Improper equipment takeover can easily lead to differential temperature corrosion
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In the olefin dehydrogenation reactor, the gas temperature is 440–560°C, and it is in a dry state, resulting in minimal corrosion of the stainless steel vessels. But the designed pressure gauge tube is tilted upward and not insulated on the outside. As a result, the gas in the pressure tube condensed to form hydrochloric acid, which flowed back downward, causing corrosion and perforation at the weld between the pressure tube and the container wall within just 48 hours. Obviously, this design is unreasonable; this corrosion problem can be solved by designing the pressure gauge tube to slope downward, insulating it from the outside to prevent heat loss, and installing a drain valve at the lowest point. This case is \"cold spot corrosion\" (temperature difference corrosion). When designing and constructing insulation for containers and piping systems that handle high-temperature gases, it is essential to consider avoiding the formation of \"cold spots\". If it is not possible to provide proper insulation for the fittings on the outer surfaces of equipment and pipelines, then effective protective measures should be taken on the inner surfaces of the shells beneath those fittings, such as by cladding them with corrosion-resistant alloys.
In the olefin dehydrogenation reactor, the poorly designed pressure gauge tube slopes upward and lacks insulation, causing gas to condense inside the tube and form hydrochloric acid, which then flows back to the welding area and induces rapid corrosion, resulting in cold spot corrosion. The solution is to design the pressure gauge tube to slope downward, add insulation, and install a drain valve at the lowest point to prevent such corrosion problems. At the same time, the inner surface of the lower shell of accessories that cannot retain heat should be given enhanced protection, such as by using corrosion-resistant alloy cladding. .
There were already devices for welding corrosion-resistant materials, but condensation corrosion still occurred due to poor external insulation. It looks like tears.