Copper and nickel alloys called cunifers (Cu, Ni, Fe and R – rest of alloy elements) have found wide application in the production of ship pipeline components in contact with sea water, such as, for example, the main engine cooling system. These alloys are characterized by a very high corrosion resistance, which is ensured by appropriately carried out passivation. However, with improperly carried out passivation, this material loses its anti-corrosion properties and is often corroded. In addition, a mistakenly conducted welding process is a factor conducive to degradation processes. The purpose of this work is to show the impact of errors created during the production process and pipeline testing for its technical condition. The subject of the research was a fragment of the pipeline made of CuNi10Fe1,6Mn alloy, coming from a vessel floating on sea waters. Macro- and microscopic examinations revealed a number of technological defects that affected the degradation of this element.