Application of 07/09Cr2AlMoRE and 08Cr2AlMo in the overhead systems of refinery units

I’ll post a passage first for everyone’s reference, as a way to spark further discussion: The crude oil and natural gas from China’s Tarim Oil Field in Xinjiang, Zhongyuan Oil Field, Sichuan oil and gas fields, and the Gannan central oil and gas fields all contain high levels of hydrogen sulfide. The corrosion of hydrogen sulfide on oil field equipment is mainly concentrated in the crude oil gathering and transportation systems. Therefore, the three-phase separators, gas-liquid separators, crude oil heaters at the gathering and transportation stations, as well as some of the gathering and transportation pipelines, suffer from severe hydrogen sulfide corrosion. To address the corrosion problem caused by wet hydrogen sulfide, the author proposed designing a rare earth-containing alloy steel with improved weldability and corrosion resistance based on the Cr2Al2Mo alloy. In 1999, the 09Cr2AlMoRE seamless steel pipe resistant to wet hydrogen sulfide corrosion was successfully developed. To further meet the requirements for steel plates used in pressure vessel shells in the refining and oil extraction industries under wet hydrogen sulfide corrosion conditions, the chemical composition of this steel grade was optimized, resulting in the development of the low-alloy steel plate 07Cr2AlMoRE, which features a more rational chemical composition and superior properties. At the same time, high-performance welding materials suitable for it have also been developed. At present, the 07/09Cr2AlMoRE material has been granted a **patent (patent number 0111435912). Its tubes, forgings, and sheets have all passed the technical evaluation by the National Standardization Technical Committee for Pressure Vessels, meeting the specifications for the manufacturing and use of pressure vessels. 　The approach to optimizing the chemical composition of 07Cr2AlMoRE steel plates is as follows: (1) Keep the carbon content at the lowest possible level in order to improve the welding properties of the material and enhance its corrosion resistance. The actual C content of this steel plate is controlled at around 0.105%. (2) The upper limit range for Al is reduced to 0150%, while the lower limit remains unchanged. This ensures both the corrosion resistance of the welded joint and prevents welding brittleness of Al after welding. (3) To ensure the reliability of pressure vessels, strict control is exercised over the S content, which will play a significant role in improving the material’s resistance to stress corrosion. The actual sulfur content control level of this steel is only around 0.1005%. Welding materials and welding properties of 07/09Cr2AlMoRE steel: While developing the 07/09Cr2AlMoRE steel material, in order to address the issues related to its welding and manufacturing processes, welding materials with suitable properties were developed in collaboration with the Welding Research Institute of Huazhong University of Science and Technology. 11 Development of welding materials for submerged arc automatic welding: The wire used in submerged arc automatic welding is produced by drawing billets made of 07Cr2AlMoRE steel; thus, the wire is of type H07Cr2AlMoRE. The flux is developed specifically for use with this welding process, and the chemical composition of the deposited metal is essentially identical to that specified for the base material. The weld metal of this material exhibits good plasticity and toughness; in particular, its low-temperature impact toughness at -20 °C is above 100 J. Such high impact toughness values contribute to improving the weld’s resistance to wet hydrogen sulfide stress corrosion. 　 The purpose of the SR reheat treatment is to appropriately reduce the strength and hardness of the welded joint. After heat treatment using SR, a significant decrease in the HV hardness value was observed, with the hardness drop being even greater in the weld area. The HV hardness values of both the weld and the heat-affected zone after SR tempering meet the requirement specified in the \"Code for Technical Inspection of Pressure Vessels\", which states that for low-alloy steels in a wet hydrogen sulfide environment, the hardness value should be ≤ 245 HV (for individual values). 21 Development of manual welding electrodes: The core of the electrode designed for 07Cr2AlMoRE steel plates is made by drawing billets of this steel, while the outer coating is that of a low-hydrogen alkaline welding electrode. The electrode code is CJ R357. The chemical composition of its deposited metal is essentially the same as that specified for the base material. Hand-welded materials have better impact toughness. Higher impact toughness values contribute to improving the resistance of welds to wet hydrogen sulfide stress corrosion. 　The purpose of the SR reheat treatment is to appropriately reduce the strength and hardness of the welded joint. After heat treatment at SR temperature, a significant decrease in the HV hardness value was observed; the reduction was particularly pronounced in the weld area, where the hardness dropped by more than 100 HV. The HV hardness values of both the weld and the heat-affected zone after SR tempering meet the requirement specified in the \"Regulations for Technical Inspection of Pressure Vessels\", which states that for low-alloy steels in a wet hydrogen sulfide environment, the hardness value should be ≤ 245 HV (per individual measurement). Microscopic analysis of the metallurgical role of rare earths in steel. The metallurgical role of rare earths in steel is widely recognized both domestically and internationally; since the 1960s, a large number of rare earth steels have been put into industrial use. Adding rare earth elements to steel primarily serves to remove sulfur and oxygen during steelmaking and welding; it also helps to effectively control the shape, size, and quantity of impurities in the steel, as well as to refine the grain structure. Adding rare earth elements to steel can significantly enhance the material’s impact toughness and corrosion resistance, while also markedly improving its weldability. Just as with the addition of nitrogen to austenitic stainless steels and duplex stainless steels, even very small amounts can result in significant improvements in the material’s properties. Light rare earths are generally used in the metallurgical industry, with lanthanum and cerium accounting for about 60% of the total content of rare earths. Since rare earths are added during steelmaking primarily to further desulfurize and control the form of residual sulfides in the steel, the amount of rare earths added is determined based on the sulfur content remaining in the steel. Under normal circumstances, it is essential to make a fairly accurate calculation of the sulfur and rare earth elements remaining in the steel billet during steelmaking. The relationship between rare earths and sulfur is: RE/S = 26 times, at which point the overall performance of the steel is optimal. When the ratio of rare earths to sulfur in steel is less than 2, the effect of rare earths on controlling harmful inclusions is not very significant; on the other hand, an excessive amount of rare earths can lead to the formation of large quantities of rare earth oxide products in the steel ingot. Due to the effect of rare earths, compared with the rare earth-free 08Cr2AlMo steel, the 09Cr2AlMoRE steel has a higher total number of inclusions; however, the total area of these inclusions as well as the amounts of different types of inclusions are significantly reduced. This has a positive impact on improving the overall properties of the steel. The total area of inclusions decreases after the addition of rare earths; the total amount of sulfides decreases, and the total amount of oxides also decreases. The inclusions in the two steels were analyzed using a scanning electron microscope and an electron probe at magnifications of 500 × and 1000 ×: Sample 1 is (C ≤0.110%) Cr2AlMo without rare earth elements added; Sample 2 is (C ≤0.110%) Cr2AlMoRE with rare earth elements added. By comparing the morphology of the inclusions (500 ×, unsoaked) in the two samples, it can be seen that the inclusions in sample No. 1, which does not contain rare earth elements, are large and elongated, with a very distinct orientation. In contrast, the inclusions in sample No. 2 containing rare earths are small and dispersed, appearing as spherical particles with a relatively uniform distribution and showing no distinct orientation. By comparing the morphology of the inclusions (1000 ×) in these two samples, it can be seen that chain-like inclusions appear in sample No. 1, which contains no rare earth elements; such inclusions are relatively dangerous brittle inclusions such as Al2O3. In contrast, the No. 2 sample only showed a distribution of fine and dispersed inclusions. Corrosion test data of new materials and applicable environments: The corrosion patterns of carbon steel materials in humid hydrogen sulfide environments mainly include uniform corrosion, hydrogen blistering, and hydrogen-induced cracking; for stainless steel, the corrosion manifests primarily as stress corrosion in weld areas and areas with stress concentration. Once hydrogen sulfide mixes with other highly acidic substances such as hydrocyanic acid and chloride ions, its corrosiveness increases significantly, posing a serious threat to the proper operation of equipment. Therefore, the evaluation of corrosion tests on new materials, along with practical usage experience, are extremely important for the safe use and proper selection of these materials. 11 H2S stress corrosion resistance test: In accordance with the standard GB4157—84 \"Method for constant-load tensile testing of metals for resistance to sulfide stress corrosion cracking\", H2S stress corrosion tests were conducted on 07/09Cr2AlMoRE steel plates and welds, with a test duration of 720 hours. The test results show that for the 07Cr2AlMoRE steel plates and their butt welds, σth = 0175σs; for the 09Cr2AlMoRE steel pipes and their butt welds, σth = 0170σs. These values far exceed the requirement specified in the NACE TM 0177–96 standard, which requires σth ≥ 0145σs. 21 Uniform corrosion tests under simulated H2S medium conditions Table 8 Comparison of uniform corrosion tests under simulated H2S medium conditions Test materials: 09Cr2AlMoRE, 12Cr2AlMoV, No. 10 steel Corrosion rate/ (10^-2 mg·cm^-2·h^-1): 1158, 2128, 9128 Note: (1) The H2S content in the oil at the top of the catalytic system was 979 ppm; the test temperature was 100 ℃, and the immersion time was 144 hours. (2) The test data were provided by Jingmen Petrochemical Research Institute. The resistance of 09Cr2AlMoRE steel to uniform corrosion is significantly better than that of the rare-earth-free equivalent steel 12Cr2AlMoV in a wet hydrogen sulfide environment, and its corrosion resistance is nearly 6 times higher than that of carbon steel grade 10. The test method adopts GB10124 —84 \"Test Method for Uniform Corrosion by Full Immersion in Metal Material Laboratories\". 31 Applicable environments (1) Sulfur-containing wastewater: In oil refining, the corrosion caused by sulfur-containing wastewater is primarily due to medium conditions involving HCN, H2S, NH3, and H2O. The 07/09Cr2AlMoRE heat exchangers have been used with great success in domestic oil refining plants, and they are now widely employed in the wastewater treatment systems of such facilities. The corrosion of wastewater at oil field gathering and transportation stations is mainly caused by the medium conditions of H2S, CO2, and H2O; compared to the equipment in refining units, the temperature is lower, so the corrosion is relatively mild. Furthermore, since CO2 is a weak acid, its corrosion rate is much lower than that of HCN. Therefore, this material will perform better in oil and gas fields. (2) Hydrogen sulfide environment containing chloride ions: The corrosion conditions at the atmospheric pressure tower top are HCl, 2H2S, and 2H2O, at a temperature of 130 °C. One set of 09Cr2AlMoRE condenser tubes at Anqing Refinery has been in stable operation for 3 years and is still being used safely, whereas the original set of No. 10 steel tubes had a service life of less than 1 year. Two sets of 09Cr2AlMoRE condenser tubes at Shengli Refinery have also been in stable operation for 3 years and are still safe to use, while the original set of No. 10 steel tubes lasted only about 1.5 years. 09Cr2AlMoRE steel condenser and heat exchanger tubes are currently being gradually used in the vacuum distillation, catalytic, and reforming units of petrochemical companies in Dalian, Guangzhou, Changling, Jingmen, Nanjing Jinling, Zhenhai, Shijiazhuang, Beijing Yanshan, Renqiu, Hohhot, Yumen, and Jinzhou. In refinery applications, over 600 heat exchangers made of 07/09Cr2AlMoRE steel have been put into use, achieving good results. In addition, equipment made from this material is now in industrial use in oil fields, with the products manufactured being high-pressure oil and gas separators and heating furnaces. In summary, the following conclusions can be drawn: (1) The development of 07/09Cr2AlMoRE steel and its welding materials was successful; the welds obtained using submerged arc automatic welding and manual arc welding exhibit excellent properties, meeting all the performance requirements for this material in terms of design and use. (2) Due to the alloying effect of rare earths, the inclusions in 07/09Cr2AlMoRE steel are distributed very evenly and finely, which significantly improves the steel’s resistance to various sulfide-corrosion types. (3) The 07/09Cr2AlMoRE steel is available in complete forms including pipes, forgings, and sheets; the welding materials have also been developed simultaneously, ensuring optimal compatibility for welding. When used on a single device, and due to the matching of materials, there is no issue of galvanic corrosion caused by potential differences between different steel types. This post was last edited by enen007 on 2008-8-27 15:36.]

It seems that really no one is willing to share their experiences in this area!

Not really. As far as I know, these two materials have not been in use for long and are not widely used.

If these materials can be successfully applied in the atmospheric and vacuum distillation tower top systems, anti-corrosion work will become much easier in the future.

Don’t trust the recommendations from manufacturers and design teams; in fact, corrosion occurs quite rapidly, especially on the side exposed to circulating water. We have used it in hydrogenation units, and its service life was less than a year.

For environments with water, it should be similar to carbon steel; it should still be able to resist corrosion caused by low levels of H2S

1. The top of the tower system: it’s the simplest type of setup. All that needs to be done is to change the design of the tube bundle; spiral baffle plates or spiral baffles are both good options. 2. If you’re not bothered, use coating for corrosion protection. With Ni-P plating, theoretically the results should be very good. In practice, however, it’s impossible to achieve complete plating at the baffle rods; in those areas where no plating occurs, electrochemical corrosion takes place, so it’s better not to apply any plating at all. Other coatings: some are clearly unsuitable for such an environment, while others are effective; applying them does no harm. 3. Material upgrade. Steel grade 09, although not expensive, is best avoided (as far as I know, it doesn’t have a large market. If it can solve the problem and the price isn’t high, then why is there no market for it? Have I misunderstood? Hehe, different people have different opinions – it’s up to you to make the choice). For titanium materials, it is recommended to line the entire tube bundle with titanium; however, this should be considered in conjunction with the one-extraction-three-injection process. If corrosion protection is not properly implemented, titanium materials are even inferior to carbon steel. It is also necessary to ensure high quality – poor-quality titanium materials can cause problems that are difficult to resolve once they have been purchased. Dual-phase steel, hehe, it’s too expensive. There’s also Monel; foreign experts in corrosion prevention were invited for discussions on how to address corrosion in tower tops. The experts said outright that Monel alloy should be used in such cases. 4. There is severe under-scale corrosion here, and it’s easy to address. A deoxygenated water supply line should be connected at the inlet of the heat exchanger (with a diameter of DN50 or larger; a smaller diameter may provide short-term relief but not long-term solutions). Regular water cleaning can effectively deal with under-scale corrosion (in fact, the most immediate effect is a reduction in pressure drop). By the way, when using a reinforced nozzle, it is normal for the fillet welds here to leak; it would be abnormal if there were no leaks. If leakage occurs, it should be sealed under pressure. Why is there a leak? Test you? 3. Strengthen top-water injection and select the appropriate one-remove-three-inject chemicals – this is the most fundamental task. It is best to cooperate with reputable manufacturers. I’ve seen an analysis report that provided a very comprehensive examination of the corrosion products. Yet for the same scale samples, most manufacturers can only analyze a few elements. Think about it: if they can’t even analyze the scale samples, how is it possible for them to find the right solution? This post was last edited by Blue Glacier on 2008-10-16 at 18:44.]

Thank you, the person above – the analysis is very thorough.

What are the normalizing temperatures for 08 and 09? How to heat-treat forgings