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Tag Archive: ASME Code 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 and 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.

    Thermal Efficiency

    Since the goal of a shell and tube heat exchanger is to transfer as much heat as possible between the product (typically in the tubes) and the utility fluid (typically in the shell), the thermal conductivity of the tube material is a key factor. Based on thermal modeling comparisons using HTRI software, copper and copper/nickel are typically the most conductive material available for exchanger tubes. Carbon steel, stainless steel and higher alloys are slightly less efficient, but all perform similarly. Plastics, graphite composites and ceramics are the least conductive materials available.

    Thermal performance can also be enhanced through modification to tubes, such as corrugating, adding external fins to the tubes, or by adding twisted tape turbulators to the inside of the tubes. However, because thermal performance among metals is so similar, this is not usually a high priority factor in heat exchanger material selection.

    Cost & Availability

    Material pricing and availability can fluctuate based on market supply and demand, the quantity required for your exchanger, and the components needed. Copper was a low-cost option a few years ago, but now due to supply, it is more expensive than stainless steel. Conversely, Titanium used to be one of the most expensive alloys but is now more reasonably priced. At the time of this article, here is the relative ranking for some of the common metal material options by price from lowest to highest: carbon steel, 304/304L SS, 316L SS, Duplex 2205, Titanium, AL6XN, Duplex 2507, Hastelloy C-276, Hastelloy C22, Monel 400, Alloy 625, and Nickel 200.

    Typically, the higher priced alloys are also in shorter supply, due to lower demand and the higher cost of carrying inventory. This directly affects the lead-time of these materials, often by 2-4 times that of more common alloys like carbon steel and stainless steel. Quantity of these higher alloys can also greatly affect price. Steel mills typically don’t run small batches of tubes or plate or they will charge for the entire mill run if they do.

    Enerquip Bundle

    U-tube water cooler built with 2205 Duplex tubes – an austenitic-ferritic stainless steel that stands up to chloride stress corrosion.

    Shell Side and Tube Side May Be a Combination of Materials

    The shell side and tube side of an exchanger can be built from different materials of construction. It is common to use a more corrosion-resistant and/or sanitary alloy for the product side of the unit, while using a lower grade alloy for the utility side of the exchanger.

    If a higher alloy is the material selection, it is more economical to use it on the tube side of the unit instead of the shell side. However, be aware that for tubing, seamless tubes are almost double the price of welded type tubes, so this should be considered as well. You may find that seamless 316L stainless tubes cost more than welded Duplex 2205 tubes, for example.

    Common parts such as fittings are less likely to fluctuate than raw materials like plate stock, tubing and forgings. There are ways to help reduce cost when using higher alloy components. Consider lap-joint flanges, where the product contact nozzle (stub end) is high alloy, while the flange is stainless or carbon steel. These also aid in ease of installation, ensuring bolting alignment with existing, mating piping or equipment. Larger parts like tubesheets, flange rings and channel covers can often be made from a lower alloy base material that is clad with a thinner layer of high alloy to reduce cost.

    Supplier Resources

    Another factor to consider when evaluating the various alloys is the number of suppliers that work with these materials, since this can affect cost and delivery. There are many fabricators that build exchangers from carbon steel and copper, so competition is high, prices are low, and lead-times are generally fast. There are fewer suppliers that work with the alloys from 304/304L SS up through the Incoloy series, but enough to keep prices and lead-times reasonable. Fabricators must have ASME compliant weld procedures for these alloys to provide pressure vessels such as shell and tube exchangers, which are classified as National Board Registered pressure vessels. Not all fabricators have these procedures for all materials, so it is wise to verify your preferred fabricator’s capabilities when considering alloy options. Since Titanium, Zirconium and Tantalum require specifically controlled environments for fabrication, supplier options are more limited. This specialty niche can be expensive with longer lead-times, so these materials are normally only used when applications require nothing less.

    Dispelling the carbon steel is cheaper myth: For most small and mid-sized exchangers up to 24 inches in diameter, it can be less expensive to upgrade carbon steel shells to a material selection of 304 stainless steel. Although the material cost is a bit higher for the stainless per foot, stainless eliminates the labor cost for priming and painting the exterior, which typically offsets the material cost difference. This, combined with reduced maintenance costs and added durability, makes stainless a better long-term value.

    Corrosion Resistance

    If corrosion resistance is critical for your application, it is best to consult a metallurgist to discuss the operating conditions and request their recommendation. Most reputable high alloy providers have metallurgists on staff. Rolled Alloys has proven to be a good resource, with responses and recommendations provided within 24 hours. Corrosion resistance charts can also be helpful for less critical applications where corrosive element concentrations are low.

    Many people are not aware that carbon steel is not only corrosive itself but can cross-contaminate stainless and higher alloys and cause them to rust. That is why it is not a good idea to use regular steel wool to clean your stainless sinks and silverware, as it will cause rouging. The same affect can be seen in heat exchangers containing carbon steel parts. Rust from carbon steel parts will attack the higher alloy parts of your equipment, potential causing premature failure. However, there are also cases where carbon steel offers better resistance to stress corrosion cracking than stainless steel, so the risks of rust corrosion need to be weighed against stress corrosion cracking during material selection.

    Copper and CuNi have moderate corrosion resistance but tend to discolor and scale easily. These softer materials are commonly used for shell and tube exchangers in utility applications, where the non-sanitary tube material and carbon steel shells do not create a product contamination issue.

    Stainless steel has become a very common heat exchanger material selection for low to moderate corrosion resistant applications. Since 316L SS is more corrosion-resistant than 304L SS, it is often selected for the tube side of an exchanger, while the shell is made from 304L SS. If additional corrosion resistance is needed, then the Duplex stainless series (2101, 2205, or 2507) is considered. Continuing up the ladder of corrosion resistance AL6XN is followed by Hastelloy alloys C-276, C22 and C2000. For higher corrosion resistance, Monel 400 and Alloy 625 are considered, before evaluating the extreme corrosion resistance of Titanium, Zirconium and Tantalum. Note: Each alloy has a specific resistance level to specific chemicals or solutions, so it is best to consult with a metallurgist during the selection process to match your process with the proper material.

    Enerquip wiped film evaporators

    This custom pair of wiped film evaporators were built for a hemp processing application. Their 304L stainless steel straight tubes were bright annealed to reduce surface oxidation.

    Cleanability

    If ease of maintenance and integrity of your product quality are high priorities, then materials that are easier to clean and maintain should be selected. The materials must stand up to your preferred cleaning regimen – whether it be chemical, mechanical or ultrasonic cleaning (or a combination). Acids, caustics and chlorides are common in cleaning solutions, but can be harmful to metals in higher concentrations or elevated temperatures. Once you decide on a material of construction, companies that provide these cleaning chemicals, like Ecolab or AFCO, can provide recommendations on concentrations that are suitable.

    Sanitary Markets Require Stainless

    In sanitary industries such as food, beverage, dairy, pharmaceutical and cannabis processing, product contact surfaces must be stainless steel or a higher alloy, and cleanable, to comply with strict guidelines such as FDA, ASME BPE or the 3-A Sanitary Standards. Because the surface finish of the material impacts its cleanability, these industries require product contact surfaces to be polished to a specific Ra (roughness average) for food, beverage and dairy, and for pharmaceutical applications. Some pharma applications also require electropolishing, which removes a very thin layer of material, aiding cleanability further. Smoother material surfaces also resist build-up and scaling on both the product and utility side of an exchanger. Therefore, many companies avoid carbon steel and copper, which can become more porous as they corrode, encouraging scaling and fouling.

    Durability

    For situations where durability is not a high priority, low cost, catalog type heat exchangers constructed from copper and carbon steel may be appropriate. Many HVAC applications fall into this category, where replacing parts from time to time is normal and acceptable. However, in production facilities, where process equipment is pushed to its limits on an ongoing basis, durability is much more critical. Equipment failures can contaminate product, stop production and even be dangerous.

    It is important that the material selected for your heat exchanger meets ASME Code requirements and can operate for an extended time at your operation’s design pressures and temperatures. The materials must withstand your cleaning regimen and environmental factors such as moisture, dust, and temperature extremes.

    In situations where dissolved solids and high tube velocities can take their toll on heat exchanger parts, it makes sense to use materials that are erosion resistant. When carbon steel and copper exchangers are designed, ASME Code requires a corrosion allowance be added to the material thickness. This is added to account for anticipated corrosion and loss of material thickness over time. These exchangers may also include anodes that corrode away before the exchanger parts do. These can be monitored and replaced periodically. When higher alloys are used in place of carbon steel and copper, these corrosion allowances are no longer required, resulting in thinner, lighter materials in a more durable piece of equipment. Stainless and higher alloys do not require painting to protect their exterior finish from corrosion, so there is no flaking and peeling paint to contend with, decreasing maintenance time and expense.

    The experts at Enerquip are happy to assist you by providing options for your shell and tube heat exchanger materials of construction. Since they work in many alloys, they can provide suggestions and feedback to help you narrow down your choices based on your priorities. For more unique cases, they will refer you to credible metallurgists who can help you finalize your heat exchanger material selection.

    Click here to learn more about Enerquip’s custom exchangers.

    Article Author: Ron Herman, Director of Business Development

    Ron Herman, Enerquip Director of Business Development

  2. Shell and tube heat exchanger standards: Part 2

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    No matter what industry you operate in, standards matter. They are the measuring stick against which companies and consumers can measure products and choose which ones best suit their needs. They are a way of demonstrating precision and care in the manufacturing of each model of a product.

    There are some industries in which meeting standards is crucial to ensuring product safety and quality. The food, beverage and dairy industries must meet guidelines set by the Food and Drug Administration to ensure products are safe for human consumption. The pharmaceutical industry must also meet these requirements so that each medicine is not only safe, but effective.

    What these industries have in common is more than consumer-facing products and FDA regulations; they also rely on shell and tube heat exchangers to help make their products as safe, effective and consistent as possible. In order for these industries to produce food, beverages and medicines that are of high quality, they must use equipment that meets specific guidelines as well.

    There are a wide range of standards a shell and tube heat exchanger can adhere to. Knowing what they mean and which ones apply to your industry and area of operation are important for successfully moving forward.

    ANSI

    The American National Standards Institute has been coordinating the voluntary standardization system in the U.S. private sector for nearly a century. Groups called standards developing organizations work together to develop and improve upon standards.

    ANSI publishes Standards Actions every week, which include calls for comments on standards proposals. In it, suggestions are made along with what machinery the standard changes would apply to. As of last year, more than 240 SDOs were accredited by ANSI, and more than 1,100 American National Standards were in place.

    3-A Sanitary Standards Inc.

    Standards for equipment design used in the dairy industry first came about in the 1920s. There were three interest groups, or associations, that worked to develop the standards: equipment fabricators, regulatory sanitarians and processors. To highlight the three associations’ collaboration, the standards became known as 3-A.

    3-A Sanitary Standards were created and are maintained to ensure that all equipment used in the food, dairy and pharmaceutical industry is kept clean so that all products coming from them are safe for consumption. According to 3-A, the ideal equipment can be mechanically cleaned through a clean-in-place or CIP system, or can be easily taken apart for thorough manual cleaning.

    API 660

    The oil and gas industry is another area in which standards are crucial. Petroleum is used in nearly every aspect of today’s world. It fuels vehicles and heats buildings, but it is also used in textiles, health and beauty essentials, cleaning products and many more applications.

    In the oil and gas industry, there are several standards companies must adhere to. Often, it is the end user or consultant who creates demand for refineries to follow these standards. The American Petroleum Institute designed standards called API Standard 660.

    A newsletter from the CoDesign Engineering Skills Academy noted that these standards were drafted based on industry experience and practical considerations. They provide specifications for the design of a shell and tube heat exchanger for use in the petroleum industry, such as how thick the tubes can be, the type of exchangers allowed in refineries and how thick the tubesheet joints can be.

    As demonstrated in the newsletter’s chart, API 660 has some similar standards as TEMA, though not always. For instance, under API 660, TEMA type P and W exchangers, which have outside packed floating heads and a floating tubesheet that is externally sealed, respectively, are not allowed to be used in a refinery. However, under TEMA’s standards, these can be used in certain situations.

    It’s important to note the differences in standards when working in an industry where meeting regulations can help define the quality of a product. Knowing your customer base and what they value is also critical, as this will help manufacturers determine which equipment and which standards are right for them.

    If you are looking for a shell and tube heat exchanger for your operations, talk to the experts at Enerquip. Their in-house engineering team will understand your needs and be able to determine which standards your equipment needs to meet.

  3. Shell and tube heat exchanger standards: Part 1

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    Shell and tube heat exchangers are important instruments in a wide variety of industries. They are used in refining oil, preparing pharmaceutical products for market, ensuring that food and dairy products are safe to eat and helping breweries create the perfect pint of beer, among other use cases.

    While these industries are widely diverse, they all encounter the same concern: which shell and tube heat exchanger to purchase for their operations. Heat exchangers have a long lifespan, especially when they are made with the highest-quality standards and materials. But, when it comes time to make a new purchase, it’s crucial that it is done right.

    Not only does the configuration matter, but so do the codes and standards the equipment meets. Industry standards help ensure all products are built in the best way possible for customers. It prevents companies from buying subpar products. The American Society of Mechanical Engineers also pointed out that costs and training time are loweredwhen everyone adheres to the same standards and methods of design.

    “Industry standards help ensure all products are built in the best way possible.”

    Ensuring your shell and tube heat exchanger is designed and built in accordance to the correct industry standards is of the utmost importance for a business. If an exchanger does not meet the right criteria, the products may not be suitable for distribution, and a new exchanger or an upgrade may need to be purchased.

    TEMA

    One of the most widely used industry standards comes from the Tubular Exchanger Manufacturers Association. This group updates its set of standards as needed, the most recent being from 1988, according to Thermopedia.

    Under TEMA’s standards, there are three subcategories:

    • Class B, used for chemical processes
    • Class C, used in general commercial applications
    • Class R, generally used in petroleum processing, but can also be used for large-scale processing applications

    The differences between the classes are subtle but important. For instance, the nature of working with petroleum creates a need for heavier and more durable construction, while chemical processing is better done with stainless steel and lighter equipment.

    ASME

    Other common standards shell and tube heat exchangers are built to adhere to are those set by the American Society of Mechanical Engineers. The ASME VIII code refers to the pressurized parts of a shell and tube heat exchanger, according to Thermopedia. These parts are the ones inside the shell, primarily the tubes.

    Section VIII is the one most often applied to shell and tube heat exchangers, though Thermopedia explained sections II and V are also used occasionally. These refer to materials and nondestructive testing, respectively. There are a total of 11 sections in ASME’s standards.

    “Different countries have varying rules regarding standards.”

    ASME was designed to be applied to many different types of equipment, not just shell and tube heat exchangers. Many exchangers will be certified by both ASME and TEMA, as the latter was in part designed to be a supplemental level of criteria for the machines.

    PED

    As heat exchangers are an important piece of equipment for many industries, they are used all over the world. Different countries have varying rules about what standards equipment need to meet to be legal. Because of this, it’s crucial that equipment manufacturers and purchasers know where an exchanger is going, and what the rules are there. It’s also important that anyone buying or using an exchanger be fully aware of the regulations in the country the exchanger will be used.

    The Pressure Equipment Directive is one such international standard that is required in the European Union. PED covers a wide scope of equipment, from boilers to piping to pressurized storage vessels. It also applies to shell and tube heat exchangers.

    PED includes rules about:

    • Materials
    • Harmonised standards
    • Essential requirements
    • Market surveillance
    • Conformity assessment

    Each of these rules is put into place to ensure workplace safety, and that products that are processed with a particular piece of equipment are safe for the public.

    CRN

    Another international standard is the Canadian Registration Number. This is required for any boiler, pressure vessel or fitting that will be in operation in Canada. Acquiring one ensures that the equipment is certified to be used in a specific province or territory.

    The CRN is written with a multi-digit number, a decimal, and one or more numbers or letters that represent a specific territory or province. For instance, “1” indicates British Columbia, while “T” represents the Northwest Territories.

    When purchasing a shell and tube heat exchanger, getting the right certifications is crucial. Enerquip’s team of engineers will know what your industry requires and will work with you to meet your needs.