How to Deal with Corrosion of Instruments

In the industrial production of the petrochemical industry, corrosion of production equipment by various acidic and alkaline raw materials is a common phenomenon. The presence of corrosion undoubtedly has adverse effects on the service life of equipment and the stability of production. Through process improvements and increased automation levels of equipment, production efficiency can be enhanced, simultaneously improving equipment stability while effectively enhancing avoidance of potential hazards.

Corrosion issues with chemical instruments are quite common and diverse, with complex causes. Severe corrosion, if left untreated, can lead to reduced efficiency and quality in chemical production, disrupt normal production processes, increase the risk of production accidents, and potentially cause economic losses to chemical enterprises. Therefore, corrosion prevention for chemical instruments is crucial.

How to Deal with Corrosion of Instruments

Types of Chemical Instruments

Chemical instruments are widely used in chemical production to detect and control variables such as temperature, pressure, flow rate, liquid level, and composition, playing a crucial role in ensuring the safety and stability of chemical production.

First, let’s understand the classification of chemical instruments. Based on the type of energy source, chemical instruments can be divided into electric chemical instruments, hydraulic chemical instruments, and pneumatic chemical instruments. Based on the measurement object, they can be categorized as temperature instruments, pressure instruments, flow instruments, level instruments, and analytical detection instruments, each corresponding to one of the five major parameters in chemical production. By their function, they are generally classified as detection instruments, display instruments, regulating control instruments, and actuators.

Common Corrosion Issues with Chemical Instruments

Corrosion of chemical instruments refers to the erosion and corrosion phenomena of the metallic or non-metallic materials constituting instrument components due to physical, mechanical, chemical, or electrochemical actions, collectively termed corrosion.

The purpose of studying corrosion prevention for chemical instruments is to analyze the types, mechanisms, and hazards of corrosion, identify the main corrosion factors and their solutions, particularly for chemical instruments used in chlor-alkali and alkali production, through experimental analysis, to improve the corrosion resistance of instruments, ensure measurement control accuracy, and enhance production efficiency with automation. The main types of corrosion for chemical instruments are electrochemical corrosion, chemical corrosion, and erosion of instrument materials due to physical or mechanical actions.

Temperature Sensor (2)

Electrochemical Corrosion

Chemical instruments used in chemical production processes are generally made of metal materials and are subjected to complex environments of high temperature and pressure for extended periods. They also need to come into direct contact with various chemical materials, making them susceptible to electrochemical corrosion. Electrochemical corrosion of chemical instruments is one of the most common and troublesome corrosion issues in chemical production. It is difficult to control and manage due to its concealed nature. When chemical instruments come into contact with ions or chemical media in the air, they form currents on the surface of the instrument, causing varying degrees of corrosion to the metal structure, affecting normal usage and reducing their service life.

Chemical Corrosion

In chemical production processes, various chemical materials are used, most of which readily undergo chemical reactions with air or other substances and possess corrosive properties. The materials composing chemical instruments mainly include benzene and ethanol, and they are generally used in environments with high temperatures and pressures. In such cases, chemical instruments gradually undergo chemical reactions as chemical media permeate into the instrument structure under the action of high-temperature steam. This leads to the instruments becoming hardened and brittle, gradually corroding until they are damaged and unusable. Chemical corrosion is the most common type encountered during the normal use of chemical instruments. For instance, in the production of pyrite in the chemical industry, boiling occurs, generating large quantities of dry gas with extremely high temperatures, resulting in rapid and severe corrosion of the metal surface of chemical instruments, affecting their normal use.

This type of corrosion is often overlooked and easily neglected. By the time corrosion issues are discovered, chemical instruments are usually severely affected and can no longer be used, necessitating replacement to restore normal chemical production processes.

Stainless steel pressure gauge

Physical Corrosion

In addition to chemical corrosion, physical corrosion is also a common type encountered during the normal operation of chemical instruments. This is because the materials used in the production of chemical instruments are quite special and often endure prolonged exposure to high temperatures and pressures, making them susceptible to physical stress, leading to a decline in performance and physical corrosion issues.

In simple terms, physical corrosion of chemical instruments is opposite to chemical corrosion. Chemical corrosion arises from chemical reactions between the chemical medium and the instrument. Conversely, physical corrosion occurs due to the impact of high temperatures and pressures during normal operation, resulting in significant pressure on the instrument. Typically, physical corrosion in chemical instruments occurs prominently in the production process of chemical synthesis of ammonia. This is because the synthesis process generates large amounts of high-temperature steam, exerting substantial physical pressure on the instrument’s core, thus leading to physical corrosion issues. Consequently, chemical instruments may fail to function properly or become completely damaged, necessitating timely repair and replacement to prevent further complications and economic losses.

Microbiological Corrosion

The production process in the chemical industry is highly complex, with most production equipment being enclosed. Such environments, coupled with persistent fouling and contamination, often promote the growth of microbiota. The proliferation of microorganisms can cause corrosion issues for chemical instruments.

Additionally, inadequate cleaning of internal spaces within chemical production equipment facilitates the growth and development of microorganisms. The increased microbial population accelerates the reproduction of bacteria and algae, disrupting the stable production environment and impacting chemical instrument functionality. Microbiological corrosion issues are not uncommon and should not be overlooked. Addressing them requires adopting effective measures based on the specific characteristics and causes of microbiological corrosion, aiming to prevent and mitigate its effects, restore a favorable production environment, minimize corrosion impact on chemical instruments, and ensure their prolonged usability.

liquid turbine flowmeter (5)

Treatment Methods for Corrosion in Chemical Instruments

Selection of Corrosion-Resistant Materials

The corrosion issues in chemical instruments predominantly stem from the materials themselves. Chemical instruments are typically made from metallic materials prone to corrosion. When these materials come into contact with chemical media and high-temperature substances, the probability and severity of chemical reactions increase, exacerbating corrosion. To address corrosion issues fundamentally and prolong instrument lifespan, it is imperative to choose suitable corrosion-resistant materials to replace traditional metallic ones. This selection reduces the damage caused by chemical production to chemical instruments, saving on maintenance and replacement costs. Material selection for chemical instruments should prioritize enhancing corrosion resistance, ensuring stability when exposed to chemical media and high temperatures, and mitigating corrosion risks effectively.

Application of Protective Coatings

Applying protective coatings on instrument components is a widely adopted corrosion prevention method in industries. Protective coatings can be categorized into metallic and non-metallic types. For chemical instruments, coating with anti-corrosion paint is a cost-effective solution. Periodic application and reapplication of anti-corrosion paint maintain a favorable corrosion-resistant environment for chemical instruments. Despite its limitations, anti-corrosion paint application remains a common and effective corrosion prevention technique for chemical instruments. Strict control over paint selection and application minimizes its adverse effects on instrument performance or production processes.

Magnetic Level Gauge

Utilization of Non-Metallic Protective Films

Applying non-metallic protective films involves chemical treatment of metal surfaces to generate oxide or phosphate films. These films act as barriers against corrosion, enhancing instrument longevity and performance.

Control of Microbial Population

Microbial activity during instrument operation can lead to corrosion. Controlling microbial populations is essential to mitigate corrosion effectively. Regular monitoring of microbial indicators such as anaerobic bacteria and fungi allows for timely intervention through disinfection treatments. The dosage and type of disinfectants should be adjusted based on the microbial species and population, ensuring minimal disruption to production processes while effectively controlling corrosion. Developing viable strategies requires rigorous theoretical validation and scientific experimentation to reduce microbial corrosion damage to chemical instruments effectively.

Strengthening the management of chemical instrumentation usage

The use of chemical instrumentation needs to strictly adhere to the corresponding operating specifications, which can effectively reduce the probability of corrosion issues. Surface corrosion of chemical instrumentation can be repaired and salvaged with minimal impact, by replacing the casing and putting it back into service. However, if internal corrosion occurs, it can lead to more serious consequences, damaging various electronic components and chips inside the instrumentation, requiring the entire instrument to be replaced to restore normal functionality, resulting in higher costs. Therefore, it is necessary to strengthen the management of chemical instrumentation usage, making effective preventive and corrective decisions regarding common corrosion issues in chemical production.

Online Concentration Monitor

Conduct isolation work

The usage environment of chemical instrumentation is highly complex, so regardless of the choice of anti-corrosive materials, some chemical reactions, physical reactions, and electrochemical reactions are inevitable during actual usage, making it impossible to completely eliminate instrumentation corrosion issues. Therefore, in order to extend the service life of chemical instrumentation as much as possible, it is necessary to actively conduct isolation work based on the actual working environment and performance characteristics of the instrumentation, thereby reducing the probability of corrosion occurrence.

Firstly, chemical enterprises can adopt monitoring instrumentation such as radioactivity, ultrasound, and optical radiation, which can completely prevent the instrumentation from being corroded and damaged by the medium, but the cost is higher, and subsequent maintenance and upkeep are also more complex. Secondly, using isolation devices, isolation membranes, isolation fluids, and other isolation measures can separate the detection part of the instrumentation from the medium, achieving the anti-corrosion effect. Isolation corrosion prevention is an effective method for instrumentation corrosion prevention. Depending on the different actual conditions and measurement control needs, methods such as adding isolation fluid, blowing air, and adding protective layers can effectively prevent or slow down the corrosion of instrumentation.

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