies, there is an error in the measurement, eg a foreign structure is connected to the pipeline, the insulation flange is disconnected, etc. on the measured section.

For easy determination of the average conductivity of the insulation, tables have been compiled for different types of pipes. Knowing the nominal size, wall thickness and insulation thickness for the frequencies 10, 15, 20, 25, 35, 80, 140, 230, 400 and 1000 [Hz] and attenuations 1 - 20 [dB / km], the average conductivity can be read from the table pipe insulation.

The invention can be used, for example, in the gas, water, petrochemical and related fields.

Claims (1)

Method for determining the average conductivity of insulation of buried pipeline in ground, characterized in that the pipeline is divided into sections, the length of which is selected according to the power of the low-frequency signal source, and the attenuation of the low-frequency signal passing through the pipeline is measured from invents Hoz are disconnected all adjacent structure connects the source of the low frequency signal and the beginning and end of this section, the measured signal level of the selective voltmeter tuned to the frequency of the source of the low frequency signal, the average conductivity of the insulation of the section [μδ / πι ^2] is calculated by relationship 10 *. -D + fa ^ tAB 21Γ * _Ζ '2 B Where A = (4a17) ^Z LC ~ (2rfRC) ^ · B · (2JTfL) D ^(2a) R-8 (7H) ^from the RLC, and the measured attenuation value per 1 km of the pipeline in [dB] at the frequency f in [Hz], which is calculated according to the relationship log AT, U, where Ui is the level of low frequency signal at the beginning of the section in [V], U ₂ is the level of low frequency signal in [V] at the end of the measured section of 1 in [km], R, L and C are pipe parameters calculated R = γ ^r 2 '2Λ ^{+ (} (Vr VrA ♦ ⁼ ' (bo ' ¹ t ^ _r ^ r + + 2-10 ^. ^) 78 / ~ ^ ^r z where η is internal pipe radius in [mm], s is pipe wall thickness in [mm], v is pipe insulation thickness in [mm], p _v is pipe resistivity in [Qmm ² / m] , pz is the soil resistivity in [fm ² / m], f is the frequency in [Hz] at which attenuation measurements are taken and, εΓ is the relative permittivity of the pipe insulation, μ ,, is the relative permeability of the steel from which the pipe is made , the resulting value of the average conductivity of the insulation of the entire pipeline is calculated as the arithmetic mean of the values calculated for each section.