Producing and mounting nickel alloy-based superheater tube coils, for steam generators, includes forming and hardening tubes in workshop before mounting and hardening weld seams on site

摘要

Superheater tube coils (1) of deposition-hardened, solution-annealed nickel-based alloy, plus sheathed connecting tubes (4), are formed and mounted in a steam generator tube wall (6) by (a) forming coils and joining sheaths with connecting pipes by welding, (b) hardening, (c) joining coils and connecting pipes in the wall, and sheaths with receivers in the wall, by welding and (d) hardening the seams. Steps (a) and (b) are carried out in a workshop, and (c) and (d) at the mounting site. Production of superheater tube coils (1) (formed from straight tubes (2) and bends (3)) and their connecting tubes (4) (formed with exterior sheaths (5)), and mounting of the coils in a steam generator tube wall (6), involves: (A) providing straight, bend precursor and connecting tubes of deposition-hardened nickel-based alloy in solution-annealed form, and sheaths of material not to be heat-treated, in a workshop; (B) forming the bends and connecting tubes in a workshop, using bending tools; (C) forming the individual coils by joining the straight tubes and bends, and joining the sheaths with the connecting tubes in the region (8) where the pipes pass through the tube wall, using weld seams (9) formed in a workshop; (D) deposition-hardening the coils and sheathed connecting tubes in a first heater in a workshop; (E) joining the coils with the connecting pipes within the tube wall, and the sheaths with preformed receivers (of material not to be heat-treated) within the tube wall, using weld seams (11) formed at the mounting site; and (F) deposition hardening these seams using local second heaters at the mounting site.