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Application Guide

Valves for Geothermal Power Plants

Geothermal power plants extract steam and brine from underground reservoirs at temperatures up to 350°C and pressures up to 100 bar, often containing high concentrations of hydrogen sulphide (H₂S), carbon dioxide, and dissolved solids including silica scale and chlorides. This combination of sour gas, high temperature, scaling fluids, and two-phase flow (steam + liquid) demands specialised valve materials and designs not typically found in conventional power or oil & gas applications. Vajra Industrial Solutions supplies Duplex 2205 and SS316L valves for wellhead and brine service with NACE MR0175 compliance, and IBR-certified gate valves for the steam turbine supply headers.

NACE MR0175 / ISO 15156ASME B16.34IBR 1950 (Steam India)API 600API 6DAPI 598ISO 9001:2015
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Which valves are used for geothermal power plants?

Geothermal power plants extract steam and brine from underground reservoirs at temperatures up to 350°C and pressures up to 100 bar, often containing high concentrations of hydrogen sulphide (H₂S), carbon dioxide, and dissolved solids including silica scale and chlorides.

Connected Engineering

Standards
API 6DASME B16.34API 598 TestingNACE MR0175
Materials
A351 CF8M (SS316)Super Duplex 2507
Failure Modes
Stress Corrosion Cracking
Services
Steam Service

Recommended Valve Types for Geothermal Power Plants

Ball Valve (Duplex 2205)

Class 600 / 900

Why: Wellhead isolation and Christmas tree - sour brine (H₂S + CO₂ + Cl⁻) at 200–300°C; fire-safe, anti-static

Materials: A890 Grade 1B Duplex 2205 body and ball; Duplex stem; PTFE seats with metal seat backup

Standards: API 6D, NACE MR0175, API 607 (fire-safe), ISO 14313

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Gate Valve (NACE MR0175)

Class 300 / 600

Why: Brine pipeline isolation and separator inlet - sour H₂S service; Class 300–600

Materials: A216 WCB with SS316 trim (NACE HRC ≤ 22); A890 Duplex for higher chloride fields

Standards: API 600, NACE MR0175, ASME B16.34

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Butterfly Valve (SS316L)

Class 150 / 300

Why: Geothermal brine reinjection headers (large bore, moderate pressure), cooling water, and condensate service

Materials: SS316L disc and shaft; EPDM seat; WCB body with SS316L overlay in contact areas

Standards: API 609, ASME B16.34

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Gate Valve (IBR Steam)

Class 150 / 300

Why: Geothermal steam turbine inlet isolation and extraction steam - IBR mandatory in Indian geothermal projects

Materials: A216 WCB (saturated steam to 180°C); SS316 trim for H₂S-containing steam

Standards: IBR 1950, ASME B16.34, API 600

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Critical Requirements

H₂S service - NACE MR0175 / ISO 15156 mandatory for all wetted metallic components; HRC ≤ 22 Rockwell hardness limit on body, trim, and fasteners
Silica scaling - full-bore valves only; no throttle positions; pipeline injection of scale inhibitor upstream of brine valves
Two-phase flow (steam + liquid brine) - metal-to-metal seat or reinforced PTFE; no soft-seat-only designs in wellhead service
IBR certification for steam turbine supply headers in India - Form III-C material and Form III-E hydraulic test certificates mandatory
Chloride stress corrosion - Duplex 2205 or SS316L (not SS304); super duplex 2507 for high-chloride (>5,000 ppm Cl⁻) fields
Geothermal flash steam often contains non-condensable gases (NCG: H₂S, CO₂, NH₃) - valve materials must resist corrosion in this mixture

Fluid & Service Challenges

Geothermal brine - complex mixture: H₂S (1–10,000 ppm), CO₂ (1–20%), Cl⁻ (1,000–100,000 ppm), silica (200–1,000 ppm), temperature 100–350°C
H₂S sour gas - sulfide stress cracking (SSC) in high-strength steels; NACE MR0175 hardness limits mandatory
Silica scale - deposits at pH > 7 or on cooling; full-bore valves and scale inhibitor required
Geothermal steam with H₂S + CO₂ - more corrosive than clean steam; SS316 or Duplex 2205 trim mandatory
Chloride-rich brine (some volcanic fields) - pitting and crevice corrosion; Super Duplex 2507 or titanium for highest chloride fields

Material Selection Guidance

Wellhead (H₂S brine, 200–300°C): Duplex 2205 (A890 Grade 1B) - PREN ≥ 35, NACE MR0175 hardness limit; confirmed against ISO 15156 Table A.3. Brine pipeline (<200°C, moderate chloride): A216 WCB with SS316 trim, NACE HRC ≤ 22. Reinjection brine (large bore, PN 10–40): SS316L butterfly valves with EPDM seats. Geothermal steam (H₂S-free after scrubbing): A216 WCB with IBR Form III for Indian projects. High-chloride volcanic fields: Super Duplex 2507 or titanium.

Typical Service Points

Wellhead and production manifold - Duplex 2205 ball valves (Class 600–900, H₂S sour brine + steam)
Flash separator inlet and outlet - WCB gate valves with SS316 trim, NACE MR0175 (Class 300)
Steam turbine supply header - IBR gate and globe valves (geothermal steam, Class 150–300)
Brine reinjection pipeline - large-bore SS316L butterfly valves (Class 150, neutral brine)
Cooling tower water - WCB butterfly valves for condenser cooling circuits
Non-condensable gas (NCG) extraction - SS316L valves for H₂S-CO₂ gas stream

FAQ - Valve Selection for Geothermal Power Plants

What material is recommended for geothermal brine with high H₂S?
For geothermal brine containing H₂S above 0.0003 MPa partial pressure (the NACE MR0175 threshold), specify Duplex 2205 (ASTM A890 Grade 1B) with hardness confirmed ≤ HRC 22 as per NACE MR0175 / ISO 15156. Duplex 2205 provides both corrosion resistance (PREN ≥ 35) and the required hardness limit. For very high H₂S fields (> 1,000 ppm) or combined high chloride + H₂S, upgrade to Super Duplex 2507 (PREN ≥ 40). Carbon steel with SS316 trim is acceptable only for H₂S below the NACE threshold.
How does silica scaling affect valve selection for geothermal brine?
Silica (SiO₂) dissolved in geothermal brine precipitates when the brine cools below the silica saturation temperature (typically 80–120°C for high-silica fields). This scale deposits on valve seats, stems, and body ports, causing seizure and leakage. Mitigation: (1) use full-bore valves - no narrow ports where scale can bridge; (2) use ball valves in the full-open position only - do not use ball valves for throttling in scaling brine (scale deposits in the partially open cavity); (3) inject scale inhibitor upstream. Knife gate valves for slurry-heavy brine cut through scale deposits better than wedge gate.

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Geothermal Power Plants

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Key Standards

NACE MR0175 / ISO 15156
ASME B16.34
IBR 1950 (Steam India)
API 600
API 6D
API 598
ISO 9001:2015

Products for This Application

Ball ValvesGate ValvesButterfly Valves

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