A method for identifying pipe sections with high failure probability

Abstract

A method for identifying pipe sections with high failure probability performs three-dimensional multiphase flow simulation on natural gas gathering and transportation pipelines to obtain flow parameters along the pipeline, conduct data acquisition, and combine the multiphase flow simulation parameters and data to clarify the pipeline internal corrosion mechanism and identify the factors affecting internal corrosion. Combined with a multi-factor collaborative corrosion prediction model, the internal corrosion rate is predicted and calculated along the pipeline. Finally, a local corrosion failure criterion (CRT) is established to determine the internal corrosion failure probability level. This method can be used to identify pipe sections with high corrosion failure probability in natural gas gathering and transportation pipelines.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas pipeline safety risk assessment, and specifically relates to a method for identifying pipe sections with high failure probability, which is mainly used for identifying pipe sections with high corrosion failure probability in natural gas gathering and transportation pipelines. Background Art

[0002] The medium transported by my country's natural gas gathering and transmission pipelines is complex, and internal corrosion and perforation accidents are prone to occur due to the synergy of multiple factors.

[0003] Internal inspection is the most accurate method for understanding the internal corrosion status of pipelines, but its application cost is relatively high. Therefore, the National Association of Corrosion Engineers (NACE) proposed direct internal corrosion assessment methods in 2002, including the Dry Gas Internal Corrosion Assessment Method (DG-ICDA), the Crude Oil Internal Corrosion Assessment Method (LP-ICDA), the Wet Gas Internal Corrosion Assessment Method (WG-ICDA), and the Multiphase Mixed Flow Internal Corrosion Assessment Method (MP-ICDA).

[0004] Direct internal corrosion assessment is primarily divided into pre-assessment, indirect detection, direct detection, and post-assessment. Pre-assessment determines the feasibility of direct internal corrosion assessment of pipelines through data collection and further identifies the area to be evaluated. Corrosion rate prediction is then performed, combined with multiphase flow calculation results, in what is known as indirect assessment. Therefore, for indirect assessment, corrosion rate prediction results are a key parameter for improving direct internal corrosion assessment. Predicting internal corrosion is a crucial step in improving the accuracy of pipeline internal corrosion protection and reducing the risk of pipeline corrosion failure. Corrosion models have also gradually evolved from empirical models and semi-mechanistic-semi-empirical models to mechanistic models.

[0005] The construction of mechanistic models is difficult due to the common multi-factor synergistic corrosion environment in industrial environments. In addition, some empirical models are highly dependent on raw corrosion data, with limited application scope, and are limited in predicting flow corrosion in gathering and transportation pipelines.

[0006] At present, the difficulties in studying the multi-factor coordinated corrosion phenomenon in natural gas gathering and transportation pipelines are as follows: the transportation medium of the gathering and transportation pipelines is different at each stage, and it is necessary to trace the medium and variation range that affect pipeline corrosion; the gathering and transportation pipelines are located in mountainous areas with large undulations and are affected by special gas-liquid two-phase flow, and the impact of flow on corrosion needs to be further clarified; the complex corrosion mechanism of factors such as CO2, SRB, and O2 is still unclear, and the multi-factor coordinated corrosion mechanism needs to be studied in depth, and a corrosion prediction model needs to be established; the possibility of corrosion failure in the pipeline has not been quantified, which has become a bottleneck problem in graded corrosion control.

[0007] The present invention performs three-dimensional multiphase flow simulation calculations on pipelines and combines a multi-factor collaborative corrosion prediction model to calculate the corrosion rate along the pipeline. By identifying the factors affecting internal corrosion and calculating the internal corrosion rate, the possibility of pipeline corrosion failure is determined, and a local corrosion failure criterion CRT is established to determine the level of internal corrosion failure possibility. Summary of the Invention

[0008] The present invention proposes a method for identifying pipe sections with high failure probability in order to identify high corrosion failure probability of natural gas gathering and transportation pipelines and reduce pipeline perforation accidents caused by internal corrosion.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] S1: Establish a three-dimensional pipeline model, perform multiphase flow simulation, calculate flow parameters along the pipeline, and collect data;

[0011] S2: Combine multiphase flow simulation parameters and data to clarify the corrosion mechanism in the pipeline;

[0012] S3: Identify the factors affecting internal corrosion by studying the internal corrosion mechanism;

[0013] S4: Combine the multi-factor synergistic corrosion prediction model to predict the internal corrosion rate;

[0014] S5: Calculate the corrosion rate along the pipeline;

[0015] S6: Establish local corrosion failure criterion CRT to determine the probability level of internal corrosion failure.

[0016] 101: Calculating Localized Corrosion Rates

[0017] 102: Where: CR l ——local corrosion rate, mm / a; h——pitting depth; t——time, h.

[0018] 103: Calculating localized corrosion failure criteria

[0019] 104: Where: CRT - the useful life of the pipeline under local corrosion, a (year); δ - the wall thickness of the pipeline project, mm; CR l ——Local corrosion rate, mm / a.

[0020] Based on the ratio of pipeline design wall thickness to corrosion rate, the probability of local corrosion failure is divided into five levels, among which level 1 is "very low" failure probability, level 2 is "low" failure probability, level 3 is "medium" failure probability, level 4 is "medium-high" failure probability and level 5 is "high" corrosion failure probability.

[0021] The method for identifying the possibility of localized corrosion failure is calculated according to the following steps:

[0022] 201: When CRT ≥ 20a, the failure probability level is judged to be 1;

[0023] 202: When 20a<CRT≤10a, the failure possibility level is judged to be 2;

[0024] 203: When 10a<CRT≤5a, the failure probability level is judged to be 3;

[0025] 204: When 5a<CRT≤3a, the failure probability level is judged to be 4;

[0026] 205: When CRT < 1a, the failure probability level is judged to be 5. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Flowchart for determining the possibility of internal corrosion failure of the present invention

[0028] Figure 2 This is the pipeline corrosion failure possibility level diagram of the present invention DETAILED DESCRIPTION

[0029] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0030] The first step is to simulate the three-dimensional multiphase flow in the pipeline. The simulation parameters are shown in Table 1:

[0031] Table 1 Pipeline simulation parameters

[0032]

[0033]

[0034] Calculate the corrosion rate along the pipeline:

[0035] Local corrosion rate

[0036] Where: CR l ——local corrosion rate, mm / a; h——pitting depth; t——time, h;

[0037] The corrosion rate along the line is calculated.

[0038] Calculation of localized corrosion failure criteria

[0039] Where: CRT - the useful life of the pipeline under local corrosion, a (year); δ - the wall thickness of the pipeline project, mm; CR l——local corrosion rate, mm / a;

[0040] The useful life of the pipeline under local corrosion is calculated.

[0041] The possibility of local corrosion failure is divided into five levels based on the ratio of pipeline design wall thickness to corrosion rate:

[0042] Among them, level 1 is "very low" failure probability, level 2 is "low" failure probability, level 3 is "medium" failure probability, level 4 is "medium-high" failure probability and level 5 is "high" corrosion failure probability.

[0043] When CRT ≥ 20a, the failure possibility level is judged to be 1;

[0044] When 20a<CRT≤10a, the failure possibility level is judged to be 2;

[0045] When 10a<CRT≤5a, the failure possibility level is judged to be 3;

[0046] When 5a<CRT≤3a, the failure possibility level is judged to be 4;

[0047] When CRT is less than 1a, the failure possibility level is judged to be 5.

Claims

1. A method for identifying pipe sections with high failure probability, characterized in that: The process includes the following: S1: Establish a three-dimensional pipeline model, perform multiphase flow simulation, calculate flow parameters along the pipeline, and collect data; S2: Combine multiphase flow simulation parameters and data to clarify the corrosion mechanism in the pipeline; S3: Identify the factors affecting internal corrosion by studying the internal corrosion mechanism; S4: Combine the multi-factor synergistic corrosion prediction model to predict the internal corrosion rate; S5: Calculate the corrosion rate along the pipeline; S6: Establish local corrosion failure criterion CRT to determine the probability level of internal corrosion failure; The local corrosion rate and failure criterion of the pipeline are calculated according to the following steps: 101: Calculating Localized Corrosion Rates Where: CR l ——local corrosion rate, mm / a; h——pitting depth; t——time, h; 102: Calculating localized corrosion failure criteria Where: CRT - the useful life of the pipeline under local corrosion, a year; δ - the wall thickness of the pipeline project, mm; CR l ——local corrosion rate, mm / a; The localized corrosion failure probability is divided into five levels based on the ratio of the pipeline design wall thickness to the corrosion rate, where level 1 is "very low" failure probability, level 2 is "low" failure probability, level 3 is "medium" failure probability, level 4 is "medium-high" failure probability, and level 5 is "high" corrosion failure probability. The localized corrosion failure probability identification method is calculated according to the following steps: 201: When CRT ≥ 20a, the failure probability level is judged to be 1; 202: When 20a<CRT≤10a, the failure possibility level is judged to be 2; 203: When 10a<CRT≤5a, the failure probability level is judged to be 3; 204: When 5a<CRT≤3a, the failure probability level is judged to be 4; 205: When CRT < 1a, the failure probability level is judged to be 5.

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