Equipment corrosion

1. The corrosion margin of heat exchange equipment can be increased, or materials with good resistance to sulfur corrosion can be selected. 2. Strengthen management measures for three separations and one injection.

※Organization and Division of Labor 1. The Mobile Department has full-time corrosion prevention managers who are responsible for formulating corrosion prevention plans and managing related technical aspects for all the equipment in the plant； The workshop equipment officer is responsible for the specific management of equipment corrosion prevention. 2. Test researchers and construction units involved in corrosion prevention management must continuously conduct surveys on equipment corrosion and protection at the head office, formulate corrosion prevention plans and initiatives, analyze the causes of corrosion and corresponding protection methods, and summarize corrosion prevention techniques based on experience and achievements. 3. The equipment department shall ensure that the materials, protection methods, and structure of corrosion-resistant equipment are correct and appropriate. The equipment manufactured by the manufacturing department (unit) must meet the design drawings and technical specifications; installers need to be aware of the properties and requirements of corrosion-resistant materials to prevent damage during installation. ※Creation of archival records and technical management: 1. For equipment, pipelines, etc. that are subject to corrosion by the production media, the Mechanical Department is responsible for creating anti-corrosion archives and cards. These records should include information such as the name and model of the equipment, its specifications, operating temperature and pressure, the type of material used, its performance characteristics, as well as the anti-corrosion measures taken. They should also cover the date of installation, the construction methods used, the equipment’s usage history, details of each inspection and maintenance session, etc. For equipment that is generally subject to atmospheric corrosion, a corrosion prevention record book should be maintained on a per-unit or per-area basis; a record should be kept each time corrosion prevention measures are taken. 2. The Maintenance Department shall, based on the corrosion issues encountered in production and the available construction resources, organize the revision of the anti-corrosion plan for the following year by June 15 each year, which shall include trial research projects and budgetary costs for the prototype development of equipment. 3. Appropriate anti-corrosion measures shall be taken for all equipment that is prone to corrosion. For equipment that already has such measures in place, these measures must not be removed without reason or altered arbitrarily. Production practice has shown that such actions are indeed inappropriate; a new proposal must be submitted by the workshop, reviewed by the Mechanical Department, and only after approval by the deputy head of equipment or the chief engineer can the original anti-corrosion measures for the equipment be modified. 4. The use of new corrosion-resistant materials and the adoption of new anti-corrosion technologies must undergo small-scale tests and medium-scale evaluations; there must be solid scientific evidence to support their use in production. 5. The Mechanics Department is responsible for organizing the relevant production workshops to conduct experimental research on atmospheric corrosion, analyzing the causes of corrosion, and proposing anti-corrosion measures as well as protection methods. Corrosion problems that cause production disruptions due to severe corrosion during manufacturing were taken as the main focus for experimental research, in order to determine appropriate anti-corrosion measures. 6. Whenever process conditions in production are changed, or equipment, pipes, and fittings are replaced or added, the corrosion resistance of the materials must be taken into consideration. ※Maintenance and repair: 1. For equipment that has undergone anti-corrosion treatment, regular inspections and planned repairs are necessary. Improvements to anti-corrosion measures (including the use of new technologies and materials) should be carried out in conjunction with planned maintenance. 2. Eliminate phenomena such as dripping, leaking, running, and escaping; do not install backflow or vent pipes arbitrarily. The exhaust gases and waste liquids released during equipment maintenance are also subject to strict treatment to prevent corrosion of the equipment and buildings. 3. When the equipment is no longer in use, anti-corrosion measures should be taken, such as emptying, purging, nitrogen filling, and degreasing. 4. Welding of components is strictly prohibited on equipment with anti-corrosion coatings. When welding is necessary, reliable measures must be in place or anti-corrosion treatment must be reapplied after welding. 5. When using special corrosion-resistant metals or alloy materials, it is necessary to strictly follow the process specifications for welding, cleaning, heat treatment, etc., during manufacturing and maintenance. In highly corrosive media, avoid using different types of metals together. 6. Hitting and striking non-metallic equipment as well as equipment and fittings with anti-corrosion coatings is strictly prohibited. 7. Strictly follow the maintenance and construction procedures for anti-corrosion equipment to ensure construction quality and personal safety. 8. Extend the service life of equipment, pipelines, and buildings by carrying out rust removal, anti-corrosion, and painting tasks in conjunction with major repairs and routine maintenance. 9. The anti-corrosion materials used must meet the technical requirements, and should be accompanied by inspection certificates and the date of manufacture. ※Inspection and recording of equipment corrosion prevention 1. The Machinery Department shall organize relevant units to conduct inspections and assessments at least once a year on the corrosion status and protection measures for the company’s equipment, pipelines, and factory buildings, and submit a written report thereon. 2. Advanced condition monitoring instruments should be gradually adopted to monitor the corrosion status of operating equipment, thereby laying a foundation for predictive maintenance. 3. The regular inspection of equipment corrosion includes the following: (1) Analysis of the type of corrosion, the depth of corrosion, the condition of welds, and analysis of corrosion products. (2) Metallographic microscopy, flaw detection, degree of aging of the anti-corrosion coating, cracking and peeling, wear, and other forms of damage. 4. The results of the inspection shall be recorded in detail (in two copies), to be filed and kept by the Machinery Department and the workshop. 5. The annual inspection is carried out on the basis of self-inspections by each unit. During inspection, for devices of the same type, 1 to 2 units are randomly selected for inspection based on their quantity. For pipes of the same type, two sections are inspected on the main pipeline or branch pipe.

For the top circulation pump of the distillation tower, pumps resistant to acids and hydrogen sulfide can be considered for replacement; such replacements require compliance with specific parameters such as temperature and pressure； The heat exchanger can be replaced by replacing its tubes, or other types of acid-resistant plate heat exchangers can be used

It is necessary to use three nozzles per separator, but the material used also needs to be upgraded. 12Cr2AlMoV steel has been widely used in the tube bundles of the condensers at the top of distillation columns recently, and it performs quite well – much better than carbon steel

It is likely to be typical low-temperature corrosion caused by hydrogen sulfide, hydrogen chloride, and water. For heat exchangers, the material should first be replaced as mentioned above, by using 12Cr2AlMoV steel, or by employing the two low-alloy steels 08Cr2AlMo and 09Cr2AlMoRe that have been developed in China and offer superior performance. In addition, process-based anti-corrosion measures are essential; electrodesalination operations should be intensified to reduce the salt content to below 5 mg/L (preferably below 3 mg/L). Furthermore, when using triple injection methods in devices such as the top circulation pumps of distillation towers and heat exchangers, it is better not to use ammonia-based neutralizers, but rather organic amine neutralizers, as ammonia solutions are difficult to control, and ammonium chloride corrosion can easily occur in heat exchanger areas.

It seems that the original poster’s question is missing one element: is it a vacuum distillation unit or a fractionation tower used in catalytic coking and hydrogenation? The degree of corrosion varies in these cases.

The analysis on floor 6 is comprehensive. Corrosion in the top circulation system is a problem that is relatively difficult to solve. We changed the material type while striving to minimize corrosive agents; aluminum-coated material is a good choice.

To address the corrosion issue of equipment such as tower tops, it is recommended to first select appropriate corrosion monitoring points based on factors such as material, manufacturing process, and environment. Then, an online corrosion and pH monitoring system should be established, along with offline testing and laboratory analysis. By analyzing the data from these monitoring activities, the causes of corrosion and its rate can be determined, allowing for targeted implementation of various anti-corrosion measures such as replacing or upgrading materials, adding suitable corrosion inhibitors, improving the filling process, or applying protective coatings.

If you need to have the corrosion situation analyzed, feel free to contact us. Please note that this is for non-commercial purposes; we are interested in understanding the impact of sulfur-containing oils on equipment corrosion. Let us introduce our expert: Professor Zhang, a council member of the Chinese Society for Corrosion and Protection, who has long been engaged in research on corrosion failure and anti-corrosion analysis. You can reach us at: ATI CHINA SHANGHAI BRANCH OFFICE, baoseti@sohu.com

We understand that much of China’s oil is currently imported from the Middle East, and the oil from the Middle East contains sulfur, which has a certain impact on the existing equipment used for extraction, transportation, and refining. However, it is not clear to what extent this impact exists, nor what level of corrosion resistance is required. Therefore, those who are interested in entering this industry would like to discuss this matter.

Select materials appropriately and strengthen the \"one removal and three injections\" process”

The area of the refinery tower top most severely affected by corrosion is the atmospheric pressure tower top of the distillation unit; here, corrosion is primarily caused by hydrochloric acid, while hydrogen sulfide has a lesser impact due to the formation of a passivation film. Proper operation of electrodesalination is necessary, but it cannot eliminate the organic chlorines present in crude oil. Secondly, the use of four types of additives (ammonia/amine, water, alkali, and corrosion inhibitor), along with a top-of-tower monitoring system and an automatic dosing system, can minimize corrosion in the top-of-tower condenser; carbon steel can be used as the material for this purpose. Alkali injection is commonly used abroad, while only a few factories in China achieve good results with this method (Zhenhai). If the crude oil varies significantly and management fails to keep up, resulting in an uncontrolled level of chloride ions at the top of the tower, it is recommended to use acid-resistant materials (Monel, 2205, titanium). 08Cr2AlMo and 09Cr2AlMoRe are not steels suitable for use in hydrochloric acid environments; they offer poor cost-performance, and their corrosion rate in normal service conditions is similar to that of carbon steel. Materials with surface treatments such as NI-P electroless plating or chloridation cannot be used, as the pinholes formed on the surface create large cathodes and small anodes, leading to rapid perforation. The tower top materials designed for new refineries are primarily titanium and 2205. The top of the coking fractionation tower, where it is subject to corrosion by hydrogen sulfide, ammonia, and ammonium chloride, is made of carbon steel. For the corrosion-resistant materials at the top of the FCC unit’s fractionation tower, carbon steel is used for hydrogen sulfide, ammonium chloride, carbon dioxide, and ammonia. In both sets of units, all the HCL at the top of the towers has reacted with ammonia; the pH is alkaline, so corrosion is low compared to distillation units.

Due to the increase in sulfur content in China’s petroleum in recent years, corrosion protection of equipment has become extremely important. For the corrosion of some tower tops, we can prevent it by adding corrosion inhibitors; as for the corrosion caused by high-temperature flue gases, we can address it by optimizing operations. Additionally, when selecting materials for the equipment, we also need to make choices based on the actual circumstances.

Anti-corrosion measures must be taken on the equipment, such as regarding materials and welding methods; however, this generally only provides temporary relief rather than a permanent solution； The anti-corrosion measures in terms of processing are good, such as one removal and three injections, the use of passivators and scale inhibitors, etc., but the cost is high.

Choosing the right chemical is crucial

What kind of device is the distillation tower that the original poster is talking about? Distillation columns are used in catalysis, hydrogenation, coking, and reforming, but the degree of corrosion varies. Fractionation towers generally do not include atmospheric and vacuum distillation towers; several people above mentioned distillation processes quite often. Stainless steels such as 08Cr2AlMo and 09Cr2AlMoRe are not suitable when the chloride concentration exceeds 100 ppm; they perform poorly in hydrochloric acid environments. Their advantage lies in their performance in hydrogen sulfide environments, as well as in high-temperature hydrogen environments

Everyone is facing the same problem; the current solutions are all the same

Select materials appropriately and strengthen the \"one removal and three injections\" process”