The degradation mechanisms of machine parts are well-known facts, usually resulting in replacement of components. However, in some cases, for instance, parts for large ship engines, repair will often seem more attractive. Time-wise, the vessel’s down-time will be reduced and the investment will be lower. This paper describes repair work performed on valve stems from a 52-year-old ship engine. Due to this long time in operation, the stems were damaged by wear and were no longer functional. The requirements for the stems were scarcely documented stating only a few specific requirements; therefore a short study of the possibilities concerning rebuild material and application method was initiated. This paper illuminates the manufacturing process used; twin wire arc spraying with Monel as the rebuild material. Monel is chosen to meet the requirements for hardness and the subsequent high precision machining. In addition, the mechanical and metallurgical properties of the rebuild coating are examined in regard to adhesion, microstructure and hardness to interpret and support the functionality.

For many decades thermally sprayed corrosion protection systems on the basis of ZnAl or Al carry out their service for structures in coastal areas, the offshore sector, as CUI (Corrosion Protection under insulation) or anywhere where the properties of thermally sprayed corrosion protection systems bring important advantages in terms of durability. A thermally sprayed corrosion protection system is about to protect the structure 25 to 30 years against corrosion. During this time it may be damaged due to factors like construction work, improper handling or simple aging. There are many standards and regulations, which describe the initial design of thermal spray systems, however they remain silent regarding repair. In particular, a mending of partial regions is hardly described. Specific repair instructions are rare and if present, they differ from one another. Overall there is a lack of knowledge of the proper procedures for partially repairing thermal spraying systems. This project was concerned with tangible corrosion-technical issues of the coating repairs: How does the critical overlap area perform? Have organic coatings benefits? To what extent does a renewed damage affect the lifetime? The aim of the study was to develop practice-relevant instructions for the repair of thermally sprayed duplex systems.

The highly cavitation erosion resistant propeller alloys CuAl9Ni5Fe4Mn and CuMn13Al8Fe3Ni2 were arc sprayed with different traverse speeds by using a mixture of nitrogen and 2 % of hydrogen as atomising gas. Residual stresses were measured by the modified hole-drilling method using ESPI. Microstructural, chemical and mechanical analyses were realised to examine adhesive and cohesive properties. Additionally, the cavitation erosion behaviour was investigated. In comparison to coatings sprayed with pressurised air, the results of the study show superior coating qualities with regard to microstructure, cavitation erosion resistance and residual stresses.