Application. Understanding the full scope of the application is the most complex portion of the selection process and most often overlooked. Regulatory concerns are always at the top of the list. Understanding what documentation is needed and what special regulations must be complied with are important; different compliance concerns may call for different material selection. Tubing materials and formulas can be tested to ensure they comply with the appropriate criteria.
Knowing the dynamics (e.g., flow rate, pressure, or viscosity) of the application will assist with material selection for clarity, durometer (relative hardness), flexural fatigue, abrasion resistance, spallation (the tendency of materials to release particulates due to impact or stress), and particulates (pyrogens). There are materials available to combat each of these concerns individually and multi-layer options to solve a mix of these factors.
Media. Knowing the media or fluid being transported and its characteristics, such as extractables level, the tendency for adsorption or absorption of fluid into the tubing material, and the tendency of media to entrap particulates, is necessary to assure high purity. Different chemicals attack various materials at different rates, so understanding all the chemicals that might be used in the tubing will help with proper selection. Cleaning agents are often the most aggressive fluids used; be aware of any chemical reactions which might be caused by cleaning or sterilizing agents. Often overlooked are the ambient chemicals (e.g., solvents) present in the atmosphere, either present in the air surrounding the tubing product or dripping by way of leaks or condensation creation. The effect of these chemicals on the tubing should also be considered. If the fluid is very aggressive, a more resistant material can be used, or multilayer tubing can be selected that assists with barrier protection but is not as costly as tubing made completely from a more resistant material.
Some tubing materials can be produced at tighter tolerances for tighter fitting connections to avoid leak points. Others can be produced with a smoother inner surface for better flushing. Understanding the fluid being conveyed can help maximize the efficiency of your project to assist with easier flushing and avoidance of costly leaks.
Safety also plays a role with material choice. Some requirements mandate viewing the fluid being conveyed. This means the material must have a sufficient level of clarity to see the fluid path and distinguish if any particulates are present. Other options require identifying marks for various chemicals through the use of colored tubing products or specific marking text. Use of these marks is a growing trend in efforts to further company’s safety improvements.
Pressure. Vacuum and positive pressure create stress on any tubing product. Ignoring these factors can create hazardous conditions during product use. Use temperature also has a significant effect on the pressure rating for materials, and proper measures must be taken. Changing the wall thickness can help increase pressure rating, as can reducing the overall OD and ID. If these measures are not an option, multilayer products of various materials can help handle the desired pressure as well as maintain the proper condition in the fluid path.
Pressures created during normal operation are not the only factor when selecting the proper tubing. Cleaning or sterilization cycles can create the most extreme pressure conditions and must be considered during the selection.