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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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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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