Diaphragms face the compliance question

David Birch, product manager, HC4 Products, Crane Process Flow Technologies, shows how greater control of diaphragm production offers increased customer confidence

In the risk adverse pharmaceutical, biotechnology and clean processing industries most process plant is constructed from stainless steel components.For many years the industry and regulatory bodies have demanded that all stainless steel wetted contact equipment is fully traceable, and carries full compliance documentation. Generally incorporated within the process system are fittings, valves and pumps, which have elastomeric seals, diaphragms or gaskets. In the case of the diaphragm type valve the elastomer must be suitable for both process conditions and any cleaning regime. Diaphragm and other wetted surface non-steel products are now rising to the top of plant engineers' agenda in terms of standard compliance and product quality.

FDA conformance

All diaphragms used in these industries have to be manufactured from FDA conforming materials. Diaphragm materials such as PTFE, EPM, EPDM, Butyl and silicone rubbers have to conform with the FDA Code of Federal Regulations (CFR) Chapter 1, Title 21, Part 177 paragraph 1550 (Perfluorocarbons) and paragraph 2600 (Rubber Articles) revised 01.04.2003. This provides the customer with a list of ingredients to show that the diaphragm has been created using only conforming substances.

A necessary pre-requisite for any diaphragm supplier is to provide not only FDA conformance but also USP Class V and VI certification, which encapsulates a detailed series of tests to determine the biological response of elastomers and polymers used in medical applications. All the certified diaphragms must meet the criteria in section '88' Biological Reactivity Tests, In Vivo Plastic Classes I to VI.

For the most part engineers have a good understanding of the metals which have a long history of use in aseptic processing. However, the critical importance of elastomeric components has tended to be overlooked. The consequences of this oversight can pose concern to process security, lead to changes in line media potency or even contribute to plant stoppages.

Elastomeric components are often 'wetted', meaning that they come into direct contact with the line media. It is important therefore that all those considerations given to selecting the appropriate stainless steel material are also applied to select the right seal, gasket or diaphragm.

complex ingredients

Customers are becoming increasingly aware of the complexities of elastomer utilisation in the total plant process system and can often provide optimised specification for an intended application. Elastomers are a complex mix of ingredients chosen to provide the right properties for both the function of the component and the intended application. Elastomer ingredients may include carbon black, fillers, process aids, activators, accelerators and curing agents as well as the base polymer. All these ingredients can to some extent affect the properties of the elastomer such as heat resistance, abrasion resistance and chemical resistance. Think of it in the same way as mixing alloys to create steel for specific applications.

physical properties

The correct base polymer is the starting point for an elastomer. This is crucial in creating the desired physical properties, environmental and chemical attributes in the finished diaphragm. Depending on diaphragm material there can be up to 40 or 50 commercially available base polymers. It is very important, therefore, to select the right one to obtain the diaphragm properties the customer is looking to achieve. It is possible that part or all of the elastomer manufacturing process is undertaken by third party rubber compounders, and it may be the case that incompatible base polymers are used for a wide selection of very differing and demanding applications.

The design, ingredients, manufacturing process and control all play a major part in ensuring the finished diaphragm provides optimum performance in the customer's process. All ingredients must be FDA conforming, but this is only the beginning.

in-house development

Over many years Crane Process Flow Technologies' Saunders expertise in polymer processes has been developed so that all diaphragm solutions are devised, processed and controlled in-house, from base polymer mixing through to reinforcing, curing, testing, packaging and shipping.

As part of the Independent testing of extractables, by the neutral industry body, Rubber and Plastics Research Association (RAPRA Technology), materials in the Saunders HC4 range are tested to ensure they comply with stringent tolerances, which can be supplied to customers in certification format.

Together with these standards, customers are now demanding traceability. CPFT has been instrumental in complying with the end user's validation requirement by providing full traceability for its range of FDA conforming Saunders HC4 diaphragms. As such, all diaphragms carry a unique moulded batch identification number that enables the product to be traced back to the individual elastomer mix.

Trust is fundamental in the relationship between the customer and the device manufacturer, and it is only through experience that suppliers learn and embed the necessary standards and requirements into their organisations. As one of the few diaphragm manufacturers to mix the base components in-house, and to provide this level of validation, the Saunders brand of diaphragms allows the customer to verify each diaphragm against actual physical properties and thus reduces the risk of affecting the integrity of the customer's process.

The industry's use of diaphragm products has to date required overly cautious risk assessment of diaphragm performance, promoting early replacement cycles rather than risk product failure.

longer lifespan

The increased level of certification and traceable support material offers the user more complete data on the capabilities of the supplied diaphragms. And this is providing demonstrable results in terms of increased lifespan of products. As with stainless steel, it is now possible to provide wetted elastomer components with equivalent traceability certificates to EN10204 3.1b.

This information is a guarantee that the product quality conforms to the supplier's specification and provides data on specific batch numbers, stating hardness, tensile strength and elongation at break. This data also enables product history to be investigated in the event of a problem during use.

The Ethylene Propylene Elastomers are the most commonly used in aseptic applications due to a number of inherent properties - excellent resistance to aqueous media, heat and ozone resistance and high performance steam resistance.

There are two main types of EPEs within the family of synthetic hydrocarbon polymers:

Ethylene Propylene Monomer (EPM)

Ethylene Propylene Diene Monomer (EPDM)

Tests demonstrate that EPM, single bonded, elastomer offers higher heat, ozone and chemical resistance than the EPDM, double bonded elastomer. Differences are created due to the addition of a diene, a pendant side chain or cyclic group containing a double bond, which is added during the polymerisation and allows the resultant product to be made faster than with some EPM elastomers.

greater stability

The effect of the carbon atom to carbon atom double bond reduces the bond strength of the elastomer meaning less energy is required to cleave the atoms apart, resulting in a less stable structure which can be prone to chemical breakdown. The single bond (EPM) requires more energy to cleave the atoms apart is therefore more stable and also offers greater resistance to oxygen and ozone.

The role of elastomers in process systems tends to be underestimated in the general market, but for many customers it has become critical. The technology is available to tailor elastomers to specific customer or application requirements, but this capability requires the control of all the steps in the production of diaphragms.

Most manufacturers' diaphragms are subjected to detailed certification and test regimes prior to release. For CPFT this involves simulation of real life application conditions and includes rigorous flex testing, steam testing and pressure testing to failure, together with diaphragm validation as part of the traceability process, which includes verifying the physical properties at various key stages of production.

The customers' requirement for full support from suppliers is driving the introduction of more rigorous manufacturing procedures and test protocols and it is up to the diaphragm producers and suppliers to stay in touch with the market. Investing in traceability, as well as the other standard compliance regimes demonstrates confidence in the products and the manufacturer's systems, which will in time build trust with the customers.