Unexposed film by X-ray will be cumulative, even if the film sensitivity is only 100, do not let it more than 5 times the X-ray machine. x-ray on the film is still there, the difference is only the degree of depth, light particles coarsening, slightly off-color, heavy strange streaks or even produce a strong gray haze.
ISO 800 rolls over 3dx 6000 airport scanner 5 times, basically waste. Image from the web. Film with a sensitivity of ISO 400 or less, over one or two times is basically not a problem, but the ISO 400 or more rolls will hang, and the higher the sensitivity, the more affected.
Not only high sensitivity film, but also reversal film, movie film, try not to go through airport security. It's important to note that different security machines have different X-ray power, so if you're safe at this airport, it doesn't mean you'll be safe at another one.