There are many differences between the two curing systems. It depends on who your customer is and what they care about to discern what would be important to them. Although the basic difference is the nature of the chemical matrix that ties the polymer together in the gasket material, this basic chemical difference leads to many other factors. For example, there are differences in appearance (silicone a bit clearer), availability (peroxide a bit more available), mechanical properties (peroxide a bit better on sealing properties, platinum-cured a bit better tear resistance), clean-steam resistance (platinum better), extractable and leachable profiles (platinum better), cost (peroxide better), and the list goes on. Of course, all of these things can vary depending on the formulation of the silicone and the purpose for which it was designed.
For the biopharmaceutical industry, platinum-cured silicone is generally preferred. For the food industry, peroxide-cure is typically used due to its better availability in most shapes and sizes, its lower cost, and the fact that steam is seldom used for sanitization in food and dairy.
Clean-in-Place is a method of cleaning the interior surfaces of pipes, vessels, process equipment, filters and associated fittings, without disassembly. The benefits to industries that use CIP is that the cleaning is faster, less labor intensive and more repeatable, and poses less of a chemical exposure risk to people. CIP started as a manual practice involving a balance tank, centrifugal pump, and connection to the system to be cleaned. CIP has evolved to include fully automated systems with programmable logic controllers, multiple balance tanks, sensors, valves, heat exchangers, data acquisition and specially designed spray nozzle systems. Simple, manually operated CIP systems can still be found in use today.
The Steam-in-Place System is responsible for repeatedly steaming areas of product contact, including vessels, flow paths, and sample ports. This may be done to reduce the bio-burden on the system, or to kill harmful materials at the end of a batch. A typical SIP system will ensure that all areas being steamed have been exposed to live steam for an adequate time to ensure the desired “kill” effect. The steam system must be able to measure and control steam temperature, pressure, and/or flow to ensure adequate steaming. Calculation of Fahrenheit/Celsius or other measures is often required to meet process needs.
A typical clamp connection consists of three elements: the gasket, the clamp and the ferrules (2) in which the gasket sits.
However, as some experts have noted, we often forget the fourth element, the person who installs the gasket!
An under-tightened gasket can lead to leaking. An over-tightened gasket can lead to squashing and destroying the gasket. A well-tightened gasket can give trouble-free operation for the lifetime of the installation.
A gasket is designed not only to prevent leaks but is also designed to simulate the process piping surfaces on the inside of the pipe. In this way, fluid can pass through the connection as if the gasket were not there and the surfaces can be cleaned and drained without internal ridges or crevices.
Because ferrules, clamps and gaskets vary so widely in design, materials and modes of operation, the simplest way to find out how tight your gasket should be is the following on a benchtop:
- Take two of the ferrules you use throughout the system (Short ferrules or tubes where you can see where the gasket seats).
- Take the clamps you use for those ferrules.
- Take a sample gasket you use for each location
- Using a torque wrench, make the connection watching the gasket as it spreads toward the inner diameter (ID) of the tubing.
- When it is flush with the ID, record the torque.
- Use that torque measurement wherever you use that combination of ferrules, clamps and gaskets throughout your piping system.
- Repeat the test for each new combination of ferrule, clamps and gaskets.
- Make sure you pressure test each combination to ensure safe operation!
While the result may not be perfect because of variation in all three elements during manufacture and the normal wear of fittings, this will give you a great start toward optimizing the performance of Newman gaskets! It should help take out the fourth element, the person!
Typical values for Newman gaskets are 15 to 25inlbs (1.7-2.8Nm) of torque for 70 durometer gaskets using MHP fittings and 25 to 60inlbs (2.8-6.8Nm) of torque for Orca, Teflon Envelope, Pure Teflon gaskets and gaskets using higher harness materials.
Webster defines Cold Flow as:
1 : the viscous flow of a solid at ordinary temperatures
2 : the distortion of a solid under sustained pressure especially with an accompanying inability to return to its original dimensions when the pressure is removed
“Cold Flow” or “Creep” in gaskets occurs in gaskets after they are clamped and under sustained compression. The pressure on the gasket from the ferrules causes the gasket material to gradually flow away from between the ferrules. The material then moves the only way it can go, into the process stream and outside the OD of the ferrules. Creep only happens in plastic gaskets like Teflon (PTFE).[i] In rubber gaskets and inserts, flow can also occur. Some portion of the flow will be reversible, some portion will not.
Cold flow occurs at room temperature. But this effect is accelerated by heat and increasing pressure from the clamp. The thinner the plastic cross-section of the gasket and the larger the gasket contact area with the ferrules, the more cold flow can be seen. Gasket material which has extruded into the process stream may also continue to flow in the direction of the process flow over time as it interacts with process fluids (seen in Figure 3).
With Newman Orca gaskets cold flow is slowed by the PTFE layer being physically attached to the rubber layer beneath as seen in Figure 4. The PTFE material cannot flow into the ID, nor does the inner rubber layer flow outside the OD to the same extent, even with temperature and pressure.
To minimize cold flow in your gaskets,
- Use the minimum torque necessary on your gaskets and hardware that that will prevent the clamps from loosening. Contact Newman for help in determining the right amount of clamp torque.
- Consider using Orca Gaskets instead of standard envelope gaskets. They will shut down clod flow before it starts!
Contact Newman for technical help, pricing and availability today!
We often get this question at Newman. There is a price difference, but why should I order one or the other if otherwise equivalent parts are available?
FDA and USP parts are made to meet the requirements of different industries. Newman FDA parts are made to meet the requirements of the food, dairy and beverage industries. Newman USP parts are made to meet the requirements of the Life Sciences (bioprocessing and some medical applications). While some materials and designs can be used in both FDA and USP applications, there is no guarantee. For example, Buna-N parts (nitriles) are preferred in many dairy applications. They cannot be used in the life sciences.
But your compound number you use is the same on my part for both the FDA and USP part numbers. Why can’t I just get the cheaper part?
- Some FDA (food grade) and USP (pharmaceutical grade) gaskets sold by Newman use the same proprietary materials (if the compound number is the same).
- However, there are significant differences between how FDA and USP parts are handled at Newman. Some differences:
- USP Parts are 100% visually inspected. This includes flash requirements and other manufacturing nonconformities that can affect cleanability on process contact surfaces. FDA parts follow an AQL schedule (Less than 100% inspected).
- USP Parts are bagged in tamper-evident packaging (sealed bags). FDA parts may be packaged in cardboard boxes with no bag.
- USP Parts come with an FDA/USP cert with each order, indicating compliance and testing information for USP processes along with lot traceability. Other relevant biopharmaceutical/medical certs are also available upon request. FDA parts come with an FDA cert only (certs relevant to the food processing industry are also available).
- USP Parts and their materials/processes are tracked carefully for changes, and notifications are issued to all USP customers before/when a change occurs. Some FDA product/process changes may not receive notification as food and dairy customers generally don’t fall under the same change notification requirements.
- USP Parts have been tested internally and by third parties to meet ASME BPE (Bioprocessing Equipment Standard) and other USP relevant requirements. Food grade requirements are very different.
- At Newman, if both FDA and USP part numbers exist for a particular gasket or O-ring, in almost every case when you order a USP part, less stringent FDA certifications will also apply. Contact us at Newman if you have any questions.
The bottom line is that if you want USP parts, you should order USP parts. They are more expensive, but you will have traceable relevant certs in case of an audit, and they follow procedures and methods suitable for USP processes. FDA parts are made for food, dairy and beverage processing, not USP processes.