Heat exchanger for gases, in particular for exhaust gases from an engine, that includes: - a heat exchanger block that includes: - a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a coolant fluid, in which the first and second fluid circuits are isolated fluidically from one another and arranged to effect a heat exchange between said gases and said coolant fluid. - at least one part that has a through-hole (h) traversing two respective opposing surfaces (Pa, Pb) of said at least one part, in which said through-hole (h) is arranged such that said gases or said coolant fluid flow therethrough, and - at least one tubular pipe joined to said at least one part such that same is in fluidic communication with said through-hole (h), wherein said at least one tubular pipe has at least one projection that extends radially outwards from one end (Ta) of the at least one tubular pipe, and wherein said at least one projection is joined to the at least one region of one of said two opposing surfaces (Pa, Pb) surrounding said through-hole (h), characterized in that the at least one projection is joined to said region of one of the two opposing surfaces (Pa, Pb) by laser welding, said heat exchanger including positioning means for positioning said at least one tubular pipe in relation to said at least one part, such that the at least one projection is in contact with said region of one of said two opposing surfaces (Pa, Pb) and is positioned such as to enable attachment thereto, and the end (Ta) of the tubular pipe from which the at least one projection extends radially outwards contains the through-hole (h), in which said positioning means include matching shapes that are arranged respectively on the at least one projection and in an area of one of the two opposing surfaces (Pa, Pb) that is adjacent to said region, in which said matching shapes fit together to prevent the at least one tubular pipe from moving in relation to the at least one part along at least one plane parallel to a plane that includes said region, in which said matching shapes include at least one recess and at least one protuberance arranged respectively on the at least one projection and in said area of one of the two opposing surfaces (Pa, Pb) that is adjacent to said region, or vice versa, in which the matching shapes include two or more recesses that are distributed within a first plane and separated angularly from one another, and two or more corresponding protuberances that are distributed within a second plane and separated angularly from one another, in which the recesses and the protuberances are arranged respectively on the at least one projection and in said area of one of the two opposing surfaces (Pa, Pb) that is adjacent to said region, or vice versa. - a heat exchanger block that includes: - a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a coolant fluid, in which the first and second fluid circuits are isolated fluidically from one another and arranged to effect a heat exchange between said gases and said coolant fluid. - at least one part that has a through-hole (h) traversing two respective opposing surfaces (Pa, Pb) of said at least one part, in which said through-hole (h) is arranged such that said gases or said coolant fluid flow therethrough, and - a first fluid circuit for the circulation of gases and a second fluid circuit for the circulation of a coolant fluid, in which the first and second fluid circuits are isolated fluidically from one another and arranged to effect a heat exchange between said gases and said coolant fluid. - at least one part that has a through-hole (h) traversing two respective opposing surfaces (Pa, Pb) of said at least one part, in which said through-hole (h) is arranged such that said gases or said coolant fluid flow therethrough, and - at least one tubular pipe joined to said at least one part such that same is in fluidic communication with said through-hole (h),