Cleaning after gas-tightness testing for welding the pipe ends of carbon steel and stainless steel

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Hello, everyone from Sichuan: At a recent company meeting focused on quality improvement, the welding department suggested that, after performing the root welding on the pipe ends of carbon steel and stainless steel products, a solution made of dishwashing liquid and sodium nitrite (for rust prevention) be used as the water for leak testing. The ratio is 1:1. The welding section reported that after conducting a gas-tightness test using this solution, even after cleaning (water washing + secondary cleaning with a solvent), it still had an impact on the welding of the cover surface; as a result, an oxide layer that was difficult to remove formed, requiring adjustments to the welding parameters. It was hard to carry out welding according to the specified parameters. I have a few questions for my fellow Sichuanese: 1. Using dishwashing liquid plus sodium nitrite solution – does this, even after cleaning, lead to an increase in harmful chemical elements in the welding area, such as sulfur and phosphorus? 2. Do any of you friends from Sichuan have any recommended liquids for checking airtightness that are more suitable than using dish soap plus sodium nitrite solution? 3. Do any of you colleagues from Sichuan have any better cleaning methods? I mentioned steam cleaning, but I’m concerned that if the moisture is not thoroughly removed from the welding area, it could affect the welding process. I wonder if any of you from Sichuan have a better way. Thank you all.