Factors to Consider in Material Selection for the Reactor Vessel Body

Factors to Consider in Material Selection for the Reactor Vessel Body

The material selection for the reactor vessel body of batch-type pyrolysis oil refining equipment needs to be comprehensively evaluated based on four core dimensions: equipment operating conditions, material characteristics, performance requirements, economy and process feasibility, to ensure that the material can long-term meet the operational requirements of high temperature resistance, corrosion resistance and sealing stability of the reactor vessel. The specific considerations are as follows:

Adaptability to Operating Conditions

This is the primary factor for material selection, which needs to be closely matched with the temperature and pressure parameters of the reactor vessel. The reactor vessel operates at a long-term temperature range of 0–500℃, and can reach 550–600℃ under some special working conditions. The material must have excellent high-temperature resistance to avoid creep deformation, distortion or sharp strength reduction at high temperatures. Meanwhile, the inside of the vessel is under a slight negative pressure environment of ≤0.02MPa, so the material needs to have sufficient structural strength to prevent vessel collapse caused by negative pressure. For example, 310S stainless steel can withstand high temperatures of 500℃, while Q345 steel cannot meet the operating requirements due to its maximum temperature resistance limit of only 300℃.

Corrosiveness of Materials and Media

Acidic gases such as hydrogen sulfide and hydrogen chloride are generated during the pyrolysis process. If processing materials like chlorine-containing waste plastics and high-sulfur rubber, the corrosiveness will be stronger. The material must have corresponding corrosion resistance, and be able to form a dense passivation film in high-temperature corrosive environments to resist pitting corrosion and intergranular corrosion. Ordinary carbon steel has no corrosion resistance at all; 310S stainless steel can resist conventional acidic corrosion with its high chromium and nickel content, while nickel-based alloys (e.g., Inconel 600) are required for high-corrosion working conditions.

Auxiliary Performance of Oxidation Resistance and Coking Resistance

At high-temperature working conditions, the surface of the material must have good oxidation resistance to prevent the formation of loose oxide layers that allow oxygen to penetrate, which would damage the oxygen-free pyrolysis environment. Meanwhile, the smoothness and anti-adhesion of the material surface will affect the degree of coking. Therefore, materials that are easy to polish and have low surface energy should be preferred, or anti-coking performance can be improved through subsequent coating treatment to reduce the impact of carbon deposition on heat transfer efficiency.

Machinability and Weldability

The reactor vessel body is a welded structure consisting of a cylinder and a head. The material must have good weldability and formability to facilitate processing procedures such as rolling, stamping and welding. In addition, the strength and toughness of the weld seam after welding should match the base material, with no defects detected by non-destructive testing, so as to avoid weld cracking and gas leakage caused by poor weldability. 310S stainless steel and nickel-based alloys have excellent weldability, while some special alloys with high brittleness are difficult to process.

Balance Between Economy and Cost-Effectiveness

There are significant cost differences between different materials; the cost of 310S stainless steel is only 1/3–1/5 of that of nickel-based alloys. On the premise of meeting working conditions and performance requirements, cost-effective materials should be prioritized to avoid cost waste caused by over-pursuing high-end materials. For example, when processing ordinary waste plastics and rubber, 310S stainless steel is fully sufficient; nickel-based alloys are only considered for customized working conditions with high corrosion and ultra-high temperatures.

Service Life and Maintenance Cost

The durability of the material directly determines the maintenance cycle and service life of the equipment. Materials with strong corrosion resistance and high-temperature resistance can reduce the number of shutdown maintenance times and lower maintenance costs such as decoking and repair welding. If the selected material has insufficient corrosion resistance, the inner wall of the vessel will be corroded rapidly, which not only shortens the service life, but also increases the frequency and cost of maintenance.