HomeApplicationsAir Separation Units (ASU)

Application Guide

Valves for Air Separation Units (ASU)

Air separation units (ASUs) produce liquid oxygen (LOX, −183°C), liquid nitrogen (LIN, −196°C), and liquid argon (LAR, −186°C) by cryogenic distillation. Oxygen service imposes the most stringent safety requirements of any industrial valve application — even trace hydrocarbons or particles in oxygen-rich streams can ignite and cause catastrophic burns and fires. All valves in oxygen service must be ASTM G93-cleaned (oxygen-cleaned), use only oxygen-compatible materials (no brass, no PTFE with high-pressure O₂), and carry EIGA Doc 13 documentation. Vajra supplies fully oxygen-cleaned extended-bonnet cryogenic valves with complete cleaning certification for ASU main column, LOX pump, and product tanker loading service.

ASTM G93 (Oxygen Cleaning)EIGA Doc 13 (Oxygen Safety)BS 6364 (Cryogenic Valves)ASME B16.34ISO 21011 (Cryogenic Valves)CGA G-4.1 (O₂ Cleaning USA)API 598
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Recommended Valve Types for Air Separation Units (ASU)

Cryogenic Ball Valve (LOX Service)

Class 150 / 300

Why: LOX pump suction, LOX column draw, LOX product loading — extended bonnet for −183°C; ASTM G93 oxygen-cleaned

Materials: A182 F316L forged body; SS316L ball; PCTFE seats (oxygen-compatible); SS316L extended bonnet (350+ mm)

Standards: BS 6364, ASTM G93, EIGA Doc 13, API 607 (fire-safe, oxygen-critical)

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Cryogenic Gate Valve (LIN/LAR)

Class 150 / 300

Why: Liquid nitrogen and argon column isolation, product draw, and storage tank isolation; extended bonnet required

Materials: A182 F316L body and stem; SS316L gate and seats; extended bonnet per BS 6364

Standards: BS 6364, ASME B16.34, ISO 21011

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Globe Valve (Control, Cryogenic)

Class 150 / 300

Why: Oxygen pressure letdown and LIN flow control — precision control; SS316L body; no elastomer seats in oxygen service

Materials: A182 F316L body; SS316L trim; PCTFE or SS316 seat; oxygen-cleaned

Standards: BS 6364, ASTM G93, ASME B16.34

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Check Valve (Cryogenic)

Class 150 / 300

Why: LOX pump discharge check, back-flow prevention on product filling headers

Materials: A182 F316L body; SS316L disc and hinge pin; PCTFE seat ring; oxygen-cleaned

Standards: BS 6364, API 594, ASTM G93

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Critical Requirements

ASTM G93 / CGA G-4.1 oxygen cleaning — all valves for LOX/GOX service must be degreased with approved solvents, then passivated; verified by UV light and/or white glove test; sealed in nitrogen-purged bags until installation
EIGA Doc 13 (European Industrial Gases Association) — comprehensive oxygen safety standard; defines material compatibility, ignition mechanisms, and design requirements for oxygen valves
No PTFE in high-pressure oxygen service (> 30 bar GOX) — PTFE can ignite in high-velocity O₂; use PCTFE or metal-to-metal seats instead; PTFE acceptable for low-pressure (<30 bar) LOX
No brass, bronze, or copper alloys — acceptable for low-pressure oxygen, but ASU practice avoids them entirely due to particle contamination risk
Extended bonnet per BS 6364 — minimum 350 mm bonnet extension for valves below −29°C to keep packing above cryogenic zone
Impact testing — all cryogenic valve components must pass Charpy V-notch impact test at −196°C per ASTM A370

Fluid & Service Challenges

⚠Liquid oxygen (LOX, −183°C) — powerful oxidiser; organic contamination causes ignition; all wetted materials must be oxygen-clean and compatible with ASTM G93
⚠Liquid nitrogen (LIN, −196°C) — inert but extremely cold; thermal shock on warm valves; vacuum-jacketed piping preferred
⚠Liquid argon (LAR, −186°C) — similar to LIN; noble gas, non-reactive, but same cryogenic and thermal shock concerns
⚠Gaseous oxygen (GOX, high pressure > 30 bar) — adiabatic compression ignition risk; fire hazard; metal burning in O₂; velocity limits apply
⚠Nitrogen in subcooled process — moisture condensation from air on cold surfaces; vacuum insulation or foam insulation prevents external condensation

Material Selection Guidance

LOX service (all pressures): A182 F316L body with PCTFE seats (oxygen-compatible); ASTM G93-cleaned and sealed. GOX below 30 bar: SS316L with PTFE seats acceptable if cleaned. GOX above 30 bar: SS316L with PCTFE or metal-to-metal seats only — no PTFE. LIN and LAR: A182 F316L with PTFE or PCTFE seats; impact-tested at −196°C per ASTM A370. Never use brass, bronze, or aluminium in oxygen-rich streams — aluminium can ignite in high-pressure GOX due to particle impact ignition.

Typical Service Points

ASU main distillation column — cryogenic extended-bonnet gate and ball valves (LOX/LIN column, −183°C to −196°C, Class 150)
LOX pump suction and discharge — ASTM G93-cleaned cryogenic ball valves (Class 150–300)
Liquid product loading — LOX, LIN, LAR tanker loading arms (cryogenic quick-connects and ball valves)
GOX product header — gaseous oxygen at 5–200 bar (ASTM G93-cleaned; PCTFE seats above 30 bar)
GAN (gaseous nitrogen) header — SS316L ball valves, utility service, no special cleaning required
Plant air and instrument air — conventional WCB butterfly and ball valves; not oxygen-service

FAQ — Valve Selection for Air Separation Units (ASU)

What is ASTM G93 oxygen cleaning and is it mandatory for all ASU valves?
ASTM G93 (Standard Practice for Cleaning Methods and Cleanliness Levels for Material and Equipment Used in Oxygen-Enriched Environments) defines the degreasing, rinsing, and verification process for components that will be in contact with oxygen. For LOX and GOX service in ASUs, ASTM G93 cleaning is mandatory — trace hydrocarbons or particles can ignite in an oxygen-rich environment. The process involves solvent degreasing (usually with non-flammable chlorinated solvents or approved alternatives), hot DI water rinse, oven drying, UV light inspection, white-glove testing, and sealing in nitrogen-purged polyethylene bags for shipment.
Why can't I use PTFE seats in high-pressure oxygen valves?
PTFE (polytetrafluoroethylene) is generally oxygen-compatible at low pressures and low flow velocities. However, above approximately 30 bar GOX, PTFE can ignite through frictional heating from high-velocity gas impingement or particle impact ignition — a mechanism unique to oxygen service. EIGA Doc 13 and CGA G-4.1 restrict PTFE in high-pressure oxygen to specific designs with defined velocity limits. PCTFE (polychlorotrifluoroethylene) is the standard alternative — it has a higher ignition temperature than PTFE and is the seat material of choice for high-pressure LOX and GOX valves above 30 bar.

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Air Separation Units (ASU)

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Key Standards

ASTM G93 (Oxygen Cleaning)
EIGA Doc 13 (Oxygen Safety)
BS 6364 (Cryogenic Valves)
ASME B16.34
ISO 21011 (Cryogenic Valves)
CGA G-4.1 (O₂ Cleaning USA)
API 598

Products for This Application

Ball ValvesGate ValvesGlobe ValvesCheck Valves

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