Corrosion damage of seam welded galvanized hot water pipelines

Abstract

Original scientific paper The aim of this paper was to determine the cause of corrosion damage on hot water seam welded galvanized pipelines. Chemical analysis of the pipeline samples as well as their microstructure analysis has been undertaken. Visual inspection of samples of the internal surface of the pipelines was conducted, as well as the chemical analysis of water samples from specific regions of the hot water pipeline. The analysed samples came from the damaged pipeline, replaced pipeline and also from the new, unused pipelines and compared. The effects of the locally developing corrosion processes have been investigated. The influence of the welded joint structure and its heat-affected zone on the corrosion process intensity was analysed. The synergistic effect of zinc from the pipeline coating and the copper ions from the heat exchanger on the water systems corrosion development has been analysed. The fundamental preconditions of formation and development of various copper corrosion types were investigated, as well as the affecting influence of copper ions. The influence of hot water temperature against corrosion processes development was inspected. The testing results have showed that the corrosion process was generated due to the increase of copper concentration in hot water pipeline. Keywords: copper corrosion; galvanized pipeline corrosion; hot water pipeline Korozijska oštećenja toplovodnih šavno zavarenih čeličnih pocinčanih cijeviIzvorni znanstveni članak Svrha ovog rada bila je utvrditi uzrok nastajanja korozijskih oštećenja na toplovodnim čeličnim šavno zavarenim pocinčanim cijevima. U tu svrhu, bilo je potrebno provesti analizu kemijskog sastava cijevi toplovoda, ispitivanje mikrostrukture uzoraka cijevi, vizualni pregled unutarnjih površina cijevi te analizu kemijskog sastava uzoraka vode iz odabranih dijelova cjevovoda. Analizirani su uzorci cijevi oštećenog toplovoda, zamijenjenog toplovoda te novih nekorištenih cijevi. Istraživani su učinci lokaliziranih korozijskih procesa. Ispitivan je utjecaj strukture zavarenog spoja na intenzitet korozijskog procesa. Analiziran je sinergijski učinak cinka iz zaštitne prevlake cijevi i bakrenih iona iz izmjenjivača topline na razvoj korozijskih procesa unutar sustava toplovoda. Istraživane su temeljne pretpostavke za nastajanje i razvoj različitih oblika korozije bakra kao i utjecaj djelovanja bakrenih iona. Ispitan je utjecaj temperature vode u toplovodu na razvoj korozijskih procesa. Rezultati ispitivanja ukazuju da je korozijski proces nastao zbog povećane koncentracije bakra u cijevima toplovoda.