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Eingeladener Vortrag
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Corrosion of Copper alloy fittings in a combined Plastic/Metal Installation for hot drinking water
(2014)
A household installation for drinking water was analysed for the water quality after an incident concerning the water distribution System in the city. Chemical analysis showed very high levels of lead in the hot water circulation System. The installation was made from multi-layer-pipes, the hot water tank from stainless Steel, no obvious source of lead could be determined. After a thorough cleaning of the piping System and the tank the lead levels rose again after short time.
Werkstoffe in der Trinkwasser-Installation - Was verändert die Novelle der Trinkwasserverordnung?
(2014)
Corrosion of copper alloy fittings in a combined plastic/metal installation for hot drinking water
(2014)
A household installation for drinking water was analysed for the water quality after an incident concerning the water distribution system in the city. Chemical analysis showed very high levels of lead in the hot water circulation system. The installation was made from multi-layer-pipes, the hot water tank from stainless steel, no obvious source of lead could be determined. After a thorough cleaning of the piping system and the tank the lead levels rose again after short time.
- INVESTIGATIONS:
Water samples and samples of the pipe connectors made from different copper alloys were taken during an inspection of the building. Results for water analysis and metallographic investigations of the samples are given. Close examination of the connectors showed selective corrosion along the grain boundaries for the connectors made from brass but not for the connectors made from gun metal.
- RESULTS:
The lead found in the hot drinking water war released from the brass connectors. Obviously the contact time of the water with the metal surfaces in the system investigated was much longer as the contact times used for the evaluation of metallic materials according to EN 15664-1. The standards for the dimensioning of hot water circulation systems available are outdated and do not consider retention time in the system but are driven by maximum availability of hot water at any time.
A new Installation for hot drinking water showed high lead concentrations in the water. The installation was constructed from plastic pipes, the hot water tank from stainless steel. A source for the lead contamination was not obvious, cleaning of the tank and the pipes did result in low lead levels after the cleaning but these rose again after short Operation times.
Water samples and samples from the installation were taken and analysed. The high lead values for hot water circulation were confirmed, the cold water System showed no detectable lead values. Metallographie investigations showed selective corrosion of various pipe fittings from dezincification resistant brass.
The cause of the lead contamination was the selective corrosion of brass combined with a long retention time of the hot water in the circulation System.
Der Zoo Hannover hat von 2008 bis 2010 eine neue Anlage für die Eisbären, Seelöwen und Pinguine errichtet. Diese stellt das Szenario einer Kanadischen Hafenanlage nach und trägt den Namen „Yukon Bay“. Die Tiere werden in künstlichem Meerwasser gehalten. Nach Inbetriebnahme der Anlage traten, beginnend vom Pinguinbecken, Korrosionsschäden in Form von Leckagen und erhöhten Abtragsraten an verschiedenen Bauteilen auf. Im Rahmen zahlreicher Untersuchungen wurden die Ursachen ermittelt und Hinweise zur Abhilfe gegeben.
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.