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From: Food Quality & Safety magazine, October/November 2008

Go With the Flow

Approved European hygienic flowmeters gaining acceptance

by Jon Archenhold

In the food and beverage and pharmaceutical and biotech industries, contamination-free processing is essential for full compliance with industry validation standards. The potential for contamination in manufacturing applications increases with the introduction of peripheral components, such as flow measurement instruments, that help maintain process parameters within acceptable limits. To prevent this from happening, these devices must themselves meet standards set by governing agencies to ensure that there are no weak links in the sanitary chain.

This article describes the development of the sanitary equipment standards governing the processing industries. It explains the differences between hygienic standards in the United States and European markets and offers guidance for end users who must ensure that their flow measurement devices comply with recognized industry regulations.

Sanitary Standards

Thanks to today’s expanding global economy, the U.S. marketplace now includes products imported from all over the world. Domestic food and beverage processors typically specify 3-A Sanitary Standards, Inc. (3-A SSI) approval on all process-related equipment. This nonprofit association, which represents equipment manufacturers, processors, regulatory sanitarians, and other public health professionals, has established a number of globally recognized sanitary standards and accepted practices for dairy and food processing equipment and systems. In some cases, food and beverage processors also require the National Sanitation Foundation (NSF) and Underwriters Laboratories (UL) labels on components that come into direct contact with the processed medium.

The sanitary standards put in place by 3-A SSI have been developed for a wide range of production equipment used in the dairy and egg processing industries. They serve as a reference under the Grade A Pasteurized Milk Ordinance (PMO), the official regulatory document for the National Conference on Interstate Milk Shipments (NCIMS). These standards may also be required under many state and local regulations.

The NSF has traditionally developed standards for equipment used in food service and retail foods. Over the last few years, however, the NSF has also been involved in developing standards for food processing equipment. The NSF and 3-A SSI recently collaborated on standards development for meats and poultry equipment (3-A/NSF 15159), the results of which are now under review by an International Organization for Standardization working group.

Equipment manufactured in Europe for sanitary processing applications must carry the European Hygienic Engineering & Design Group (EHEDG) stamp of approval. Unlike 3-A SSI, EHEDG does not establish sanitary standards. Rather, it publishes guidelines for the construction and design of food processing equipment, as well as for cleanability testing performed in EHEDG laboratories.

Industry Challenges

The primary intent of 3-A SSI and EHEDG—the application of sound sanitary principles in food equipment manufacture—is the same. Both organizations represent equipment manufacturers, food industries, research institutes, and public health authorities with the aim of promoting hygiene during the processing and packaging of food products.

For many years, authorization to use the 3-A SSI symbol on flowmeters and other process equipment was determined by a system of self-certification. This system changed in 2003, when the requirement for a third party verification (TPV) inspection was implemented for 3-A licensees. The TPV procedure was completed for all standards in 2007.

The TPV program is designed to enhance the integrity of the 3-A SSI programs by affirming that equipment fabricated in accordance to 3-A sanitary standards or processing systems are manufactured and installed in accordance to 3-A accepted practices. The independent inspection programs of 3-A SSI provide assurance of hygienic equipment design, thereby benefiting regulatory sanitarians, equipment fabricators, processors, and consumers.

While 3-A SSI’s requirement for TPV more closely aligns its certification process with that of EHEDG, key differences in equipment design requirements remain. This divergence is due, in part, to the different levels of cleanliness specified by each organization.

For the U.S. food, beverage, and pharmaceutical industries, which typically base their verification procedures on 3-A SSI sanitary standards, the situation brings up an important question: Should end users recognize EHEDG as equivalent to 3-A on hygienic-approved flow measurement equipment?

Sanitary Requirements

Liquid flow measurement is an inherent aspect of many production processes in the food and beverage industries. For some manufacturers, the ability to obtain accurate flow measurements can make the difference between profit and loss. In other cases, inaccurate flow measurements or failure to take measurements can cause serious—even disastrous—results.

Many industries require a “sanitary” condition for their flow measurement equipment. In this case, the word sanitary refers to a highly clean and hygienic condition. The design requirements and specifications for sanitary flowmeters originated in the dairy industry, where the handling and packaging of perishable products like milk required equipment that did not contribute to the bacterial growth or decay of product.

Sanitary flowmeters are designed to ensure that flowing product or residue is not trapped in the meter body where it can spoil. For example, sanitary turbine flowmeters employ 316 stainless steel construction and a smooth finish that eliminates cracks and crevices where bacteria breed. Typical applications include measuring or batch controlling USP or deionized water, vaccines, pharmaceuticals, milk, vegetable oil, wine, beer, spirits, soft drinks, juices, and any other clean, consumable liquid. Other flowmeter designs, such as positive displacement meters, are suited for accurately measuring thick fluids in applications for which batch repeatability is desired.

Some sanitary electromagnetic flow-meters are manufactured from 304 stainless and lined with polytetrafluoro- ethylene for added durability in process plant applications. Mag meters, available with Hastelloy C electrodes, offer enhanced corrosion resistance, while a potted and sealed electrode housing helps to eliminate the damaging effects of humidity.

Liquid clamp-on ultrasonic flowmeters are an ideal solution for many different types of sanitary environments. These meters, which can be installed on the outside of existing process piping, use the ultrasonic transit time method to determine flow rate.

End users should become familiar with the key design considerations for flowmeters and other sanitary process instruments. These issues are detailed below with a comparison of 3-A SSI standards and EHEDG guidelines.

Food Contact Surfaces

One of the most critical considerations in the construction and design of sanitary equipment is the food contact surface. Why? Because contamination of these surfaces will more than likely contaminate the food itself. Therefore, all food contact surfaces should be smooth, impervious, free of cracks and crevices, nonporous, nonabsorbent, nonreactive, corrosion resistant, nontoxic, and cleanable. These standards also apply to any nonmetal coatings on a surface.

The standards established by 3-A SSI require that all surfaces and coatings maintain corrosion resistance and be free of surface delamination, pitting, flaking, chipping, blistering, and distortion under conditions of intended use. Likewise, EHEDG requires consideration of important issues:

  • compatibility with food stuffs and ingredients;
  • chemical resistance (cleaning and disinfectants);
  • temperature resistance in use (upper and lower use temperatures);
  • steam resistance (clean in place/steam in place);
  • stress-crack resistance;
  • hydrophobicity/reactivity of the surface;
  • cleanability;
  • effect of surface structure and smoothness;
  • residue accumulation;
  • adsorption/desorption;
  • leaching;
  • hardness;
  • resilience;
  • cold flow resistance; and
  • abrasion resistance.

Stainless steel is by far the preferred metal for food contact surfaces due to its corrosion resistance and durability in most food applications. Not all stainless steel is equal, however. For most surfaces, 3-A SSI requires 316 stainless steel; 304 stainless steel can only be used for utility pipes, and 303 stainless steel is restricted.

EHEDG has similar guidelines:

“Where good resistance to general atmospheric corrosion is required, but the conditions of intended use will involve only solutions with a pH of between about 6.5 and 8, low levels of chlorides (say, up to 50mg/l [ppm]) and low temperatures (say, up to 25ºC), the most common choice would be AISI-304, an austenitic 18%Cr/10%Ni stainless steel, or its low-carbon version AISI-304L (DIN 1.4307; EN X2CrNi18-9), which is more easily welded.”

If both the level of chlorides and the temperature exceed amounts that are approximately double these values, the material will require greater resistance to the crevice and pitting corrosion that may result from chlorides concentrating locally. In this case, 316 stainless steel should be used to improve corrosion resistance; this grade is recommended for components such as valves, pump casings, rotors, and shafts, while its low-carbon equivalent AISI-316L is recommended for pipework and vessels due to its enhanced weldability. Alternatively, titanium may be appropriate.

As temperatures approach 150ºC, even 316 stainless steels may suffer from stress-corrosion cracking where regions of high stress are exposed to high levels of chloride. If this is the case, 410, 409, and 329 stainless steel, or even Incoloy 825, may be required for their high strength and/or high corrosion resistance, although they may be more costly.

Surface Texture and Finish

Any surface that is textured, polished, or ground should have a finish that is free of cracks and crevices. Both 3-A SSI and EHEDG have adopted an industry-recognized method for determining an acceptable food contact surface, the roughness average or Ra value. The Ra value is found using a profilometer with a diamond-tipped stylus to measure peaks and valleys in a surface. According to 3-A SSI, ground or polished stainless steel must meet a No. 4 ground surface, while unpolished surfaces must meet a No. 2B or mill finish.

EHEDG also has guidelines for surface finish:

  • “Large areas of product contact surface should have a surface finish of 0.8 µm Ra [32 µinch Ra], or better, although the cleanability strongly depends on the applied surface finishing technology, as this can affect the surface topography.
  • “It should be noted that cold-rolled steel has a roughness of Ra = 0.2 to 0.5 µm [8 to 20 µinch Ra] and therefore usually does not need to be polished in order to meet surface roughness requirements, provided the product contact surfaces are free from pits, folds and crevices when in the final fabricated form.
  • “A roughness of Ra >0.8 µm is acceptable if test results have shown that the required cleanability is achieved because of other design features or procedures such as a high flow rate of the cleaning agent. Specifically, in the case of polymeric surfaces, the hydrophobicity, wettability and reactivity may enhance cleanability.”

It is also important to remember that food equipment should be designed and fabricated in such a way that all food contact surfaces are free of sharp corners and crevices. All mating surfaces must also be continuous (e.g., substantially flush). Construction of all food handling or processing equipment should allow for easy disassembly for cleaning and inspection. Where appropriate, equipment such as vessels, chambers, and tanks should be self-draining and pitched to a drainable port with no potential holdup of food materials or solutions.

Another consideration is internal angles. As 3-A SSI sanitary standards state, “all internal angles 135° or less should have a minimum radii of 1/4 inch (6.35mm).” The standards allow for smaller radii where needed for function, within certain specifications.

EHEDG guidelines stipulate a preference for corners with a radius equal to or larger than 6 mm; the minimum radius is 3 mm. Sharp, 90° corners must be avoided. If used as a sealing point, however, corners must be as sharp as possible to form a tight seal at the point closest to the product/seal interface. In this situation, a small break edge or radius of 0.2 mm may be required to prevent damage to elastomeric seals during thermal cycling. If any of these criteria cannot be met due to technical and functional reasons, the loss of cleanability must be compensated for in some way, and the effectiveness of this compensation must be demonstrated by testing. In addition, both 3-A SSI and EHEDG require joints to be smooth, continuous, and butt type.

Testing

Perhaps the biggest difference between 3-A SSI and EHEDG is in the testing of process manufacturing equipment. For 3-A approval, the certified conformance evaluator uses personal knowledge and experience to conduct a detailed physical evaluation of the equipment, engineering drawings, and documentation associated with the equipment to be verified. This is very much “opinion engineering.”

For EHEDG approval, a very sensitive test method is used to prove whether or not microorganisms can be removed from the interior surfaces of the equipment. This method ensures that, even with all the design criteria stated above, it can be proven once and for all whether or not the equipment is cleanable to a microbial level. EHEDG believes that because of typical flow behavior in certain equipment, it is always better to perform tests with live microorganisms sticking to the wall.

It is evident that 3-A SSI and EHEDG are driving in the same direction, and collaboration between the two organizations bodes well for the improvement and standardization of future sanitary equipment regulations and guidelines. Industry cooperation will bring consensus to achieve technically equivalent hygienic design standards on a scientific and technical basis, thus removing national or regional standards as non-tariff barriers to trade.

The EHEDG guidelines and testing procedures described in this article should demonstrate to U.S. food and beverage processors that the EHEDG stamp of approval is equal to the one given by 3-A SSI and should be accepted as such on flow measurement instrumentation.

Archenhold is the industrial market manager for Flow Technology, Inc. Reach him at (619) 319-7769 or jarchenhold@ftimeters.com.

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