How to read Piping and Instrumentation Diagrams (P&IDs) ? | EveryEng

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Self-paced Beginner

How to read Piping and Instrumentation Diagrams (P&IDs) ?

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81 min

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English

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Process Engineering World

Oil & Gas Upstream

Pharmaceutical & Healthcare

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Process Engineering World

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You work in Oil & Gas Upstream or Pharmaceutical & Healthcare
You're a Chemical & Process professional
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You need a different specialisation outside Chemical & Process
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Course details

Piping and Instrumentation Diagrams (P&IDs) are crucial in representing the intricacies of process systems in various industries. Accurately reading and understanding P&IDs is essential for efficient design, operation, and maintenance. This course teaches you how to decipher P&IDs, unlocking the secrets to effective process and system management.

Course suitable for

Key topics covered

Understanding P&ID’s. Reading P&ID’s, Key ideas and tips to understand hidden points in P&ID’s.

Course content

The course is readily available, allowing learners to start and complete it at their own pace.

3 lectures1 hr 21 min

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Questions and Answers

Q: You're reading a P&ID and trying to reconcile line sizing during HAZOP. The long-tail phrase you're searching is "how to calculate control valve Cv from P&ID steam service". The P&ID shows a control valve on saturated steam at 10 barg, 180 °C, design flow 5,000 kg/h, with a noted allowable ΔP of 1.5 bar. Using IEC 60534 assumptions, what Cv should you expect to see on the valve datasheet?

A: The hard boundary here is the 1.5 bar allowable ΔP called out on the P&ID. Steam sizing under IEC 60534 with expansion factor gives a Cv just under 100 for 5,000 kg/h at 10 barg. Treating it as liquid or taking full line pressure drop pushes Cv high, while ignoring downstream pressure depresses it unrealistically.

Q: During an HSE walkdown you're asked to explain an alarm shown on the P&ID. The search phrase in your head is "P&ID level control valve fails open effect on separator". The inlet level control valve to a three-phase separator is marked FC. Instrument air pressure is lost. What happens next and what response aligns with the intent shown on the P&ID?

A: The key marker is the FC notation. Loss of air drives the valve open. On a separator this drains liquid inventory, exposing internals and pushing gas into liquid outlets. The P&ID intent is upstream flow reduction, not emergency blowdown.

Q: You're on a COMAH site doing loop checks under audit pressure. The exact phrase you're googling is "P&ID loop check transmitter range mismatch datasheet". The P&ID shows PT-201 ranged 0–100 barg feeding a HH trip at 90 barg. In the field, the transmitter datasheet says calibrated 0–160 barg. What’s the correct action before sign-off?

A: The number that matters is the 90 barg HH relative to MAWP and control logic. A wider sensor span dulls resolution but doesn't change protection if scaling is right. Under audit, undocumented re-ranging or silent acceptance fails immediately.

Q: Reviewing a P&ID for a produced water system, you're thinking "carbon steel corrosion risk P&ID produced water CO2". The line is tagged CS, 60 °C, 3 barg, with dissolved CO₂ noted upstream. No corrosion allowance is shown. What degradation mechanism dominates?

A: The threshold is simply the presence of free water and CO₂ at modest temperature. That points straight to sweet corrosion. The other mechanisms need conditions that aren’t on the P&ID.