There are ever-growing applications for polymer or plastic tubing in laboratory environments. This increase is mainly attributable to ease of use, purity, costs, flexibility and chemical compatibilities. Even though many kinds of tubing applications operate at pressures <150 psig and with inert gases, safety hazards still exist. As a result, it is important to know the key factors for properly selecting, using and terminating poly tubing.
Keep these tips in mind to ensure the right tube is selected for every job.
Establish the Application Requirements
Develop a well-understood set of requirements to avoid the selection process creating a potential hazard.
Engaging a safety process that includes a review by the center’s Pressure System manager can help avoid unanticipated outcomes,” said David Hartsell, Pressure Systems manager, Jet Propulsion Laboratory.
When selecting plastic tubing, review or identify:
- Gases or fluids being used
a. Type (inert, flammables, toxics, acids/alkalides, other)
b. Temperatures and pressures
c. Material compatibilities
d. Flow rates
A Recent Close Call Involving Plastic Tubing
In a recent close call, personnel conducted a pressure test on a reinforced polyester, multi-layered tubing that was incorrectly terminated with compression fittings. Before pressurizing the tube to full operating pressure, the tubing was pressured to 50 psig to perform a leak test. At 50 psig, the tubing blistered and popped. This startled employees and created an acute acoustic ringing in the test cell.
- Environment
a. Vibration, abrasion, chaffing
b. Exposed temperatures
c. Exposure to elements such as solar, wind, rain
d. Proximity to other surrounding chemicals
e. Ventilation air exchange rates of labs
f. Support structures and restraints
g. Termination Interfaces (fittings)
h. Vacuum compatibility (internal or exterior)
Select the Right Material
A variety of plastic tubing types and materials are available for use, including Polytetrafluoroethylene (PTFE — also known as Teflon®), polyethylene, nylon, polyester, vinyl and many others.
Each type comes with varying and specific characteristics such as chemical compatibility, rigidity, stiffness, flexibility, pressure/temperature ratings and termination (fittings). Carefully consider the application requirements to help mitigate risk and select the appropriate materials.
Know the Construction
Some plastic tubing is fabricated with single monolithic walls (solid walls), or, in the case of reinforced polyester tubing, made from several outer layers over the primary pressure boundary tubing.
The outer layers for these types of tubing may differ from the primary material tubing. This means that even though the primary tubing may have the correct material compatibility, the outer layers may not be compatible with the fluids or other chemicals in the laboratory.
Consider Termination Interfaces
When using plastic tubing, the method used to terminate the tubing to interfaces with pressure sources and instruments is often a secondary concern. With many choices such as barbed, compression and push-to-connect fittings, improper selection can present hazards even in low-pressure applications.
Improper gas application fitting selection can present exposure concerns to personnel and create other hazardous conditions in the lab space.
Compression fittings on a multi-layered hose allow even low-pressure gas to seep beneath a compression fitting.
This pressurizes the outer protective layer, which is not rated for pressure. Compression fittings are mostly used with hard tubing and have walls rigid enough to resist the compression forces applied by the ferrule. Common tubing choices include metallic (such as stainless steel or copper) and stiff plastic (such as polyetheretherketone — or PEEK — nylon, Teflon®, Kynar® or polyethylene).
Follow Proper Disposal Protocols
Consider the full life cycle of the tubing. Based on the chemicals used, proper waste disposal methods of impregnated tubing must be understood before selection and use.
Plan Ahead and Choose Carefully
Welcoming plastic tubing innovations and expanded use practices present solid business model decision-making. However, to be successful, these decisions need to be paired with a safety review and careful planning, which includes appropriate use and life cycle considerations.
Be cautious when making termination interface selections, always utilize the center Pressure System Manager’s expertise and reference the ASTM.
“We address safety at all sizes, pressures, materials and uses — from standard to non-traditional applications, new materials, and everything in between,” said Clifton Arnold, Pressure Systems program executive. “The Pressure System Manager reviews each safety concern equally.”
For more information, contact Arnold.