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Browse previously asked/answered questions below.

  • Is my gas purity adequate for my process?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    Industrial gases (such as nitrogen, hydrogen, and argon) for furnace atmospheres are characterized by their very high purity (>99.995%). Typical impurity levels are much less than 10 parts per million by volume (ppmv) oxygen and less than 3 ppmv moisture (<– 90° F dew point). This purity is typically adequate for many processes involving a wide array of materials. Some materials, though, due to their high reactivity, may require additional purification to reach even lower levels of impurity, especially with gases supplied via bulk or tube trailer supply modes. Some facilities install in-line purifiers as an added precaution against impurities picked up from the houseline. In-line purification typically involves the removal of oxygen and moisture. Sometimes with argon supply, it is necessary to remove trace nitrogen impurities. The choice of purifier is dependent on the gas and the type and amount of impurities to be removed.

    If you are having a process issue that you think may be related to gas purity, please call Air Products at 800-654-4567.

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  • Is a drier furnace atmosphere always a better furnace atmosphere?

    Mark Lanham
    Applications Engineer
    Since the reducing potential of a hydrogenbased furnace atmosphere is defined by the ratio of pH2/pH2O, the first answer that comes to most people’s minds is “yes.” And, in some cases, they are correct. Lower dew point readings (lower pH2O) lead to more reducing conditions and, in many cases, better furnace atmosphere performance. However, there are situations where that is not always the case. One example of that is hydrogenbased belt furnace atmospheres where the dew point can reach values drier than –50°F or even –60°F under certain conditions. The reducing potential of this atmosphere is more than enough for the typical parts processed, but it can lead to unnecessarily strong reducing conditions that actually decrease belt life. Another example might be a brazing atmosphere that is too reducing and prone to excessive braze flow. Air Products’ new Atmosphere Humidification System allows for precise and consistent moisture additions to furnace atmospheres for just the right amount of moisture to improve belt life performance and/or braze flow while still maintaining adequate reducing conditions for the sintering or brazing operations being performed.

    To find out more details, give us a call at 800-654-4567.

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  • We anneal and passivate 300 series stainless tube and sometimes get a “grey” coloration on the ID—can we keep it bright?
    Zbigniew Zurecki
    Research Associate

    Formation of oxide film is a function of hydrogen/water partial pressure ratio, temperature, and time, all of which can change significantly at the furnace exit. An elevated dew point due to air ingress reacting with hydrogen, combined with reduced temperature, will lead to oxidation if the time within the exit area is sufficiently long. Additionally, the ID surface of the tubing may cool more slowly than the OD, causing inconsistent oxidation. Countermeasures include increasing the tubing’s travel speed, increasing the hydrogen flow rate over all tubing surfaces, and applying a nitrogen curtain at the exit to dilute air ingress and assist in cooling. There are technological, safety, and cost considerations associated with each countermeasure. Contact Air Products’ technical specialists for assistance at 800-654-4567.
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  • My ceramic carrier tiles are deteriorating faster than expected. Could my atmosphere be affecting it?
    Robert Kelly
    Principal Applications Specialist

    Refractories are affected by atmospheres in several ways. Although stable at room temperature, a number of oxides are reduced in the presence of hydrogen or free carbon at elevated temperatures—thus shortening their lives. The customer's process and desired output dictate the design atmosphere. However, crystallography of the ceramic material will have a major impact on its resistance to that atmosphere. By understanding the effects of atmosphere gases on refractories and by selecting refractories that are more stable at operating temperatures and in the presence of specific gas species, you can enhance the performance of your furnace. Air Products' engineers can work with you to optimize your process. Give us a call at 800-654-4567 to schedule an audit of your operation.
    Traditionally, high-pressure gas cylinders have been the supply mode for users in the low- to medium-volume range. This has left companies vulnerable to safety risks associated with moving cylinders and exposure to high pressure. Consolidating to a centralized microbulk system eliminates the need to handle cylinders and reduces the risk of product mix-up. Further benefits include decreased exposure to high-pressure containers and reduced traffic congestion with less frequent supplier deliveries.

    Air Products developed the microbulk supply option as a cost-effective, reliable alternative to high-pressure cylinders for nitrogen, argon, oxygen and carbon dioxide supply. In addition to efficient and flexible storage systems, innovative piping solutions are available to help you have a smooth transition from cylinders to microbulk.
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  • How can I provide customer documentation proving my heat treat process was controlled while treating their products?
    Quality programs that require information about how you process a part for your customers are becoming more common. Understanding what variables you control and what effect they have on your parts is an important step in starting this effort. Variables such as temperature, time, atmosphere flow rates and composition, and utility consumption are good places to start tracking.

    A monitoring system makes this task easier day to day and increases the accuracy of recorded data. Air Products' PURIFIRE® process management system automates data monitoring and collection, and provides additional benefits such as remote monitoring of your process, alarming to indicate problems, and custom report generation for customer documentation. Our engineers help you determine what variables are important for you to monitor and then customize a system that fits both your specifications and those of your customers.

    Benefits such as reduced scrap, elimination of manual data collection, faster problem troubleshooting, and increased product quality can enhance your customer relationship and help your bottom line.

    For more information please call us at 800-654-4567.
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  • I know my flowmeter tells me that I have a certain gas flow rate, but how can I be sure?
    Flowmeters must be sized properly for each particular application, type of gas, gas pressure, and operating range. First, make sure that your flowmeter is calibrated for the specific gravity of the gas that you are metering. Check the label or the glass tube of the flowmeter or call the manufacturer to be sure. Second, operate the flowmeter only at the pressure for which it was calibrated. As an example, a variable-area flowmeter calibrated for 80 psi and reading 1000 scfh will really only be delivering 760 scfh if it is operated at 40 psi. This is a 24% error! Third, for best accuracy and to allow room for adjustment, size the flowmeter so that your normal flow rate falls within 30%–70% of full scale. These three steps will help ensure that you have good control over your gas flows and, ultimately, your process.

    For a free copy of Gas Atmosphere Analysis Guidelines, please call 800-654-4567.
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  • What is the optimum atmosphere system for furnace brazing stainless steel components?
    Tom Philips
    Sr. Principal Applications Engineer

    Traditionally, the atmosphere used in stainless steel brazing has been dissociated ammonia. However, due to cost, safety and environmental concerns with the storage and use of anhydrous ammonia, companies are converting to a nitrogen/hydrogen blended gas mixture. A nitrogen/hydrogen atmosphere can also help you improve flexibility in your operation and minimize the potential for nitriding.

    If you need to produce high quality, bright, stainless steel components, an atmosphere composition with a minimum concentration of 25% hydrogen should be adequate. Or, you can achieve higher corrosion resistance and better hermetic sealing for your steel components with an atmosphere containing up to 80% hydrogen.

    To produce a well brazed joint, it’s important that your brazing furnace has metal muffle and that the dew point in the furnace’s hot zone is maintained below -40oF. It is also critical to keep the oxygen content in the cooling zones below 15 ppm (parts per million) to help avoid oxidation and discoloration of the stainless steel.

    For more information and help designing an optimum atmosphere system for your operation, get in touch with an Air Products applications engineer by calling us at 800-654-4567.
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  • I use high-pressure gas cylinders and am concerned about safety. Is there a better way?
    John Tapley
    Microbulk Business Development Manager

    Traditionally, high-pressure gas cylinders have been the supply mode for users in the low- to medium-volume range. This has left companies vulnerable to safety risks associated with moving cylinders and exposure to high pressure. Consolidating to a centralized microbulk system eliminates the need to handle cylinders and reduces the risk of product mix-up. Further benefits include decreased exposure to high-pressure containers and reduced traffic congestion with less frequent supplier deliveries.

    Air Products developed the microbulk supply option as a cost-effective, reliable alternative to high-pressure cylinders for nitrogen, argon, oxygen and carbon dioxide supply. In addition to efficient and flexible storage systems, innovative piping solutions are available to help you have a smooth transition from cylinders to microbulk.
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  • I’m experiencing intermittent oxidation in my furnace. Could leaks in the nitrogen houseline be the problem?
    Don Bowe Don Bowe
    Sr. Applications Engineer

    Yes, leaks in any pressurized high-purity gas line can cause intermittent oxidation. There are several possible causes. One is through retrodiffusion—the movement of impurities from the surrounding air to a high-pressure, low-impurity gas houseline. This is driven by concentration gradients, not pressure gradients, and is aggravated by changes in flow rate, pressure or piping temperature.

    Air Products industry specialists can help you determine the cause of your problem. Since the oxidation is intermittent, you’ll need to continuously monitor your nitrogen houseline for leaks with a trace oxygen analyzer. For combustible gas lines, a combustible gas sniffer can also be used. Once impurities are found, the source of the leak can be identified using various techniques, including soap bubble testing, static pressure testing or helium mass spectrometry. Leaks often occur in weld cracks, mechanical joints, valve packing and loose fittings.

    To help minimize wasted product and part oxidation, call us for a leak detection or full process audit at 800-654-4567.
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  • Is it true that NFPA 86C has changed?
    Mark Lanham
    Applications Engineer

    Yes, it's true. In fact, NFPA 86C no longer exists. The requirements for "Industrial Furnaces Using a Special Processing Atmosphere," formally defined in the 1999 version of NFPA 86C, have been incorporated into NFPA 86 as of July 18, 2003. Now, NFPA 86 combines the furnace safety requirements for all types of industrial furnaces, including Class A – Food and Baking Ovens, Class B – Melting Furnaces, Class C – Furnaces Using Special Processing Atmospheres, and Class D – Vacuum Furnaces.

    The previous contents of NFPA 86C are now primarily found in Chapter 11 of NFPA 86. A notable change is that NFPA 86 recommends that users of Class C furnaces include a low temperature alarm panel to indicate an overdraw condition on the ambient air vaporizers used for emergency purging. Previously, NFPA 86C required the use of a low temperature flow-restricting device that could potentially limit available purging capacity. Air Products' PURIFIRE® nitrogen supply monitoring system is designed to help you comply with this new recommendation.

    Users of furnaces with special processing and flammable atmospheres should fully understand the requirements and recommendations of NFPA 86 and determine how the changes from the old NFPA 86C may affect their furnace operations. For help in understanding these specifications or for more information about our PURIFIRE nitrogen supply monitoring system, contact us at 800-654-4567.
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  • What nitrogen purity do I need for my heat treatment process?
    Rob Edwards
    Heat Treatment Specialist

    That depends on your process. Nitrogen based atmospheres for metals processing have been successfully proven over many years, and due to the enormous range of requirements in furnaces for various materials and surface needs, the use of gas mixtures is now an industry standard. Different products can tolerate differing concentrations of oxidising components in the furnace atmosphere due to additional reducing or reactive components in the blend. For this reason, the use of on-site generated nitrogen with residual amounts of oxygen can be tolerated. By understanding your oxygen tolerance levels we can help you reduce your costs.

    The paper below will give you an overview of the different systems for nitrogen generation and the appropriate oxygen concentrations for different products and materials in furnaces. For most materials, although free oxygen is not tolerable, some oxidising impurities may be permitted. In these cases, the on-site production of high purity nitrogen for the heat treatment of very sensitive materials may be commercially viable. Examples and descriptions of these systems will also be provided in the paper. Click here to view our expert paper.
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  • Can I determine if the oxidation in the cooling section of my continuous furnace is caused by air ingress or a water leak?
    Tom Philips
    Sr. Principal Applications Engineer

    A simple copper/ steel test can differentiate oxidation by air (O2) or water (H2O). The test is performed by sending a piece of clean bright copper strip alongside a piece of clean carbon steel strip through the continuous furnace and observing the oxidation on each test coupon. Take care to keep the furnace temperature below 1981˚F, the melting point of copper. The steel strip will discolor or oxidize if the atmosphere has an air or water leak; however, the copper strip will only oxidize if an air leak is present. You can use this test for nitrogen-based or generated type atmospheres like endothermic or dissociated ammonia. And it can be done without oxygen or dew point analyzers.

    For more details on this and other atmosphere troubleshooting tips, give us a call at 800-654-4567.
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  • How can I prevent copper filler metal from spreading away from the brazed joints in my steel parts?
    Tom Philips
    Sr. Principal Applications Engineer

    In furnace brazing, this tendency for the melted copper filler to flash and spread is generally caused by one of four factors:

    • Your brazing zone temperature is set too high. Copper melts at 1984ºF. For carbon steel brazing, the brazing zone should be set at 2050 ± 10ºF.
    • The reducing power of your atmosphere is too high, caused by too low a dew point or too high a concentration of hydrogen in the brazing zone. For carbon steels in a muffle type furnace, dew points should range from -10º F to +10ºF, with 5% hydrogen.
    • The joint gap is too wide, producing lower capillary forces for the melted copper to flow into the joint; this causes the copper to flow away from the joint.
    • The part is in the "hot zone" of your furnace for too long.

    You can help prevent this tendency by avoiding these scenarios.

    For a free copy of our technology guide, "Introduction to Furnace Brazing," please call us at 800-654-4567.
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  • Can I remotely monitor what’s happening in my furnaces and other process equipment while I’m away from my plant?
    Chris Ward Chris Ward
    Engineering Associate

    With the proper instrumentation and controls, you can securely monitor and control your heat treating or thermal process from nearly anywhere in the world! This is possible using a variety of hardware and communication methods, including Internet, dial-up, and cell phones. Alarm and warning notifications can also be proactively delivered to you so you can react to upsets, trends, and events before it’s “too late.” It’s important to identify the key parameters, equipment and instrumentation you want to monitor, and then select the hardware and software that best match your needs. Contact Air Products’ team of remote process monitoring and control specialists at 800-654-4567 for an assessment and recommendations as to how to get started.
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  • How do I know if I’m wasting gas due to leaks in my gas piping?
    John Green
    Research Technician

    Gas piping leaks can result from various conditions, including improper thread sealing, missed brazed joints, defective piping, over pressurization, or even vibration and shocks. A pinhole leak can cost you tens of thousands of dollars per year, depending on the size, number and severity of the leak(s). There are many ways to detect leaks; for instance, using soap tests, pressure drop tests, mass spectrometry or thermal conductivity tests. They all have their place; however, they also often come with limitations in precision, speed, difficulty or cost.

    Air Products’ leak detection service can identify and repair costly leaks in your piping to help improve your part quality and bottom line.

    In a short video, various methods for identifying leaks are described in more detail. You can view it online at www.airproducts.com/experts2. If you’d like to speak to a specialist about a leak detection audit of your facility, give us a call at 800-654-4567, and mention code 833.

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  • What are the recommended procedures to safely introduce a flammable atmosphere into a continuous belt furnace?
    Tom Philips
    Sr. Principal Applications Engineer

    For sintering and brazing atmospheres in a continuous belt type furnace with open ends, you must follow NFPA 86 Standard for Ovens and Furnaces. Typically, atmospheres containing greater than 4% hydrogen in nitrogen are considered flammable. In fact, any mixed atmosphere—even if it contains less than 4% hydrogen—is considered “indeterminate” and must be treated as if it were flammable.

    NFPA 86 recommends you satisfy the following conditions before introducing any flammable or indeterminate atmosphere is into the furnace:

    • At least one zone of the furnace must be hotter than 1400oF.
    • The furnace must be purged with an inert gas until the atmosphere analysis indicates it’s below 50% of its LEL (lower explosive limit). General recommendation is to use five volume changes of inert gas flow.
    • There must be visible indication of purge flow. Plus, purge piping should have normally open solenoid valves.
    • The atmosphere system should be designed with interlocks so the flammable gases are shut off using normally closed solenoid valves in the event of power failure, a temperature drop below 1400oF, or insufficient flow of the main atmosphere component.

    Download a copy of our paper about the impact of temperature on flammability limits and furnace safety. Or, contact us online or call
    800-654-4567.
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