BM TECH — NBS Europe — is the sole Authorized Representative of NBS Corporation in Europe, providing supply, installation and full lifecycle service for NBS UNIFLOW and UNICON valves in air separation units producing liquid and gaseous oxygen, nitrogen and argon across Europe, the Middle East and North Africa.
Of all industrial gas production processes, the cryogenic air separation unit places the most extreme demands on valves and process equipment. Temperatures as low as −196°C for liquid nitrogen service and −183°C for liquid oxygen. Pressure differentials from sub-atmospheric cold box conditions to high-pressure oxygen compression at 200 bar and above. Media ranging from cryogenic liquids that instantly vaporise on contact with ambient-temperature surfaces to gaseous oxygen at concentrations and pressures where ignition energy thresholds are orders of magnitude lower than in normal air.
In this environment, valve selection is not a procurement decision. It is an engineering decision with direct consequences for plant safety, product quality and operational continuity. A valve that performs reliably at ambient temperature may fail catastrophically at cryogenic conditions. A valve with inadequate oxygen compatibility may become an ignition source in high-pressure oxygen service. A valve that leaks past its seat in cold box service wastes the refrigeration energy that has been invested in bringing the process stream to cryogenic temperature.
NBS Corporation has developed the UNIFLOW and UNICON valve series through decades of engineering collaboration with the world’s leading air separation plant builders — validated in the cold boxes, product lines and utility systems of ASU installations operated by Air Liquide, Air Water, Taiyo Nippon Sanso Corporation, Daesung Industrial and Kobelco Air Water Cryoplant across Japan, Asia and globally.
As NBS Europe, BM TECH brings that validated cryogenic valve technology — and the full service capability to support it throughout the plant’s operational life — directly to European air separation plant operators.
A cryogenic air separation unit separates atmospheric air into its component gases — primarily oxygen, nitrogen and argon — by cooling the air to cryogenic temperatures at which the components liquefy at different temperatures, then distilling the liquid mixture in a column system. The process involves multiple distinct valve duties, each with specific technical requirements:
Water Washing Cooling Tower (peripheral valves) Feed air enters the ASU at ambient temperature and must be cooled and purified before entering the cold box. Cooling tower peripheral valves handle ambient-temperature water and air service — standard industrial duty with no cryogenic requirements, but requiring reliable continuous operation as part of the feed air conditioning train.
MS Absorption Tower (peripheral valves) Molecular sieve adsorbers remove water vapour, CO₂ and trace hydrocarbons from the feed air before it enters the cold box — contamination that would freeze and block heat exchangers and column internals at cryogenic temperatures. Peripheral valves on the MS adsorber system handle ambient-temperature air service with switching cycles similar to PSA operation, as the adsorbers alternate between adsorption and thermal regeneration phases.
Main Heat Exchanger The main heat exchanger is the thermal heart of the ASU — cooling feed air from ambient temperature to near its liquefaction point by heat exchange with returning product streams. Valves on the main heat exchanger handle the transition between ambient and cryogenic temperature conditions — experiencing the full thermal gradient of the ASU in their operating environment. These valves require materials and designs that accommodate the thermal contraction associated with cryogenic cool-down without loss of sealing performance or structural integrity.
Expansion Turbine — Outlet Valve and Bypass Valve The expansion turbine produces the refrigeration that drives the cryogenic separation process — expanding high-pressure air to lower pressure and lower temperature, with the energy extracted appearing as shaft work. The turbine outlet valve and bypass valve are critical process control points:
Both valves operate in the cryogenic temperature zone of the cold box — requiring full cryogenic material qualification and extended bonnet design to protect actuators and control equipment from direct exposure to cryogenic temperatures.
Cold Box — Cryogenic Process Valves The cold box contains the distillation columns, heat exchangers and associated piping that perform the actual separation of air into its components at cryogenic temperatures. Valves within the cold box operate continuously at temperatures between −150°C and −196°C, in oxygen-enriched or pure oxygen streams at pressures up to 10 bar, and in liquid service where flash vaporisation on valve operation can produce two-phase flow conditions.
Cold box valve design requirements are the most demanding in the ASU:
Argon Distillation Tower — Ar Product Line Argon recovery from the ASU requires a dedicated distillation column operating at cryogenic temperatures with specific purity requirements. Valves on the argon product line must maintain the purity of the argon stream from the distillation tower to storage or downstream processing — tight seat shutoff preventing backflow of nitrogen or oxygen into the argon product.
Product Gas Lines Gaseous and liquid oxygen, nitrogen and argon product lines connect the cold box to storage, compression and distribution systems. Product line valves handle a range of conditions — from cryogenic liquid at cold box outlet to ambient-temperature gas at the delivery point — and must maintain product purity integrity throughout.
The engineering requirements for ASU cryogenic valves go beyond simply specifying stainless steel and calling the valve “cryogenic rated.” Each design element must be specifically addressed for ASU service:
Material selection at cryogenic temperatures At −196°C, many materials that perform reliably at ambient temperature become brittle — losing the ductility and impact resistance needed to withstand pressure loading and thermal shock. Carbon steel becomes brittle below approximately −30°C. Standard cast iron fails at cryogenic temperatures. Austenitic stainless steels (304, 316L) maintain ductility to −269°C and are the standard body material for cryogenic valve service. Aluminium alloys are used where weight is critical. All materials must be impact-tested at the minimum design temperature.
Extended bonnet design The valve packing — the seal around the stem — must be maintained at a temperature above the minimum operating temperature of the packing material. PTFE packing, standard in most industrial valves, becomes brittle and loses its sealing capability at temperatures below approximately −50°C. The extended bonnet creates a temperature gradient along the stem between the cryogenic process connection and the packing — ensuring packing temperature remains within its operating range even when the valve body is at −196°C.
Thermal contraction accommodation All materials contract when cooled — but different materials contract by different amounts. A valve body in stainless steel, a stem in a different steel grade and a seat ring in a third material will all contract by different amounts when cooled from ambient to cryogenic temperature. If these differential contractions are not accounted for in the valve design, the result is either a valve that cannot be operated at cryogenic temperature (because thermal contraction has locked the stem) or a valve that leaks (because differential contraction has opened a gap in the seat).
NBS cryogenic valve designs account for differential thermal contraction — ensuring that the valve operates correctly and seals reliably across the full temperature range from ambient cool-down to minimum operating temperature.
Oxygen service cleanliness In high-pressure oxygen service, contamination of valve internals with hydrocarbon oils, greases or particulates creates ignition hazards — particles and films that are inert in air become fuel in high-pressure oxygen. All valves for oxygen service must be cleaned to defined cleanliness standards before installation, with documented verification that cleaning requirements have been met. NBS valves for oxygen service are assembled under oxygen-clean conditions with compatible lubricants and documented cleanliness certification.
Seat design for two-phase service In liquid oxygen and liquid nitrogen service, valve operation can cause local vaporisation of the cryogenic liquid — producing two-phase flow conditions at the valve seat. Two-phase flow is erosive and can cause rapid seat wear in standard valve designs. NBS cryogenic valve seat designs accommodate two-phase flow conditions without excessive seat erosion.
NBS Corporation UNIFLOW/UNICON valves have been installed in ASU plants built and operated by:
Air Liquide Japan Ltd. — including Air Liquide China operations Japan Air Gases Co. — Air Liquide group, Japan Air Water INC. — including Kobelco Air Water Cryoplant, Ltd. Taiyo Nippon Sanso Corporation — one of Japan’s largest industrial gas producers Daesung Industrial — Korea
These are large-scale cryogenic ASU installations — producing liquid and gaseous oxygen, nitrogen and argon for industrial, medical and electronics manufacturing customers. The valve performance requirements of these installations are among the most demanding in industrial process engineering. NBS Corporation’s position as the valve supplier of choice for these operators reflects decades of validated cryogenic performance.
As NBS Europe, BM TECH provides European ASU operators with direct access to the same proven valve technology and the service infrastructure to support it.
Cryogenic Valve Condition Assessment
ASU cryogenic valves operate continuously in an environment that makes visual inspection during operation impossible — cold box valves are insulated, at cryogenic temperature and inaccessible without a plant shutdown. Condition assessment must therefore rely on performance data and on systematic inspection during planned maintenance shutdowns.
BM TECH provides structured cryogenic valve condition assessment during ASU planned maintenance outages — covering:
Assessment findings are documented with recommendations for repair, replacement or continued service — supporting plant maintenance planning for the next scheduled outage.
Planned Maintenance — ASU Shutdown Coordination
ASU planned maintenance is a major logistical event — the cold box must be warmed to ambient temperature before internal components are accessible, a process that takes days and consumes significant energy. Every maintenance activity must be completed within the shutdown window to avoid an unplanned extension.
BM TECH coordinates ASU valve maintenance activities within planned shutdown programmes — providing advance parts availability, pre-mobilisation of service engineers and documentation review to ensure that valve inspection, maintenance and replacement activities are completed within the planned outage window without extension.
Oxygen Service Valve Management
Valves in oxygen service require specific handling, cleaning and documentation procedures that differ fundamentally from standard industrial valve maintenance. BM TECH service engineers are trained in oxygen service valve handling — maintaining oxygen cleanliness during inspection and maintenance, using compatible lubricants and tools, and providing the documentation required to certify oxygen service compliance after maintenance.
Cold Box Valve Replacement
When a cold box valve reaches end of service life or is damaged beyond economical repair, replacement requires a valve that meets all of the original specification requirements — cryogenic material qualification, extended bonnet design, oxygen cleanliness certification and dimensional compatibility with the existing piping. BM TECH supplies NBS replacement valves with full specification documentation, and coordinates installation within planned shutdown windows.
Rapid Response for Product Line Valve Failures
While cold box valves are accessible only during planned shutdowns, product line and utility valves may be accessible for maintenance during plant operation. BM TECH provides rapid response service for product line valve failures — on-site intervention and expedited spare parts supply — to restore product delivery capability with minimum delay.
For ASU operators managing their valve population between planned maintenance shutdowns, BM TECH recommends monitoring the following performance indicators:
Cold box heat leak — increasing heat leak into the cold box, indicated by rising liquid consumption in the cold box refrigeration balance, may indicate valve seat leakage allowing warm process streams to bypass heat exchangers or cold product streams to lose refrigeration through leaking isolation valves.
Product purity trends — gradual decline in oxygen, nitrogen or argon purity without corresponding changes in feed air composition indicates seat leakage in product line or distillation column valves — allowing cross-contamination between product streams.
Expansion turbine performance — declining turbine efficiency or instability in cold box liquid inventory may indicate incorrect operation of the turbine outlet or bypass valve — requiring valve inspection at the next available opportunity.
MS adsorber cycle performance — increasing CO₂ or moisture breakthrough from the molecular sieve adsorbers, or declining adsorber cycle time, may indicate valve seat leakage in the adsorber switching valve circuit — allowing feed air contamination of the regeneration stream.
Actuator air consumption — increasing compressed air consumption by cold box actuators, monitored through instrument air supply flow measurement, indicates seal wear or external leakage in actuator circuits serving cold box valves.
Systematic tracking of these parameters between planned maintenance outages allows ASU operators to prioritise valve inspection activities during the next shutdown — focusing resources on the valves most likely to require intervention.
Whether you are specifying NBS valves for a new air separation unit, planning valve inspection and maintenance during an upcoming ASU shutdown, assessing the condition of an ageing cold box valve population, or dealing with an urgent product line valve failure — BM TECH is ready to assist.
Contact NBS Europe:
Request Service Support Request a Spare Parts Quote Schedule a Valve Assessment Download NBS UNIFLOW/UNICON Technical Data
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Cold box warm-up from cryogenic operating temperature to ambient typically takes several days — the exact duration depends on cold box size and insulation. This warm-up period must be included in the total planned shutdown duration. BM TECH recommends factoring the full warm-up and cool-down cycle into ASU maintenance planning to ensure sufficient time for valve inspection and maintenance.
In high-pressure oxygen service, hydrocarbon contamination of valve internals creates ignition hazards — oils and greases that are inert in air become fuel in high-pressure oxygen. Oxygen service cleanliness requires removing all hydrocarbon contamination from valve internals before installation or after maintenance, using compatible cleaning agents and lubricants, and verifying cleanliness to defined standards. BM TECH service engineers are trained in oxygen service handling procedures.
An extended bonnet is a lengthened valve bonnet that creates a temperature gradient between the cryogenic valve body and the packing. Standard PTFE packing becomes brittle below approximately −50°C. The extended bonnet ensures that packing temperature remains within the packing’s operating range even when the valve body is at −196°C — maintaining stem sealing performance throughout cryogenic operation.
Yes. Expansion turbine outlet and bypass valves are among the most critical cryogenic valve duties in the ASU — directly affecting cold box refrigeration and liquid inventory. BM TECH provides inspection, maintenance and replacement services for turbine valve positions, coordinated with the ASU planned shutdown schedule.
BM TECH recommends prioritising maintenance based on valve criticality (consequence of failure), condition assessment findings (proximity to end of service life) and accessibility (some positions require more shutdown time than others). We provide a prioritised maintenance plan for each ASU shutdown — ensuring that the most critical valves receive attention within the available window.