Protected carbon steel pipe for fire tube heat exchange devices, particularly boilers

The present invention relates to a protected carbon steel pipe for fire tube heat exchange devices, particularly boilers.

It is known that fire tube heat exchange devices exist which provide pipes designed to convey flue gases generated by combustion in appropriate furnaces, such pipes being provided within a vessel which contains the fluid to be heated; among such devices, boilers for generating hot water or another heat transfer fluid are particularly important.

The pipes comprised within said devices are made of carbon steel in order to ensure optimum quality of the welded joints between the pipes and the structures of the devices, which are also made of carbon steel; however, in the case of devices, such as for example condensing boilers, in which the water vapor contained in the flue gases condenses inside the flue gas conveyance pipes, condensation forms which attacks strongly by corrosion the wall of the pipes.

Pipes of the described type are not typical only of boilers, but can be present also in other devices of industrial thermal cycles, such as for example condensers, economizers and heat exchangers.

The aim of the present invention is to provide a carbon steel pipe adapted to convey flue gases which is entirely protected against the danger of corrosion caused by condensation and further ensures high efficiency in the transmission of heat from the flue gases to the fluid, and in particular to the water, to be heated.

The proposed aim is achieved by a protected carbon steel pipe for fire tube heat exchange devices, particularly boilers, according to the invention, characterized in that it comprises the features disclosed in the appended claims.

With reference to the FIGS. 1 and 2, the reference numeral 1 generally designates a fire tube boiler with a burner 2, a furnace 3, a flue gas reversal chamber 4a, a vessel 5 which contains the water to be heated with couplings 5a, 5b respectively for inflow and outflow, pipes 6 designed to convey the gases generated by combustion in the furnace which arrive from the reversal chamber 4a and are sent to the output chamber 4b according to the arrows shown in FIG. 1.

The boiler 1 is of the type known as condensing boiler, and therefore the water vapor contained in the flue gases condenses therein as they flow within the pipes such as 6; the structure of said boiler is made of carbon steel.

An important characteristic of the invention consists in that the pipe 6 is made of carbon steel and comprises internally, bonded thereto, a layer 7 made of a corrosion-resistant material, such as aluminum or stainless steel.