Material Selection Guidelines for Geothermal Power Systems—An Overview

Abstract

Perhaps the most important difference between traditional electric power generation and geothermal power generation is the potentially severe corrosion of metals caused by the use of the geothermal fluids. The object of this overview is to present the principal results of work conducted for the U.S. Department of Energy under Contract EG-77-C-04-3904. Process streams are identified by the presentation of nine geothermal power cycles applicable to four types of liquid-dominated geothermal resources found in the United States. Of the many constituents in geothermal fluids, seven key chemical species are identified that account for most corrosion phenomena in geothermal power systems. These species are: oxygen, hydrogen sulfide, carbon dioxide, ammonia, chloride, sulfate, and hydrogen ion concentrations. Based on analyses of actual geothermal materials test data and test methods, the performance of metals in geothermal fluid, steam, and condensate is presented for carbon and stainless steels, titanium, nickel, copper, and many other alloys. The applicability of new nonmetallic materials in geothermal systems is also addressed. Finally, the similarities and differences between seawater and geothermal corrosion phenomena are discussed.

Application of geochemistry to resource assessment and geothermal development projects

“…Most geothermal facilities are designed assuming corrosion related to hydrogen sulfide in steam and air and chloride in brine will be mitigated by appropriate material selection [17]. Most geothermal facilities are designed assuming corrosion related to hydrogen sulfide in steam and air and chloride in brine will be mitigated by appropriate material selection [17].…”

The chemistry of geothermal waters: its effects on exploitation

“…All types of corrosion can be found in geothermal equipment, i.e. uniform corrosion, pitting, crevice corrosion, stress corrosion cracking, sulphide stress cracking, hydrogen blistering, intergranular corrosion, glavanic coupling, corrosion fatigue, erosion corrosion and cavitation (Conover et al, 1980;Corsi, 1986). Corrosion has various effects on equipmentweakening with resultant reduced resistance to stress and shorter life, holes which can cause undesirable leaks, troublesome tarnishing of electrical and switchgear equipment, and the formation of scaleall leading to a fall in production rates.…”

“…The corrosive potential of geothermal fluids on metals depends mainly on several key chemical species (Conover et al, 1980;Miller, 1980;Corsi, 1986): Hydrogen ion IpH): The corrosion of carbon steels increases as pH decreases. Furthermore, the passivity of a metal is generally dependent on pH, and local breakdown of passivity can lead to pitting, crevice corrosion and stress corrosion cracking.…”

“…The aggressive nature of all the above species depends on the material used and the type of corrosion. In addition, the interaction of two or more species has a different effect from that of each species individually (Conover et al, 1980).…”

Influence of Heat Treatments on Corrosion Behaviour of Alloy 625 Forged Rod

“…Nickel alloy 625, typically containing 22 wt.% Cr, 9 wt.% MO, 3,7 wt.% Nb and < 5 wt.% Fe , combines good mechanical properties, weldability and corrosion resistance (1). It has numerous applications in chemistry, pulp and paper (2), offshore and marine industries (3), and in geothermal power systems (4).…”