Árbók VFÍ/TFÍ - 01.06.1997, Blaðsíða 312

Ragnheiður Inga Þórarinsdóttir
Tæring eirröra í hitaveituvatni
Ragnheiður Inga Þórarinsdóttir hefur
starfað á Iðntækni-
stofnun íslands frá
_ 1994. Hún útskrifaðist
'W'9* tfW sem efnaverkfræ^n9-
ur með civ.ing. próf
frá DTH í Danmörku
1993 og stundar nú
Ph.d. nám við DTU.
Abstract
The district heating systems in Iceland main-
ly make use oi' geothermal resources and are
different in several ways i’rom the conven-
tional district heating systems based on fossil
fuel. The hot water is normally pumped
directly to the consumers and used both for
space heating and as hot tap water. The sytems
are most frequently single-pipe systems,
^^where the water is disposed to the sewage
after use. The few double-pipe systems are mainly made to cool the forward flow and not to
utilize the remaining energy in the outlet water. The water contains some amounts of sílica
and hydrogen sulphide and a negligible amount of dissolved oxygen, the pH is typically 9.5.
Copper and copper alloys are widely used in district heating systems, i.e. in sntaller pipes
inside buildings, valves, ilow meters and other components. These materials are normally
corrosion-resistant materials, but tend to corrode in hydrogen sulphide environment with the
formation of copper sulphide. Brass alloys are prone to dezincifícation, especially in sea
water and the susceptibility increases with increased zinc content. The opposite is the case
in sulphide containing systems as the corrosion resistance increases with high zinc contents.
Dissolved zinc from brass alloys can react with the sílicates present in the geothermal water
and form hard zinc-sílicate scales, which make the movable parts inoperative in radiator
valves or flow meters.
This paper describes the results of an investigation on the corrosion of copper and sol-
dering metals from pipelines in a house in Kópavogur. The house has received geothermal
water from 1978 and heated fresh water containing sulphide from 1990. Significant corro-
sion was observed and black copper sulphide scaling has occurred on the inner surface of
the pipe walls. The corrosion is in the form of an almost uniform attack, the corrosion
proucts are poorly adherent and peel off easily in flakes when the pipes are cut through. The
two soldering metals investigated were brass and lead-tin. The corrosion attack is more sig-
nifícant on the copper pipes than on the soldering metals.