A boiler is a closed vessel in which water or other fluid is heated.
The fluid does not necessarily boil.(In North America the term "furnace" is normally used if the purpose is not actually to boil the fluid.) The heated or vaporized fluid exits the boiler for use in various processes or heating applications,12 including water heating, central heating, boiler-based power generation, cooking, and sanitationŹródło: https://en.wikipedia.org/wiki/Boiler
Galvanized steel potable water supply and distribution pipes are commonly found with nominal pipe sizes from 3?8 inch (9.5 mm) to 2 inches (51 mm).
It is rarely used today for new construction residential plumbing.
Steel pipe has National Pipe Thread (NPT) standard tapered male threads, which connect with female tapered threads on elbows, tees, couplers, valves, and other fittings.Galvanized steel (often known simply as "galv" or "iron" in the plumbing trade) is relatively expensive, and difficult to work with due to weight and requirement of a pipe threader.It remains in common use for repair of existing "galv" systems and to satisfy building code non-combustibility requirements typically found in hotels, apartment buildings and other commercial applications.It is also extremely durable and resistant to mechanical abuse. Black lacquered steel pipe is the most widely used pipe material for fire sprinklers and natural gas. Źródło: https://en.wikipedia.org/wiki/Plumbing
Therefore, the scope of hydraulic works performed in cities is very wide.