Abstract: A process for manufacturing a copper tube with a tinned inner surface by circulating a substitution-type electroless tin plating solution inside the copper tube. The process is characterized by comprising a first plating step wherein the rate of deposition of a tin film is adjusted so that the total copper ion concentration in the plating solution, immediately after flowing from the copper tube, after having been circulated inside the tube divided by the tin (II) ion concentration in this plating solution is 0.8 or less, and a second plating step wherein plating is carried out at a plating solution temperature higher than the plating solution temperature in the first plating step. A plating solution comprising 0.05-0.3 mol/l of Sn.sup.2 ion, 0.5-2.0 mol/l of thiourea, 0.5-2.0 mol/l of sulfuric acid, 0.05-2.0 mol/l of alkyl benzene sulfonic acid, and 0.5-5.0 g/l of a nonionic surface active agent is preferably used.

Abstract: A method of monitoring the inner surfaces of copper-alloy condenser tubes of a condenser through which seawater flows as a coolant by controlling a ferrous-ion injecting operation to inject ferrous ions into the coolant for forming a protective film on the inner surfaces of the condenser tubes, and a sponge-ball cleaning operation to clean the inner tube surfaces by passing sponge balls through the condenser tubes. During an initial period of exposure of the condenser tubes to the coolant after installation of the condenser tubes in the condenser, the ferrous ions are injected into the coolant to form the protective film on the inner surfaces of the condenser tubes until the polarization resistance of the condenser tubes has reached 10.sup.4 .OMEGA.cm.sup.2. Subsequently, the ferrous-ion injecting operation and the sponge-ball cleaning operation are executed while the polarization resistance and heat transfer rate of the condenser tubes are monitored.

Abstract: A condenser including a plurality of condenser tubes through which a coolant is caused to flow, a device for injecting ferrous ions into the coolant before it passes through the condenser tubes to form a protective film on an inner surface of the condenser tubes, and a device for introducing sponge balls into the condenser tubes for cleaning their inner surfaces. The condenser has a by-pass line extending outside the body of the condenser, in parallel connection with the condenser tubes. The by-pass line has a monitor tube of the same material and size as the condenser tubes, so that the coolant flows through the monitor tube under the same conditions as the coolant flowing through the condenser tubes. The monitor tube is equipped with a device for measuring a polarization resistance of the monitor tube, and a device for sensing a fouling condition of the inner surface of the monitor tube.