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In our catalytic reforming unit, DM water and CCl4 are used as dosing to keep the water and chloride balance within the prescribed limit. Material of both injection lines is stainless steel 304 whereas the main line of the feed (DSN) is carbon steel as per design. Line pressure and temperature of feed line are 24 kg/cm2 and 151deg C and both injection points are connected to the feed line. From a corrosion point of view, if i replace the injection line of DM water & CCl4 with carbon steel pipe will there be any problem ? If no then please give me the reason for using SS 304, or what type corrosion can take place in the injection line for DM water and CCl4?. Currently we are facing some leakage at the elbow weld joint. In addition, when we tried to repair by welding, again a leak/fissure was found just ahead of the welded point.
04/07/2020 A: Dipankar Phukan, Indian Oil Corporation, dipankarphukan79@yahoo.com
The exact location of the leakage is not given. Are you using same line for dosing both CCL4 and DM water? Although I am not a metallurgical engineer, here are my two cents if you find them helpful. The saturation level of water is denoted by Langelier's saturation index(LSI). It defines the corrosive or scale forming nature of water. The condition of the water may be determined thus:

pH + TF + CF + AF - 12.1 < 0 implies aggressive water

pH + TF + CF + AF - 12.1 > 0 implies scaling water

where : pH = Measured pH Value

TF = Temperature Factor

CF = Calcium Hardness Factor

AF = Alkalinity Factor

Normally for DM water this value is in the 0 to negative zone and hence corrosive. Hence, carbon steel is not recommended for DM water.

CCL4 itself is not corrosive in the pure form but when it comes in contact with water/moisture in the presence of iron it forms HCl. Iron acts as a catalyst for the reaction.
03/07/2020 A: James Chacko, Suez Water Technologies & Solutions, james.chacko@suez.com
Ideally these two injections should be through separate lines. This is intended for individual control of moisture and chlorides on catalyst on a need basis

CCl4 has a certain solubility in water and due to that the chloride content in water would go up. In SS metallurgy, this creates pinholes and weld leaks as this type of corrosion affects crystal structures.

Please review the above hardware correction idea and you should have no issues.

In any event, please do not shift the metallurgy to Carbon steel