An experimental device and method for simulating corrosion of a pipeline steel under a foam insulation layer

Abstract

The application belongs to the technical field of material corrosion and protection, and discloses an experimental device and method for simulating pipeline steel corrosion under a foam insulation layer. The device comprises a base, a PE protective cap and a foam insulation layer material. The base is made of a chemically inert and insulating high-elasticity material. A groove is formed in the upper part of the base for embedding a pipeline steel sample and achieving interference fit with the pipeline steel sample. The longitudinal depth of the groove is greater than or equal to the height of the pipeline steel sample. The top of the PE protective cap is provided with an opening for simulating damage of the foam insulation layer material. The foam insulation layer material is placed in the PE protective cap, and the PE protective cap is sealed and covered on the upper part of the base. Optionally, the surface of the pipeline steel sample facing the foam insulation layer material is coated with a corrosion-resistant coating. Further optionally, an artificial simulated defect is arranged on the corrosion-resistant coating. The device and method of the application can simulate the surface corrosion process and rules of the pipeline steel under the foam insulation layer.

Description

Technical Field

[0001] This invention belongs to the field of material corrosion and protection technology, and more specifically, relates to an experimental apparatus and method for simulating corrosion of pipe steel under a foam insulation layer. Background Technology

[0002] As the lifeblood of the national economy, pipelines are widely used for transporting media such as oil, natural gas, and chemical raw materials. In crude oil and heavy oil pipelines, to ensure the efficiency and operational safety of buried crude oil pipelines, pipelines in northern regions generally use epoxy powder coating as the anti-corrosion layer, polyurethane foam insulation layer, and high-density polyethylene protective layer for corrosion protection and insulation. However, during service, groundwater often enters the insulation layer structure due to sealing failure at joint overlaps or aging of the outer protective layer. This creates a high-temperature, high-humidity localized corrosive environment beneath the insulation layer, which is a major factor inducing and accelerating external corrosion of the pipeline. Corrosion beneath the insulation layer of buried pipelines is highly concealed and difficult to detect in a timely manner, representing a high-risk form of pipeline corrosion.

[0003] Laboratory simulation of pipeline corrosion behavior under polyurethane foam insulation is crucial for analyzing the corrosion process and key influencing factors, evaluating material properties, and predicting pipeline lifespan. Current research primarily uses dense gaskets such as rubber pads, polytetrafluoroethylene (PTFE), and polyethylene (PE) to simulate insulation materials. However, existing simulation methods have several limitations: First, existing simulation methods often simplify polyurethane foam insulation layers into dense gaskets, neglecting the "corrosive medium carrier" characteristics of the porous foam structure and the media transport and retention behavior it mediates. The porous structure of polyurethane foam itself is a "reservoir" and "transmission channel" for corrosive media. Second, polyurethane degrades in long-term humid and hot environments, potentially releasing small molecules such as organic acids. These degradation products not only alter the pH of the local microenvironment but may also provide nutrients for corrosive microorganisms such as sulfate-reducing bacteria (SRB), triggering microbial corrosion. Existing simulation methods completely fail to reflect this coupling effect of material aging and biological corrosion. Third, residual catalysts and foaming agents in polyurethane foam contain large amounts of corrosive inorganic salts (such as sulfates, chlorides, and fluorides). During service, these ions are slowly released and participate in the corrosion process. Using inert, dense polymer gaskets for simulation ignores this important source of ions and chemical factors, making the experimental environment significantly different from the local environment under damaged insulation layers in pipelines, inevitably leading to systematic biases in the obtained corrosion data.

[0004] Secondly, the corrosion of pipes under the insulation layer is closely related to the performance and damage morphology of the pipe body protective coating. However, existing research has limitations and fails to fully cover the complex factors in actual engineering. Many existing patents and literature focus on the influence of the geometric parameters (such as gap height and depth) of the ideal gap formed by the "metal-gasket" on the corrosion of occluded cells, but neglect the synergistic influence of the external protective coating. Actual defects in pipe body protective coatings include peeling, localized blistering, and cracking. Most existing methods can only simulate regular gaps and are unable to simulate effects such as oxygen concentration cells caused by localized open damage. Existing simulation methods generally do not systematically consider the coating and its defects as controllable variables.

[0005] Furthermore, there are issues with the convenience and compatibility of the testing system: if electrochemical testing is required, it involves welding or complex encapsulation of the sample, which may cause inconvenience to sample processing and analysis after the experiment.

[0006] In summary, existing technologies suffer from several core defects: The simulated environment is severely distorted; the use of dense, inert gaskets not only fails to simulate the characteristics and transport behavior of porous materials as "corrosion media carriers," but also ignores the potential effects of insulation degradation products and endogenous corrosion ions on the corrosion process (especially microbial corrosion); the operating condition coverage is extremely incomplete, focusing too much on ideal gap geometry while neglecting the complex coupling of multiple actual operating conditions, including insulation material properties, damage morphology, coating condition, and microbial environment; due to these numerous limitations, the results of existing technologies cannot accurately reproduce on-site operating conditions and cannot predict or explain the complex corrosion behavior of on-site pipelines.

[0007] Therefore, there is an urgent need in this field for a simulation experimental device and method for corrosion of insulated pipe steel that can highly reproduce the on-site working conditions of corrosion of pipe steel materials under foam insulation layer and can conduct corrosion assessment more conveniently and comprehensively. Summary of the Invention

[0008] The purpose of this invention is to overcome the limitations of existing technologies and to propose an experimental apparatus and method for simulating corrosion of pipe steel under foam insulation layers. The apparatus and method of this invention can simulate the corrosion process and patterns on the surface of pipe steel under foam insulation layers.

[0009] To achieve the above objectives, the present invention provides an experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer, the apparatus comprising a base, a PE protective cap, and foam insulation layer material; The base is made of a chemically inert and insulating highly elastic material; a groove is provided on the upper part of the base, the groove is used to embed the pipe steel sample and achieve an interference fit with the pipe steel sample, and the longitudinal depth of the groove is greater than or equal to the height of the pipe steel sample. The PE protective cap has a hollow cover structure with an opening at the top. The opening is used to simulate the damage to the foam insulation material caused by damage to the protective layer. The foam insulation material is placed inside the PE protective cap, and the PE protective cap seals and covers the upper part of the base, so that the lower surface of the foam insulation material is pressed against the surface of the base with the groove. Optionally (depending on experimental requirements), the surface of the pipe steel specimen facing the foam insulation material is coated with an anti-corrosion coating; further optionally (depending on experimental requirements), the anti-corrosion coating is provided with artificially simulated coating defects.

[0010] The base is the main support structure. According to the present invention, preferably, the base is a cuboid or cylindrical block.

[0011] According to the present invention, preferably, the base is made of polytetrafluoroethylene and / or fluorinated ethylene propylene copolymer.

[0012] In this invention, as a preferred embodiment, the groove is formed in the upper center of the base.

[0013] According to the present invention, preferably, both the groove and the pipe steel sample are cylindrical; The diameter of the groove is 0.5-2.0 mm smaller than the diameter of the pipe steel sample, thereby achieving an interference fit between the groove and the pipe steel sample. In this invention, the interference fit is to ensure that the pipe steel sample is accurately pressed into the groove to form a lateral seal, preventing corrosive media from entering from the side. Furthermore, when the longitudinal depth of the groove is greater than the height of the pipe steel sample, a cylindrical gap is formed between the surface of the pipe steel sample facing the foam insulation material or the anti-corrosion coating surface of the pipe steel sample and the sidewall of the groove. The cylindrical gap is used to simulate the gap of the insulation layer peeling off.

[0014] In this invention, the surface of the pipe steel sample facing the foam insulation material is the working surface, which is exposed to a corrosive medium environment during the experiment. Based on the simulated working conditions parameters (anti-corrosion coating material, anti-corrosion coating defect morphology) required for the experiment, an anti-corrosion coating can be applied to the surface of the pipe steel sample facing the foam insulation material. Further, optionally, the anti-corrosion coating may also have artificially simulated defects, which are at least one of artificially created scratches, artificially created pinholes, and artificially created localized peeling.

[0015] According to the present invention, preferably, the foam insulation layer material is in a state of being untreated, soaked in a corrosive ionic solution to achieve saturation adsorption, or subjected to accelerated aging treatment.

[0016] According to the present invention, preferably, the material of the foam insulation layer is at least one selected from polyurethane foam, polyisocyanurate foam, phenolic foam, glass wool, and rock wool.

[0017] In this invention, the foam insulation layer material can be the same insulation material used for the on-site pipelines, such as polyurethane foam. Its significance lies in the fact that it not only simulates the physical transport behavior of porous media, but more importantly, as an active material that may release degradation products (such as organic acids) and contain or enrich corrosive ions, it can realistically reproduce the coupled effects of these chemical and biological factors on pipeline steel corrosion, which cannot be achieved using any inert polymer gasket.

[0018] According to the present invention, preferably, a sealing strip (such as a silicone or fluororubber strip) is provided around the area of ​​the base that seals with the PE protective cap. The sealing strip is used to achieve a sealing fit between the PE protective cap and the upper part of the base, ensuring the sealing of the mating surface between the PE protective cap and the upper part of the base.

[0019] In this invention, the opening is used to simulate the damage to the foam insulation layer material caused by damage to the protective layer. Therefore, the shape and area of ​​the opening can be flexibly determined according to the "shape of the damaged foam insulation layer material and the area of ​​the damaged foam insulation layer material" that need to be simulated.

[0020] According to the present invention, preferably, the device further includes a multi-core copper conductor; The base has a wire hole at its lower part; one end of the wire hole is located on the lower surface of the base, and the other end of the wire hole is located at the bottom of the groove in the base. The wire passes through the wire hole, so that the exposed core end of the wire with the insulation layer removed is laid flat in a radial or circumferential shape at the bottom of the groove and makes reliable electrical contact with the pipe steel sample. A sealing material (epoxy resin or silicone rubber) is provided in the gap formed between the sidewall of the end of the wire hole located on the lower surface of the base and the wire to seal it and prevent corrosive media from entering.

[0021] In this invention, when the pipe steel sample is pressed into the groove, the pressure of the pipe steel sample being pressed in achieves tight electrical contact (i.e., reliable electrical contact). This method completely avoids the thermal effects, weld corrosion and physical damage that welding may cause to the pipe steel sample, ensuring that the pipe steel sample can be completely and undamaged after the experiment for weight loss analysis or other surface analysis.

[0022] Another aspect of the present invention provides an experimental method for simulating corrosion of pipe steel under a foam insulation layer. The method uses the aforementioned apparatus and includes the following steps: S1: The pipe steel is processed into a pipe steel sample that achieves an interference fit with the groove; optionally, an anti-corrosion coating is applied to the surface of the pipe steel sample facing the foam insulation material; further optionally, artificial defects are set on the anti-corrosion coating. S2: Test the mass of the pipe steel sample obtained in step S1; then press the pipe steel sample obtained in step S1 vertically into the groove; then place the foam insulation material inside the PE protective cap and seal the PE protective cap on the upper part of the base, so that the lower surface of the foam insulation material presses on the surface of the base with the groove, thus obtaining a device with a pipe steel sample assembled. S3: Immerse the device with the assembled pipe steel sample completely or partially in the corrosive medium to conduct an experiment simulating pipe steel corrosion under a foam insulation layer; after the preset experimental time is reached, remove the pipe steel sample after the experiment from the device with the assembled pipe steel sample (since there is no welding and the sealing is reliable, the integrity of the pipe steel sample after the experiment is excellent), and perform corrosion product removal and analysis, weight loss corrosion rate calculation, macroscopic corrosion morphology observation and / or microscopic corrosion morphology observation.

[0023] In step S1 of the present invention, the step of processing the pipe steel into a pipe steel sample that achieves an interference fit with the groove includes: performing a series of sanding, polishing, cleaning, degreasing, and drying treatments on the surface of the pipe steel sample facing the foam insulation layer material.

[0024] According to the present invention, preferably, the method further includes electrochemical testing, the method for electrochemical testing comprising: In step S2, the wire is first passed through the wire hole, so that the exposed core end of the wire with the insulation removed is laid flat at the bottom of the groove in a radial or circumferential shape, and the other end of the wire is connected to the electrochemical workstation; then the pipe steel sample obtained in step S1 is pressed vertically into the groove, so that the wire and the pipe steel sample make reliable electrical contact. The gap formed between the wire and the sidewall at one end of the lower surface of the base of the wire hole is sealed with a sealing material. The electrochemical test uses the pipe steel sample obtained in step S1 as the working electrode and performs a non-destructive electrochemical test through the wire.

[0025] According to the present invention, preferably, the non-destructive electrochemical test includes at least one of open-circuit potential monitoring, potentiodynamic polarization curve scanning, and electrochemical impedance spectroscopy measurement.

[0026] According to the present invention, preferably, the working condition parameters simulated by the method include at least one of the following: the height of the gap where the insulation layer peels off (simulated by the cylindrical gap height of the present invention), the shape of the broken foam insulation layer material (simulated by the shape of the opening of the PE protective cap of the present invention), the area of ​​the broken foam insulation layer material (simulated by the area of ​​the opening of the PE protective cap of the present invention), the pipe steel grade, the anti-corrosion coating material, the anti-corrosion coating defect morphology (simulated by artificially simulating defects in the coating provided on the anti-corrosion coating of the present invention), the foam insulation layer material material, the foam insulation layer material thickness, the foam insulation layer material moisture content, the foam insulation layer material state (untreated, immersed in a corrosive ionic solution to achieve saturation adsorption, or subjected to accelerated aging treatment), the characteristics of the corrosive medium, and the corrosion time (simulated by the preset experimental time of the present invention). The characteristics of the corrosive medium include its temperature and the Cl content within it. - Concentration of SO4 in corrosive media 2- The concentration, pH value of the corrosive medium, and whether the corrosive medium is inoculated with at least one of the following: concentration, pH value of the corrosive medium, and whether the corrosive medium is inoculated with microorganisms (such as SRB sulfate-reducing bacteria).

[0027] In this invention, other experimental environment parameters can be simulated according to experimental requirements.

[0028] The beneficial effects of the technical solution of this invention are as follows: The device (integrated testing device) and method of this invention can simulate the corrosion process and law of the steel surface of pipelines under foam insulation layers, and are particularly suitable for corrosion safety assessment, life prediction and anti-corrosion design optimization of pipeline engineering in oil, natural gas, chemical and other industries. Specifically: Highly realistic environmental simulation: This invention abandons non-representative dense polymer gaskets and uses real pipe porous foam insulation material (such as polyurethane foam) to reproduce the behavior of medium transmission and accumulation, with high simulation fidelity.

[0029] This invention reveals the chemical effects of the material itself: By using porous foam insulation material for pipelines, the experiment can naturally cover the role of its degradation products as a microbial carbon source or environmental acidifying factor, as well as the influence of its internal ions directly participating in the electrochemical process. It can realistically reproduce the corrosion environment under porous media, and simultaneously reflect the influence of the aging degradation products of the foam insulation material and the internal residual / enriched ions on the corrosion process, ensuring the authenticity of the simulated working conditions. This allows for a more comprehensive evaluation of the active role of the foam insulation material in pipeline corrosion, and the prediction results are closer to engineering reality.

[0030] The simulation of working conditions is accurate and flexible: "The opening of the PE protective cap" simulates the damage, and "the depth difference between the groove of the base and the pipe steel sample" defines the gap of the insulation layer peeling. The modular design realizes the accurate and flexible construction of various working conditions (that is, through the ingenious mechanical structure design, it can flexibly and accurately simulate various single or coupled corrosion scenarios such as local damage and peeling of the insulation layer and defects in the outer coating of the pipe). The system studies the influence of single or coupled factors such as the damage morphology of the insulation layer, the height of the cylindrical gap, and the state of the anti-corrosion coating. The experimental design is highly scientific and has a wide coverage.

[0031] The testing methods are perfectly compatible: Under the requirements of electrochemical testing, a welding-free and reliable electrical connection method is provided. The innovative "multi-core crimping" electrical connection and all-round sealing technology solve the contradiction between electrochemical testing and weight loss testing in sample handling, ensuring that both types of data come from the same sample and the same process, with extremely high correlation and reliability (that is, while facilitating electrochemical testing, it maintains the integrity of the sample to the greatest extent and ensures the accuracy of subsequent analyses such as weight loss measurement).

[0032] The device has a simple structure and is easy to operate: the whole device has few parts, is easy to process, has a simple assembly and disassembly process, good repeatability, which is conducive to standardized operation and high-throughput parallel experiments. It is highly practical and easy to promote and apply in scientific research and engineering testing.

[0033] Significant guiding significance: The corrosion data obtained by this invention more accurately reflects the actual corrosion risk of pipelines under insulation layer defects, providing important engineering guidance for accurately assessing the safety of in-service pipelines, optimizing insulation layer structural design, and formulating scientific anti-corrosion maintenance strategies. In other words, the methods and apparatus provided by this invention are not only applicable to basic corrosion mechanism research but can also directly serve engineering practice, for example: Evaluation of new pipeline corrosion protection systems: assessment of the long-term corrosion resistance matching and reliability of different combinations of "corrosion protection coating + insulation layer" materials under defect conditions; Risk prediction for in-service pipelines: Simulate known defect morphologies of insulation layers of specific pipelines to predict their corrosion development rate and remaining life, providing a basis for maintenance decisions; Verification of new materials and technologies, screening and evaluation of the applicability of new corrosion-resistant pipe steel, high-performance protective coatings and aging-resistant insulation materials; Pipeline integrity management support provides scientific and reliable data support for the development and optimization of pipeline external corrosion control standards and insulation layer maintenance procedures; Evaluation of local repair effectiveness involves testing the long-term protective performance of various local pipeline repair materials (such as patch sleeves and repair tapes) in environments with existing insulation layer defects.

[0034] This invention has significant advantages in terms of advancement, practicality, and broad application prospects.

[0035] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0036] The above and other objects, features and advantages of the present invention will become more apparent from the more detailed description of exemplary embodiments of the invention in conjunction with the accompanying drawings, wherein the same reference numerals generally represent the same components in the exemplary embodiments of the invention.

[0037] Figure 1 The diagram shows a schematic of the experimental apparatus provided by the present invention for simulating corrosion of pipe steel under a foam insulation layer.

[0038] Figure 2 The diagram shows a cross-sectional view of the experimental apparatus provided by the present invention after assembly to simulate corrosion of pipe steel under a foam insulation layer.

[0039] Figure 3 The figure shows a bar chart comparing the average corrosion rate of X70 steel and a blank control sample that is fully immersed without any obstruction under the simulated point damage condition of polyurethane foam insulation material in Example 2 of the present invention (“corrosion rate”).

[0040] Figure 4 The image shows a macroscopic corrosion morphology photograph of an X80 steel sample after an experiment under the coupled conditions of simulated insulation layer damage and peeling and anti-corrosion coating scratches, as described in Example 3 of the present invention.

[0041] Figure 5 shows the SEM morphology of the X65 steel sample after the experiment under the simulated insulation layer damage and peeling of the pipe steel under sulfate-reducing bacteria corrosion conditions in Example 4 of the present invention (Figure 5(a) and Figure 5(b) are both SEM morphology images of the surface of the bacteria-inoculated sample in Example 4. In Figure 5(a), SRB can be seen before the corrosion products are removed, and in Figure 5(b), obvious pitting corrosion can be seen on the sample surface after the corrosion products are removed).

[0042] The annotations in the attached figures are explained as follows: 1-Base; 1.1-Sealing strip; 2-Groove; 3-Wire hole; 3.1-Sealing material; 4-Pipe steel sample; 4.1-Anti-corrosion coating; 5-Multi-core copper wire; 5.1-Exposed core end of multi-core copper wire with insulation removed; 6-PE protective cap; 7-Opening; 8-Foam insulation material; 9-Cylindrical gap. Detailed Implementation

[0043] Preferred embodiments of the invention will now be described in more detail. While preferred embodiments of the invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0044] In the following embodiments: The dry polyurethane foam insulation material in Examples 2 and 3, without any treatment, is brand new insulation material taken from the Changhu Line site before construction.

[0045] Example 1

[0046] This embodiment provides an experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer, such as... Figure 1-2 As shown, the device includes a base 1, a PE protective cap 6, a foam insulation layer material 8, and a multi-core copper wire 5.

[0047] The base 1 is made of polytetrafluoroethylene and is a rectangular block. A groove 2 (cylindrical) is provided in the upper center of the base 1. The groove 2 is used to embed the pipe steel sample 4 (cylindrical) and achieve an interference fit with the pipe steel sample 4. The longitudinal depth of the groove 2 is greater than the height of the pipe steel sample 4.

[0048] The PE protective cap 6 has a hollow cover structure with an opening 7 at the top. The opening 7 is used to simulate the damage to the foam insulation material caused by damage to the protective layer. The foam insulation material 8 (which is untreated polyurethane foam insulation material) is placed inside the PE protective cap 6. The PE protective cap 6 is sealed to the upper part of the base 1 (a sealing strip 1.1 is provided around the area of ​​the base 1 where the PE protective cap 6 is sealed to achieve a sealed seal between the PE protective cap 6 and the upper part of the base 1), thereby pressing the lower surface of the foam insulation material 8 against the surface of the base 1 where the groove 2 is located.

[0049] The surface of the pipe steel sample 4 facing the foam insulation material 8 is coated with an anti-corrosion coating 4.1, and the anti-corrosion coating 4.1 is provided with artificial coating defects (not shown); the anti-corrosion coating surface of the pipe steel sample 4 and the side wall of the groove 2 form a cylindrical gap 9, which is used to simulate the gap of the insulation layer peeling.

[0050] The base 1 has a wire hole 3 at its lower part; one end of the wire hole 3 is located on the lower surface of the base 1, and the other end of the wire hole 3 is located at the bottom of the groove 2 inside the base 1. The multi-core copper wire 5 passes through the wire hole 3, so that the exposed core end 5.1 of the multi-core copper wire with the insulation layer removed is laid flat in a radial or circumferential shape at the bottom of the groove 2 and makes reliable electrical contact with the pipe steel sample 4; a sealing material 3.1 is provided in the gap formed between the side wall of the end of the wire hole 3 located on the lower surface of the base 1 and the multi-core copper wire 5.

[0051] The device described in this invention, through its modular design, can flexibly realize simulation experiments under various single or coupled factors. The corrosion simulation experiments of this invention under coupled factors are described in detail below through three typical embodiments.

[0052] Example 2: Simulation Experiment of Pipeline Steel Corrosion under Point Damage to Polyurethane Foam Insulation Material Only

[0053] This embodiment provides an experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer. The apparatus includes a base 1, a PE protective cap 6, and foam insulation material 8, as shown below. Figure 1 , 2 As shown, but without using multi-core copper wire 5 (no electrochemical tests were performed, and no wire hole was opened).

[0054] The base 1 is made of polytetrafluoroethylene and is a rectangular block. A groove 2 (cylindrical) is provided in the upper center of the base. The groove 2 is used to embed the pipe steel sample 4 (cylindrical, X70 steel) and achieve an interference fit with the pipe steel sample 4. The longitudinal depth of the groove (Φ49.0mm×5.0mm) is equal to the height of the pipe steel sample (Φ50.0mm×5.0mm) (without the gap of the insulation layer peeling off).

[0055] The PE protective cap 6 is a hollow cover structure with a Φ5mm circular opening 7 at the top, which is used to simulate point damage to the polyurethane foam insulation material. The foam insulation material 8 (dry polyurethane foam insulation material without any treatment, Φ60mm×20mm) is placed inside the PE protective cap 6. The PE protective cap 6 seals and covers the upper part of the base 1 (the area of ​​the base that seals and covers the PE protective cap is provided with a sealing strip 1.1 (silicone rubber), which is used to achieve a seal between the PE protective cap and the upper part of the base), thereby pressing the lower surface of the foam insulation material 8 against the surface of the base 1 with the groove.

[0056] The surface of the pipe steel sample 4 facing the foam insulation material 8 was not coated with an anti-corrosion coating 4.1.

[0057] This embodiment also provides an experimental method for simulating corrosion of pipe steel under a foam insulation layer. Using the apparatus described in this embodiment, the corrosion behavior of X70 pipe steel in NS4 soil simulated solution is studied under the condition of small-area point damage to the polyurethane foam insulation layer. The method includes the following steps: S1: Process the pipe steel into a pipe steel sample 4 that achieves an interference fit with the groove 2 (including: performing a series of sanding, polishing, cleaning, degreasing and drying treatments on the surface of the pipe steel sample facing the foam insulation material).

[0058] S2: Test the mass of the pipe steel sample obtained in step S1; then press the pipe steel sample 4 obtained in step S1 vertically into the groove 2; then place the foam insulation material 8 into the PE protective cap 6 and seal the PE protective cap 6 on the upper part of the base 1, so that the lower surface of the foam insulation material 8 is pressed on the surface of the base 1 with the groove 2, thus obtaining the device with the pipe steel sample assembled.

[0059] S3: The device assembled with the pipe steel sample was completely immersed in the corrosive medium (NS4 soil simulation solution, specifically composed of: NaHCO3 0.483g / L, KCl 0.122g / L, CaCl2 0.137g / L, MgSO4·7H2O 0.131g / L, prepared using analytical grade reagents and distilled water) to conduct an experiment simulating pipe steel corrosion under a foam insulation layer (stationary at room temperature 25±2℃ for 30 days); after 30 days, the pipe steel sample was removed from the device assembled with the pipe steel sample, and corrosion products were removed, the weight loss corrosion rate was calculated, and the macroscopic corrosion morphology was observed.

[0060] In this embodiment, a fully submerged X70 steel sample without any obstruction was used as a blank control.

[0061] Analysis of experimental results in this embodiment: Weight loss data: Calculations show that the average corrosion rate of X70 steel under the simulated conditions in this embodiment is 0.020 mm / a, while the corrosion rate of the blank control sample is 0.015 mm / a. (See attached data.) Figure 3 The corrosion rate under simulated working conditions in this embodiment is about 33.3% higher than that of the blank control sample in this embodiment, indicating that the local differential environment formed by the point damage of the insulation layer material significantly promotes corrosion.

[0062] Macroscopic corrosion morphology shows that the sample surface in this embodiment exhibits an uneven annular corrosion band in the area corresponding to the opening and its surroundings, while the blank control sample shows relatively uniform corrosion. This embodiment confirms the localized corrosion characteristics caused by point damage to the insulation layer material.

[0063] Example 3: Simulation Experiment of Pipeline Steel Corrosion under Coupled Insulation Layer Damage and Peeling and Anti-corrosion Coating Scratches

[0064] This embodiment provides an experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer, such as... Figure 1-2 As shown, the device includes a base 1, a PE protective cap 6, a foam insulation layer 8, and a multi-core copper conductor 5 (1.0 mm² cross-sectional area). 2 ).

[0065] The base 1 is made of polytetrafluoroethylene and is a rectangular block. A groove 2 (cylindrical) is provided in the upper center of the base 1. The groove 2 is used to embed the pipe steel sample 4 (cylindrical, X80 steel) and achieve an interference fit with the pipe steel sample. The longitudinal depth of the groove (Φ49.0mm×6.6mm) is greater than the height of the pipe steel sample (Φ50.0mm×5.0mm).

[0066] The PE protective cap 6 is a hollow cover structure with a circular opening 7 at the top, measuring Φ50.0mm. The opening 7 is used to simulate damage to the foam insulation material caused by damage to the protective layer. The foam insulation material 8 (dry polyurethane foam insulation material without any treatment, Φ60mm×25mm) is placed inside the PE protective cap 6. The PE protective cap 6 seals over the upper part of the base 1 (a sealing strip (silicone rubber) is provided around the area of ​​the base where it seals over the PE protective cap, and the sealing strip 1.1 is used to achieve a seal between the PE protective cap and the upper part of the base), thereby pressing the lower surface of the foam insulation material 8 against the surface of the base 1 where the groove 2 is located.

[0067] The surface of the pipe steel sample 4 facing the foam insulation material 8 is coated with an anti-corrosion coating 4.1 (i.e., a 100μm thick epoxy primer, cured at room temperature for 7 days). The anti-corrosion coating 4.1 has artificial defects, i.e., a scratch (10mm long and 1mm wide) is made on the surface of the anti-corrosion coating 4.1 that penetrates the coating to the metal substrate. The anti-corrosion coating surface of the pipe steel sample 4 forms a cylindrical gap 9 (approximately 1.5mm high) with the sidewall of the groove 2. The cylindrical gap 9 is used to simulate the gap of the insulation layer peeling off.

[0068] The base 1 has a wire hole 3 at its lower part; one end of the wire hole 3 is located on the lower surface of the base, and the other end of the wire hole 3 is located at the bottom of the groove 2 inside the base 1. The multi-core copper wire 5 passes through the wire hole 3, so that the exposed core end 5.1 of the multi-core copper wire with the insulation layer removed is laid radially at the bottom of the groove 2 and makes reliable electrical contact with the pipe steel sample 4; a sealing material 3.1 (epoxy resin sealant) is provided in the gap formed between the side wall of the end of the wire hole 3 located on the lower surface of the base 1 and the wire.

[0069] This embodiment also provides an experimental method for simulating corrosion of pipe steel under a foam insulation layer. Using the apparatus described in this embodiment, the corrosion risk of X80 pipe steel is evaluated under coupled conditions where the insulation layer peels off and the pipe coating has scratches. The method includes the following steps: S1: Process the pipe steel into a pipe steel sample 4 that achieves an interference fit with the groove 2 (including: performing a series of sanding, polishing, cleaning, degreasing, and drying treatments on the surface of the pipe steel sample facing the foam insulation material); apply an anti-corrosion coating 4.1 (i.e., a 100μm thick epoxy primer, cured at room temperature for 7 days) to the surface of the pipe steel sample 4 facing the foam insulation material 8; and set artificial defects in the anti-corrosion coating 4.1 (i.e., create a scratch (10mm long and 1mm wide) on the surface of the anti-corrosion coating that penetrates the coating to the metal substrate).

[0070] S2: Test the quality of the pipe steel sample obtained in step S1; pass the wire through the wire hole 3, so that the exposed core end 5.1 of the multi-core copper wire (without insulation) is laid radially at the bottom of the groove, and connect the other end of the wire to the electrochemical workstation; then press the pipe steel sample 4 obtained in step S1 vertically into the groove 2, so that the multi-core copper wire 5 makes reliable electrical contact with the pipe steel sample 4, and at the same time use sealing material 3.1 to seal the gap formed between the side wall of the wire hole 3 located on the lower surface of the base 1 and the multi-core copper wire 5; then place the foam insulation material 8 inside the PE protective cap 6 and seal the upper part of the base 1 with the PE protective cap 6, so that the lower surface of the foam insulation material 8 presses against the surface of the base 1 with the groove 2, thus obtaining the device with the pipe steel sample assembled.

[0071] S3: The device assembled with the pipe steel sample was completely immersed in the corrosive medium (water sample from the vicinity of a pipeline at a certain site on the Changsha-Hubei Railway) to conduct an experiment simulating the corrosion of pipe steel under a foam insulation layer (experiment at 30±2℃ for 42 days). The electrochemical test used the pipe steel sample obtained in step S1 as the working electrode. The open circuit potential of the working electrode was monitored periodically through a multi-core copper wire 5. Electrochemical impedance spectroscopy (EIS) tests were performed on days 1, 7, 14, 28, and 42 of the experiment. After 42 days, the pipe steel sample assembled with the pipe steel sample was taken out of the device after the experiment for macroscopic corrosion morphology observation.

[0072] Analysis of experimental results in this embodiment: Macroscopic corrosion morphology display ( Figure 4 After the experiment, severe localized corrosion occurred at the scratches on the anti-corrosion coating of the sample in this embodiment. Corrosion products accumulated, and the corrosion extended significantly along the edge of the scratches to the intact anti-corrosion coating by about 2-3 mm.

[0073] Electrochemical data: The open-circuit potential gradually shifted negative in the later stages of the experiment. EIS spectra showed that the impedance modulus of the anti-corrosion coating was relatively high in the early stages of the experiment (>1.2 × 10⁻⁶). 9 Ω·cm 2 As time progressed, the impedance decreased significantly, dropping to approximately 5.1 × 10⁻⁶ at 21 days. 6 Ω·cm 2 Furthermore, the presence of two time constants in the EIS spectrum indicates a decline in the protective performance of the anti-corrosion coating and corrosion of the metal substrate.

[0074] Conclusion: Under the coupled effect of the gaps formed by the peeling of the insulation layer and the scratches on the anti-corrosion coating, corrosive ions in the water sample around the pipeline at a certain site of the Changhu Line tend to accumulate at the gaps and defects, which significantly accelerates the initiation and development of local corrosion. Scratches on the anti-corrosion coating are the preferred sites for corrosion.

[0075] Example 4: Simulation Experiment of Sulfate-Reducing Bacterial Corrosion of Pipeline Steel with Damaged and Detached Insulation Layer

[0076] This embodiment provides an experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer, such as... Figure 1-2 As shown, the device includes a base 1, a PE protective cap 6, a foam insulation layer 8, and a multi-core copper conductor 5 (1.0 mm² cross-sectional area). 2 ).

[0077] The base 1 is made of polytetrafluoroethylene and is a rectangular block. A groove 2 (cylindrical) is provided in the upper center of the base 1. The groove 2 is used to embed the pipe steel sample 4 (cylindrical, X65 steel) and achieve an interference fit with the pipe steel sample. The longitudinal depth of the groove (Φ58.0mm×7mm) is greater than the height of the pipe steel sample (Φ60.0mm×5.0mm).

[0078] The PE protective cap 6 has a hollow cover structure with an opening 7 at the top, which is 60.0mm × 1.0mm in shape. The opening 7 is used to simulate longitudinal scratches and damage to the foam insulation material caused by damage to the protective layer. The foam insulation material 8 (a polyurethane foam insulation material that has peeled off after 2 years of service in Daqing Oilfield, Φ70mm × 20mm) is placed inside the PE protective cap 6. The PE protective cap 6 is sealed and covered on the upper part of the base 1 (the area of ​​the base where it is sealed and covered by the PE protective cap is surrounded by a sealing strip 1.1 (sterilized silicone rubber), which is used to achieve a sealed cover between the PE protective cap and the upper part of the base). This allows the lower surface of the foam insulation material 8 to press against the surface of the base 1 where the groove 2 is located.

[0079] The surface of the pipe steel specimen 4 facing the foam insulation material 8 is not coated with an anti-corrosion coating 4.1. The surface of the pipe steel specimen 4 facing the foam insulation material 8 forms a cylindrical gap 9 (2.0 mm high) with the sidewall of the groove 2. The cylindrical gap 9 is used to simulate the gap of insulation layer peeling.

[0080] The base 1 has a wire hole 3 at its lower part; one end of the wire hole 3 is located on the lower surface of the base 1, and the other end of the wire hole 3 is located at the bottom of the groove 2 inside the base 1. The multi-core copper wire 5 passes through the wire hole 3, so that the exposed core end 5.1 of the multi-core copper wire with the insulation layer removed is laid flat in a radial or circumferential shape at the bottom of the groove 2 and makes reliable electrical contact with the pipe steel sample 4; a sealing material 3.1 (epoxy resin sealant) is provided in the gap formed between the side wall of the end of the wire hole 3 located on the lower surface of the base 1 and the wire.

[0081] In this embodiment, all components of the device are placed in an anaerobic chamber and purged with high-purity nitrogen for at least 12 hours, or sterilized by autoclaving and then transferred to an anaerobic environment to cool while still hot. The device is then assembled according to the relevant steps described in the invention, with aseptic operation throughout.

[0082] This embodiment also provides an experimental method for simulating corrosion of pipe steel under a foam insulation layer. Using the apparatus described in this embodiment, the corrosion behavior of sulfate-reducing bacteria (SRB) on X65 pipe steel is studied in the crevice environment formed by the peeling of the insulation layer due to damage. The method includes the following steps: S1: Process the pipe steel into a pipe steel sample 4 that achieves an interference fit with the groove 2 (including: performing a series of sanding, polishing, cleaning, degreasing, and drying treatments on the surface of the pipe steel sample facing the foam insulation material, and then sterilizing it for 30 minutes in an anaerobic workstation or ultraviolet sterilizer).

[0083] S2: Test the quality of the pipe steel sample obtained in step S1; pass the wire through the wire hole 3, so that the exposed core end of the wire (without insulation) is laid radially at the bottom of the groove, and connect the other end of the wire to the electrochemical workstation; then press the pipe steel sample 4 obtained in step S1 vertically into the groove 2, so that the wire and the pipe steel sample 4 make reliable electrical contact, and at the same time use sealing material 3.1 to seal the gap formed between the wire and the side wall of the wire hole 3 located on the lower surface of the base 1; then place the foam insulation material 8 inside the PE protective cap 6 and seal the upper part of the base 1 with the PE protective cap 6, so that the lower surface of the foam insulation material 8 presses against the surface of the base 1 with the groove 2, thus obtaining the device with the pipe steel sample assembled.

[0084] S3 (conducted in an anaerobic incubator): In an anaerobic incubator, the device assembled with the pipeline steel sample was completely immersed in a corrosive medium (produced water from a field in Daqing Oilfield, inoculated with SRB at 5% of the produced water mass under anaerobic conditions) to conduct an experiment simulating pipeline steel corrosion under a foam insulation layer (constant temperature incubation at 35±2℃ for 21 days). The electrochemical test used the pipeline steel sample obtained in step S1 as the working electrode, and the open circuit potential of the working electrode was monitored periodically through a wire. Electrochemical impedance spectroscopy (EIS) tests were performed on days 1, 3, 5, 7, 10, 14, and 21 of the experiment. After 21 days, the pipeline steel sample was removed from the device assembled with the pipeline steel sample under anaerobic conditions for corrosion product removal and analysis (XPS, to detect characteristic products such as FeS), weight loss corrosion rate calculation, and microscopic corrosion morphology observation (SEM).

[0085] In this embodiment, a sterile X65 steel sample that is fully immersed without any obstruction is used as a blank control.

[0086] Analysis of experimental results in this embodiment: Electrochemical data: In this embodiment, the open-circuit potential of the inoculated sample shifted significantly to the negative direction (approximately -50mV) after 7 days of incubation, and maintained a stable negative shift trend. EIS spectra showed that the inoculated sample group in this embodiment exhibited obvious diffusion characteristics (Warburg impedance) at low and mid frequencies, and the capacitive arc diameter was smaller than that of the sterile blank control group, presenting typical electrochemical characteristics of microbial corrosion.

[0087] Microscopic corrosion morphology and corrosion product analysis: According to the SEM observation in Figure 5, the surface of the inoculated sample in this embodiment is covered with a dense SRB biofilm and extracellular polymer, and there are obvious pitting corrosion pits on the metal surface under the film; XPS analysis detected the characteristic peak of FeS in the corrosion products, confirming that SRB metabolites participated in the corrosion process; while the surface corrosion of the sterile blank control sample is relatively uniform, with no obvious pitting corrosion.

[0088] Weight loss and pitting corrosion: The average weight loss corrosion rate of the inoculated sample in this embodiment is comparable to that of the sterile blank control sample, but the maximum pitting depth is 3-4 times that of the latter, and the pitting density is also significantly increased. This indicates that in the simulated system of this embodiment, the main hazard of SRB corrosion is the induction of severe local pitting corrosion, rather than uniform thinning.

[0089] Analysis of the role of the insulation layer: The polyurethane insulation layer may slowly degrade in an anaerobic environment, and the released small molecule organic matter provides an additional carbon source for SRB. This embodiment may simulate and reproduce to some extent the potential accelerating effect of on-site insulation layer aging on microbial corrosion.

[0090] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. An experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer, characterized in that, The device includes a base, a PE protective cap, and a foam insulation layer. The base is made of a chemically inert and insulating highly elastic material; a groove is provided on the upper part of the base, the groove is used to embed the pipe steel sample and achieve an interference fit with the pipe steel sample, and the longitudinal depth of the groove is greater than or equal to the height of the pipe steel sample. The PE protective cap has a hollow cover structure with an opening at the top. The opening is used to simulate the damage to the foam insulation material caused by damage to the protective layer. The foam insulation material is placed inside the PE protective cap, and the PE protective cap seals and covers the upper part of the base, so that the lower surface of the foam insulation material is pressed against the surface of the base with the groove. Optionally, the surface of the pipe steel sample facing the foam insulation material is coated with an anti-corrosion coating; more preferably, the anti-corrosion coating is provided with artificially simulated coating defects.

2. The experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer according to claim 1, wherein, The base is a cuboid or cylindrical block; The base is made of polytetrafluoroethylene and / or fluorinated ethylene propylene copolymer.

3. The experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer according to claim 1, wherein, Both the groove and the pipe steel sample are cylindrical. The diameter of the groove is 0.5-2.0 mm smaller than the diameter of the pipe steel sample, thereby achieving an interference fit between the groove and the pipe steel sample. Furthermore, when the longitudinal depth of the groove is greater than the height of the pipe steel sample, a cylindrical gap is formed between the surface of the pipe steel sample facing the foam insulation material or the anti-corrosion coating surface of the pipe steel sample and the sidewall of the groove. The cylindrical gap is used to simulate the gap of the insulation layer peeling off.

4. The experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer according to claim 1, wherein, The foam insulation layer material is in a state of being untreated, soaked in a corrosive ionic solution to achieve saturation adsorption, or subjected to accelerated aging treatment. The foam insulation layer material is made of at least one of polyurethane foam, polyisocyanurate foam, phenolic foam, glass wool, and rock wool.

5. The experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer according to claim 1, wherein, A sealing strip is provided around the area of ​​the base that seals with the PE protective cap. The sealing strip is used to achieve a sealed seal between the PE protective cap and the upper part of the base.

6. The experimental apparatus for simulating corrosion of pipe steel under a foam insulation layer according to claim 1, wherein, The device also includes multi-core copper conductors; The base has a wire hole at its lower part; one end of the wire hole is located on the lower surface of the base, and the other end of the wire hole is located at the bottom of the groove in the base. The wire passes through the wire hole, so that the exposed core end of the wire with the insulation layer removed is laid flat in a radial or circumferential shape at the bottom of the groove and makes reliable electrical contact with the pipe steel sample. A sealing material is provided in the gap formed between the sidewall of the wire hole at one end of the lower surface of the base and the wire.

7. An experimental method for simulating corrosion of pipe steel under a foam insulation layer, characterized in that, The method employs the apparatus according to any one of claims 1-6 and includes the following steps: S1: The pipe steel is processed into a pipe steel sample that achieves an interference fit with the groove; optionally, an anti-corrosion coating is applied to the surface of the pipe steel sample facing the foam insulation material; further optionally, artificial defects are set on the anti-corrosion coating. S2: Test the mass of the pipe steel sample obtained in step S1; then press the pipe steel sample obtained in step S1 vertically into the groove; then place the foam insulation material inside the PE protective cap and seal the PE protective cap on the upper part of the base, so that the lower surface of the foam insulation material presses on the surface of the base with the groove, thus obtaining a device with a pipe steel sample assembled. S3: Immerse the device with the assembled pipe steel sample completely or partially into the corrosive medium to conduct an experiment simulating pipe steel corrosion under a foam insulation layer; after the preset experimental time is reached, remove the pipe steel sample from the device with the assembled pipe steel sample and perform corrosion product removal and analysis, weight loss corrosion rate calculation, macroscopic corrosion morphology observation and / or microscopic corrosion morphology observation.

8. The experimental method for simulating corrosion of pipe steel under a foam insulation layer according to claim 7, wherein, The method further includes electrochemical testing, the electrochemical testing method comprising: In step S2, the wire is first passed through the wire hole, so that the exposed core end of the wire with the insulation removed is laid flat at the bottom of the groove in a radial or circumferential shape, and the other end of the wire is connected to the electrochemical workstation; then the pipe steel sample obtained in step S1 is pressed vertically into the groove, so that the wire and the pipe steel sample make reliable electrical contact. The gap formed between the wire and the sidewall at one end of the lower surface of the base of the wire hole is sealed with a sealing material. The electrochemical test uses the pipe steel sample obtained in step S1 as the working electrode and performs a non-destructive electrochemical test through the wire.

9. The experimental method for simulating corrosion of pipe steel under a foam insulation layer according to claim 8, wherein, The non-destructive electrochemical testing includes at least one of open-circuit potential monitoring, potentiodynamic polarization curve scanning, and electrochemical impedance spectroscopy measurement.

10. The experimental method for simulating corrosion of pipe steel under a foam insulation layer according to claim 7, wherein, The simulated working condition parameters include at least one of the following: the height of the gap where the insulation layer peels off, the shape of the broken foam insulation layer material, the area of ​​the broken foam insulation layer material, the pipe steel grade, the anti-corrosion coating material, the anti-corrosion coating defect morphology, the foam insulation layer material material, the foam insulation layer material thickness, the foam insulation layer material moisture content, the foam insulation layer material state, the characteristics of the corrosive medium, and the corrosion time. The characteristics of the corrosive medium include its temperature and the Cl content within it. - Concentration of SO4 in corrosive media 2- Concentration, pH value of the corrosive medium, and whether the corrosive medium is inoculated with at least one of the following:

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