Zavarivanje, Vol. 61 No. 1-2, 2018.
Prethodno priopćenje
CORROSION OF HOT DIP GALVANISED PIPES IN FRESH WATERS
Ivan Esih
; Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu,Zagreb,Hrvatska
Ivan Stojanović
; Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu,Zagreb,Hrvatska
Vinko Šimunović
; Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu,Zagreb,Hrvatska
Vesna Alar
; Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu,Zagreb,Hrvatska
Sažetak
Hot dip galvanised welded carbon steel pipes are used in distribution networks for consumable fresh water,ie for cold potable water as well as for cold and warm sanitary water.
Thereby,layers of corrosion products (like basic Zn-carbonate) are formed on Zn-surface.They protect Zn and steel substrate from further corrosion.However,deep local damages by groooving corrosion appear rather frequently.
They form discontinuous grooves near the central line of the weld.
Therefore,an investigation of circumstances stimulating grooving corrosion is carried out.
To the intensity of that phenomenom are contributing:
-heterogeneous structure of steel in the weld,particulary under the centarl line,
-presence of rugged bur inside the pipes after welding by electric resistance tecnique and
-direct or indirect contact of water,galvanised pipes and parts of more noble metal ( such as Cu-pipes in boilers for consumable water) that provokes bimetallic corrosion of Zn-or Fe-anodes in galvanic cells,if galvanised pipes are used downstream in relation to more noble (cathodic) metal or in recirculation systems with it.
Heterogeneity of the weld is decreased by application of steel with very low sulphur content,by appropriate heat treatment (eg normalisation) or by alternative welding procedure.
Deburring of the inside of pipes by mechanical cleaning is indispensable and bimetallic corrosion has to be avoided by proper construction.The effect of mechanically or chemically damaged Zn-coating on the behaviour of hot dip galvanised steel pipes in fresh water is separately discussed.
This effect depends significantly on temperature and composition of water.The period of incubation up to serious grooving corrosion in fresh water increases with thickness and quality of Zn-coating.
Ključne riječi
welded galvanized steel pipes; Grooving corrosion; hot water
Hrčak ID:
200994
URI
Datum izdavanja:
20.3.2018.
Posjeta: 1.244 *