Fatigue of thin walled tubes in copper alloy CuNi10

The current work concerns the investigation of the fatigue resistance of CuNi10 tubes, which are frequently used in heat exchangers of large ship engines. The lifetime performances of the exchanger tubes are greatly affected by the environmental conditions, where especially the temperature fluctuations and the harsh chloride environment cause fatigue and corrosion problems, respectively. A failure of the tubes will trigger an instantaneous shutdown of the engine. Thus, the paper will focus on a model for fatigue life estimation of the CuNi10 material. In the current case of a ship engine, the temperature fluctuations occur when the engine starts and stops. The difference in temperature at cool down or warm up between the exchanger and the exchange media will cause straining of the tubes. To investigate this phenomenon, a series of strain-based fatigue tests are carried out. Results are evaluated by means of the ASTM E739 guideline and one-sided tolerance limits factor method. The tests show good fatigue resistance and the risk for a failure is low in aspect to the case of a ship heat exchanger.