A primer to drive sales.

Nick Wojnicz,
Specialty Gas Equipment manager, at Linde Gas LLC

Stainless steel lines transport gas at DAF Trucks' central gas-supply system.

DAF Trucks CGS lines are divided into sections, which can be closed off for service and maintenance without stopping the total system.

Each process stream has its own point-of-use regulator that allows for individual pressure control and prevents pressure fluctuations between the different steps in the process.

Linde Gas can equip its CGS system gas lines with air-operated shut-off valves that facility personnel can shut off from a central point in emergencies.

With a CGS system, such as this from Linde Gas, cylinders containing 2,200 psi (±150 bar) are connected to manifolds, which reduce the gas pressure to 150 --200 psi (±10-14 bar). The manifolds are purged each time a cylinder is exchanged.

Typically, customers with individual cylinders at workstations or next to analytical equipment are apprehensive about replacing their local systems with a central gas-supply (CGS) system. They shouldn't be however. It's the distributor's role to educate target customers on how CGS systems can help them slash labor and other operating costs. Distributors doing so quickly position themselves as solution providers and will reap the benefits of increased sales.

Bringing in a CGS system involves removing gas cylinders from the laboratory workplace and placing them in a single controlled area. From this area, an engineered piping network carries gas to multiple points-of-use throughout a facility, with regulators at each point controlling pressure and flow.

Often, customers believe that such systems are cost-prohibitive. But once they consider product costs, rent charges, and the cost of having redundant equipment, they'll understand how CGS systems can save them money. An extra benefit: CGS systems also free up laboratory space.

With CGS systems, customers may fear that if one component or stretch of piping goes down, so will the entire system. That's not true. Piping can be looped so that a section can get isolated for repair, letting gas flow without interruption throughout the rest of the facility. Also, CGS system designs can incorporate redundant critical components.

Potential customers may also worry that piping will spring leaks. However, local building codes typically demand proper gas-detection equipment to immediately alert personnel in the unlikely event of any leaks. Combining such gas-detection equipment with emergency shut-off valves automatically stops unplanned gas flows and lets proper personnel take immediate corrective measures.

CGS system design
Distributors should meet with company owners, architects, and local code authorities at the beginning of the CGS system-design process. The goals of such meeting should be to guide projects through the regulatory system and prevent unexpected hurdles later in the project. Distributors may also find significant equipment opportunities.

In planning and installing CGS systems, designers often fail to account for local building codes. That's a mistake because these codes clearly spell out how to use compressed gases: safe handling, fire protection, cylinder-separation distances, gas detection, abatement systems, and equipment such as excess-flow and emergency shut-off valves.

Local codes are typically based on standards from the Compressed Gas Association, National Fire Protection Agency, and others. Distributors can obtain appropriate building codes through local building departments, local fire marshals, or local libraries.

Component choice
Selecting CGS system components depends on the type of gas distributed and the acceptable level of contamination allowed for that gas (for its designed application). In picking the right component, distributors must consider the potential of gas permeation (both inboard and outboard), off-gassing from polymers or cleaning agents, and surface-finish quality.

The inner surface finish of any piping system is critical to the final gas purity at the point-of-use. Good inner surface finishes are easier to clean and prevent particles from being released into the gas stream. Most piping systems are either copper or stainless steel.

With copper, it's important to note its incompatibility with gases such as acetylene. In cases where copper is deemed appropriate, use only cleaned copper tubing. Also, the use of fluxless solder joining techniques is critical.

Stainless steel, the preferred material for pure and specialty gas applications, cleans and purges easily and can be supplied with a high-quality, electropolished surface finish.

It also withstands corrosive environments. This material is gaining in popularity thanks to the increasing use of chemically reactive gases and greater demands on purity. Orbital welding, great for assembly in confined areas, joins stainless steel systems while maintaining high levels of cleanliness and finish.

Typically, the gas-quality requirementsfor CGS systems determine component-material selection:

Standard-purity specialty gases

• Component: Stainless steel or highpurity brass, depending on the gas used.
• Piping: Electropolished stainless steel cleaned for oxygen service is recommended, but oxygencleaned copper may also suffice.
• Connection: Orbital welding is preferred for stainless, but compression fittings, designed to clamp onto the pipe, can be used. These fittings require the tubing to have a good degree of roundness and give a seal equivalent to 10- ⁶ bar cm3/s.

Ultra-high-purity specialty gases

• Component: Stainless steel or highpurity brass, depending on the gas used. Regardless of the choice, these components must be designed for high-purity applications.
• Piping: Stainless steel cleaned for oxygen service is recommended.
• Connection: Orbital welding and VCR-style fittings are recommended. VCR fittings are sealed by using a pointed profile that — under pressure from two sides — is pressed into a metallic packing. The coupling gives a seal equivalent to 10- ⁸ to 10- ¹⁰ bar cm3/s. Special post-cleaning and testing should be performed for proper installation and to ensure the system is leak-free.

Why use a CGS system? Specialty-gas users gain several advantages by using central gas-supply systems with multiple points of use: Safety Reduces accidents by eliminating cylinder handling inside the workplace. Reduces the frequency of cylinder changes (where most gas leaks occur) and narrows the number of personnel doing the changing to a consistent, dedicated staff. Ensures only low-pressure equipment and small gas quantities are present in the workplace. Collects gas cylinders under one roof, facilitating removal and safety management. Cost savings Continuous gas supply to each work station means fewer unplanned disruptions changing cylinders. Fewer and larger gas cylinders supply all users, streamlining cylinder management and cutting rental and transportation charges. Working environment Outlets at each workstation are convenient and easy to use. Working with distributors, customers can design the work place for maximum space management and ergonomics.

About the author
Nick Wojnicz, Specialty Gas Equipment manager at Linde Gas LLC, Cleveland, has 14 years of experience with the design and installation of gascontrol equipment and systems.

For more information on CGS systems, contact Wojnicz at nicholas.wojnicz@us.linde-gas.com.

All pictures were taken at DAF Trucks, N.V. Eindhoven, The Netherlands.