Heat transfer tube for steam generator and method for producing the same

Abstract

In a heat transfer tube for a steam generator, a surface roughness of an inner surface of the tube is measured along a longitudinal direction and an amount of dimensional variation in a length of 50 mm taken from a measured roughness chart is 4 μm or less and an amount of bend crookedness in a portion of a length of 1000 mm from a tube end is 1 mm or less. Hence, when the tube is produced, an inspection of the tube by an eddy current flaw detection can be conducted at a high S/N ratio and hence an inspection efficiency can be improved, and when the tube is assembled into a heat exchanger, the assembling operation can be easily performed.

1 . A heat transfer tube for a steam generator, wherein an amount of dimensional variation in a specific length of 50 mm taken from a roughness measurement chart, which is obtained by measuring a surface roughness of an inner surface of the tube along a longitudinal direction, is 4 μm or less and an amount of bend crookedness in a portion a length of 1000 mm from a tube end is 1 mm or less. 
     
     
         2 . The heat transfer tube for a steam generator according to  claim 1 , wherein the tube is produced by the steps of: cold drawing by use of a high-pressure lubricating oil of 40 MPa or more in pressure; solid solution heat treatment, and straightening by a roll straightening machine. 
     
     
         3 . The heat transfer tube for a steam generator according to  claim 2 , wherein the roll straightening machine is a roll straightening machine using at least five pairs of concave globoidal drum type straightening rolls arranged opposite to each other in a vertical direction and in a crossing manner where directions of rotating shafts cross each other. 
     
     
         4 . The heat transfer tube for a steam generator according to  claim 1 , wherein a chemical composition of the tube consists of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities. 
     
     
         5 . A method for producing a heat transfer tube for a steam generator, wherein when a tube subjected to cold drawing by use of a high-pressure lubricating oil of 40 MPa or more in pressure and to solid solution heat treatment is straightened by use of a roll straightening machine in which at least five pairs of concave globoidal drum type straightening rolls, each pair of rolls being arranged opposite to each other in a vertical direction and in a crossing manner where directions of rotating shafts cross each other, and in which a stand interval is set at 300 mm or less, the tube is subjected to offsetting that is formed by three points literally along a tube axial centerline as being crossing positions of at least successive three pairs of upper and lower straightening rolls of the roll straightening machine and that allows η expressed by Formula (1) described below to satisfy 0.9×10 −3  or more and to ensure an offset amount of 5 mm or less:
   η=1/ R ×( d/ 2)  (1)
 
 
       where given that an outside diameter of the tube is d (mm) and a stand interval of the roll straightening machine is L (mm) and an offset amount is δ (mm), R=(δ 2 +L 2 )/2δ is established. 
     
     
         6 . The method for producing a heat transfer tube for a steam generator according to  claim 5 , wherein a chemical composition of the tube consists of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities. 
     
     
         7 . The heat transfer tube for a steam generator according to  claim 2 , wherein a chemical composition of the tube consists of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities. 
     
     
         8 . The heat transfer tube for a steam generator according to  claim 3 , wherein a chemical composition of the tube consists of, in mass %, C: 0.15% or less, Si: 1.00% or less, Mn: 2.0% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 40.0%, Ni: 8.0 to 80.0%, Ti: 0.5% or less, Cu: 0.6% or less, Al: 0.5% or less, and N: 0.20% or less, the balance being Fe and impurities.