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Control method for the corrosion margin inside the reactor
Oct 21, 2020

There are many technological factors that affect the thermal crack generation during welding of the reactor, such as joint form, process specification, preheating temperature, structural stiffness and clamping condition of workpiece, etc., which all have certain influence on the thermal crack resistance of the welding seam of the reactor. Welding process and specification for reactor. The process measures such as high current, fast welding, single layer welding, straight line moving forward, etc., which are easy to cause welding stress in the reactor, will cause thermal cracks. Therefore, when conditions permit, small current and multilayer welding should be used as far as possible to reduce the tendency of thermal cracks.


The corrosion margin of the reactor refers to the wall thickness margin increased in advance considering that the material is corroded by the contact medium (including atmosphere) during the service period. Also known as "corrosion margin". The value is determined by the corrosion rate of the medium to the material and the design life of the parts. For steel pressure vessels, the relevant specifications stipulate that the corrosion allowance of carbon mace and low alloy steel materials should be no less than 1mm; When stainless steel is used and the corrosive medium is very small, the corrosion allowance can be zero.


The basic meaning of corrosion allowance in the design of chemical environmental protection engineering is the maximum allowable corrosion depth during the normal life of equipment (container, pipe, flange, valve and pump, etc.) when the equipment fails due to the corrosion effect of environmental media.


In order to prevent thinning and weakening of container components due to corrosion and mechanical wear, corrosion allowance shall be considered for cylinders, heads, nozzles, human (hand) holes and internals in contact with working media. For corroded or worn elements, the corrosion allowance should be determined based on the expected container life and the rate of corrosion of the medium to the metallic material.


The corrosion allowance can be generally determined according to the uniform corrosion rate of steel in the medium and the design life of the vessel. Because different use condition, different material and structural characteristic have detailed design reference value commonly, consult concerned design manual know. In the absence of special corrosion, the corrosion allowance for carbon steel and low alloy steel is not less than 1mm. For stainless steel, when the corrosive medium is very small, desirable corrosion allowance is zero.


However, the corrosion allowance is only meaningful to prevent uniform corrosion failure. For non-uniform corrosion such as stress corrosion, hydrogen embrittlement and crevice corrosion, the method of increasing corrosion margin is used to prevent poor corrosion effect. At this time, it should be more important to choose corrosion resistant materials or carry out appropriate corrosion prevention treatment.

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