"吹扫用的气体" can be translated into English as "purging gas" or "gas for purging".
Both expressions are commonly used in industrial and technical contexts to refer to the gas employed for purging operations (e.g., removing contaminants, moisture, or residual substances from pipes, vessels, or equipment).
For example:
The purging gas used in this process is nitrogen. （此过程中使用的吹扫气体是氮气。）
Ensure proper ventilation when using purging gas. （使用吹扫气体时，请确保适当通风。）