With dissolved CO₂, H₂S, chloride and high temperature, geothermal fluid is an aggressive environment for carbon steel. Corrosion shortens the life of well equipment and pipelines, and the iron it releases makes scaling worse.
Types of corrosion
- CO₂ corrosion: carbonic acid causes general thinning and pitting of carbon steel.
- H₂S: forms iron sulphide films; under some conditions creates a risk of sulphide stress cracking.
- Oxygen ingress: air entering at reinjection tanks, pump seals and heating circuits accelerates corrosion many times over.
- Chloride: increases the risk of pitting and stress corrosion in stainless steels.
How does a corrosion inhibitor work?
Film-forming corrosion inhibitors create a thin protective layer on the metal surface that reduces contact with the fluid. Stability at high temperature, compatibility with the scale inhibitor and no harm to the reinjection well are decisive in selection. Biyopol’s BiyoGeo CI is designed for geothermal environments containing CO₂ and H₂S.
Keeping oxygen out
A chemical programme has limited effect unless oxygen ingress is controlled. Gas blanketing of reinjection tanks, seal checks and, where needed, an oxygen scavenger reduce corrosion significantly. In closed circuits such as district heating, a closed-loop corrosion inhibitor and regular water analysis are recommended.
| Monitoring method | What it provides |
|---|---|
| Corrosion coupons | Average corrosion rate (mm/year) over a period and pitting type |
| ER / LPR probes | Real-time corrosion rate |
| Iron concentration in the fluid | Indirect indicator of corrosion |
| Dissolved oxygen measurement | Detection of air ingress |
Frequently asked questions
Can a corrosion inhibitor be used with a scale inhibitor?
Yes, in programmes where compatibility has been verified. The products are usually fed from separate injection points.
What corrosion rate is acceptable?
The acceptable value depends on the equipment and material; the target is set with site engineering and tracked with coupons.
Does stainless steel solve the corrosion problem?
Partly. Chloride and temperature can cause pitting and stress corrosion in stainless steels too; material selection and chemical programme should be assessed together.
Related guides
- Geothermal power plant chemicals (overview)
- Calcite scaling in geothermal wells
- Silica and metal silicate scaling
- Downhole dosing via capillary tubing
- Heat exchanger and ORC fouling
- Scaling in reinjection lines and wells
- Geothermal heating and greenhouse systems
- Sulphide scales (stibnite, iron sulphide)
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