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Tag Archive: Corrosion Resistant Heat Exchangers

  1. Heat Exchanger Material Selection Based on Common Criteria

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    With so many factors to consider in choosing a material for your shell and tube heat exchanger, you may have a lot of questions. To start, you’ll need to decide which criteria are most critical to your operation. Criteria like:

    • thermal efficiency
    • cost
    • availability
    • corrosion resistance
    • cleanability
    • durability

    You can then weigh the pros and cons of the options that best meet your priorities, since there is typically more than one good alternative. For example, the best material for heat transfer may not be sanitary enough for your application; or the most corrosion-resistant option may far exceed your budget. In most cases, there is a heat exchanger material option that can balance most of your priorities.

    Here are a few tips and suggestions for evaluating the heat exchanger material options based on these common criteria.

  2. Rouging: What it is and how to avoid it

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    Pharmaceutical manufacturers carefully choose their process equipment to ensure a completely sanitary final product. Most commonly, manufacturers turn to stainless steel shell and tube heat exchangers and other equipment, Pharmtech.com explained. Not only is it affordable, but it’s very durable, stain resistant and has a low risk of corrosion.

    Though stainless steel is highly resistant to corrosion, it’s important to realize what risk there actually is for this equipment to wear down or become unsanitary. Though titled “stainless,” the reality is that steel of any kind can actually become stained. Stainless steel just wards off this reaction for longer than others.

    Stainless steel resists staining by forming a passive layer filled with oxides. The layer forms naturally when in the presence of oxygen, and it protects the stainless steel from reacting with any chemicals passing through the piece of equipment.

    Rouging in stainless steel equipment

    Passivation, or the formation of the passive layer, is only possible under specific circumstances. When the chromium-to-iron ratio begins to fall, passivation becomes more difficult and the all-important oxide-rich layer may not form.

    Rouging in stainless steel equipment

    Passivation, or the formation of the passive layer, is only possible under specific circumstances. When the chromium-to-iron ratio begins to fall, passivation becomes more difficult and the all-important oxide-rich layer may not form.

    “Stainless steel is highly resistant to corrosion, but rouging can still occur.”

    Eventually, the stainless steel may begin to corrode. The process usually produces a thin colorful layer with a red, orange or yellow hue. Sometimes it produces pink, purple or brown. This phenomenon is typically called “rouging” for the more commonly seen reddish colors.

    Rouging is not corrosion, but rather the symptom of it. If you see rouging, you know there’s likely an underlying problem of some sort.

    There’s no singular identified cause of rouging, the British Stainless Steel Association pointed out. It’s typically composed of iron oxides, though the exact chemical composition can change, leading to a rainbow of reactions that all fall under the category of rouging.

    Manufacturers who have noticed rouging in their stainless steel equipment often cite causes like poor welding or construction; vulnerabilities in the passive layer; high iron content in materials that come in contact with the equipment; and surface contamination, including small steel particles or dust that lands on the equipment, according to Pharmaceutical Engineering.

    The truth is, though, that no one really understands completely how to predict rouging or exactly what causes it, Michelle Gonzales explained in Pharmaceutical Engineering. Nonetheless, manufacturers can – and should – take steps to ward off this colorful phenomenon.

    Choose materials of construction carefully

    The most popular stainless steel to use for sanitary shell and tube heat exchangers is 316L because of its low carbon content and its ability to endure heat treatment, Gonzales pointed out. It’s an austenitic metal, which means it’s highly durable and resistant to corrosion.

    Duplex stainless steel is another material that’s highly resistant to rouging. This style of stainless steel is a combination of austenitic steel, like 316L, as well as ferritic steel, which gives it greater durability under heat applications.

    When having a new piece of equipment fabricated, be sure to bring up the subject of rouging with the manufacturer. Explain clearly what the conditions are in your facility and how the equipment will be used, including what products will come in contact with the metal and how you plan on cleaning. Be open to suggestions based on the engineer’s expertise.

    Purchase equipment from a trusted fabricator

    Pharmaceutical manufacturers have reported rouging occurring in pieces of equipment that have flawed welding or construction. The simple way to avoid this is by doing your research and choosing a fabricator that can be trusted to present you with a high-quality piece of equipment.

    Find out whether the fabricator has experience with the type of equipment you need. Also ask about their experience with relevant industry regulations, such as ASME-BPE, which is commonly referred to in pharmaceutical and other bioprocessing manufacturing.

    Understand common causes of rouging

    Though rouging is not always predictable, there are certain conditions that are more likely to cause it than others. For example, elevated temperatures above 140 degrees Fahrenheit for long periods of time are known to cause rouging. Additionally, extreme pH levels and surface damage are all common predecessors of rouging.

    “Rouging is not always predictable, and there’s no specific known cause.”

    In many cases, high temperatures and solutions with a specific pH are necessary for the processes in a manufacturing plant. In these situations, it’s important to periodically check the equipment for beginning signs of rouging or surface damage.

    Rough surfaces encourage rouging more than sleek ones. Electropolishing gives stainless steel a smooth surface where rouging is less likely to occur, according to BSSA. Electropolishing also provides an ideal environment for the passive layer to form and helps it maintain stability.

    Once you’ve experienced rouging once or twice, you will gain an understanding of the unique conditions under which the phenomenon occurs in your specific operation. When you know this, you can be on the lookout for the first signs of rouging.

    Learn how to react to rouging

    When you see rouging, you know that there could be unknown chemical compositions inside your process equipment. As such, it’s important to not use any chemical cleaners or treatments right away.

    Rather, manufacturers need to take the time to evaluate the rouging and determine what’s causing it, what chemicals are involved and whether it’s a danger to the final product. Gonzales pointed out that, sometimes, the rouging looks more worrisome than it really is.

    Correcting rouging can be a time-consuming project, PharmTech.com pointed out. A manufacturer may want to enlist the help of an expert who can identify the ultimate cause and practical solutions to fix it.

    If you’re in the market for a high-quality stainless steel shell and tube heat exchanger, reach out to the knowledgeable and helpful engineers at Enerquip. They have the knowledge and experience to help you select the appropriate material to combat rouging while meeting your codes and standards. They also can passivate your exchanger before shipping it to you.

  3. Hastelloy C-276 resists corrosion in some of the harshest environments

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    Before choosing a shell and tube heat exchanger for your operation, it’s crucial to know the strengths and weaknesses of the many alloy options available to you. Different applications will have different requirements in terms of resistance to corrosion, heat or pressure. Learning about these traits is imperative to choosing an alloy that will best meet your needs.

    Alloys are created when specific metals are combined to create a new material. Each element has particular properties that change the characteristics of the resulting alloy. For example, nickel is typically used to increase strength and the alloy’s ability to harden, but without sacrificing ductility, Manufacturers’ Monthly explained. Nickel-based alloys are optimal for operations that require equipment that has high resistance to stress corrosion cracking.

    There is a whole rainbow of nickel-based alloy options that are durable and corrosion resistant. One of the most popular is Hastelloy C-276, which is composed of:

    • Nickel
    • Molybdenum (which reduces brittleness)
    • Chromium (which improves ductility and wear resistance)
    • Tungsten (which offers additional corrosion resistance)

    How it’s made

    When choosing an alloy for a shell and tube heat exchanger, it’s not enough just to choose a material that meets your needs. Making sure it meets government regulations and industry standards is also critical. These guidelines are set by a wide variety of entities. One such organization is ISO, which creates international standards for industries ranging from agriculture to technology.

    ISO 15156 is a standard that corresponds to the petroleum and natural gas industries, and includes recommendations and requirements for the materials that help create equipment used in highly corrosive environments. This standard lists five nickel-based alloys that are ideal for use in hydrogen sulfide-rich environments, Manufacturers’ Monthly reported. The five alloys are categorized on their chemical composition as well as the method in which they were formed. Two ways to create alloys are through solution annealing and cold-working.

    According to ISO, annealing is the process of heating the material to a particular temperature and holding it at that temperature until the metal becomes a solid solution. Once cooled, it becomes easier to cut and work with, and isn’t as hard.

    Cold working refers to the manipulation of the material at a temperature below the recrystallization point, according to Total Materia. This can improve strength, though it can make the metal harder to work with. To offset this effect, cold-worked metals are often intermittently annealed.

    Reducing the hardness is important in some applications, Manufacturers’ Monthly pointed out. Cold-worked nickel alloys can make great tubular structures as a part of larger pieces of equipment, as long as the hardness is lower than 40 on the Rockwell hardness scale.

    Standing up to hydrogen sulfide

    ISO 15156 also offers recommendations on how to address areas where hydrogen sulfide is abundant. This chemical compound is commonly found in natural gas and crude oil, and tends to collect in spaces with little air flow, according to the Occupational Safety and Health Administration. As such, it’s highly abundant in offshore drilling applications.

    “Hydrogen sulfide can wreak havoc on the wrong material.”

    Additionally, hydrogen sulfide can be especially abundant in sour reservoirs, or those where abiotic and biotic reactions begin to occur. Manufacturers’ Monthly reported that sour reservoirs in the northern Caspian Sea can have hydrogen sulfide contents as high as 20 percent.

    Hydrogen sulfide can wreak havoc on the wrong material, and as ISO 15156 points out, equipment failure due to chemical corrosion can pose great health and safety risks to those in the vicinity of the operation, as well as the environment. Noting how resistant to hydrogen sulfide corrosion a material is should be a key priority to manufacturers working in these industries.

    Hastelloys 825, 625, and C-276 that are solution-annealed can work efficiently in high-hydrogen sulfide environments, Manufacturers’ Monthly pointed out. Hastelloy C-276 is particularly useful and able to withstand higher pressures of hydrogen sulfide than the 825 and 625 alloys.

    Acidic Environments

    In addition to hydrogen sulfide, plenty of chemical compounds can induce corrosion or other weakening or undesirable reactions. Acidic environments are particularly damaging to many alloys. Hastelloy C-276, for example, doesn’t hold up well to nitric acid, Corrosion Materials noted. However, it has shown considerable resistance to negative effects caused by other common acids and compounds, including:

    • Hydrochloric acid.
    • Sulfuric acid.
    • Acid chlorides.
    • Phosphoric acid.
    • Acetic and formic acids.
    • Hypochlorites.
    • Wet chlorine gas.
    • Acetic anhydride.

    Given the ability to withstand a host of potentially dangerous substances, Corrosion Materials commented that Hastelloy C-276 is one of the most corrosion-resistant materials on the market today.

    Heating up Hastelloy

    As metals warm up, their physical properties begin to change. It’s important to know what limitations your alloy has under certain temperature conditions. The nature of the operation, as well as environmental factors, must be taken into consideration before choosing an alloy. For example, temperatures around oil drilling operations can rise quickly, regardless of climate. But an oil rig near the equator will likely have different requirements than a rig in Alaska or Russia.

    Hastelloy C-276 has a melting point of between 2,415 and 2,500 degrees Fahrenheit, according to Corrosion Materials. As such, it can withstand incredibly high temperatures:

    • At 2,000 degrees Fahrenheit, it maintains oxidation resistance.
    • At 1,900 degrees Fahrenheit, it continues to fight pitting, corrosion and cracking.
    • At 1,600 degrees Fahrenheit, it can still carry loads.
    • At 1,000 degrees Fahrenheit, it has a thermal conductivity of 11 Btu/ft•h•°F.

    Choosing a powerful alloy for your shell and tube heat exchanger is a critical decision to make. Depending on where you are operating, you may have very specific needs. In many cases, Hastelloy C-276 has the ability to withstand the harshest environments while continuing to work efficiently. However, it’s best to speak with a knowledgeable professional before making any concrete decisions.

    If you’re looking to invest in equipment that is highly corrosion resistant, durable and long-lasting, give consideration to a nickel-based alloy. For more information about how your operation can benefit from incorporating Hastelloy C-276, reach out to the engineers at Enerquip. These professionals are among a select few in the shell and tube heat exchanger space that have experience incorporating Hastelloy C-276 in process equipment.

  4. Duplex stainless steel makes an excellent choice for manufacturers

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    Designing a shell and tube heat exchanger involves many decisions that must be made carefully and intentionally. One crucial choice that’s important to every exchanger is the material from which it’s made.

    Engineers have a wide variety of options when choosing the right material from which to build a shell and tube heat exchanger. Steels and alloys come in various compositions, each with their own unique properties, benefits and disadvantages.

    What makes one material more suited for an exchanger over another largely depends on how the equipment will be used – including what chemicals will be introduced to it, the temperature and pressure settings it will be subjected to, and what kind of environment it will be housed in. In addition, the composition material must be cost-effective and easily acquired by the manufacturer.

    Many manufacturers find duplex stainless steel to be an ideal material for shell and tube heat exchangers in a wide variety of industries, including the pharmaceutical, oil and gas and biotechnology industries. Duplex stainless steels are composed of ferrite and austenite, and thus can withstand high-stress applications.

    Ferrite and austenite

    Stainless steels come in many forms. Austenitic stainless steels are the most popular, as they are the most versatile. They are very weldable, according to the American Welding Society, but they do have a tendency to crack when overheated or under too much pressure.

    “Duplex stainless steels can withstand high stress applications.”

    Ferritic stainless steels are another good option for a variety of applications. Though they aren’t as durable as austenitic steels, they have high resistance to corrosion and are fairly formable, making them a versatile solution.

    When combined to create duplex stainless steel, the best properties of both the austenite and ferrite come out. Austenite lends its strength while ferrite resists corrosion and cracking.

    Duplex stainless strength
    Since duplex stainless steels are so strong, engineers have found they can reduce the weight and thickness of materials made from it while still maintaining durability and corrosion resistance. According to Process Heating, duplex stainless steels usually have double the strength of austenite stainless steel. Thinner tubes mean less material is needed, reducing the building cost of the equipment. The exchanger may also be able to be more efficient because of the lower weight.

    In addition to having a strong, efficient exchanger, manufacturers seek out those that can resist corrosion best. Corroded or pitted tubes become weak in time and can eventually spring a leak. A cracked tube is never a good thing, and can cause:

    • Fouling
    • Cross contamination
    • Damaged tube sheets, shells or other important features of the exchanger.

    Damaged tubes are also difficult and expensive to replace.

    Corrosion can occur anytime a substance is introduced to the exchanger that naturally reacts with the chemical composition of the tubes or shell. Chlorine is a common cause of pitting, and can be a major concern for manufacturers operating in a chlorine-heavy environment with an austenite stainless steel heat exchanger. Duplex stainless steels, on the other hand, resist the ill effects of chlorine well and are sought after in industries that work with chlorine frequently.

    Duplex stainless steels’ ability to withstand high temperatures also make them a prime choice for shell and tube heat exchangers. When chloride and tensile stresses are both at play, it only takes a temperature of 150 degrees Fahrenheit to endanger austenitic stainless steel, according to the International Molybdenum Association. When duplex stainless steels are in use, however, temperatures can rise to around 250 degrees before they become risky.Rouging is another problem that some industries need to fend off. Rouging refers to the oxygenation of the metal, represented through a rainbow of colors including red, blue, gold, gray and dark brown. However, IMOA noted that the causes of rouging aren’t always completely understood, but can be greatly affected by the grade of steel equipment is made from.

    When rouging builds up on equipment in the pharmaceutical and biotechnology industries, it’s imperative that it gets cleaned to prevent product contamination. The biggest challenge in this is the time and money that goes into this process. Choosing a rouging-resistant material to build equipment is ideal. IMOA explained that the 316L grade of austenitic stainless steel is a favorite among the pharmaceutical industry because it is resistant to rouging to a certain extent. However, duplex stainless steel has also been found to be just as resistant to it, if not more so.

    Cost benefits

    In addition to information about how well one alloy performs in operation compared to another, manufacturers also need to know whether the material is available to them, how difficult it is to obtain it and how much it costs. Process Heating noted that duplex stainless steels have lower nickel and molybdenum contents compared to austenitic stainless steels, bringing down their price point. It also protects the alloy from a volatile raw materials market, which can cause alloy and metal prices to swing upward dramatically at times.

    “Lower nickel and molybdenum contents bring down the price point of duplex stainless steel.”

    Additionally, since the stronger duplex stainless steel can be made durable with less material than an austenitic or ferritic steel, the cost to build it can be reduced.

    Manufacturers also need to look at cost comparisons over the long term. For example, a material that costs less upfront but has weak properties will eventually cost more in the long run through maintenance and replacement costs. Since duplex stainless steel can stand up to higher temperatures and pressures, as well as more corrosive materials, than austenitic or ferritic stainless steels, less maintenance would theoretically be needed to keep the exchanger in working order.

    Using equipment that is made from the proper elements is crucial to having a healthy and productive manufacturing operation. If you’re in the market for a long-lasting shell and tube heat exchanger,

    speak to the engineers at Enerquip, where we’ll be able to identify the best materials and configuration for your operation.