Investigation of cold water pitting corrosion failure of deoxidized high phosphorus (DHP) copper tube

Abstract

Purpose The purpose of this paper is to identify the corrosion failure mechanism of a Cu tube in a hydraulic installation and recommend corrective actions to improve the reliability of the entire unit. Design/methodology/approach Failure investigation process includes mainly stereo-, light optical microscopy and scanning electron microscopy as the main analytical tools for material characterization and root-cause analysis. Findings The investigation findings, obtained by corroded surface analysis and metallographic evaluation in transverse sections, suggest strongly that the failure was caused by the operation of Type I pitting corrosion mechanism initiated from the inner side and propagated towards the outer tube surface, assisted by the flowing medium composition. Originality/value This paper deals with an applied failure analysis/case history, summarizes the stages involved in the mechanism of pitting corrosion Type I, taken place in cold water systems together with the main parameters and corrosive species that enhance corrosion rates, shortening pipeline operation life.

Failure investigation of Cu-DHP tubes due to ant-nest corrosion

“…Malachite nodules constitute the upper layer of the “sandwich” layered structure, covering normally cuprite crystals, are shown in Figures 7 and 8. These carbonate salts have a typical morphology or radiated needle crystals forming spherical aggregates; similar structures were depicted in relevant studies (Pantazopoulos, 2009; Pantazopoulos et al , 2016). The coarse deposits were also contaminated by S, Al, K and C, coming from species contained in the flowing medium (Figure 8), which were found to a similar, but different case, denoted as Case C.…”

“…A valuable review concerning the pitting corrosion mechanisms of Cu was presented by Edwards et al (1994). A case study summarizing the main morphological aspects of cold water pitting corrosion (Type I) of Cu-DHP water tube is presented in a recent paper by Pantazopoulos et al (2016), while hot water pitting corrosion (Type II) was addressed in a relevant paper (Tzevelekou et al , 2013). Another Cu failure mechanism is related to stress corrosion cracking, driven by the presence of tensile stresses and corrosive environment, containing species, such as chlorides, ammonia, amines and moisture; characteristic studies are elaborated by Pantazopoulos et al (2011) and recently by Metcalfe and Pearce-Boltec (2018).…”