Alaska Liquefaction Unit — P&ID Sheet 3
Alaska — May 11, 2026
Critical Issues
Missing pressure safety valve on compressor discharge header
Compressor discharge header C-301A/B operating at 1,450 psig shows no PSV or rupture disc on drawing. ASME B31.3 requires overpressure protection on all high-pressure gas headers.
ASME B31.3 §322.6.3 — Pressure relief devices required on all gas systems operating above 1,000 psig
Ref: ASME B31.3-2022 §322.6.3; Alaska Oil & Gas Conservation Commission §20 AAC 25.260
Recommendation: Add a PSV with set pressure ≤ 1,450 psig upstream of the first isolation valve on discharge header.
Emergency shutdown valve ESD-3201 missing fail-safe designation
ESD valve on the gas feed line to HX-301 has no fail-safe position indicated. For cryogenic service, the fail-safe position must be explicitly documented per NFPA 59A §7.3.2.
NFPA 59A §7.3.2 — All ESD valves in LNG service must show fail-safe position (FC/FO) on P&ID
Ref: NFPA 59A-2023 §7.3.2; API 14C Table 3
Recommendation: Add FC designation to ESD-3201 symbol. For feed isolation, fail-closed is the standard position.
Major Issues
Instrument tags missing on three temperature elements
Temperature elements at HX-301 shell-side outlet, V-302 vapor space, and P-303A suction are shown without tag numbers. Untagged instruments cannot be cross-referenced in the instrument index or control narrative.
ISA 5.1-2022 §4.2 — All instruments shown on a P&ID shall have a unique tag number
Ref: ISA 5.1-2022 §4.2
Recommendation: Assign and label tag numbers for all three temperature elements before issuing for design.
Pipe specification break missing at cryogenic/ambient boundary
Line 3"-GAS-3014-A4B transitions from cryogenic to ambient service at V-302 without a spec break symbol. Mixing cryogenic and ambient specs on a single line without designation is a common root cause of material selection errors.
ASME B31.3 §323.2 — Pipe spec changes shall be clearly identified at the point of change
Ref: ASME B31.3-2022 §323.2
Recommendation: Add a spec break diamond at the point where cryogenic service ends. Label upstream and downstream specs.
Atmospheric vent on V-302 lacks minimum height callout
Atmospheric vent on flash drum V-302 is shown but discharge elevation is not noted. Alaska regulations require elevated venting ≥ 3 m above grade or adjacent structures for flammable gas service.
Alaska Administrative Code 20 AAC 25.215(b) — Vent discharge shall be at least 3 m above grade
Ref: 20 AAC 25.215(b); API 521 §5.4
Recommendation: Add elevation callout to vent line or reference a vent riser drawing that documents compliance.
Warnings
Manual isolation valve upstream of ESD-3201 not shown as locked open
The manual block valve upstream of ESD-3201 has no LO (locked open) designation. If inadvertently closed, it defeats the ESD system. This may not apply if the valve is required for maintenance isolation.
API 14C §4.3.3 — Block valves that defeat safety devices shall be designated LO
Ref: API 14C-2017 §4.3.3
Recommendation: Add LO designation if this is not a maintenance block. If it is, add a note referencing the LOTO procedure.
Revision block does not include P&ID revision number
The title block shows a project revision (Rev C) but no P&ID-specific revision number. Most owner standards require separate P&ID revision tracking to support document control.
Ref: ISA 5.1-2022 Annex A
Recommendation: Add a P&ID revision column to the title block separate from the project revision field.
Informational
ASME B31.3 applies to all process piping on this sheet
All process piping shown on this sheet falls under ASME B31.3 Process Piping jurisdiction based on fluid service classification. No violations detected for checked parameters.
Ref: ASME B31.3-2022 §300.1.1
Electrical area classification boundaries not assessed
Hazardous area classification per NFPA 497 / API RP 505 is outside the scope of this P&ID check. A separate area classification drawing should accompany this P&ID for full compliance review.
Ref: NFPA 497-2022; API RP 505
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