A reservoir that cannot be switched off, and valves that may not seat.
Geothermal is the clearest case in this library of an energy source with no isolation device. There is no valve between the crew and the reservoir. A well is killed with brine and held dead by a hydrostatic column — a maintained condition under continuous monitoring, not a lock on a device.
The valves that do exist are working against silica scale and chlorides. A geothermal master valve that reads closed may not be seated, which is why the bleed between barriers is the evidence and the handwheel position is not.
Everything downstream carries hydrogen sulphide. The non-condensable gas stream off a turbine condenser is the most concentrated H₂S on the plant, and H₂S deadens the sense of smell well below the concentration that kills.
The well is dead because a brine column is holding it. Stop monitoring, or lose the column, and it is a live well again with a lock on a valve.
The handwheel is wound shut and tagged. The seat is scaled and passing, and nobody opened the bleed to find out.
Brine at 240 °C between two closed valves flashes to steam the moment a flange is cracked.
Real isolation-point structure, illustrative tags, equipment that does not exist. Free to read and download. An example to learn from — not a document to adopt.
Master valve change on a two-phase geothermal production wellhead. Covers a reservoir that cannot be switched off, quench and kill lines, silica-scaled valves that may not seat, flashing brine and hydrogen sulphide.
- 12 isolation points
- 6 must stay energised
- 1 cannot be isolated — managed by other means
- 3 with a stored-energy dwell
Condenser entry and non-condensable gas system service on a geothermal steam turbine. Covers steam admission from a header shared with other units, vacuum, turbine overspeed on residual steam, and an H2S-rich NCG stream.
- 12 isolation points
- 1 must stay energised
- 5 with a stored-energy dwell
The reservoir is recorded as a point that cannot be isolated, with the compensating controls named, rather than left off the procedure because no device exists to lock.
Bleed and vent points carry a required dwell the engine enforces at acknowledgment, so a flange is not cracked on a line that has not finished flashing.
A wellhead job runs across shifts with a well held dead by monitoring. Custody is a two-party, credential-attested handover, so responsibility is never ambiguous.
Plans are per site, per year, unlimited users — see pricing.