阅读说明：本技术 一种油气田管道阴极保护系统失效原因的分析方法 (Analysis method for failure reasons of oil-gas field pipeline cathode protection system ) 是由 唐德志 陈宏健 杨莉娜 李冰 谷坛 付勇 徐英俊 于 2020-05-07 设计创作，主要内容包括：本发明公开了一种油气田管道阴极保护系统失效原因的分析方法,属于管道腐蚀控制领域。该方法包括：确认待排查油气田管道的阴极保护系统类型；若为牺牲阳极阴极保护系统,判断牺牲阳极自身是否失效,若否,则进行步骤S3；若为外加电流阴极保护系统,则判断外加电流阴极保护装置是否失效,若否,则进行步骤S3；步骤S3、判断绝缘装置是否失效,若否,则进行步骤S4；步骤S4、判断管道杂散电流干扰水平是否在接受范围内,若否,则待排查油气田管道阴极保护系统失效原因为管道杂散电流干扰。该方法针对性地对油气田管道阴极保护系统的失效原因进行分析,具有较高的准确度,获得较好的排查效果。(The invention discloses an analysis method for failure reasons of an oil-gas field pipeline cathode protection system, and belongs to the field of pipeline corrosion control. The method comprises the following steps: confirming the type of a cathodic protection system of an oil-gas field pipeline to be investigated; if the sacrificial anode is a sacrificial anode cathode protection system, judging whether the sacrificial anode per se fails, and if not, performing step S3; if the system is an impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails, and if not, performing step S3; step S3, judging whether the insulation device fails, if not, performing step S4; and step S4, judging whether the interference level of the pipeline stray current is in an acceptable range, if not, judging that the reason of the failure of the oil-gas field pipeline cathode protection system to be inspected is the pipeline stray current interference. The method analyzes the failure reason of the oil-gas field pipeline cathode protection system in a targeted manner, has high accuracy and obtains a good investigation effect.)

1. A method for analyzing failure reasons of a cathodic protection system of an oil and gas field pipeline is characterized by comprising the following steps:

step S1, according to the design scheme of the cathodic protection system of the target oil and gas field pipeline system, confirming that the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system or an impressed current cathodic protection system;

step S2, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system, judging whether the sacrificial anode per se fails, if so, judging that the reason for the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is that the sacrificial anode per se fails, and if not, performing step S3;

if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is an impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails, if so, judging that the cause of the failure of the impressed current cathodic protection system of the oil and gas field pipeline to be inspected is the failure of the impressed current cathodic protection device, and if not, performing step S3;

step S3, judging whether the insulating device fails, if so, determining that the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the insulating device, and if not, performing step S4;

and S4, judging whether the interference level of the stray current of the pipeline is within an acceptable range, if so, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the damage of the anticorrosive coating of the pipeline, and if not, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the interference of the stray current of the pipeline.

2. The method for analyzing the failure reason of the oil and gas field pipeline cathodic protection system according to claim 1, wherein said determining whether the impressed current cathodic protection device fails comprises:

step 201, judging whether the constant potential rectifier fails, if so, judging that the reason for the failure of the oil-gas field pipeline cathode protection system to be inspected is the failure of the constant potential rectifier.

3. The method for analyzing the failure reason of the oil and gas field pipeline cathodic protection system according to claim 2, wherein said determining if the impressed current cathodic protection device has failed further comprises:

if the potentiostat is not in failure, the step 202 is carried out to judge whether the anode ground bed is in failure, and if so, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the anode ground bed.

4. The method for analyzing the failure reason of the oil and gas field pipeline cathodic protection system according to claim 3, wherein said determining if the impressed current cathodic protection device has failed further comprises:

if the anode ground bed does not fail, step 203 is carried out, whether the reference electrode fails or not is judged, if yes, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is that the reference electrode fails, and if not, step S3 is carried out.

5. The method for analyzing the failure reason of the oil and gas field pipeline cathode protection system according to claim 1, wherein the judging whether the sacrificial anode itself fails comprises:

obtaining critical grounding resistance Rz of sacrificial anode group in sacrificial anode cathodic protection system_max；

Measuring the actual grounding resistance Rz of a sacrificial anode group in service in a sacrificial anode cathodic protection system;

if Rz<Rz_maxThe sacrificial anode set is valid;

if Rz>Rz_maxAnd if so, the sacrificial anode group fails, so that the sacrificial anode self is judged to fail.

6. The method for analyzing the failure reason of the oil and gas field pipeline cathode protection system according to claim 5, wherein the judging whether the sacrificial anode itself fails further comprises:

according to the critical grounding resistance Rz of the sacrificial anode group in the sacrificial anode cathodic protection system_maxObtaining the critical grounding resistance Rd of the single sacrificial anode in the sacrificial anode group_max；

Measuring the actual grounding resistance Rd of the single sacrificial anode;

if Rd<Rd_maxThen the single sacrificial anode is effective;

if Rd>Rd_maxAnd if so, the single sacrificial anode fails, so that the judgment sacrificial anode fails.

7. The method for analyzing the failure reason of the oil and gas field pipeline cathode protection system according to claim 1, wherein the judging whether the insulation device fails comprises the following steps:

measuring the potential difference of two ends of the insulating device by using a potential method;

if the potential difference is less than or equal to 100mV, the isolation device is disabled, otherwise, the isolation device is enabled.

8. The method for analyzing the failure reason of the oil and gas field pipeline cathode protection system according to claim 1, wherein the judging whether the interference level of the pipeline stray current is within an acceptable range comprises the following steps: testing the alternating current density i of the oil-gas field pipeline to be inspected_ac；

If i_ac＞100A/m²If the pipeline stray current interference level is not within the acceptable range;

if i_ac≤100A/m²And then the interference level of the stray current of the pipeline is within the acceptance range, and the polarization potential E of the pipeline of the oil and gas field to be inspected is further measured_p；

If E_pThe interference level of the stray current of the pipeline is less than or equal to-850 mV, and the interference level of the stray current of the pipeline is in an acceptable range;

if E_p> -850mV, the pipe stray current interference level is not within the acceptable range.

9. The method for analyzing the failure reason of the oil and gas field pipeline cathode protection system according to claim 3, wherein the judging whether the anode bed fails comprises the following steps:

if the grounding resistance of the anode ground bed meets the requirement of the following formula, the anode ground bed does not fail, otherwise, the anode ground bed fails;

I_cpmax·R_g＜0.7U

in the formula I_cpmaxIs the maximum expected protection current requirement in units of a;

R_gis an anodeThe ground resistance of the ground bed is in omega;

u is the rated output voltage of the potentiostat and has the unit V.

10. The analysis method for the failure reason of the oil and gas field pipeline cathode protection system according to claim 4, wherein the judging whether the reference electrode fails comprises the following steps:

acquiring the potential of the reference electrode;

judging whether the error between the potential of the reference electrode and the potential of a standard reference electrode exceeds 5 mV;

if it exceeds 5mV, the reference electrode fails, otherwise, the reference electrode does not fail.

Technical Field

The invention relates to the field of pipeline corrosion control, in particular to an analysis method for failure reasons of an oil-gas field pipeline cathode protection system.

Background

Cathodic protection refers to the process of energizing the protected object to become a cathode, thereby slowing and avoiding corrosion, and comprises two types: one is impressed current cathodic protection, also known as forced (current) cathodic protection, and the other is sacrificial anodic cathodic protection. The cathodic protection system is widely applied to corrosion control outside oil and gas field pipelines.

Due to the complexity of oil and gas field pipelines and the particularity of service environment, an oil and gas field pipeline system is usually jointly protected by two modes of impressed current cathodic protection and sacrificial anode cathodic protection, for example, a plurality of oil and gas field pipelines are jointly protected by different types of cathodic protection systems, and the daily maintenance difficulty of the oil and gas field pipeline cathodic protection is increased to a great extent. At present, a troubleshooting method aiming at a long-distance pipeline cathode protection system is generally adopted to troubleshoot the oil and gas field pipeline cathode protection system so as to obtain the failure reason of the cathode protection system.

In the process of implementing the invention, the inventor finds that the prior art has at least the following technical problems:

when the failure reason of the long-distance pipeline cathode protection system is analyzed by adopting a troubleshooting method of the long-distance pipeline cathode protection system, wrong analysis results are often obtained, and the troubleshooting effect is poor.

Disclosure of Invention

In view of the above, the invention provides an analysis method for failure reasons of an oil and gas field pipeline cathode protection system, which is used for analyzing the failure reasons of the oil and gas field pipeline cathode protection system in a targeted manner, has high accuracy and can obtain a good investigation effect.

Specifically, the method comprises the following technical scheme:

a method for analyzing the cause of failure of an oil and gas field pipeline cathodic protection system, the method comprising:

step S1, according to the design scheme of the cathodic protection system of the target oil and gas field pipeline system, confirming that the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system or an impressed current cathodic protection system;

step S2, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system, judging whether the sacrificial anode per se fails, if so, judging that the reason for the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is that the sacrificial anode per se fails, and if not, performing step S3;

if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is an impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails, if so, judging that the cause of the failure of the impressed current cathodic protection system of the oil and gas field pipeline to be inspected is the failure of the impressed current cathodic protection device, and if not, performing step S3;

step S3, judging whether the insulating device fails, if so, determining that the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the insulating device, and if not, performing step S4;

and S4, judging whether the interference level of the stray current of the pipeline is within an acceptable range, if so, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the damage of the anticorrosive coating of the pipeline, and if not, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the interference of the stray current of the pipeline.

In one possible implementation manner, the determining whether the impressed current cathodic protection device fails includes:

step 201, judging whether the constant potential rectifier fails, if so, judging that the reason for the failure of the oil-gas field pipeline cathode protection system to be inspected is the failure of the constant potential rectifier.

In a possible implementation manner, the determining whether the impressed current cathodic protection device fails further includes:

if the potentiostat is not in failure, the step 202 is carried out to judge whether the anode ground bed is in failure, and if so, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the anode ground bed.

In a possible implementation manner, the determining whether the impressed current cathodic protection device fails further includes:

if the anode ground bed does not fail, step 203 is carried out, whether the reference electrode fails or not is judged, if yes, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is that the reference electrode fails, and if not, step S3 is carried out.

In one possible implementation, the determining whether the sacrificial anode itself fails includes:

obtaining critical grounding resistance Rz of sacrificial anode group in sacrificial anode cathodic protection system_max；

Measuring the actual grounding resistance Rz of a sacrificial anode group in service in a sacrificial anode cathodic protection system;

if Rz<Rz_maxThe sacrificial anode set is valid;

if Rz>Rz_maxAnd if so, the sacrificial anode group fails, so that the sacrificial anode self is judged to fail.

In a possible implementation manner, the determining whether the sacrificial anode itself fails further includes:

according to the critical grounding resistance Rz of the sacrificial anode group in the sacrificial anode cathodic protection system_maxObtaining the critical grounding resistance Rd of the single sacrificial anode in the sacrificial anode group_max；

Measuring the actual grounding resistance Rd of the single sacrificial anode;

if Rd<Rd_maxThen the single sacrificial anode is effective;

if Rd>Rd_maxAnd if so, the single sacrificial anode fails, so that the judgment sacrificial anode fails.

In one possible implementation, the determining whether the insulation device fails includes:

measuring the potential difference of two ends of the insulating device by using a potential method;

if the potential difference is less than or equal to 100mV, the isolation device is disabled, otherwise, the isolation device is enabled.

In a possible implementation manner, the determining whether the pipe stray current interference level is within an acceptable range includes: testing the alternating current density i of the oil-gas field pipeline to be inspected_ac；

If i_ac＞100A/m²If the pipeline stray current interference level is not within the acceptable range;

if i_ac≤100A/m²And then the interference level of the stray current of the pipeline is within the acceptance range, and the polarization potential E of the pipeline of the oil and gas field to be inspected is further measured_p；

If E_pThe interference level of the stray current of the pipeline is less than or equal to-850 mV, and the interference level of the stray current of the pipeline is in an acceptable range;

if E_p> -850mV, the pipe stray current interference level is not within the acceptable range.

In one possible implementation, the determining whether the anode bed fails includes:

if the grounding resistance of the anode ground bed meets the requirement of the following formula, the anode ground bed does not fail, otherwise, the anode ground bed fails;

I_cpmax·R_g＜0.7U

in the formula I_cpmaxIs the maximum expected protection current requirement in units of a;

R_gis anode ground bed grounding resistance with the unit of omega;

u is the rated output voltage of the potentiostat and has the unit V.

In one possible implementation, the determining whether the reference electrode fails includes:

acquiring the potential of the reference electrode;

judging whether the error between the potential of the reference electrode and the potential of a standard reference electrode exceeds 5 mV;

if it exceeds 5mV, the reference electrode fails, otherwise, the reference electrode does not fail.

The technical scheme provided by the embodiment of the invention has the beneficial effects that at least:

the analysis method for the failure reasons of the oil and gas field pipeline cathode protection system provided by the embodiment of the invention aims at the characteristics of diversity and complexity of the oil and gas field pipeline cathode protection system and determines the type of the oil and gas field pipeline cathode protection system to be inspected in a targeted manner according to the design scheme of the cathode protection system of the target oil and gas field pipeline system. Different failure reasons are analyzed for the sacrificial anode cathodic protection system and the impressed current cathodic protection system respectively, the failure reasons of the cathodic protection system are analyzed step by step according to the sequence of whether the sacrificial anode fails (whether the impressed current cathodic protection device fails), whether the insulating device fails and whether the stray current interference level is acceptable, and the analysis efficiency and the precision of the failure reasons of the oil and gas field pipeline cathodic protection system can be obviously improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a flowchart of an analysis method for failure reasons of the oil and gas field pipeline cathodic protection system provided by the embodiment of the invention.

Detailed Description

In order to make the technical solutions and advantages of the present invention clearer, the following will describe embodiments of the present invention in further detail with reference to the accompanying drawings.

The embodiment of the invention provides an analysis method for failure reasons of an oil-gas field pipeline cathode protection system, which comprises the following steps as shown in the attached figure 1:

and step S1, according to the design scheme of the cathodic protection system of the target oil and gas field pipeline system, determining that the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system or an impressed current cathodic protection system.

And S2, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system, judging whether the sacrificial anode per se fails, if so, judging that the reason for the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is that the sacrificial anode per se fails, and if not, performing S3.

If the type of the cathodic protection system of the oil and gas field pipeline to be inspected is the impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails, if so, judging that the cause of the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is the impressed current cathodic protection device failure, and if not, performing step S3.

And S3, judging whether the insulating device fails, if so, determining that the failure reason of the oil-gas field pipeline cathode protection system is the failure of the insulating device, otherwise, performing S4.

And step S4, judging whether the interference level of the stray current of the pipeline is within an acceptable range, if so, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the damage of the anticorrosive coating of the pipeline, and if not, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the interference of the stray current of the pipeline.

The analysis method for the failure reasons of the oil and gas field pipeline cathode protection system provided by the embodiment of the invention aims at the characteristics of diversity and complexity of the oil and gas field pipeline cathode protection system and determines the type of the oil and gas field pipeline cathode protection system to be inspected in a targeted manner according to the design scheme of the cathode protection system of the target oil and gas field pipeline system. Different failure reasons are analyzed for the sacrificial anode cathodic protection system and the impressed current cathodic protection system respectively, the failure reasons of the cathodic protection system are analyzed step by step according to the sequence of whether the sacrificial anode fails (whether the impressed current cathodic protection device fails), whether the insulating device fails and whether the stray current interference level is acceptable, and the analysis efficiency and the precision of the failure reasons of the oil and gas field pipeline cathodic protection system can be obviously improved.

The above steps are described as follows:

and step S1, according to the design scheme of the cathodic protection system of the target oil and gas field pipeline system, confirming that the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system or an impressed current cathodic protection system.

The target oil and gas field pipeline system can comprise one oil and gas field pipeline and a plurality of oil and gas field pipelines, and when the failure reason of the cathode protection system is analyzed, a single oil and gas field pipeline or a certain section of each oil and gas field pipeline needs to be analyzed and checked one by one. In the embodiment of the invention, a certain pipe or a certain section of pipe in the target oil and gas field pipeline system, which needs to be subjected to the failure reason analysis of the cathode protection system, is called as an oil and gas field pipeline to be inspected.

The design scheme of the cathode protection system of the target oil and gas field pipeline system refers to the service scheme of the cathode protection system of the target oil and gas field pipeline system. According to the design scheme, the specific type of the cathodic protection system used by the oil and gas field pipeline to be inspected can be determined, wherein the cathodic protection system is either a sacrificial anode cathodic protection system or an impressed current cathodic protection system.

For step S2, it includes step S2a and step S2b, as follows:

s2a, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system, judging whether the sacrificial anode per se fails;

if so, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the self failure of the sacrificial anode; if not, the process proceeds to step S3.

The following method can be adopted to determine whether the sacrificial anode itself fails, and specifically includes:

obtaining critical grounding resistance Rz of sacrificial anode group in sacrificial anode cathodic protection system_max；

Measuring the actual grounding resistance Rz of a sacrificial anode group in service in a sacrificial anode cathodic protection system;

if Rz<Rz_maxThe sacrificial anode set is valid;

if Rz>Rz_maxAnd the sacrificial anode group fails, so that the sacrificial anode is judged to be failed.

Further, judging whether the sacrificial anode per se fails further comprises:

according to the critical grounding resistance Rz of the sacrificial anode group in the sacrificial anode cathodic protection system_maxObtaining the critical grounding resistance Rd of the single sacrificial anode in the sacrificial anode group_max；

Measuring the actual grounding resistance Rd of the single sacrificial anode;

if Rd<Rd_maxThen the single sacrificial anode is effective;

if Rd>Rd_maxAnd if so, the single sacrificial anode fails, so that the sacrificial anode is judged to be failed.

It is to be understood that the above-mentioned "single sacrificial anode" refers to the sacrificial anode in the evaluation analysis.

The specific analysis method for determining whether the sacrificial anode itself fails can be found in the related documents (CN104060279A, the validity criterion of the sacrificial anode cathodic protection system and the method for predicting the remaining life).

For the step S2b, if the cathodic protection system type of the oil and gas field pipeline to be inspected is an impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails;

if so, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the impressed current cathode protection device; if not, the process proceeds to step S3.

Wherein, judge whether impressed current cathodic protection device is invalid, can further include the following step again:

firstly, step 201 is carried out, whether the potentiostat fails or not is judged, and if yes, the failure reason of the oil-gas field pipeline cathode protection system to be checked is that the potentiostat fails.

The judgment criteria for whether the potentiostat fails are as follows:

if any one of the output current, the output voltage and the reference control potential of the constant potential rectifier is unstable or discontinuously adjustable, the constant potential rectifier can be judged to be invalid.

If the output current, the output voltage and the reference control potential of the constant potential rectifier are stable and continuously adjustable, the constant potential rectifier can be judged to be in an effective state without abnormality.

If the potentiostat does not fail, step 202 is carried out to judge whether the anode ground bed fails, if so, the failure reason of the oil-gas field pipeline cathode protection system is to be checked to be the failure of the anode ground bed.

The criteria for determining whether the anode bed has failed are as follows:

judging whether the grounding resistance of the anode ground bed meets the requirements of the following formula;

if so, the anode bed does not fail; if not, the anode bed fails;

I_cpmax·R_g＜0.7U。

in the formula I_cpmaxIs the maximum expected protection current requirement in units of a;

R_gis anode ground bed grounding resistance with the unit of omega;

u is the rated output voltage of the potentiostat and has the unit V.

Wherein the maximum expected protection current requirement I_cpmaxFor fixed value, the method is generally obtained from a corresponding cathodic protection system design file (for example, SY/T0036-99 'design Specification for impressed current cathodic protection of buried steel pipeline systems');

the anode bed ground resistance R can be obtained by testing the anode bed ground resistance according to the long ground resistance test method provided in section 10.1 of GB/T21246-_g；

The rated output voltage U of the potentiostat is a constant value and is generally described in the specification of the potentiostat.

If the anode ground bed does not fail, step 203 is performed to judge whether the reference electrode fails, if so, the failure reason of the oil and gas field pipeline cathode protection system to be checked is that the reference electrode fails, and if not, step S3 is performed.

The judgment standard for whether the reference electrode fails is as follows:

the potential of the reference electrode is obtained.

And judging whether the error between the potential of the reference electrode and the potential of the standard reference electrode exceeds 5 mV.

If it exceeds 5mV, the reference electrode fails, otherwise, the reference electrode does not fail.

Wherein, the error between the potential of the reference electrode and the potential of the standard reference electrode refers to: the absolute value of the difference between the potential of the reference electrode and the potential of the standard reference electrode.

In the embodiment of the invention, the standard reference electrode is a calibrated copper sulfate reference electrode.

According to the embodiment of the invention, the potentiostat fault analysis, the anode ground bed effectiveness analysis and the reference electrode effectiveness analysis are sequentially carried out according to the fault probability of each device, so that the analysis efficiency can be obviously improved and the analysis time can be reduced on the premise of ensuring the analysis accuracy.

For the sacrificial anode cathodic protection system and the impressed current cathodic protection system, after analyzing whether the sacrificial anode itself and the impressed current cathodic protection device fail, if the sacrificial anode itself and the impressed current cathodic protection device do not fail, the next step is performed as the judgment in step S3.

For step S3, it is determined whether the insulation device has failed;

if so, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the insulating device; if not, the process proceeds to step S4.

Wherein, the judgement standard whether insulating device is inefficacy includes:

the potential difference between the two ends of the insulating device is measured by a potential method, wherein the potential method can refer to the potential method related to section 9.2 in the national standard GB/T21246-2007.

If the potential difference is less than or equal to 100mV, the insulating device fails; conversely, if the potential difference is greater than 100mV, the isolation device is effective.

Wherein, for the pipeline of waiting to investigate, its initiating terminal and end all install insulating device, when the analysis, need all carry out the analysis to the insulating device of these both ends department.

And if the failure reason of the oil-gas field pipeline cathode protection system to be investigated is not the failure of the insulating device, the step S4 is carried out.

Wherein, step S4 further includes: judging whether the interference level of the pipeline stray current is within an acceptable range;

if so, the failure reason of the oil and gas field pipeline cathode protection system to be inspected is the damage of the pipeline anticorrosive coating;

if not, the failure reason of the oil-gas field pipeline cathode protection system to be inspected is pipeline stray current interference.

Specifically, judging whether the interference level of the pipeline stray current is in an acceptable range includes: testing alternating current density i of oil and gas field pipeline to be inspected_ac；

If i_ac＞100A/m²If the interference level of the pipeline stray current is not in the acceptable range, the pipeline stray current interference is the failure reason of the oil-gas field pipeline cathode protection system to be inspected;

if i_ac≤100A/m²If the interference level of the stray current of the pipeline is within the acceptable range, the polarization potential E of the pipeline of the oil and gas field to be inspected can be further measured_pAnd the analysis precision is further improved.

If E_pLess than or equal to-850 mV (relative to a copper sulfate reference electrode), the interference level of the stray current of the pipeline is within an acceptable range;

if E_pAnd the level of the pipeline stray current interference is not in an acceptable range if the voltage is > -850mV, which means that the pipeline stray current interference is caused by the failure of the oil and gas field pipeline cathode protection system to be inspected.

In summary, the embodiment of the present invention provides a method for analyzing the failure cause of an oil and gas field pipeline cathodic protection system, which includes the following steps:

and step S1, according to the design scheme of the cathodic protection system of the target oil and gas field pipeline system, determining that the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system or an impressed current cathodic protection system.

S2a, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is a sacrificial anode cathodic protection system, judging whether the sacrificial anode per se fails, if so, judging that the reason for the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is that the sacrificial anode per se fails, and if not, performing S3.

Wherein, judge whether sacrificial anode itself is invalid, include:

obtaining critical grounding resistance Rz of sacrificial anode group in sacrificial anode cathodic protection system_max；

Measuring the actual grounding resistance Rz of a sacrificial anode group in service in a sacrificial anode cathodic protection system;

if Rz<Rz_maxThe sacrificial anode set is valid; if Rz>Rz_maxAnd the sacrificial anode group fails, so that the sacrificial anode is judged to be failed.

According to the critical grounding resistance Rz of the sacrificial anode group in the sacrificial anode cathodic protection system_maxObtaining the critical grounding resistance Rd of the single sacrificial anode in the sacrificial anode group_max；

Measuring the actual grounding resistance Rd of the single sacrificial anode;

if Rd<Rd_maxThen the single sacrificial anode is effective; if Rd>Rd_maxAnd if so, the single sacrificial anode fails, so that the sacrificial anode is judged to be failed.

S2b, if the type of the cathodic protection system of the oil and gas field pipeline to be inspected is an impressed current cathodic protection system, judging whether the impressed current cathodic protection device fails, if so, judging that the reason for the failure of the cathodic protection system of the oil and gas field pipeline to be inspected is that the impressed current cathodic protection device fails, and if not, executing the step S3.

The method for judging whether the impressed current cathodic protection device fails comprises the following steps:

step 201, judging whether the potentiostat fails, if so, checking that the pipeline cathode protection system of the oil and gas field fails because the potentiostat fails.

If the potentiostat is not failed, proceed to step 202: and judging whether the anode ground bed fails, if so, determining that the failure reason of the oil-gas field pipeline cathode protection system to be inspected is the failure of the anode ground bed.

If the anode ground bed does not fail, step 203 is performed to judge whether the reference electrode fails, if so, the failure reason of the oil and gas field pipeline cathode protection system to be checked is that the reference electrode fails, and if not, step S3 is performed.

And S3, judging whether the insulating device fails, if so, determining that the failure reason of the oil-gas field pipeline cathode protection system is the failure of the insulating device, otherwise, performing S4.

And step S4, judging whether the interference level of the stray current of the pipeline is within an acceptable range, if so, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the damage of the anticorrosive coating of the pipeline, and if not, determining that the failure reason of the cathodic protection system of the oil and gas field pipeline to be inspected is the interference of the stray current of the pipeline.

The analysis method for the failure reason of the oil and gas field pipeline cathode protection system provided by the embodiment of the invention is further described by the following specific embodiment:

the cathodic protection and outer corrosion prevention layer combined control outer corrosion measures are adopted for a certain oil and gas field gathering and transportation trunk pipeline, and after a cathodic protection system operates for 5 years, a field cathodic protection potential test result shows that the polarization potential of the pipeline measured at TP35 and TP36 test piles within a range of 2km close to the tail end of the pipeline cannot meet the requirement of a cathodic protection standard of minus 850mV (relative to a copper sulfate reference electrode), namely the pipeline cathodic protection system fails. The method provided by the embodiment of the invention is adopted to carry out fault analysis on the pipeline cathode protection system, and the steps are as follows:

firstly, a cathodic protection design scheme of the pipeline to be inspected is called, according to the design scheme, an impressed current cathodic protection system is adopted on the whole line of the pipeline to be inspected, no sacrificial anode is applied to TP35 and TP36 test piles with the cathodic protection potential not reaching the standard, and then the cathodic protection system of the pipeline to be inspected is judged to be the impressed current cathodic protection system.

And secondly, judging whether the potentiostat fails, and finding that the potentiostat outputs 3.5V of voltage, 2A of current and-1200 mV (relative to a copper sulfate reference electrode) of control potential through fault analysis. And respectively carrying out increasing or decreasing operation on the output voltage, the output current and the control potential, finding that the output voltage, the output current and the control potential are all continuously adjustable, and judging that the potentiostat is abnormal.

Thirdly, testing the grounding resistance of the anode ground bed to be 4 omega by using a long grounding body grounding resistance method provided by the national standard GB/T21257-2017, knowing that the maximum expected protection current requirement of the pipeline is 5A from a cathode protection design book, indicating that the rated output voltage of the potentiostat is 60V by a potentiostat specification,

the anode bed did not fail because 4 Ω × 5A ═ 20V < 0.7 × 60V ═ 42V.

And fourthly, testing the performance of the insulating devices at the starting end and the tail end of the pipeline to be inspected by using a potential method provided by the national standard GB/T21257-2017.

The test result shows that the potential difference between the two ends of the start end insulating device is 500mV, which is more than 100mV, so the start end insulating device does not fail.

The potential difference between the two ends of the tail end insulating device is 5mV which is far less than 100mV, so the tail end insulating device fails, which means that the failure of the cathode protection system of the pipeline to be inspected in the section is caused by the failure of the tail end insulating device, and the analysis of the failure reason of the cathode protection system is completed.

The above description is only for facilitating the understanding of the technical solutions of the present invention by those skilled in the art, and is not intended to limit the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.