Corrosion inspection plan for major equipment overhauls

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Corrosion is a problem faced by various industries and sectors. In our country, the total cost associated with corrosion amounts to about 5% of GDP, resulting in numerous casualties and economic losses. Since chemical industry operations often take place under high temperature and pressure conditions, and the reactants and media involved are hazardous, accidents caused by corrosion of equipment and pipelines in chemical plants cannot be ignored; therefore, it is particularly important to carry out anti-corrosion measures for equipment and to inspect for corrosion in industrial installations. Corrosion classification: To prevent corrosion, it is first necessary to understand its classification. Corrosion can be divided into metal corrosion and non-metal corrosion based on the type of material. Corrosion is classified into general corrosion and local corrosion based on surface morphology ； Local corrosion includes pitting corrosion, stress corrosion cracking, crevice corrosion, galvanic corrosion, wear corrosion, and so on ； Metal corrosion can be classified into physical corrosion, chemical corrosion, electrochemical corrosion, etc., based on its mechanism. Physical corrosion: The degradation of a material due to purely physical effects, usually caused by dissolution or penetration, such as the dissolution of metal containers in molten metals, or the dissolution and penetration of these containers by high-temperature molten salts or alkalis. Chemical corrosion: Damage caused by a direct chemical reaction between a metal and a non-electrolyte; no electric current is generated during the corrosion process. The corrosion process is a pure oxidation-reduction reaction; the corrosive medium collides directly with the atoms on the metal surface to form corrosion products, and no electric current is generated during this reaction, in accordance with the laws of chemical kinetics. Electrochemical corrosion: Damage caused by an electrochemical reaction between a metal and an electrolyte solution. During the reaction process, the anode loses electrons while the cathode gains electrons, along with the flow of electrons (current); this process follows the laws of electrochemical kinetics. The main causes of corrosion in chemical production processes are the presence of various corrosive substances in these processes. The type, chemical composition, concentration, pH value, impurities, moisture content, and oxygen level of these substances are all factors that contribute to corrosion. The faster the flow velocity of the medium, the more susceptible it is to corrosion, as the flowing medium erodes the protective film, creating vortices, turbulence, and bubbles that lead to severe impact wear and cavitation corrosion. Furthermore, improper material selection can also lead to problems: if the surface of the equipment comes into contact with corrosive substances and the equipment itself is not corrosion-resistant, surface corrosion will occur. The rougher the surface, the more prone it is to corrosion, and the resulting symptoms include leakage, premature wear, damage, and noise. Uniform surface corrosion can occur in two forms: with film formation and without film formation. Corrosion without film formation is very dangerous, and the corrosion process proceeds at a certain rate; this is mainly caused by incorrect material selection. Lack of anti-corrosion measures or poor construction quality all create an environment conducive to corrosion damage. Different environments require different materials. During the production of equipment, it is often not possible to balance material selection with resistance to environmental corrosion. Differences in temperature, concentration, and pressure lead to different material choices and varying levels of corrosion. Moreover, poor quality control during construction results in inadequate construction standards, making corrosion an inevitable issue. Over-temperature and over-pressure during operation, inadequate equipment management, and a lack of emphasis are also among the causes of corrosion damage. Generally, the higher the temperature of the medium, the higher the pressure, and the faster the corrosion occurs, as corrosion is a chemical reaction; for every 10°C increase in temperature, the corrosion rate increases by 1 to 3 times. The corrosion inspection plan: Corrosion inspection refers to the use of various instruments, tools, and analysis methods to determine the rate of corrosion of materials in process media environments. It provides engineering and technical personnel with information on equipment corrosion, enabling them to take effective measures to slow down corrosion and prevent corrosion-related accidents. Corrosion inspection during major plant overhauls involves formulating a corrosion inspection plan tailored to the specific conditions of the plant. During the shutdown for overhauls, a specialized team is assembled to carry out inspections of the equipment and pipelines using macroscopic examination as well as other effective testing methods, in order to assess the morphology and condition of corrosion. Based on these findings, the mechanisms behind corrosion are analyzed, the corrosion rate is calculated, and the extent of damage is determined. 01 The purpose of the corrosion inspection during the major overhaul of the unit is to determine the degree of equipment damage and corrosion after one cycle of continuous operation. Evaluate the effectiveness of the equipment and process anti-corrosion measures adopted for this unit during this cycle. It verifies the accuracy of the RBI risk assessment results, providing reliable validation to guide the assessment of pressure vessels and pressure pipelines using RBI. To provide a basis for determining the equipment and process anti-corrosion measures to be adopted for this unit in the next cycle. 02 Tasks related to corrosion inspection during unit overhauls: I. Collection of original data for corrosion inspection – including the unit’s process flow diagrams, operating procedures, detailed lists and individual drawings of equipment and pipelines, the unit overhaul plan, inspection plans for pressure vessels and pipelines, historical thickness measurement records, historical maintenance and inspection records, as well as historical laboratory test results (including data on crude oil evaluation, analysis data, electrodesalination analysis data, and analysis data on triple-top condensate, etc.). Overhaul project plan (phone numbers of the responsible persons from each construction unit are preferred); equipment operation procedures; individual equipment diagrams; equipment documentation records; evaluation and analysis of raw materials used in the previous production cycle; device calibration reports; historical corrosion records; completion documents (including installation documents); records of maintenance or emergency repairs over the years; DCS historical records for the past six months, as well as records of overpressure and overheating alarms; sampling and analysis data from the past six months and the most recent device calibration reports; data from fixed-point thickness measurement and online corrosion monitoring. II. Formulation of corrosion inspection plan: Based on the actual conditions of the device (process flow, process parameters, equipment characteristics), along with the results of the RBI risk assessment, it is necessary to determine the corrosive agents acting on different parts of the device; possible corrosion mechanisms; the failure modes associated with these mechanisms, and the appropriate detection methods. Thereby determining the focus of the corrosion investigation and the inspection strategy. III. On-site corrosion inspection is carried out in accordance with the corrosion investigation plan ； Analyze the corrosion condition of equipment and devices ； Preliminary analysis of corrosion mechanism ； Report on Recommendations for Corrosion Protection of the Equipment ； Prepare on-site reports for corrosion inspections. IV. Introduction to the Comprehensive Corrosion Inspection Report Generator ； Analysis of the device’s corrosion over the years, as well as the operation status and analysis of the device during the previous cycle ； Inspection status of equipment for major workshop repairs ； Overhaul details (mainly the completion status of opening containers, repairing, and modifying equipment pipelines) ； Analysis of inspection data for pressure vessels and pressure pipelines ； Analysis of thickness measurement data from major equipment overhauls ； Non-destructive testing data analysis for plant overhauls ； Detailed Table of Equipment and Pipeline Corrosion Inspections ； Report on Analysis of Typical Corrosion Cases and Corrosion Mechanisms ； Selection of monitoring points and types for online corrosion monitoring ； Analysis of fixed-point thickness measurement scheme ； In-service inspection, inspection plan analysis ； Sampling point selection and analysis of testing plans ； Analysis of the overall corrosion condition of the device ； Analysis of the Current Status of Process Anti-corrosion and Optimization Solutions ； Analysis of the Current Anti-corrosion Status of Equipment and Optimization Solutions ； V. The assessment of the equipment’s safety status involves determining whether, under the existing material conditions and current process anti-corrosion measures, the corrosion rate remains within acceptable limits. What measures can be taken to reduce the corrosion rate if it exceeds the allowable range? VI. Assessment of weak points in the installation: In accordance with the relevant regulations of Sinopec Corporation, an actual corrosion rate of more than 0.25 mm/a indicates that the material grade used in that area is insufficient, and it is necessary to upgrade the material. The parts where the corrosion rate is above the limit and the risk of failure is high are the weak points of the device. Generally, a material upgrade plan for the next cycle should be formulated. VII. Process adaptability assessment: In petrochemical plants, changes in the properties of raw materials and process conditions occur frequently. In particular, some process modifications are carried out during each major plant overhaul. It is necessary to determine what impact these changes will have on equipment and pipelines, whether new problems will arise, and what measures should be taken to prevent them. VIII. Others include various tests, simulations, experiments, and analyses of active sulfur carried out during the same period to complete the aforementioned report.