The Effect of Thermal Cycling on Clamp-Type Fittings - How to control compressive loads on seal materials. - BioPharm International

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The Effect of Thermal Cycling on Clamp-Type Fittings
How to control compressive loads on seal materials.


BioPharm International
Volume 23, Issue 6

ABSTRACT

Thermal cycling is a major factor that affects the reliability of valves and fittings used in a bioprocessing system. This article examines gasket-sealed, clamp-type sanitary fittings and provides test results showing the impact a gasket extrusion dam may have on the cleanliness, drainability, and sterilization capabilities of a bioprocessing system. The article also presents a comparison of ISO 2852 and alternative fittings using computational fluid dynamics (CFD), flow tests, and thermal cycling tests.


Baxter International
Valves and fittings account for the largest number of seals used in a bioprocessing system, potentially numbering in the thousands throughout an entire facility. The reliability of these seals is a function of design, quality, material selection, and installation. After the components are in service, a major factor that affects the reliability of the seals is thermal cycling.

Seals must be leak-tight throughout an entire bioprocessing system to avoid the release of potentially hazardous materials and to maintain sterile conditions inside the system. Thermal cycling is the most difficult condition valves and fittings must withstand. It affects the durability of the plastic and elastomer seal materials and is a common cause of leaks.

Gasket-sealed, clamp-type sanitary fittings usually are used when connections in process (hygienic) and clean utility systems are to be repeatedly made and broken. The most often selected type is the ISO 2852. The gasket seal in ISO 2852 fittings, however, may extrude radially outward into the tubing or pipe as a result of over-tightening clamps or thermal cycling. The extrusion creates a dam that compromises drainability in a bioprocessing system and increases flow velocity. In addition, this extrusion compromises the ASME BPE standard that requires gaskets in a made-up sanitary fitting to be flush with the bore of the tubing or pipe.1

This article examines gasket-sealed, clamp-type sanitary fittings and provides test results showing the impact a gasket extrusion dam may have on the cleanliness, drainability, and sterilization capabilities of a bioprocessing system. The article also presents a comparison of ISO 2852 and alternative fittings using computational fluid dynamics (CFD), flow tests, and thermal cycling tests.

THE BIOPROCESSING SYSTEM

A complete system for manufacturing the drug substance for a biopharmaceutical product is made up of tanks and vessels, pumps, centrifuges, and various operation-specific equipment.

Fluids are transferred from device to device by means of tubing, pipes, and hoses. Fittings connect all parts of the system together, and valves control the fluid in the system. The process system is supported by certain clean utility services, such as pure water, sterile air, and steam for sterilization. The seals in all of the equipment and subsystems and the clean utilities are critical to the reliable operation of the complete system.

After use, each piece of equipment through which fluid had been transferred must be drained, cleaned, and sterilized in preparation for the next production run. Valves and fittings can have a direct effect on how effective the cleaning and sterilization process will be. These components must be:

  • completely drainable, leaving no entrapment areas or puddles where contaminants can accumulate;
  • cleanable using current clean-in-place (CIP) methods;
  • sterilizable, allowing all internal surfaces to be in contact with steam; and
  • able to withstand the thermal cycling of repeated sterilization processes.

Seals must be leak-tight throughout the entire process. Leaks out of the system can result in the release of potentially hazardous materials, and leaks into the system can destroy the sterile condition inside the system. Internal leaks can compromise the process, cleanliness, sterile environment, and instrumentation and control procedures.


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