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ON-SITE MATERIAL DAMAGE EVALUATION FOR LOW ENTHALPY GEOTHERMAL VENTURE BASED ON SALINE CRETACEOUS FORMATION WATER

Objective

CONTROLLING CORROSION ALWAYS LEADS TO A MORE ECONOMICAL EXPLOITATION.
In order to evaluate the corrosion and deposition damage, which may occur in geothermal water, a water characterization and materials test station was connected to the geothermal circuit. In addition to the numerous results obtained from the various materials tested, general conclusions could be drawn from the 2 test periods:
In general alloyed steels and synthetic materials were little affected.
The water quality of the geothermal well remained constant, except for occasional oxygen variations at operational interruptions.
Oxygen, chlorine and sulphur were identified as the main agents causing enhanced corrosion of carbon steel, aluminium, hastelloy B and nickel aluminium bronze.
Deposition rates depend on the material the deposit forms on.
No major chemical interaction between the deposits and the exposed material coupons could be observed.
The amount of deposited material was higher in the cold leg of the geothermal circuit than in the hot leg.

The Maastrichtiaan aquifer, situated at the top of a Cretaceous formation, extends over a relatively large area in the north of Belgium. At first well situated in the urban centre of Turnhout (depth, 800 m; temperature at well head, 37 C) was taken in operation at the end of 1985 for feeding a thermal power station. In order to evaluate the corrosion and deposition damage, which may occur in this geothermal water, a water characterization and materials test station has been connected to the geothermal circuit, which has been operated during a first relatively short period (2 months) and has now been taken in operation for a relatively long period (12 months).

The report analyses the water chemistry evolution during the 2 month test campaign; gives results of the instantaneous corrosion rate measurements and presents detailed analyses of the exposed material coupons. Correlations are proposed between the amounts of deposits observed and the construction materials of the system. Bacteriological analyses were carried out and the performance of some important components of the geothermal station monitored.

The preliminary conclusions drawn from the research are as follows:
higher corrosion rates were observed in the cold leg of the geothermal circuit probably because of a higher oxygen content;
in general alloyed steels and synthetic materials were little or not affected after the 2 month exposure to the geothermal water flow;
the water quality of the geothermal well during the 2 month test period remained constant, except for occasional excursions at operation interuptions;
oxygen, chlorine and sulphur were identified as the main agents causing enhanced corrosion of carbon steel, aluminium, Hastelloy B and nickel aluminium bronze;
interruption of the operation of the geothermal station gave rise to enhanced corrosion rates;
deposition rates depend on the material the deposit forms on (synthetic materials retain larger amounts of deposition products than met allic materials);
no major chemical interaction between the deposits and the exposed material coupons could be observed (at higher flow rates lower amounts of deposited material were found);
the amount of deposited material was higher in the cold leg of the geothermal circuit than in the hot leg of the geothermal circuit.
A GEOTHERMAL WELL IS OPERATIONAL IN TURNHOUT FEEDING ON THE MAASTRICHTIAAN AQUIFER.
IN ORDER TO EVALUATE THE CORROSION AND DEPOSITION DAMAGE, WHICH MAY OCCUR IN THIS GEOTHERMAL WATER, A WATER CHARACTERIZATION AND MATERIAL TEST STATION WILL BE CONNECTED TO THE GEOTHERMAL CIRCUIT AND OPERATED DURING A RELATIVELY SHORT PERIOD (TWO MONTHS) AND A RELATIVELY LONG PERIOD (TWELVE MONTHS).
THE TEST STATION COMPRISES DIFFERENT ON-LINE WATER CHARACTERIZATION UNITS (PH, ELECTRIC CONDUCTIVITY, OXYGEN CONTENT, GAS SEPARATION), FOUR MATERIAL COUPON TEST SECTIONS (HIGH AND LOW TEMPERATURE, TWO FLOW VELOCITIES) WATER AND GAS SAMPLING LINES AND ELECTROCHEMICAL CORROSION RATE SENSORS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

BELGIAN NUCLEAR RESEARCH CENTRE
Address
200,Herrmann Debrouxlaan 40-42
1160 Bruxelles
Belgium