As an OEM for PSG Dover’s Quattroflow product line, Holland Applied Technologies is excited to announce the addition of the QF30SU Single-Use Diaphragm Pump to the Quattroflow Single Use Product line. As the leading brand of quaternary diaphragm pumps, the Quattroflow series of pumps has been one of our offerings that continues to innovate by offering our biopharmaceutical customers scalability, flexibility, and performance that traditional product offerings can’t match. Today, we will look at their latest product offering, the QF30SU, which has been developed for lower flow rates in single-use applications.
Quattroflow QF30SU
Until very recently, the Quattroflow single-use pumps have been available in the QF150SU, QF1200SU, QF4400SU, QF5050SU, and the QF20kSU sizes. Quattroflow has now extended its Single-Use product line to the lower end. Featuring a flow range from 0.06 to 30 lph, the new QF30SU is the ideal solution for your pharmaceutical and biotech applications requiring a lower flow rate that the QF150SU couldn’t quite reach.
Retrofittable on both QF150S (Multiple Use) and QF150SU (Single Use) drives, the QF30SU pump features a disposable polypropylene (PP) wetted pump chamber with tool-free installation. Offering a small footprint with a high turndown ratio at 500:1, the QF30SU pump is ideally suited for lab and low flow applications such as chromatography, TFF and virus filtration operations.
While the maximum motor speed of a QF150 drive is 3000 rpm, the QF30 has a proportional (linear) motor speed to flow characteristic that goes up to 1000 rpm. At higher motor speeds, the flow characteristic (performance curve) starts to flatten. The brushless single phase, 230V (110V as option) 90W motor drives that are standard with the QF150 drives can be changed to limit the motor speed to 1000 rpm.
The QF30SU polypropylene pump head features 4 mm (1/8”) hose barb connectors. All soft parts are fully characterized, made of USP Class VI materials with extractable and leachable reports available. Available accessories for the QF30SU include a power box, diaphragm sensor and PID pressure controller.
With the new QF30SU, the Quattroflow series of pumps now cover a range of flow rates from 1 lph with the QF30SU to 16000 lph with the QF20kSU. For any questions about your next biopharmaceutical application or to see if any of the Quattroflow series of pumps is right for you, feel free to contact a Holland Sales Engineer.
Product Focus: Gore Sta-Pure Pump Tubing
In today’s post we are going to take a look at the Gore Sta-Pure peristaltic pump tubing. The Gore Sta-Pure product line offers two series of products; the Series PFL and the Series PCS. Gore’s pump tubing products are engineered to deliver consistent flow even at high pressures (up to 100 psig) and chemically aggressive applications. Let us dive into what distinguishes each product.
The Gore Sta-Pure Pump Tubing Series PFL is manufactured with a patented composite of expanded polytetrafluoroethylene (ePTFE) and platinum-cured perfluoroelastomer for increased reliability with aggressive chemicals in peristaltic pumps. It is free from plasticizers, acid acceptors and other processing aids, making it one of the most pure tubing products available. The Series PFL handles nearly all aggressive chemicals, including organic solvents such as methyl ethyl ketone, toluene, and acetone. Let’s find out why…
Gore Sta-Pure Series PFL Tubing
Expanded polytetrafluoroethylene is created when PTFE—a linear polymer consisting of a carbon backbone completely surrounded and protected by fluorine atoms—is expanded, creating a microporous structure with desirable characteristics such as a high strength-to-weight ratio, biocompatibility, and high thermal resistance. This expansion process, innovated by W.L. Gore & Associates in 1969, is what makes GORE products so unique. This unique process significantly improves the mechanical properties while also maintaining the positive chemical attributes of the PTFE base material.
PTFE Structure. The Carbon-Fluorine bond is among the strongest and most stable bond in organic chemistry.a caption
A perfluoroelastomer, represented by the letters FFKM or FFPM (ASTM and ISO designations, respectively), is very similar to PTFE except that PTFE is a more crystalline, or plastic, material while FFKMs can be thought of as the elastomeric form of PTFE in that it is soft and flexible at room temperature. Given the chemical structure and performance similarities between perfluoroelastomers and PTFE, it should be no surprise that perfluoroelastomers are used in sealing applications involving high temperature and/or aggressive chemicals.
Perfluoroelastomer Structure
Combining the two compounds provides better chemical compatibility than silicone and thermoplastic elastomer (TPE) tubing. In addition, the patented structure of the composite enables consistent flow rates over extended production cycles up to 60 psig. The Series PFL also withstands the rigors of clean-in-place and steam-in-place (CIP/SIP) processing, which helps simplify sterile fluid applications.
Series PCS Tubing
The Series PCS is a composite of platinum-cured silicone and reinforced with expanded polytetrafluoroelthylene (ePTFE) for added strength and resilience. With a unique composition of silicone and PTFE, the Series PCS has superior burst resistance up to 100 psi. This tubing is widely used for ultra-pure applications such as ultra-filtration, live cell transfer, fermentation, and bioreactor feed.
While platinum-cured silicone products are known for their extremely low levels of extractables and leachables and have gained a reputation for being the highest purity products, they may balloon or rupture under high pressure. The Series PCS employs a unique composite structure that overcomes this limitation and provides greater reliability and security against rupture. In a peristaltic pump, at a back pressure of 60 psi (4 atm), Series PCS tubing lasts over 1,000 hours under continuous use at 200 rpm. Under transfer conditions, it lasts more than 18 times longer than silicone rubber tubing, and almost twice as long as thermoplastic elastomer tubing at 360 rpm. The Series PCS has also been validated to operate after steam-in-place/clean-in-place (SIP/CIP) and autoclave sterilization.
Expanded polytetrafluoroethylene, or ePTFE, is the core material in many of Gore’s solutions. You likely may be familiar with the many products Gore has to offer. Today, we have seen that Gore can tailor ePTFE for chemically aggressive high purity applications in their Series PFL tubing, or high-pressure and physically demanding applications in their Series PCS.
If you have any questions on your peristaltic pump application or any of our single use products, contact a Holland Sales Engineer today.
Introducing the New Hollandapt.com
Today, we are excited to announce the launch of our newly designed website—Hollandapt.com
Our new Homepage!
Our revamped website has a very new look and feel to it. It features a responsive web design and is mobile friendly so that we can provide our visitors and business partners an easy way to learn about the various products, services, and solutions that Holland Applied Technologies has to offer. Other highlights include:
The Engineering Toolbox
In addition to aesthetically re-designing our website, one of the main goals of the new site is to provide a resource for many of the CAD files and downloads we’re often asked for. Thus, the ‘Engineering Toolbox’ section was created to host these files and other product literature & technical documentation such as brochures, manuals, and parts lists. We will be adding these files overs the coming months. If there’s something you want to see here, let us know!
Products
What else has changed? We have refined our products and offerings into a single drop-down menu—the ‘Products’ section. If you’d like to learn more about all of the products and services we offer, then the products section is where you will find this information. The Blog, Request a Quote, and other resources are still a single click away.
We hope you find the new website to have a fresh look and easy to access information. We have designed the new site with many additional functionalities in mind that will be launched at a later date. Our blog and monthly Newsletter will continue to be an important source of any new exciting information and announcements.
We value the feedback of our customers and business partners. We invite you to view and explore the new website and let us know your thoughts.
Sanitary PD Pump Rotor Clearances- Chart
Today, we give you even more information on PD pump rotor clearances. Below is an easy to use chart that provides the rotor clearance data for the Waukesha Cherry-Burrell Universal 1, 2, & 3 positive displacement pumps.
These tables will help you to determine the proper back face, rotor to body, and front face clearances. Please note that the assembly clearances stated in these tables are for reference only. Actual pump clearances may vary based on pump performance testing.
For non-standard rotors, or if the process uses special clearance rotors, please contact a Holland Sales Engineer with the serial number of the pump.
The above information was taken from the Waukesha Universal 1, 2, 3 Maintenance Manuals.
Sanitary PD Pump Rotor Clearances
In today’s post, we are going to look at the different clearance options that are available on a Waukesha Cherry-Burrell Universal 1, 2, & 3 PD Pump.
As you may know, the Waukesha Alloy 88 is the standard rotor material for the Universal 1, 2, & 3 PD pumps. This alloy was developed to provide the advantage of excellent corrosion resistance and close operating clearance requirements. The clearance between rotating parts (rotor) and stationary parts (pump head) is very important in limiting slip and maximizing efficiency.
Slip is proportional to clearance to the 3rd power
Here is a summary of the different clearance options for a U1 & U2 PD pump:
“Standard” and “Wine” clearance rotors may be used with liquid temperatures up to 180°F (82°C).
However, between 160°-200°F (71°-93°C), it is best to consider other application factors such as:
- Speed of operation
- Differential pressure
- Lubricating properties of liquid being pumped
- Product viscosity
If these factors trend toward a difficult application (high speed, high pressure, non-lubricating) then “Front Face” or “Hot” clearance rotors are recommended. Wine clearance rotors (same operating parameters as listed for standard rotors) provide additional clearance between the rotor hub and the cover bore area only. They give extra protection against contact in this area.
“FF” (Front Face) clearance rotors provide additional clearance in the front face area only. They are recommended for use with liquid temperature between 180°F (82°C) to 200°F (93°C). They give better pumping efficiency (less slip) than “Hot” clearance rotors when used with low viscosity liquids. Do not use “FF”, however, rotors if they will be subjected to temperature shock (extreme, rapid temperature change.)
“Hot” clearance rotors are recommended for use with liquid temperatures between 180°F (82°C) to 300°F (149°C). They provide additional clearance in the front face area plus rotor to body areas. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm.) VHP (viscous horsepower) is slightly lower when using hot clearance rotors. Hot clearance rotors are also used when the product viscosity is above 200 CPS.
“316SS” clearance rotors are used with rotors made from 316 stainless steel material (in place of standard non-galling alloy 88) and recommended for use at temperatures up to 200°F (93°C). These rotors provide additional clearance all around (more than Hot clearance alloy 88 rotors) to insure no running contact between the 316 SS rotors and other 316 SS pump components. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm). VHP (viscous horsepower) is slightly lower when using “316SS” clearance rotors.
Some models in some series have a “316SS Hot” clearance rotor option for temperature above 200°F (93°C).
NOTE: Consult Holland Technical Services for applications near 300°F or above 200°F with 316 SS rotors.
“Extra Hot” clearance rotors are recommended for use with products such as chocolate, which tend to “plate out” and build up on rotor surfaces. These rotors require special selection procedures. Contact SPX FLOW Technical Services for assistance.
The model U3 pump uses slightly different nomenclature and clearance options:
“Low Viscosity” rotors are similar to the U1 & U2 “standard” clearance rotors in that they may be used with liquid temperatures up to 180°F (82°C). Between 160° (71°C) and 200°F (93°C), other application factors must be considered such as; speed of operation, differential pressure, lubricating properties of liquid being pumped, and product viscosity. If these factors trend toward a difficult application (high speed, high pressure, non-lubricating) then “Standard” clearance rotors are recommended.
“Standard” clearance rotors are recommended for use with liquid temperatures between -40°F (-40°C) and 300°F (149°C). They provide additional clearance in the front face area plus rotor to body areas. Because of this additional clearance there is more slip (inefficiency) with low viscosity liquids, which the pump must overcome with higher operating speed (rpm.) VHP (viscous horsepower) is slightly lower when using standard clearance rotors. Standard clearance rotors are also used when the product viscosity is above 200 CPS.
There are many factors to consider when sizing a PD pump for a specific application. The different rotor clearance options available on the Waukesha Universal series positive displacement pumps allow our Holland Sales Engineers to size a pump that will maximize pump performance. Contact a Holland Sales Engineer today with your next sanitary pump application.
Stainless Steel Finishes: What Makes A Weld Sanitary?
In today’s post, we are going to focus on welding and what makes a weld sanitary in today’s sanitary (hygienic) processing facilities.
To start, let’s look at a very general definition and overview of welding. Welding is the joining process in which two (or more) parts are coalesced at their contacting surfaces by application of heat and/or pressure. Welding is achieved by two basic categories; fusion welding and solid state welding. Fusion welding is accomplished by melting the two parts to be joined, and in some cases, adding a filler metal to the joint. Examples of fusion welding processes include arc welding, resistance welding, and laser beam welding. Solid state welding involves the application of heat and/or pressure but no melting of base metals occurs and no filler metal is added. Some examples include forge welding, diffusion welding, and friction welding.
The American Welding Society AWS D18 Committee was formed by the request of the 3A Sanitary Standards Committee for help in outlining welding standards for use in the manufacture and construction of dairy and food product processing plants. Within the AWS D18.1/D18 Specification is where it is defined that all welds for austenitic stainless steel tube and pipe are to be done by the gas tungsten arc welding (GTAW) process (also known as the tungsten inert gas, or TIG, process). This process uses a non-consumable tungsten electrode along with an inert gas (argon or helium) for arc shielding. The purpose of arc shielding is because at high temperatures, metals are chemically reactive to the oxygen, nitrogen, and hydrogen that is present in air, and thus without a shielding gas the mechanical properties of the joint are subject to oxidation. So the advantage of the GTAW welding process is that it produces high quality welds with little or no post-weld cleaning.
GTAW Welding
According to the AWS D18.1/D18 Specification, welds are to be fully penetrated to the ID to prevent the formation of crevices which could entrap product and lead to contamination. In order to determine acceptable oxidation levels, the AWS D18.2/D18 Specification provides a visual examination guide to aid in the inspection of color in the heat affected zone (HAZ) for welds in piping systems. The heat affected zone is the area of base metal that has experience temperatures below melting point, but high enough to cause changes in the properties and microstructure of the metal.
AWS Weld Discoloration & Acceptance Criteria Scale
As the demands of the bioprocess industry for clean, smooth product contact surfaces increased, advances in process piping technology and equipment fabrication technology have followed. Orbital welding was developed as an automated process to address the risk of operator error in GTAW processes. Orbital welding offers the advantage of a computer controlled system that combines arc current, feed and speed to allow the ‘orbital weld head’ to travel around the tube in a steady manner in order to produce consistent and repeatable weld profiles. Hooray for automation.
The 3A Standard was extensively used by the pharmaceutical food and dairy industries but with the emerging bioprocess industry, higher standards were needed for equipment design that would be both cleanable and sterilizable. The ASME published the first edition of the ASME Bioprocessing Equipment Standard in 1997 (BPE-97) to help address this need. Part MJ (Materials Joining) of the ASME BPE Standard requires that the weld criteria of ASME B31.3 – Process Piping be met for acceptable metallic materials. While ASME B31.3 prohibits weld discontinuities such as cracks, voids, porosity, lack-of fusion, and incomplete penetration, the ASME BPE Standard also provides visual examination acceptance criteria to determine the hygienic condition of the piping system. It should be noted that the BPE standard specifies orbital welding as the preferred joining technology for bioprocess tubing, and that manual welding may be performed with owner/user and contactor agreement.
Acceptable and Unacceptable Weld Profiles
Hopefully this blog has provided a good overview of the welding practices used in our industry and what criteria and standards define practices to be sanitary. For over 50 years, Holland Applied Technologies has built a reputation as being one of the highest quality sanitary stainless steel fabricators in the US. All sanitary welding is done using cryogenic Argon and our orbital welders have automated Oxygen sensing systems. If you have a custom sanitary process piping application, call us at (800) 800-8464. We can help you with your design and work with you to come up with the most cost effective, high quality solution for your application.
Sanitary Surface Finish Chart
Below is a comprehensive graphic for surface finishes that we hope you find useful. The Surface Roughness Conversion Chart will help to convert surface finish between selected industry standard units. The Common Names table lists some common surface finish names and how they are defined by their Ra number. Lastly, the Sanitary & BPE Surface Finishes table defines the surface finish requirements as established by the ASME BPE 2016 Standard. This table is also useful in that it relates surface finish codes from various manufacturers to the ASME BPE Standard.
N = New ISO (Grade) Scale numbers
Ra = Roughness (average), measured in microinches (µin) or micrometers (µm)
RMS = Root Mean square, microinches (µin)
Stainless Steel Finishes: Know What You Need
This blog is the first in a series of posts about sanitary surface finishes. In this post, we will cover surface finishes as they pertain primarily to sheet metal and subsequent posts will provide further detail on surface finish standards for fluid process components.
How is a specific level of finish defined and how can that level of finishing be achieved? For our industry, surface finishes are a standard set by regulatory agencies (3A, ASME BPE, etc.) and manufacturers who specify a certain level of finishing on processing equipment in order to ensure cleanability and sanitation. These bodies require sanitary finishes to have a minimum Ra (roughness average) typically measured in microinches (µin) or micrometers (µm). But what is considered clean in one application will likely be different from the surface finish requirement in another application. For example, the 3A requirement is generally equivalent to, or smoother than a 32 Ra (microinch) while the ASME BPE standard categorizes several different surface finishes ranging from 0 to 32 Ra through the means of mechanical polishing and electropolishing.
You may know what type of finish you need for your application, but if you want to really understand the various terms and definitions used for stainless steel surface finishes then you can read about them here where we define important terms such as Ra, roughness, and grit.
Surface finishes can be enhanced through various means of mechanical and chemical treatments. In our industry we typically see these treatments achieved via the following methods.
Sanitary Tubing with an Electropolish Finish
Mill Finish is the baseline finish used for comparison. Mill finishes will have a dull or matte non-uniform appearance with a Ra of at least 100 µin. This finish does not meet sanitary processing finishing requirements.
2B Mill Finish will have a more reflective appearance—almost like a cloudy mirror. This finish is more common in industrial, chemical and food applications and will have a large range of Ra values.
No. 4 Finish will have a Ra of 29 to 40 microinches. Although it can be found in clean rooms and in food processing equipment, it is not compliant for 3A standards (32 Ra or less).
No. 4A Finish is similar to the no. 4 finish in that is characterized by short, polished brush lines but uses a finer grit polish. This finish is required to meet the basic 3A standards and will have a Ra of 18 to 31 microinches.
Bead blasting uses a fine bead material, such as glass, at a high pressure to provide a certain level of finish. Ra values are typically greater than 45 Ra, depending on the blasting process.
Passivation means removing the excess iron or iron compounds from the surface of the metal using an acid solution (nitric or citric acid). Removing these impurities allows the formation of an oxide layer that protects the rest of the steel from corrosion. Passivation has little effect on Ra values.
Electropolishing is an electrochemical process where the surface metal is dissolved and the embedded contaminants are removed. This creates a “smooth” mirror finish and can result in increased smoothness.
As you can see, there are many manufacturing and chemical processes used to achieve various levels of finishes. When selecting equipment with higher-end finishes, often times we see processors elect to exceed the minimal standards set by regulatory agencies in order decrease bacteria risk. Hopefully this post proves as a useful reference when weighing the various stainless steel finishes on sanitary equipment.
ASME BPE – More Than Just a Standard for Fittings
Many people have heard the term ‘ASME BPE’ when buying fittings and tubing for the Biotech and Pharmaceutical industry. If you haven’t heard of ASME BPE, or are unfamiliar with this standard, then I’d like to refer you to one of our past blogs where we give a general overview of ASME BPE, what they do, and why it is so important to our industry.
The ASME BPE Standard is probably most known for having specifications on dimensions and surface finish for fittings and tubing. We’ve highlighted some of the key differences between ASME BPE tubing and standard sanitary tubing before, which you can read about here.
Today, however, we are going to give a general overview of just what kind of equipment and design standards the ASME BPE standard covers.
The current ASME BPE Standard was published in 2016 and has an extensive chapter on Systems Design (Chapter 2, Part SD). The purpose of this subcommittee is to establish design guidelines applicable to bioprocessing equipment, components, assemblies, and systems. This chapter contains information regarding, but not limited to, the items and topics listed below.
- Steam-In-Place (SIP). ASME BPE states that ‘equipment parts and components that are subjected to SIP should be designed and constructed to withstand continuous exposure to saturated steam at a minimum temperature of 266 F for a duration of at least 100 hr under continuous steady-state conditions’.
- Drainability. The systems ability to facilitate drainage, mainly achieved by gravity.
- Connections, Fittings, and Piping. These are the common process components of hygienic piping systems which you are likely to be most familiar with. Dead legs are discussed within this topic.
- Hose Assemblies. Design and installation guidelines for hygienic hose assemblies (both their flexible element and the end connections).
- Pumps. System application such as the cleanability, drainability, and installation of diaphragm pumps, centrifugal pumps, positive displacement pumps, and rotary lobe pumps.
- Vessels. This section defines the requirements that are to be met in the design, fabrication, and supply of both pressurized and unpressurized biopharmaceutical vessels.
- Agitators and Mixers. Design, cleanability, material construction, etc. of process contact surfaces of these equipment as well as their sub-components such as shafts and keyways, impellers, bearings, and mechanical seals.
- Heat Exchangers. These include plate-and-frame heat exchangers and shell & tube heat exchangers. Design for cleaning/steaming and fabrication techniques are discussed by the ASME BPE standard.
- Transfer Panels. As defined by ASME BPE, a transfer panel is ‘a panel to which process and/or utilities are piped that mechanically precludes erroneous cross connections’.
- Filters. Housing design of filters and the testing and validation of the cartridge according to ASME BPE Code 7.
- Steam Sterilizers/Autoclaves. This section defines the design and cleaning requirements of autoclaves that are used in bioprocessing.
Chapter 3 covers the materials that are considered applicable for use in hygienic service, both for Metallic Materials (Part MM) and Polymers and other nonmetallic materials (Part PM).
Chapter 4 outlines Process Components. The Dimensions and Tolerances section (Part DT) provides the guidelines for automatic weld ends for 316L-type alloys and sanitary clamp gaskets. Instruments for level, pressure, and temperature are addressed in the Process Instrumentation section (Part PI) of the Standard. Conductivity sensors, flowmeters and sight glass information can also be found under the Process Instrumentation section. Sealing Components (Part SG) provides the design and performance requirements for sealing components such as mechanical seals, O-rings, and diaphragms for valves.
Chapter 5 highlights Fabrication, Assembly, and Erection. Here you can find the requirements for Materials Joining (Part MJ). The Materials Joining section has color charts and vast information on welding/joining of materials, for both metallic and polymeric materials. Process contact surface finish requirements are covered in Part SF.
Chapter 6 establishes the requirements for obtaining a Certificate of Authorization and the ASME Certification Mark.
The Mandatory Appendix provides guidance to ASME BPE Standard users who wish to submit requests for revisions/additions to the BPE Standard, requests for Code Cases, and requests for interpretation of the BPE Standard.
Finally, the Non-Mandatory Appendix contains helpful information on Rouge and Passivation procedures. It contains information on Ferrite, Corrosion Testing and Electropolishing. This section also contains examples of incoming inspection material examination data sheets used by Quality Control and Mechanical Contracting personnel.
Holland Applied Technologies personnel work with ASME BPE equipment each day. In fact, our own Troy Hobick sits on many of the BPE subcommittees. For any questions regarding ASME BPE equipment please contact us at 800-800-8464 or our website www.hollandapt.com. Or, if you’d like to read the ASME BPE Standard for yourself, it can be found at asme.org or you can call 1.800.THE.ASME.
Guest Post- Material Trends for High Purity & Sanitary Applications
By: Ken Kimbrel- Special Alloys Product Manager, VNE Corporation
For almost 60 years, Holland Applied Technologies has been providing customers with the best high purity process products in the industry. Today, we’re excited to share our first guest post, highlighting our newest sanitary fitting product offering, as well as providing an excellent overview of what makes a material corrosion resistant. Enjoy!
For several years stainless steel has been the workhorse processors have used in tough corrosive environments. For the most part, it has performed well. In recent years, however, in many new installations or even repairs to existing process lines, today’s stainless steel doesn’t perform as well in the same application as stainless steel of years past. Additionally, with the advent of newer buffer solutions in the pharmaceutical industry we are experiencing higher than ever chloride levels which attack stainless steel causing pitting and crevice corrosion.
As with all industries, imports, competitive markets and technological advances have enabled and even forced steel manufacturers to become more competitive in the steel making process. The most significant of these advancements impacting the steel industry was realized nearly 40 years ago with the introduction of argon-oxygen-decarburization (AOD) refining. The use of AOD allows the extensive use of scrap metal. In fact, some heats are nearly all remelted scrap metal. The only disadvantage is a continual build-up of non-specified tramp elements like copper, boron and calcium. The AOD process allows precise gas manipulation to achieve the desired result and refines stainless steel by gradually replacing oxygen by means of blowing argon through the molten metal to eliminate impurities.
The American Society for Testing and Materials (ASTM) specification shows the chemical composition of any alloy in ranges with a minimum and maximum allowable limit to meet the requirements for the specific alloy. For example, the chemical composition for 316L stainless is as follows.
| 316L | Chromium | Nickel | Molybdenum | Carbon | Iron |
| Minimum | 16% | 10% | 2% | ||
| Maximum | 18% | 14% | 3% | 0.035% | Balance |
Today, when alloying 316L stainless steel the AOD process allows precise control of alloying elements, enabling the mills to make a product to an exact chemical composition. This also allows the elements to be controlled to the minimum range allowed for the specification. Compared to decades past when alloying 316L, the amounts of alloying elements were added with little control and often pushed or exceeded the upper limits of the maximum requirements. The resulting steel was a product with corrosion resistant properties superior to 316L stainless steel that is manufactured by using today’s methods. Today we see melts of steel meet the requirements of the specification on the low end, resulting in the overall mean corrosion resistance of the material trending downward. If a higher alloyed, but within-grade 316L composition is desired, it typically requires a special order of a full heat of material. Due to the cost or purchasing a complete melt, it is often more practical to specify a more corrosion resistant grade such as 904L, duplex stainless steel or a 6% Mo grade to obtain small quantities than to special order an enhanced 316L composition.
Determining the corrosion resistance of any alloy is always a challenging task. Varying service environments, aggressive cleaning and sterilization practices, and even multiple product forms of materials used in equipment fabrication can have a negative impact on corrosion resistance of materials. Because of these ever-changing conditions, the best corrosion data available is often the service history of the system itself. When choosing the correct materials of construction, it is recommended that a qualified Materials Engineer be consulted for evaluating the solutions, compounds and operating conditions the system will be exposed to. The most widely accepted materials of construction beyond 316L stainless steel in high purity and sanitary applications are the super-austenitic, nickel, and duplex alloys. These alloys can vary in their chemical make-up resulting in different levels of performance in certain corrosive or acidic environments. Table MM-2.1-1 in the current edition of the ASME BPE Standard identifies materials acceptable for use in the Biopharmaceutical industries that have been proven they can meet the requirements of welding and surface finishes listed within the Standard. Of these materials listed, this paper is going focus on Type 316L austenitic, superaustenitic stainless steels 904L, Ultra6XN, AL-6XN® and nickel alloys C-22® and Alloy 22.
ASTM Composition of Wrought Steels
| UNS | Alloy | EN | C | Mn* | Cr | Ni | Mo | N* | Cu | PREN |
| S31603 | 316L | 1.4404 | 0.030 | 2.00 | 16.00-18.00 | 10.00-14.00 | 2.00-3.00 | 0.10 | … | 24 |
| N08904 | 904L | 1.4539 | 0.02 | 2.00 | 19.0-23.0 | 23.9-28.0 | 4.0-5.0 | – | 1.0-2.0 | 36 |
| N08367 N08926 | Ultra 6xn | 1.4529 | 0.02 | 2.00 | 19.0-21.0 | 24.0-26.0 | 6.0-7.0 | 0.15-0.25 | 0.75 | 45 |
| AL-6XN® | AL-6XN® | – | 0.03 | 2.00 | 20.0-22.0 | 23.5-25.5 | 6.0-7.0 | 0.18-0.25 | 0.75 | 45.2 |
| N06022 | C-22® | 2.4602 | 0.01 | 22 | 56 | 13 | 0.5 | 68 | ||
| N06022 | Alloy 22 | 2.4602 | 0.015 | 22 | 56 | 13 | 0.5 | 68 |
*Maximum
Note: Sulfur is limited to 0.030 max and Phosphorous to 0.045
When comparing alloys for corrosive environments, the most important elements of the materials chemistry for corrosion resistance is Chromium, Molybdenum, Nickel and Iron. None of these listed elements alone are magical in preventing corrosion but alloyed correctly and manufactured properly, can improve corrosion resistance and the life expectancy of a high purity system.
- Chromium – Cr is a key component of stainless steel that accounts for its passive nature. Chromium significantly improves corrosion resistance when the composition contains a minimum of 10.5%. When at or above these levels, an adherent and insoluble surface film, known as the passive film, is instantaneously formed that prevents diffusion of oxygen into the surface thus prevents oxidation of the iron in 316L stainless steel. Chromium is also the weak link in stainless steel when in contact with chlorides by reacting with the chromium oxide in the passive layer to form chromium chloride, which is very soluble. This leaves a layer of iron and iron-nickel on the surface, an active film which will allow the stainless steel to corrode and the metal to be consumed.
- Molybdenum – Mo increases the resistance to localized corrosion in the forms of pitting and crevice corrosion. The higher the molybdenum content, the better the corrosion resistance to higher chloride levels by enhancing the passive film, making it stronger and helping it to re-form quickly if it is disrupted by chlorides.
- Nickel – Ni is an alloying element critical to stainless steels and results in the formation of the austenitic structure that increases strength, impact strength and toughness, while also improving resistance to oxidization and corrosion. It also increases toughness at low “cryogenic” temperatures. Nickel has no direct impact in the formation of the passive layer, but it does offer improvement in resistance to acid attack.
Another alloying element that has a positive impact and found in 316L, Ultra 6XN and AL-6XN® is Nitrogen-N, which increases the austenitic stability of stainless steels and improves yield strengths in low carbon grades of steel containing less than 0.03%. It can also enhance resistance to localized pitting and intergranular corrosion.
A guide to the corrosion resistance of alloy can be found in the calculation of its Pitting Resistance Equivalency Number (PREN). The chemical composition of the alloy along with this formula (Cr + 3.3Mo + 16N=PREN) will result in a number ranking the alloy. The higher the number, the more resistant the alloy is to localized corrosion. PREN’s can be found in the materials table above.
Those alloys containing 6% molybdenum content may require special fabrication methods beyond what is generally found in 316L stainless steel systems. However, they are common place and manufacturing practices are available to guide fabricators and suppliers. All the alloys listed in the table above are available in common sizes found in most sanitary designs and product forms such as tubing, fittings and valves.
For information regarding pricing and specifics of fabrication please contact the author.
AL-6XN® in a registered trademark of Allegheny Technologies Inc.
C-22® is a registered trademark of Haynes International Inc.
About the Author:
Ken Kimbrel is Product Manager – Special Alloys for VNE Corporation in Janesville, WI. He is responsible for specialty alloy sales, market planning, process and material evaluation in corrosive environments. He attended Tulsa Comm
Ken Kimbrel
unity College and has an extensive background in engineering, equipment manufacturing, and is a NACE International Board-Certified Corrosion Technician. His expertise includes corrosion evaluation, material selection, surface finish evaluation, and rouge remediation.
Ken is the current Chair of the ASME BPE. He has served as inaugural Chair of Subcommittee on Metallic Materials and as past Chair of the Surface Finish Subcommittee. He is a member of the Subcommittees on Accreditation, the Standards committee, Executive committee and author of several technical papers.
He is a member of the International Society for Pharmaceutical Engineering (ISPE), ASM International (ASM), the International Metallographic Society (IMS), the National Association of Corrosion Engineers (NACE).
Contact information:
E-mail: kkimbrel@vnecorp.com | Ph: 800-356-1111 | Cell: 417-827-2526