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Improving Hygienic Design

What do you consider to be the most important benefit of Single-Use solutions?  

According to Aspen Alert’s 7th Annual Single Use Market Survey the leading answer is Reduced Cleaning at 39% followed by Ease of Use at 31% and Quick Turnaround at 23%.  Coming in a distant fourth in the survey was Cost Savings at 7%.  Since our initial involvement with the introduction of the first wide scale implementation of single-use technology in both the upstream and downstream process, single use technologies of all types have gained the vast majority of press coverage and one could argue, overall interest from the customers we serve.  Some market analysis predict this trend to continue but will eventually reach some type of equilibrium with stainless steel systems.  It is interesting that in the face of formidable competition from single-use systems, the design of hard piped stainless steel process systems has changed very little.  The industry group ASME-BPE has moved in several areas to implement adaption of standardization in specifications and dimensions but overall system piping design has changed little.  Independent research and indeed practical knowledge point to several key areas where hygienic piping systems can be improved.

The standard piping  “T” with the leg in either the “up” or “down” position has been shown to contribute significantly to a reduced ability to clean and sterilize.  Many times the “T” in a process system, is created with a weir style diaphragm valve.  Due to the inherent design of the weir valves, a dead-leg is built in to the valve and subsequently the piping system.  Weir valves also present issues with reliable “fine” cleaning at the point where the diaphragm meets the valve body.  The last piping component which has been widely overlooked is sanitary clamp gasket seals.

The standard “T” presents problems for cleaning do the creation of areas of low turbulence and in the case of the inverted “T”, an air pocket which affects both cleaning and steam sterilization.  Of course having the “T” with the down leg presents challenges in flushing the area with enough turbulent flow to clean and then with enough steam over time to heat the collected condensate.

In the real world, the standard “T” and the associated dead-legs can be reduced but not eliminated when using the industry standard kit of weir valves.  And while the radial right angle valve design greatly improves on the weir valve, there are several versions that create problems because of a dual body seal and bellows design of the diaphragm.  Weir valves also suffer from the problem of the body seal having to act as both a static and dynamic seal.  This movement invariably has the effect of pumping product between the valve body and the diaphragm.  This design also creates an asymptotic or infinite angle dead-leg which is very difficult to clean and takes time.

The preferred material for sanitary piping systems is the EPDM based rubber compound.  However recent independent testing proves not all elastomers are the same.  For years, bioprocess engineers have struggled with poor performing EPDM sanitary gasket and O-ring seals.  The market has viewed all EPDM elastomers as a commodity and so looked predominantly at price as a deciding factor.  The prerequisite for an EPDM gasket to be suitable for service was based on the elastomers ability to pass various laboratory tests against cyto-toxicity as well as leachables and extractables.  Unfortunately, passing the USP Class VI tests has no bearing at all on how an elastomer will perform in today’s demanding CIP/SIP bioprocess systems.  One key aspect of an elastomers performance is known as compression set.  This is the amount of permanent movement an elastomeric article will have under load (pressure and temperature).  The smaller the number the better.  Gaskets with a high compression set will squeeze into the inner pipe diameter, acting as an orifice plate of sorts.  This in turn creates a number of problems that must be addressed.  Once protruding into the ID of the pipe the gaskets create small dams that prevent complete draining.  This can adversely affect an entire CIP system or flow rates for critical systems such as column packing.  In addition chemical and flow erosion is accelerated on the exposed gasket material.  And with more material inside the pipe ID there is less material inside the ferrules.  This can be identified by loose clamps after a steam cycle.  The direct result of leachables and extractables is evident with gaskets and O-rings that adhere to the ferrules, in some case literally gluing themselves in place.  Damage to piping and instrumentation can take place while maintenance technicians struggle to take these connections apart.

Getting back to single-use technologies, there is a clear justification for their implementation.  However many of the perceived benefits of single-use over stainless systems can be greatly mitigated once the industry moves away from the old and on to the new.

There is a better way

A greater use of zero dead-leg connections on vessels as well as in-line instrument ports can have a big effect on cleaning and sterilization by eliminating the unused pipe segments and shadow areas that “T’s” and inline valves create.  In repeated tank sterilization studies performed by a large pharmaceutical customer, connections that employed a zero dead-leg flange came up to temperature in line with the side wall of the tank.   Other connections using even short sanitary clamp ferrules lagged behind the rest of the tank as much as 10°C.  In order to get these points up to temperature both the steam pressure and time had to be increased.  In connections where a standard weir valve was installed onto a zero dead–leg flange the result of the increased pipe length resulted in the same increased time, pressure and temperature to effectively sterilize.  The use of a radial diaphragm valve such as the Rattiinox CAD valve with an extended diaphragm puts the sealing point of the valve virtually in-line with the tank wall, positively affecting both cleaning and sterilization cycles.

In the case of instruments that need to be connected in-line or on process vessels, the zero dead-leg instrument port, which we also helped introduce, reduces the effective dead-leg to one pipe diameter or less.  There has also been recent advancements from instrument suppliers such as WIKA to supply integrated temperature and pressure solutions with a completely smooth product flow path.

The CAD radial diaphragm from Rattiinox addresses all the issues with poor system design related to weir valves as well as the poor design of other radial valves with regards to dual seals and bellows.

The James Walker EPDM compound EP75B has been tested both independently and by customers to be the highest performing EPDM compound.  This particular EPDM compound has a 4% compression set and very low extractables and leachables.  Even after repeated exposure to CIP 100 and CIP 200 and steaming, does not extrude into the product flow path or adhere to stainless ferrules.