Material selection for hydrogenation reactors in the presence of inorganic bases
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Currently, chromium-molybdenum steel is generally used for hydrogen-handling reactors, but I have a reactor whose feed consists mainly of liquid ammonia and hydrogen, with small amounts of inorganic bases such as NaOH and KOH, as well as very little water. The maximum temperature is 170 degrees, and the maximum pressure is 40 MPa. I would like to ask everyone: Under such high H2 partial pressures, when inorganic bases are also present, what kind of material would be most suitable? I’m not sure if 1.25Cr-0.5Mo can withstand it
For your situation, it is recommended to choose alloy materials with high corrosion resistance, such as stainless steel (316L, 904L, etc.), nickel-based alloys (Inconel 625, Hastelloy C-276, etc.), or titanium alloys (Ti Gr.2, Ti Gr.12, etc.). These materials can resist the erosion of ammonia, alkalis, and other corrosive substances, and they also possess good resistance to high temperatures and high pressures. 1.25Cr-0.5Mo has relatively poor corrosion resistance, and its use in such special environments is not recommended. At the same time, after selecting the materials, design and construction must be carried out based on actual conditions to ensure the safe and stable operation of the reactor. .
Starting with the steel grades used in hydrogenation reactors, for my current operating conditions, considering only H2, 1.25Cr-0.5Mo should be sufficient. However, when NaOH/KOH is added, it’s harder to say – there’s a risk of alkali embrittlement. Nickel-based alloys and titanium alloys are just too expensive. I wonder if you have any experience in this area
In environments containing inorganic bases, the issue of base embrittlement does indeed need to be taken into consideration. The alkali resistance of 125Cr-05Mo steel is relatively poor, and it may suffer from brittle fracture due to alkali embrittlement. Therefore, it is recommended that you choose a steel grade with certain alkali resistance. Common steel grades available on the market currently include: 1.5Cr-0.5Mo steel, 2.25Cr-1Mo steel, 9Cr-1Mo steel, etc. These steel grades exhibit good mechanical properties and corrosion resistance under high temperature and pressure, and they are also cost-effective and practical. You can choose the appropriate steel grade based on your needs. As for nickel-based alloys and titanium alloys, their prices are indeed high, but they still have their uses. If your process requirements are extremely high regarding the material and these cannot be met, then you may consider using nickel-based alloys or titanium alloys to ensure the performance of the reactor. .
Thank you so much. Our current plan is to use chromium-molybdenum steel combined with surfacing made of stainless steel/nickel-based alloys, but we’re still not sure which specific stainless steel or nickel-based alloy to choose. Additionally, due to current limitations, it is not possible to conduct corrosion tests; I was wondering if you are aware of any organizations that can carry out such tests.
When choosing between stainless steel and nickel-based alloys, the following points can be considered: 1. Stainless steel: It is more suitable for use in environments with temperatures below 200°C and low alkali concentrations. 316L stainless steel is a type of stainless steel with good corrosion resistance, and it is also one of the materials commonly used in hydrogen-handling reactors. However, if the temperature and concentration are high, it is recommended to choose other more corrosion-resistant materials. 2. Nickel-based alloys: Nickel-based alloys possess excellent corrosion resistance and heat resistance, making them suitable for use in high-temperature, high-pressure, and corrosive environments. Nickel-based alloys such as Inconel 625 and Hastelloy C-276 are also among the commonly used materials in hydrogen-handling reactors. For corrosion testing, you can contact relevant laboratories or testing agencies for consultation. For example, agencies such as the General Administration of Quality Supervision, Inspection and Quarantine, Sinopec Testing Center, and CNPC Research Institute for Testing and Inspection can all provide relevant corrosion testing services. It is recommended to consult a laboratory or testing center in your area. .