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The generation of active disinfectants by electrochemical processes gains market share due to the lack of need for transportation and storage of dangerous goods as well as the ease of operation. Usually the process involves the use of specific electrodes for electrolysis of water to produce active chlorine species, sometimes supported by addition of chlorides to the process water. The resulting ECA (ElectroChemically Activated) solutions can cause corrosion due to the content of free active chlorine (FAC) or due to the chloride content of the process solution. These fluids are widely used because they show a good chemical and microbiological stability, are well suited for the standard cleaning procedures and allow to reduce germ concentrations to meet hygienic standards. The influence of the respective agents to alloy 1.4301 is investigated by storage experiments and by electrochemical investigations. The results show, that the influence of chlorides is higher for short-term experiments. ECA-Fluids with low chloride concentrations are preferable. The goal of the investigations is to creat evaluation guidelines for the application parameters to provide a sufficient cleansing effect without causing corrosion of the surfaces.
The generation of active disinfectants by electrochemical processes gains market share due to the lack of need for transportation and storage of dangerous goods as well as the ease of operation. Usually the process involves the use of specific electrodes for electrolysis of water to produce active chlorine species, sometimes supported by addition of chlorides to the process water. The resulting ECA (ElectroChemically Activated) solutions can cause corrosion due to the content of free active chlorine (FAC) or due to the chloride content of the process solution. These fluids are widely used because they show a good chemical and microbiological stability, are well suited for the standard cleaning procedures and allow reducing germ concentrations to meet hygienic standards. The influence of the respective agents to alloy 1.4301 is investigated by storage experiments and by electrochemical investigations. The results show, that the influence of chlorides is higher for short-term experiments. ECA-Fluids with low chloride concentrations are preferable. The goal of the investigations is to creat evaluation guidelines for the application parameters to provide a sufficient cleansing effect without causing corrosion of the surfaces.
Trinkwasseranlagen in Neubauten funktionieren in der ersten Zeit einwandfrei. Das Wasser ist klar, die Ventile sind leichtgängig und es fließt genug Wasser aus den Armaturen. Erst im Laufe der - längeren oder kürzeren - Betriebszeit treten Störungen auf. Braunes Wasser deutet auf Korrosionsvorgänge hin. Kommt nur wenig Wasser aus den Armaturen, ist das ein Hinweis auf Inkrustationen. Ein schleichender Prozess, der Jahre und Jahrzehnte dauern kann. Doch spritzt erst einmal Wasser aus der Leitung, muss zumindest das betroffene Teilstück saniert werden. Viel Dreck, ein vorübergehender Ausfall der Wasserversorgung und ein hoher Koordinationsaufwand entstehen immer dann, wenn sich die Leitungen unter Putz und in bewohnten Gebäuden befinden. Damit es zu einem Totalausfall erst gar nicht kommt, raten auf Sanierung von Trinkwasseranlagen spezialisierte Unternehmen zu einem Beschichtungsverfahren mit Epoxidharz: Die gesamte Installation wird mit diesem Stoff von innen ausgekleidet. Das Beschichtungsmittel Epoxidharz allerdings wird kontrovers diskutiert. Nach Meinung der Kritiker gehen von ihm viele Gefahren aus. Die Befürworter sehen das hingegen ganz anders. Wir haben zwei Vertreter gebeten, ihre Argumente zusammenzutragen. Ist die Sanierung mit Epoxidharz ein unbedenkliches Verfahren?
A vessel for the hardening of aerated concrete exploded after modification. The modification was implemented by welding additional barrels to extend the vessel. Two and a half years after the modification (about 500 load cycles) the vessel exploded showing a longitudinal crack starting in one of the new segments. After the modification the dimensions of the vessel were 2000 mm diameter and 31,000 mm length, operational pressures ranged from 0.3 to 16 bar. The material of both the old and new parts of the vessel and the properties of the welds showed no deviations from the specifications. The geometry of the longitudinal weld showed a roofing deviation from circularity. Fractographic investigations showed a crack of 1.6 m length following the longitudinal weld which developed over long time caused by corrosion fatigue. At the time of the explosion, the wall thickness was reduced from 13.5 mm down to about 2 mm leading to longitudinal cracking of the vessel throughout the new parts followed by a circular crack which resulted in a complete separation of the pressurized vessel. The crack development is shown by optical and SEM-micrographs.
Calculations of nominal stresses show that the geometrical deviations by linear misalignment and roofing cause a stress (tension load) increase of about 4.8 of the mean tensile load value. Adjacent to the weld this causes a local tension overload; in combination with operation conditions (overheated steam of 203 °C, cyclic operation) this causes corrosion fatigue due to cracking of corrosion layers. The crack formed by this mechanism caused a remaining wall thickness of less than 2 mm followed by a ductile residual fracture.
Susceptibility of 304 Stainless Steel to Crevice Corrosion in Electrochemically Active Fluids
(2020)
The susceptibility of Type 304 stainless steel (SS) to crevice corrosion upon contacting with electrochemically active fluids was investigated using exposure tests and stepwise potentiostatic polarization. Crevice materials made of 304 SS and polyether ether ketone (PEEK) were focused on in this study. The combined influence of oxidant and chloride concentration on crevice corrosion was examined in detail in the two types of crevice combinations (304 SS-to-PEEK and 304 SS-to-304 SS). The 304 SS specimens were strongly susceptible to crevice corrosion when coupled with 304 SS. Even at a low concentration of 5 mg/L free chlorine and 150 mg/L chloride, which is below nominal dilutions in beverage industries, the examined specimens underwent crevice corrosion in both crevices. The effect of water composition on crevice corrosion was also studied, indicating high susceptibility of 304 SS to crevice corrosion in low pH (pH ≤ 5) solutions. The corroded surface morphology was analyzed using scanning electron microscope, energy dispersive x-ray, and confocal.
Susceptibility of 304 stainless steel to crevice corrosion in electrochemically active fluids
(2019)
The susceptibility of AISI 304 stainless steel to crevice corrosion on the effect of contact with electrochemically active fluids was investigated using exposure and stepwise potentiostatic polarisation. Crevice materials made up of 304 SS and Polyether ether ketone (PEEK) forming two kinds of crevices including 304 SS-to-PEEK and 304 SS-to-304 SS were tested.
Susceptibility of 304 stainless steel to crevice corrosion in electrochemically active fluids
(2019)
The susceptibility of AISI 304 stainless steel to crevice corrosion on the effect of contact with electrochemically active fluids was investigated using exposure and stepwise potentiostatic polarisation. Crevice materials made up of 304 SS and Polyether ether ketone (PEEK) forming two kinds of crevices including 304 SS-to-PEEK and 304 SS-to-304 SS were tested.
Die Korrosion in ihren zahlreichen Erscheinungsformen beschäftigt Fachleute und Laien. Um-so wichtiger ist es, die einzelnen Phänomene korrekt und eindeutig zu benennen. Nur so kann man eine saubere Beschreibung der Korrosionsvorgänge erreichen und damit in der wörtlichen und schriftlichen Kommunikation richtig verstanden werden. An zahlreichen Beispielen wird der richtige und normgemäße Sprachgebrauch beschrieben.
Die Korrosion in ihren zahlreichen Erscheinungsformen beschäftigt Fachleute und Laien. Um-so wichtiger ist es, die einzelnen Phänomene korrekt und eindeutig zu benennen. Nur so kann man eine saubere Beschreibung der Korrosionsvorgänge erreichen und damit in der wörtlichen und schriftlichen Kommunikation richtig verstanden werden. An zahlreichen Beispielen wird der richtige und normgemäße Sprachgebrauch beschrieben.
The elemental dissolution of Cu-Zn alloys was investigated as a function of Zn content ranging from 0 to 45 wt%. Atomic emission spectroelectrochemistry (AESEC) was utilized to directly monitor Cu2+ and Zn2+ release and oxide growth as function of time during potentiodynamic experiments. It was determined that Cu dissolution undergoes a simultaneous mechanism of Cu2O formation and Cu2+ release. The addition of Zn in Cu-Zn alloy does not measurably change the dissolution mechanism of Cu2+ and the rate of aqueous Cu2+ was only dependent on the potential. Zn dissolution was however blocked by the formation of a Cu(0) film which shifted the Zn dissolution in the anodic direction.
In the late 1980s, a new type of corrosion appeared in drinking water installations where galvanized steel pipes failed forming a deep groove with no corrosion at the other surfaces. The reason was discussed quite fiercely between failure analysts and material suppliers. In the end the discussion lead to the solution: inductive welded pipes of a certain sulphur content were prone to selective corrosion. The history of the arguments is discussed using old communications between Wilhelm Schwenk and Wolfgang Stichel, who later published the results in a paper unfortunately only I german.
Thus the knowledge got lost and new cases based on the same material problems are observed in application of so-called C-Steel piping systems. Failure cases are shown.
In the late 1980s, a new type of corrosion appeared in drinking water installations where galvanized steel pipes failed forming a deep groove with no corrosion at the other surfaces. The reason was discussed quite fiercely between failure analysts and material suppliers. In the end the discussion lead to the solution: inductive welded pipes of a certain sulphur content were prone to selective corrosion. The history of the arguments is discussed using old communications between Wilhelm Schwenk and Wolfgang Stichel, who later published the results in a paper unfortunately only I german.
Thus the knowledge got lost and new cases based on the same material problems are observed in application of so-called C-Steel piping systems. Failure cases are shown.
Kaltwasserzirkulationssysteme haben sich in diversen Bereichen (Kliniken, Hotels, Schiffsbau usw.) etabliert. Die hydraulische Funktionsweise und das Berechnungsverfahren orientieren sich an der bewährten Warmwasser-Zirkulation, dennoch besteht für dieses „neue System“ eine gewisse Einführungsskepsis. Die elementare Anforderung der Trinkwasserverordnung (TrinkwV) besteht darin, dass „Trinkwasser […] so beschaffen sein [muss], dass durch Genuss oder Gebrauch eine Schädigung der menschlichen Gesundheit […] nicht zu besorgen ist.“ Diese Anforderung gilt als erfüllt, wenn mindestens die allgemein anerkannten Regeln der Technik (a.a.R.d.T.) bei Planung, Bau und Betrieb einer Trinkwasser-Installation eingehalten werden, das Trinkwasser den mikrobiologischen, chemischen, radiologischen Anforderungen der TrinkwV entspricht und es rein und genusstauglich ist. Da die Kaltwasserzirkulation aktuell noch dem Stand der Technik zuzuschreiben ist und die Einhaltung chemischer Anforderungen in Bezug auf erhöhte Schwermetallmigration in der Diskussion steht, wurden entsprechende chemische Parameter in Bestandsanlagen untersucht. Die Ergebnisse werden nachfolgend vorgestellt und sollen Betreibern, Fachplanern und ausführenden Fachunternehmen die Vorteile des Systems aufzeigen und Unsicherheiten ausräumen.