psi
Pound-force per square inch, the dominant pressure unit in US oil and gas practice.
Learning objectives
- Explain psi in technician-friendly language.
- Identify where converting psi to bar, kPa, and MPa for cross-system comparison appears in live plant work.
- Connect the topic to pressure measurement, calibration, or loop checking.
- Avoid the main field mistake: assuming 1 psi is the same magnitude as 1 bar in mental estimates.
psi is part of the Pressure Measurement master module. Pound-force per square inch, the dominant pressure unit in US oil and gas practice.
The main focus is converting psi to bar, kPa, and MPa for cross-system comparison. In the field, the technician must read the tag, confirm the pressure reference and unit, check the process connection, and compare the instrument reading with the expected plant condition. The topic also links to calibration records, DCS scaling, alarm settings, and safe isolation before any instrument work.
A practical way to study this topic is to ask four questions: what pressure is being measured, what reference is used, how the signal reaches the DCS, and what failure would make the reading unsafe or misleading. This keeps the lesson tied to real maintenance and commissioning decisions rather than only theory.
Field examples
- US-origin SIS specification sheets often list trip setpoints in psi while plant DCS graphics use bar.
- Compare the local gauge, transmitter HART value, and DCS indication before deciding which value is credible.
- Record the unit, range, LRV, URV, and tag number before calibration or loop checking.
Common mistakes
- assuming 1 psi is the same magnitude as 1 bar in mental estimates
- Trusting one reading without checking the pressure reference, unit, range, and process condition.
- Opening tubing, manifolds, or vents without proving isolation and zero stored pressure.
Safety
Trip setpoints in wrong units can cause early trip or missed trip; confirm the active unit in the DCS.
Key takeaway
psi helps a technician understand pressure readings, field installation, and safe troubleshooting. Always verify the unit, reference, range, and isolation state before acting on the measurement.
Imported study note from pressure_lesson_061. The app generates this text from a lesson seed. It is not a long textbook page.