CZ4709U1 - Circuit arrangement for measuring values for determining corrosion state or cathodic protection degree of metal piping located in a steel protector - Google Patents

Description

Wiring for measuring values to determine the corrosion state or degree of cathodic protection of a metal pipe housed in a steel conduit

Technical Field The technical solution relates to a circuit for measuring values to determine the ^L corrosion state or degree of cathodic protection of a metal pipe housed in a steel pipe, in particular in pipe pipes under groundwater containing roads. The section of metal normally insulated piping located in the conduit under the rail or road is more or less electrically shielded from the point of view of the direct electric field, depending on the magnitude of the transient resistance - conduit affecting the current path between the conduit and the conduit. The proposed technical solution makes it possible to determine the degree of corrosion protection even in cases where the value of the transient resistance is between 0.1 and 1.0 Ohm.

BACKGROUND OF THE INVENTION

Economic and ecological reasons, as well as the operational safety of pipelines, especially of the sections housed in pipelines, require that corrosion velocity, particularly in areas of damaged external pipeline insulation, be limited to a depth of 40 years after the required economic service life. disturbing the wall only such that the pipe is still suitable for safe operation. The method of placing the metal piping in the steel conduit and the two ends of the conduit should not cause metal contact between the conduit and the conduit, and appropriate solutions should further ensure that ground water is not collected in the conduit. As these conditions are not often met, it is recommended in the relevant standards to check the condition of this system most often by measuring the transition resistance between the pipe and the conduit. If this resistance is greater than 1.0 ohm, the installation is considered to be OK. If the transient resistance was measured less than 1.0 ohms, it was assumed for cathodically protected pipelines that a greater or lesser part of the protective current enters the outer surface of the pipeline and flows directly through the galvanic-ion current path so that the pipeline at the interface - water electrolyte - the pipeline is not of sufficient current density to provide corrosion protection. The electrical shielding of the piping in the duct also occurs in the case of an insulated outer surface of the duct without being detected by conventional measurements on the terrain surface. So far, there is no suitable measuring technique to show that even with partial galvanic contact (with non-zero resistance between the conduit and the pipe) or shielding the insulation of the conduit, costly repairs or expensive remediation measures are not necessary. One of these measures is to fill the space between the pipe and the slurry protector, which is characterized by both high sealing capability and bactericidal and corrosion-inhibiting effects without toxic effects to higher organisms, for example based on bentonite with sodium benzoate and zinc oxide.

The method of measuring the transient resistance between the conduit and the piping R _n can be supplemented by a new measuring technique so that the above-mentioned deficiencies are largely eliminated. By analyzing the measured R _p value, its individual components can be obtained: ^»

-1GB 4709 U1

The resistance of two measuring cables and test leads - R _k , the longitudinal resistance of the adequate conduit section, and the longitudinal resistance of the adequate conduit section are in series in the ohmic meter circuit, while the two longitudinal resistors can be neglected while maintaining accuracy. Furthermore, in series, there is a transient resistance - pipe Rp '. Two series combinations of galvanic and ion current resistors are connected in parallel to this resistor Rp ': resistance of the external surface of the protector to ground - resistance of the respective soil electrolyte volume - resistance of the adequate section of insulated pipeline to ground. The second series combination: the resistance of the inner surface of the conduit against the water electrolyte - the resistance of the respective volume of water electrolyte between the conduit and the conduit - the resistance of the relevant section of insulated piping in the conduit including defects in the insulation against the water electrolyte.

These two parallel resistors (their series combination) are usually one order of magnitude greater than the resistance Rp '(with partial electrical shielding of the pipe section in the conduit), so that the overall measured Rp value somewhat affects the measurement in the direction of greater operational safety. up to 40% less than the actual value R ', so we can write the relation for the actual transient resistance h * pipe - pipe:

Rp '= Rp - R _k (ohms) (1) where Rp is the value measured by an ohmmeter (ohms)

R _k is the ohmic resistance of the measuring leads and connecting cables (determined by calculation according to the distance, cross-section and material of these conductors).

If the value of R _p '> 0 (practically at least 0.05 ohm), it is not a complete electrical contact (short circuit) and it is advantageous to follow the new technical solution.

The essence of the technical solution

These drawbacks are largely eliminated by the value measurement wiring to determine the corrosion state or degree of cathodic protection of the metal pipe housed in the conduit, which is based on the connection of an existing series-parallel circuit with a series combination of resistors with galvanic and ion current path: preferably high ohmic voltmeter - measuring cable - portable reference electrode, preferably immersion Cu / CuSO ₄ electrode - water electrolyte in the conduit - bare surface in defects of metal pipe insulation in the conduit - metal conduit to the conduit - insulated metal test lead

- measuring cable - measuring instrument. At the same time, an analogous measuring circuit is formed: a measuring device, preferably a high ohmic voltmeter

- measuring cable - portable reference electrode, preferably immersion Cu / CuSO ₄ electrode - water electrolyte in the conduit - inner bare surface of the conduit - conduit - insulated conductor of the conduit of the conduit of the conduit - measuring cable - measuring instrument.

The above connections, which are only implemented in cases where

-2E 4709 U1 when groundwater is permanently present in the conduit, they allow additional corrosion survey of the underpasses under the roads with cathodic protection on and off or under the influence of stray currents. These are mainly the following measurements:

- switch-on potential isolated section pipes in the pipe U ₂ (p) - tripping - U _at (p) - switch-on potential inner bare surface protectors U _z (ch) - tripping - H - - U _in From these measurements it is possible to determine the ohmic component of the potential in the aqueous electrolyte inside the protector (anodic and cathodic potential gradient): Au _ir = (Υ (Α) 1 + (υ (κ) || (mV) (2) where Δϋ (Α) = U _z (ch) - U _in (mV) (3) Δυ (κ) = _u (p) - u _z (p) (mV) (4)

Combining equations (3) and (4) we get:

Au _IR = U ₂ (ch) -U _v (ch) + U _v (p) -U _z (p), (mV) (5) where the resulting positive value corresponds to the current flow in the ground direction

- protector (anode - its inner surface) - aqueous electrolyte

- pipe (cathode) - current source.

At Δ U _IR > 10 mV (ie for current density j _Q = up to 20 mA.m ^-2 ), the piping in the conduit (bare spots in insulation defects) is protected with an efficiency of at least $ = 40 to 50%, which is sufficient purpose of protection (perforation does not occur even after 50 years of pipeline operation).

The connection can also be modified for areas with stray currents where the electric field intensity changes over time and depending on the stray current direction. Therefore, an additional connection to the ground surface is also created with a series combination of resistors, with a galvanic and ion current path, namely: portable multimeter

- measuring cable - portable reference electrode - soil electrolyte

- portable reference electrode - measuring cable - portable multimeter, wherein the reference electrodes are at least 1 m apart, preferably 10 m, in a direction perpendicular to the axis of the metal pipe. When using two high ohm voltmeters, the potentials of the lead-water electrolyte and the lead-water electrolyte are measured over a selected period of time, at least one pair of U _z (ch), U _z (p) being read and recorded at any one time. average state of stray currents in the locality. Next, a pair of values is determined which corresponds to the state where the stray current neither enters nor exits U _v (ch), U _v (p), then the ohmic potential component is determined from formula (5).

The corresponding potential values can also be determined by measuring the voltage gradient on the soil surface according to the connection described above, by recalculating the determined measured values over a distance of 1 m

-3GB 4709 U1 as the electric field intensity E (mV.m ^-1 ). The results of the measurement of the potential U (ch), u (p) and the electric field intensity E (with simultaneous reading on three instruments) are evaluated by plotting the E values on the ordinate axis and the U (ch) or U (p) values on the abscissa axis. we determine by extrapolation or interpolation (ie especially when E = 0).

The new technical solution fully respects the fact that the magnitude of the ohmic potential component Δϋ _ΙΚ depends not only on the intensity of the electric field in the given location, but also on the extent of damage of the corrosion insulation of the metal piping stored in the conduit.

Another embodiment of the invention can be concretized such that at least one auxiliary steel electrode simulating a defect in the metal pipe insulation is provided in the space between the protector and the insulated section of the metal pipe housed in the conduit, whose measuring cable is connected directly to the metal pipe via the above-ground measuring object. or via a portable multimeter for control measurements.

Overview of Figures in the Drawing Groundwater Measuring Circuits

The technical solution will be explained in more detail by means of the drawing, in which FIG. 1 shows the connection of the DC electrical circuit of an underground insulated metal pipe (with defects in insulation) housed in a protective tube which has been detected in the interspace (eg smell). of this invention and an additional measuring circuit useful only in stray current areas. Fig. 2 shows a wiring with an additional measuring circuit with an auxiliary steel electrode connected, usable in some cases of (complicated) underpasses under roads.

Examples

The connection can be practically shown on two examples, which are based on the basic parallel-parallel circuit of long-distance insulated steel piping, which is located in the steel underpass in the centering sleeves, which should guarantee electrically non-conductive bearing, the fronts of the tubes are sealed. Nevertheless, ground water has been detected in the duct, so that the pipeline (at the site of damaged insulation) in the duct may be corroded. From the point of view of the direct current circuit, the ion current path is also used in addition to the galvanic current path according to FIG. In the present case, two parallel resistors, consisting of series combinations, are connected between the resistor 18, i.e. the soil electrolyte and the resistor 7, i.e. the metal pipe buried in the ground (outside the conduit). In the first - galvanic current path, these are the resistors: .10., Ie the outer bare surface of the protector (ground resistance) - 12, ie the protector (as a conductor) - 13 ie the transient resistance of the metal pipe against the protector R _p '- 6 ie metal pipes in the conduit (as a conductor). In the second galvanic-ion current path, the following resistors are in series: 12 ie the conduit (as conductor) - 11 ie the inner bare surface of the conduit (transient resistance to water in the conduit) - 4. ie. water electrolyte in the conduit (resistance of the respective water volume) -5 ie bare surface in defects of the metal pipe in the conduit (transient resistance of bare spots against water) - 6 ie the metal pipe

-4GB 4709 UI in the conduit.

There are 2 measuring circuits connected to this basic circuit according to the technical solution. The first circuit is for potential measurement: metal pipe 5 - water electrolyte 4: measuring instrument 1 preferably high / coohm voltmeter - measuring cable 2 - immersion Cu / CuS0 ₄ reference electrode £ - water electrolyte in the protector £ - bare surface in de / fects metal pipe insulation 5 - metal pipe in the conduit (as conductor) - insulated conductor of the metal pipe measuring outlet 8 - measuring cable 9 - measuring instrument 1.

The second measuring circuit is for measuring the potential: inner bare surface 11 - water electrolyte 4: meter 1 - measuring cable 2 - immersion Cu / CuS0 ₄ electrode £ - water electrolyte in the duct 4 - inner bare surface 11 - duct 12 as conductor - insulated conductor of test lead 14 - measuring cable 9 - measuring instrument 1.

In stray current areas, additional wiring is used to determine the electric field strength: portable multimeter 15.

- measuring cable 16 - portable Cu / CuSO ₄ reference electrode 17

- soil electrolyte 18, ie placement of a reference electrode diaphragm on the ground surface - portable Cu / CuSO ₄ reference electrode - measuring cable 20 - portable multimeter 15.

Fig. 2 shows the connection of the measuring series combination of resistors to the basic wiring of the conduit-pipe system as a corrosion sample in the conduit: auxiliary steel electrode 21 - water electrolyte in the conduit 4 - metal conduit in the conduit 5 - test leads 22, 23 - auxiliary steel electrode 21. For periodic measurements, a portable multimeter 15 is connected between the cables 22 and 23.

The advantages of wiring according to the technical solution can be demonstrated on two examples from practical application. Example 1 shows a case of steel pipe with asphalt insulation of average quality cathodically protected, embedded in a steel pipe (with bare surfaces) under the road. Example 2 describes the practical application of the method in stray current regions.

Example 1

Steel pipes 5, 6, 7 of profile 720/9 mm provided with external asphalt insulation of thickness. 4 mm below the 1st class road is located in a steel pipe 10, 11, 12 DN 1200 length 53 m. On both ends of the pipe is a steel sniff DN 80 led above the ground and piping 6 and protector 12 are connected measuring leads 8, 14 .. Standard measurements have shown that the groundwater rises to a level of 1.0 m below the surface and the interspace in the conduit 5 - 11 is completely filled with water 4, the transient resistance of the conduit - pipe 13 was detected by an ohmmeter Standard D 3950 R _n = 0.27 of which, the resistance of the connecting conductors 2, 8, 9, 14 R _k = 0.08 ohm. It is therefore a partial metal contact between the pipe 5 and the conduit 11, although the contractor has already carried out a repair under the complaint procedure (reconstruction of the conduit fronts). Completely removing this part of the tangent metal contact would require costly and very difficult repairs, and additionally would result in a loss of at least 1.0 million CZK of natural gas from the relevant section of the pipeline.

An on-site investigation revealed that the pipeline has been in operation for more than 2 years, is cathodically protected, and the nearest cathodic protection station is 1.7 km away. After insertion of the auxiliary steel electrode 21 by the snifter into the conduit, a transition resistance between this electrode 21 and the 5-6 R ₂₁ ⁼ 185.7 ohm line was found.

Using the conversion factor for the shape and area of the electrode 21 S = 20 m ² , the specific water resistance in the protective tube was determined:

(λ = a. R ₂₁ = 0.14 - 185.7 = 26 ohmmeter.

After connecting the auxiliary steel electrode 21 to line 6, the switching potential was measured on the other side of the underpass by the Unigor 6e using a submersible Cu / CuSO ₄ reference electrode 3, which was pushed into the space between the protector 11 and line 5 by the sniffer. in cases where the auxiliary steel electrode 21 has been connected or disconnected from line 6, it is therefore an average quality of insulation. The potential measurement was then carried out by switching the cathodic protection station on and off at 30 s intervals for 10 minutes with the following results:

u ₂ (ch) = -0.55 V; U _z (p) = -0.615 volts

U _v (ch) = -0.55V; U _v (p) = -0.575V

Ohmic potential component according to (5):

Δ U _IR = -0.55 + 0.55 - 0.575 + 0.615 = 0.040 V

For the selected area of damaged pipe insulation 5 in the protector 11 for S = 20 m ² , the protective current density is calculated from the relation:

where

Joυ jo =

IR (mA.m ^-2 )

ČP? S ^1/2 + _ir ft Au = 40 mV i.e. ohmic potential component (6) yeah

S t

?

= 0,4, ie shape coefficient for round plate = 0,002 m ² ie simulated bare pipe insulation area = 0,004 m ie insulation thickness = 26,0 ohmm ie water resistivity in the duct

0.4. 26 .0,002

1/2 + 26

0.004

0.465 + 0.104 = 70.3 mA.m

-6GB 4709 U1

From the existing cathodic protection system was derived dependence of polarization components of the potential protective current density i.e. _Δυ ρο1 = f (jg) of still water for resistivity in the range of y '= 5 to 40 ohm m: j _Q value = 70.3 mA .m “ ² corresponds

AUpoi = 70 mV.

For given conditions the following dependence on the polarization component of the potential Δυ _ρο1 (ν) is valid for the efficiency of cathodic protection:

° - ² - ^Au pol = 100 - 10 θ ' ¹ (%) (7)

0.2 - 0.07 θ · = 100 - 10 ^0/1 = 80

At corrosion rate in spontaneous corrosion conditions K =

0.15 mm.a ” ¹ and cathodic protection efficiency 9 = 80% will be metal loss in cathodic protection:

K ’=

K (100 - 3) (mm.a mm.year ^-1 ) (8)

After reaching

K ¹

100 ALIGN!

0.15 (100 - 80)

0,03 mm.year

100 ALIGN!

At the required economic service life of the pipeline τ = 40 years and at a corrosion rate K '= 0.03 mm.year “ ¹ , the depth of failure at the end of operation shall be: h = 40. 0.03 = 1.2 mm.

For pipe thickness t = 9.0 mm and depth of failure h =

1.2 mm remains intact t - h = 9.0 - 1.2 = 7.8 mm wall, which fully satisfies. There is therefore no need for further action.

Example No.2 "Steel pipes 5, 6, 7 DN 500 is stored in the protector 10, j ϋ / 12 DN 800 in a length of 65 m below the road close to ^a measuring DC electrified railway. Pipe resistance 13 R _p = 0.66 ohms, conductor resistance 2, 8, 9, 14 R _k = 0.56 ohms (this is a long combined conductor), so the intrinsic resistance R _p '= 0.66 0.56 = 0.1 ohm; it is therefore a partial galvanic contact between pipe 5 and protector 11. The protector is flooded with water 4 with a resistivity of $ = 12.4 ohm.m. A reference Cu / CuSO ₄ electrode in immersion treatment 3 was inserted into the space between the conduit 11 and the pipe 5 by the sniffer DN 80. Two measuring instruments 1 Unigor 6e were always connected to this electrode χ by-7GB 4709 U1, the minus pole of one instrument was connected to the measuring terminal 8 from pipeline 6 DN 500, the minus pole of the other instrument 1 was connected to the measuring terminal 14 12 DN 800. A pair of portable Cu / CuSO ₄ electrodes 17, 19 were placed near the end of the conduit, on the ground surface 18, at a distance of 14 m perpendicular to the pipe 7. The distal electrode 17 was connected to the plus pole of the meter 15. Unigor 4p, closer electrode 19 k minus pole »* instruments 15. Results of measurement of potentials U and slope

Δυ (simultaneous reading on three instruments 1, 1, 15):

1. Δυ (14m) = 100mV; U ₂ (ch) = -0.57 V; U _z (p) = -0.61 volts

E ·, = 100/14 = 7,14 mV.m ^-1 ie average value in given locality

2. =υ = 250 mV; U _p (ch) = -0.56 V; U _p (p) = -0.75 V

E ₂ = 250/14 = 17,85 mV.m “ ¹ ie max value

3. Δυ = 0? U _v (ch) = -0.58 V; U _v (p) = -0.54 V

E ₃ = 0; Note - Subtracted, not extrapolated.

According to relationship (5):

Δϋ _ΙΚ = -0.57 + 0.58 - 0.54 + 0.61 = 0.080 V

The ohmic component of the potential of 80 mV (this is an average value, the pipeline is located in the cathodic range of stray currents) provides sufficient protection even for large pipe insulation failures, eg for S = 0.1 m ² ; by relation (6):

j ₀ = -7-73- = 4 9.4 mA.m *

0.4. 12.4. 0.1 ^{1 / ζ} + 12.4. 0.004

This corresponds to Δυ _ρο ^ = 56 mV and 72%.

Therefore, no further action is needed.

The wiring according to the technical solution should be used for bare or externally insulated steel piping installed on steel insulated pipelines, which are cathodically protected or are affected by stray currents from DC electrified rail transport. It can be used for both pipelines and distribution networks in built-up areas. 0

Claims (5)

1. Measurement values wiring to determine the corrosion state or cathodic protection level of metal piping embedded in a steel conduit »producing a parallel-parallel circuit with a dominant conduit-conduit resistance affecting the current path at the conduit-conduit interface, A series combination of resistors with a galvanic and ionic current path is connected to the series-parallel circuit in the order of a measuring instrument (1), preferably a high ohm voltmeter, a measuring cable (2), a portable reference electrode (3), preferably a submersible Cu / CuSO ₄ electrode, aqueous electrolyte (4) in the conduit, bare surface in metal pipe insulation defects (5) in the conduit, metal conduit (6) in the conduit, insulated conductor (8) of the metal conduit measuring lead, measuring cable (9) and measuring device (1) ). Connection according to claim 1, characterized in that a further series combination of resistors with a galvanic and ion current path is connected to the series-parallel circuit in the order of a measuring instrument (1), preferably a high ohm voltmeter, a measuring cable (2), a portable reference electrode ( 3) preferably an immersion Cu / CuSO ₄ electrode, aqueous electrolyte (4) in the conduit, inner bare surface of the conduit (11), conduit (12), insulated conductor (14) of the conduit measuring outlet, measuring cable (9), measuring instrument ( 1). Connection according to claims 1 and 2, characterized in that at least one portable reference electrode (3) is arranged in the space between the bare surface in the insulation defects of the metal pipe (5) in the duct and the inner bare surface of the duct (11). to the first pole of the meter (1), the second pole of the meter (1) being connected to the metal pipe (6) and then to the protector (12). Connection according to claims 1 and 2, characterized in that it comprises an additional connection on the ground surface with a series combination of resistors with a galvanic and ion current path, comprising a portable multimeter (15), a measuring cable (16), a portable reference electrode (17) , a soil electrolyte (18), a portable reference electrode (19), a measuring cable (20), a portable multimeter (15), wherein the reference electrodes (17, 19) are at least 1 m apart, preferably 10 m, in a direction perpendicular to the axis of the metal pipe (7). Connection according to claim 1, characterized in that at least one auxiliary steel electrode (21), preferably steel, is arranged in the space between the bare surface in the defects of the insulation of the metal pipe (5) in the duct and the inner bare surface of the duct (11). simulating a defect in the metal pipe insulation which is detachably connected to the metal pipe (6) or to the portable multimeter (15).