Synthetics for piping systems. More and more pipes on board are made from synthetics, not only for accommodation and sanitary means but also for ballast systems. The main advantage is the corrosion resistance of synthetics. The small weight is another advantage. The pipes are easier to handle on board as well as on the yard and the reduced weight allows the ship to carry more cargo. Disadvantages are the sensitivity to temperature changes and the lower strength compared to steel. Classification Societies often state that “synthetic pipes may be used when they have no adverse effect on the continuity of vital installations in the event of breakdown or fire.” Means of repair for synthetic pipes are compulsory when a vessel makes use of synthetic pipes.
from Karl Van Dokkum’s Ship Knowledge: a Modern Encyclopedia, 2003.
Now I’ve seen these things in the wild: in the ballast systems of semi-submersibles, but I don’t know much about them. Who has the reference material?