Method of making apparatus for the exchange of heat using zirconium stabilized ferritic stainless steels

Claim 2

In the method for making an apparatus for the exchange of heat in which a plurality of thin walled tubular metal members are formed, finned and welded to tube sheets in an array with gaps between said members, the improvement of using as the metal for the walls of said members a zirconium stabilized corrosion resistant ferritic stainless steel consisting essentially of, in weight percent: Carbon=0.025% max Nitrogen=0.025% max Carbon+Nitrogen=0.045% max Silicon=1.0% max Manganese=1.0% max Phosphorous=0.04% max Sulfur=0.03% max Chromium=18-20% Molybdenum=1.75-2.25% (Zirconium/Carbon)≧18 the balance being iron and incidental impurities.

Claim 3

In the method for making moisture separator reheater and feedwater preheater apparatus for the exchange of heat in which a plurality of thin-walled tubular metal members are formed, finned and welded to tube sheets in an array with gaps between said members, the improvement of using as the metal for the walls of said members a zirconium stabilized and corrosion resistant ferritic stainless steel resistant to sensitization during long-term operation at intermediate temperatures in said apparatus for the exchange of heat and consisting essentially of, in weight percent: Carbon=0.025% max Nitrogen=0.025% max Carbon+Nitrogen=0.045% max Silicon=1.0% max Manganese=1.0% max Phosphorous=0.04% max Sulfur=0.03% max Chromium=17-20% [Zirconium/(Carbon+Nitrogen)]≧16 the balance being iron and incidental impurities.

Claim 4

In the method for making moisture separator reheater and feedwater preheater apparatus for the exchange of heat in which a plurality of thin-walled tubular metal members are formed, finned and welded to tube sheets in an array with gaps between said members, the improvement of using as the metal for the walls of said members a zirconium stabilized and corrosion resistant ferritic stainless steel resistant to sensitization during long-term operation at intermediate temperatures in said apparatus for the exchange of heat and consisting essentially of, in weight percent: Carbon=0.025% max Nitrogen=0.025% max Carbon+Nitrogen=0.045% max Silicon=1.0% max Manganese=1.0% max Phosphorous=0.04% max Sulfur=0.03% max Chromium=17-20% [Zirconium/(Carbon+Nitrogen)]≧16 the balance being iron and incidental impurities.

Claim 5

In the method for making moisture separator reheater and feedwater preheater apparatus for the exchange of heat in which a plurality of thin-walled tubular metal members are formed, finned and welded to tube sheets in an array with gaps between said members, the improvement of using as the metal for the walls of said members a zirconium stabilized corrosion resistant ferritic stainless steel consisting essentially of, in weight percent: ______________________________________ Carbon 0.025% max Nitrogen = 0.025% max Carbon + Nitrogen = 0.045% max Silicon = 1.0% max Manganese = 1.0% max Phosphorous = 0.04% max Sulfur = 0.03% max Chromium = 11-13% the larger percentage of zirconium satisfying the Zirconium = criteria: (1) Zr/C ≧ 20 or (2) Zr/(C + N) ≧ 15 ______________________________________ the balance being iron and incidental impurities, said thin-walled members being resistant to sensitization during long-term operation at intermediate temperatures.

Claim 6

In the method for making moisture separator reheater and feedwater preheater apparatus for the exchange of heat in which a plurality of thin-walled tubular metal members are formed, finned and welded to tube sheets in an array with gaps between said members, the improvement of using as the metal for the walls of said members a zirconium stabilized corrosion resistant ferritic stainless steel consisting essentially of, in weight percent: ______________________________________ Carbon 0.025% max Nitrogen = 0.025% max Carbon + Nitrogen = 0.045% max Silicon = 1.0% max Manganese = 1.0% max Phosphorous = 0.04% max Sulfur = 0.03% max Chromium = 11-13% the larger percentage of zirconium satisfying the Zirconium = criteria: (1) Zr/C ≧ 20 or (2) Zr/(C + N) ≧ 15 ______________________________________ the balance being iron and incidental impurities, said thin-walled members being resistant to sensitization during long-term operation at intermediate temperatures.