Thought you knew all there was to know about this intriguing topic? Well, think again. Answer the following 23 questions and consider yourself an expert. Of course, if you find it hard to remember it all, you can always bookmark this page onto your favorites and refer back to it whenever you get the urge.
What is a high purity (H-P) ball valve?
H-P ball valves are flow control devices that meet the industry criteria for purity of materials and design.
Valves in high purity processes are used in two broad areas of application:
Valves that are in direct contact with the final (or intermediate) product, and
Valves that are not in contact with the final (or intermediate) product. These applications are in support systems such as handling clean steam for cleaning and temperature control.
In the pharmaceutical industry, ball valves are never used in applications or processes where they may be in direct contact with the final product.
What are the industry criteria for high purity valves?
The pharmaceutical industry derives the valve selection criteria from two sources:
ASME/BPE-1997 (Specifications for Bioprocessing Equipment), and
FDA material and design specifications.
What is ASME/BPE-1997?
ASME/BPE-1997 is the evolving specification document that addresses the design and use of equipment for the pharmaceutical industry. The standard is intended for design, materials, construction, inspection and testing of vessels, piping and related accessories, such as pumps, valves and fittings, for use in the biopharmaceutical industry. Essentially, the document states, "...all parts that contact either the products, raw materials or product intermediates during manufacturing, process development or scaleup ... and are a critical part of product manufacture, such as Water-For-Injection (WFI), clean steam, ultrafiltration, intermediate product storage and centrifuges."
Today, the industry relies on ASME/BPE-1997 to determine ball valve designs for use in applications where they are not in contact with the product. The key areas covered by the specification are:
welded component materials
II. Surface Condition
valve design for minimum hold-up volume
IV. Areas of Valve and Piping Systems
Water For Injection (WFI)
Clean Dry Air (CDA)
V. Material Composition
certification (MTRs, FDA, etc.)
VII. Marking Information
What valve types does ASME/BPE address?
Valves typically used in bio-pharm process systems include ball, diaphragm and check valves. This engineering document will be limited to discussions on ball valves.
What is "validation"?
Validation is a regulatory procedure that intends to assure repeatability of a processed product or formulation. The procedure indicates that mechanical process components, formulation times, temperatures, pressures and other conditions be measured and monitored. Once a system and the product of that system have proven repeatable, all components and conditions are deemed validated. No changes may be made to the final "package" (process system and procedures) without re-validating.
There is also the related issue of material verification. Material Test Report (MTR) is a statement from casting producers that documents the composition of the casting and verifies that it has come from a specific run in the casting process. This degree of traceability is desirable in all critical piping component installations in many industries. All valves supplied for pharmaceutical applications must be accompanied by MTRs.
Seat material manufacturers provide a composition report to ensure that valve seats meet FDA guidelines (FDA/USP Class VI). Acceptable seat materials include PTFE, RTFE, Kel-F and TFM.
What industries/systems use high purity ball valves?
gas delivery systems
What is ultra-high-purity?
Ultra-High-Purity (UHP) is a term that intends to emphasize the need for extremely high levels of purity. It is a term widely used in the semiconductor marketplace, where absolute minimal amounts of particles in the flow stream are demanded. Valves, piping systems, filters and many materials used in their construction often meet this UHP level when prepared, packaged and handled under specific conditions.
What standards are used in the semiconductor industry for H-P ball valves?
The semiconductor industry derives valve design specifications from a compilation of information managed by the SemaSpec group. The production of microchip wafers requires extremely strict adherence to standards to eliminate or minimize contamination from particles, outgassing and moisture.
SemaSpec's standards detail sources of particles generation, particle size, sources of gasses (via soft valve components), helium leak testing and moisture from within and without the valve boundary.
Why does the H-P market use ball valves in their systems?
Ball valves are proven in the most rigorous applications. Some key advantages of the design include:
- economical -- compared to most other valve designs;
- high flow rate through an unobstructed flow path;
- quick, quarter-turn operation;
- easy to automate pneumatically or electrically;
- inherently flexible to meet a wide range of pressures and temperatures;
- simple maintainability
- self-flushing design.
What is mechanical polishing? Electro polishing?
Mill finishes, welds and surfaces that have been in service have differing surface characteristics when viewed under magnification. Mechanical polishing reduces all surface ridges, pits and discrepancies to a uniform roughness.
Mechanical polishing is accomplished using aluminum oxide abrasives on rotary equipment. Mechanical polishing can be achieved by hand held tools for large surface areas, such as reactors and vessels in place, or by automatic reciprocating machines for pipe or tubular components. A series of grit polishes is applied in a successively finer sequence, until the desired finish or surface roughness is achieved.
Electropolishing is the electrochemical removal of microscopic irregularities from metal surfaces. It results in a general leveling or smoothing of the surface, that when viewed under magnification, appears virtually featureless.
As a result of electropolishing, a metal surface exhibits the following properties:
- Surface roughness is significantly reduced, thus reducing adhesion properties;
- Surface area is reduced as much as 7:1;
- Surface friction and drag are reduced
- Corrosion resistance is increased due to a chromium enrichment of the surface and the removal of surface contaminants that may promote corrosion.
Stainless steel has a natural resistance to corrosion due to its high chromium content (stainless steels are typically 16 percent chromium or higher). Electropolishing enhances this natural resistance because the process dissolves more iron (Fe) than chromium (Cr). This leaves higher levels of chromium on the stainless steel surface (passivation).
How is surface finish measured?
The result of any polishing procedure is to create a "smooth" surface defined as the Roughness Average (Ra). According to ASME/BPE: "All polishes shall be referred to in Ra, micro-inch (m-in) or micro-meter (mm)."
Surface smoothness is generally measured with a profilometer, an automatic instrument with a stylus-type reciprocating arm. The stylus is traversed across a metal surface, measuring peak height and valley depth. The average peak height and valley depth is then expressed as a roughness average in terms of millionths of an inch -- or micro inch, frequently referred to as Ra.
Micrometers is a common European standard, the metric equivalent to micro inches. One micro-inch is equal to approximately 40 micrometers. For example, a finish specified as 0.4 micro meter Ra is equal to 16 micro-inch Ra.
What fluids are typically handled by high purity ball valves?
Due to the inherent flexibility of the ball valve design, it is readily available in a wide range of seats, seals and body materials. As a result, ball valves are produced to handle fluids such as:
steam -- process temperature control/cleaning
Clean Dry Air (CDA) -- purging
alcohol -- deliver alcohol to final product (cosmetics)/cleaning
When are valves selected with ETO or Tri-Clamp end connections? What other ends are used?
Whenever possible, the bio-pharm industry prefers to install "sealed systems." Extended Tube O.D. (ETO) connections are welded inn line to eliminate contamination from outside the valve/piping boundary and to add rigidity to the piping system. Tri-Clamp (Hygienic Clamp Connections) ends add flexibility to the system and may be installed without welding. With Tri-Clamp ends, piping systems may be disassembled and re-configured more readily.
H-P systems (such as in the food/beverage industry) may also use Cherry-Burrell fittings branded under the names "I-Line", "S-Line" or "Q-Line".
What is ETO?
An Extended Tube O.D. (ETO) end is one that permits in-line welding of the valve into the piping system. The dimension of the ETO end matches the tubing (piping) system diameter and wall thickness. The extended tube length accommodates orbital welding heads and provides sufficient length to prevent body seal damage due to the heat of welding.
How do ball valves compare to diaphragm valves in piping/system design?
Ball valves are widely used in process applications because of their inherent versatility. Diaphragm valves offer a limited service range for temperature and pressure and do not meet all of the standards for industrial valves.
Ball valves are available for:
- cryogenic service
- high temperature/low temperature
- high velocity/low velocity
- high pressure/low pressure
- wider range of seat materials
- wider range of body materials
- wider range of end connections
- fire-safe designs
In addition, ball valve center sections are removable to allow access to the inner weld bead, where cleaning and/or polishing may then be performed.
What is drainability?
Drainability is important for maintaining bioprocess systems in a clean and sterile condition. Fluid remaining after draining becomes a colonization site for bacteria or other microorganisms, creating an unacceptable bioburden to the system. Sites where fluid accumulates also may become a corrosion-initiation site, adding additional contaminants to the system. The design part of the ASME/BPE Standard calls for hold-up volume, or that amount of liquid which remains in the system after draining is complete, to be minimized by design.
What is "deadleg"?
A deadleg in a piping system is defined as a pocket, tee or extension from a primary piping run that exceeds a defined number of pipe diameters (L) from the ID of the primary pipe (D). A deadleg is undesirable because it provides an area of entrapment, which may not be reached by cleaning or sterilizing procedures, and thus leads to contamination of the product. For bioprocessing piping systems an L/D ratio of 2:1 is considered to be achievable for most valve and piping configurations. See Also our page on deaglegs.
Where are fire-safe valves used?
Fire-safe valves are designed to prevent flammable fluids from spreading in the event of a process line fire. The design uses metal back-up seats and an anti-static feature to prevent ignition. The biopharmaceutical and cosmetics industries often prefer fire-safe valves in alcohol delivery systems.
What are the acceptable seat materials for H-P ball valves?
FDA-USP23, Class VI approved seat materials for ball valves include; PTFE, RTFE, Kel-F, PEEK and TFM.
What is TFM?
TFM is chemically modified PTFE that fills the gap between conventional PTFE and melt-processable PFA. According to ASTM D 4894 and ISO Draft WDT 539-1.5, TFM is classified as a PTFE.
Compared to conventional PTFE, TFM has the following enhanced properties:
- much lower deformation under pressure (cold flow) at room and elevated temperatures;
- lower permeability
- may be used at higher pressures.
What are cavity-filler seats and how are they used?
Cavity-filler seats are intended to prevent the build up of materials that may --when entrapped between the ball and body cavity -- solidify or otherwise inhibit the smooth operation of the valve closure member. H-P ball valves used in steam service should not use this optional seat arrangement, as the steam will find its way under the seat surface and become an area for bacterial growth. Due to this larger seating area, cavity-filler seats are difficult to properly sanitize without disassembly.
What are the typical options available with H-P ball valves?
- end connections
- purge ports
- sampling valve
- tank bottom design
- lateral valve configuration
- fire-safe design
What are the common cleaning procedures used with H-P ball valves?
H-P ball valves may be cleaned and packaged according to BPE or Semiconductor (SemaSpec) requirements.
Area & Equipment
- Cleaning is performed in a room segregated from the normal valve production area to eliminate contamination.
- The room is outfitted with one alkaline cleaning tank, a DI rinse tank and a hot air drying tank.
- Work areas are freshly covered with particle-free plastic sheeting before each cleaning.
- Bubble-tight valve testing equipment utilizes clean, dry, oil-free air.
- Capping and bagging is performed on the particle-free surface.
- All bags are 4 mil and are heat-sealed. Double bag option is available.
The basic cleaning is performed using an ultrasonic cleaning system, with an approved alkaline agent for cold cleaning and de-greasing in a residue-free formulation.
VOC emission level = 0.
- Each valve component is thoroughly washed in the cleaning agent tank, then rinsed in a de-ionized water tank.
- The components are then dried in a hot air drying vessel.
- Valve assembly is performed in a Class 100 room on a particle-free surface using latex gloves.
- Clean, grease-free tools are used in the assembly of valves.
- After assembly, the valves are nitrogen purged with 99.999-percent pure N2 filtered with 0.01 micron-rated filters.
- The fully assembled valve is tested for leakage using clean, dry, oil-free air according to industry standards.
- Each valve is capped, bagged (4 mil) and heat-sealed to ensure product quality and purity until installed.
- Each finished (dry, completed, inspected and approved) end connector is covered with "clean" Aclar or Nylon film, and then capped with non-shedding end caps -- which do not come in contact with the inner surfaces.
- Each finished valve is bagged in 4 mil thick, clean polyethylene with a full filtered nitrogen (0.01 micron) purge, to prevent contamination.
- The bag is then sealed to provide a waterproof environment.
- Valves with sharp edges are additionally padded to prevent puncturing during shipment.
- Packaging is done in the same clean room where the cleaning procedure was performed.
- Components are not removed from the clean room until they are properly packaged and sealed.
- Valves are only removed from the clean room environment in sealed, non-shedding containers or with appropriately capped ends.
All valves are permanently marked with the following information:
- manufacturer's name or logo
- heat number on each component part of the fitting if more than one heat is used
- material type
- specification number referencing the BPE standard
- internal surface symbol for the appropriate bpe specification
- color-coded handles (if applicable).
Certificate of Traceability
Pressure-containing components are marked with heat numbers and backed by appropriate analysis certificates.
Mill Test Reports (MTR's) are recorded for each size and heat number.
These documents include:
- alloy-ASTM designation
- heat number
- year and month of manufacture
- chemical analysis
- mechanical properties
- heat treatment
About the Author
Anton Dooley is a Piper with over 25 years experience covering process plant engineering, design & training. He is the founder of pipingdesigners.com