Technical note

5 Safety Essentials for HPHT Laboratory Testing

Pressure relief, material compatibility, pre-run leak testing, temperature ramp control, and operator training: the five fundamentals that keep high-pressure, high-temperature core and fluid testing from becoming an incident report.

Coretest Systems, Inc. · Laboratory practice

HPHT laboratory testing operates at conditions that replicate deep reservoir environments: pressures exceeding 10,000 psi and temperatures above 150°C are routine. At those parameters, a component failure is not an inconvenience. It is a potential fatality. The margin between a controlled experiment and a catastrophic event is determined almost entirely by how rigorously the five fundamentals below are applied: before every run, on every system, without exception.

1. Pressure relief and burst disc protection

Every pressure vessel in an HPHT system must be protected by at least two independent overpressure devices. Relying on a single back pressure regulator is not an acceptable safety architecture. The BPR handles controlled process pressure; the burst disc is the last line of defense against uncontrolled pressure excursions.

Sizing matters as much as presence. Both the BPR set point and the burst disc rated pressure must be selected below the working pressure rating of the weakest component in the system. ASME Boiler and Pressure Vessel Code Section VIII defines the calculation methodology for burst disc sizing and provides guidance on combination device installations where a rupture disc is installed upstream of a pressure relief valve.

Burst discs must be inspected before each test. Fatigue from repeated pressure cycling can cause premature failure, or an elevated burst pressure if the disc is deformed. Replace burst discs on a defined service interval regardless of visual condition and document every replacement in the system maintenance log.

Never bypass either device to save time before a run. A blocked vent path on a burst disc has caused more laboratory incidents than almost any other single factor.

2. Material compatibility with process fluids

Fluid chemistry at HPHT conditions is significantly more aggressive than at ambient conditions. Elevated temperature accelerates corrosion kinetics; elevated pressure drives dissolved gases deeper into metal lattices. Selecting materials based on ambient-condition corrosion tables is a common and dangerous error.

For systems processing H2S, CO2, or high-salinity brine, Hastelloy C-276 is the standard choice for wetted metal components. Specifying HC-276 fittings and valves throughout the wetted flow path eliminates the galvanic mismatch problems that occur when lower-grade alloys are used at individual connection points. Titanium grade 2 or grade 5 is required when hydrofluoric acid is present in any concentration.

Elastomer selection is equally critical. Viton (FKM) is the default seal material for most hydrocarbon and brine service up to approximately 200°C. However, Viton degrades in the presence of steam, hot water above 150°C with high pH, and some ketone-based solvents. PTFE is chemically inert across virtually all process fluids but cannot be used in dynamic seal applications. Check compatibility tables against your specific fluid matrix before every new test fluid type is introduced into the system.

3. Pressure testing before every run

A hydraulic leak test at 1.1 times the planned working pressure is mandatory before each test run. This is a pre-run checklist item, not a one-time commissioning procedure.

The test medium must be liquid, typically water or a compatible hydraulic fluid. Never perform a pressure integrity test using gas as the primary pressurizing medium. Compressed gas stores energy proportional to volume and pressure; a vessel failure under gas pressure releases that energy instantaneously. The same failure under hydraulic pressure results in a leak with far lower energy release.

The test procedure: fill the system completely with liquid, eliminate all trapped air through bleed valves, pressurize incrementally to test pressure, hold for a minimum of 15 minutes, and inspect every fitting, connection, valve packing, and seal face. Pay particular attention to recently disturbed connections. Any fitting that was opened for sample access or maintenance must be treated as a new connection and retested.

Record the test pressure, hold duration, and pass/fail result in the run log. A system that leaks gets repaired and retested. There is no middle ground.

4. Temperature ramp protocols

Thermal management in HPHT systems is a pressure management problem as much as a temperature control problem. As temperature rises, fluid expands. In a closed system with no available volume, that expansion translates directly into pressure increase. At HPHT conditions, a 20°C uncontrolled temperature excursion can generate pressure increases of several hundred psi in a fluid-filled system.

Always confirm the vent path is open and functional before applying heat. For experiments where pore pressure is controlled by a back pressure regulator, verify the BPR is set and responding before the heating jacket is energized.

Ramp rates should be defined in the test protocol and should not exceed the thermal shock tolerance of the core sample or the vessel material. A maximum ramp rate of 1–2°C per minute is appropriate for most geological samples. Monitor pore pressure and confining pressure throughout the heating phase. If either exceeds the setpoint without a corresponding BPR response, halt heating immediately and investigate before continuing. The same equilibration logic applies to displacement experiments; our note on core flooding setup covers the thermal hold criteria in detail.

For experiments using CO2 or other fluids with phase transitions within the test P-T range, map the phase diagram before designing the ramp protocol. Crossing a phase boundary during heating can generate pressure spikes that no BPR can respond to quickly enough.

5. Personnel training and SOP documentation

The most precisely engineered HPHT system will fail if the operator does not understand what they are running. HPHT laboratory work involves enough variables, interdependencies, and failure modes that undocumented tribal knowledge is a safety hazard.

Every procedure that takes place in an HPHT laboratory must exist as a written standard operating procedure. SOPs must cover normal operation, startup, shutdown, and emergency response. They must be version-controlled, reviewed annually or after any incident, and physically available at the workstation.

Operator qualification should be documented and tiered. A technician who has completed supervised training on a specific system type should be signed off before operating independently. New system configurations, new fluid types, or new pressure-temperature envelopes require additional qualification, not an assumption that existing competence transfers automatically.

Emergency shutdown drills must be conducted at a defined interval, at minimum annually, and must include the full sequence from incident recognition through system depressurization and personnel accounting. Where ATEX-classified zones are applicable, equipment selection, maintenance intervals, and hot work procedures must conform to ATEX Directive 2014/34/EU requirements.

Equipment quality is the foundation that all five of these practices rest on. A burst disc installed in a poorly machined port will not seat correctly regardless of how carefully it is sized. A Viton seal in an endcap with an out-of-tolerance groove will extrude at pressure regardless of how correctly the material was specified. Specifying and procuring precision-machined vessels, certified components, and traceable materials is the first safety control in any HPHT laboratory program.

Related equipment: Coretest autoclaves and pressure vessels and HC-276 fittings and valves are engineered for HPHT service with certified materials and traceable documentation.