Why were they going to load sprinkler parts on a cruise ship? Does cruise ships also carry cargo? Wouldn't a cruise ship already be fitted with an (anti-fire) sprinkling system?
I'm sure Cruise ships take on some freight and mail.
Spare parts for that system.
If those sprinklers had any trace of nitrogen compounds on them, and the detector was set to maximum gain, it would go off.
Want to have some semi-harmless fun? Stick a bag of spinach in your luggage next time you go flying. You'll get hauled into secondary for intensive questioning, your luggage will be blown up, and you'll be on the no-fly list. All for a bag of spinach.