Insights from industry

High-Temperature Measurement: Expert Insights into Advanced Thermocouple Technology

insights from industryJoep van den BrinkHead of Business Development - Heating & AutomotiveKamet Trading BV

In this interview, industry expert Joep van den Brink delves into the specialized world of high-temperature thermocouples, discussing key differences, innovative designs, and tailored solutions that enhance performance in extreme environments.

Which types of high temperature thermocouples are available on the market?

We typically talk about high temperature thermocouples if temperatures exceed 1200°C. Beyond this point, we usually advise the noble metal thermocouples, such as type S, type R or type B. Equally, for even higher temperatures we normally advise type C and type D thermocouples.

What are the key differences between Type C/D thermocouples and other common types available in the market?

Type C and D thermocouples are specialized varieties of thermocouples used primarily in high-temperature applications, differing significantly in their construction, materials, and performance characteristics compared to more common types like Type K, J, T, and E.

Type C/D thermocouples are made from Tungsten-rhenium alloys, which mean they can measure temperatures up to 2300°C. Type C/D thermocouples can be used in vacuum, inert and reducing atmospheres, but not in oxidizing since this could harm the thermocouples.

Other types of thermocouples have different material compositions, making them less attractive for usage at such elevated temperatures. Type C/D thermocouples are often used as a more economic alternative to thermocouples with noble metal alloys such as type S/R/B thermocouples. But, when type S/R/B thermocouples are the design requirement, another option to reduce costs for high temperature thermocouples could be to opt for a transition style thermocouple.

How does the transition style thermocouple design provide an advantage over traditional designs in extreme temperature environments?

The main advantage of a transition style thermocouple is costs. Often we get requests from customers for a type S/R/B thermocouple with Pt10%Rh sheath which, in most cases, is extremely costly. Furthermore, such a specification is often a bit of an overkill, as the extreme temperatures are typically only encountered at the sensor's tip. In these instances, a transition-style thermocouple can be a suitable alternative.

Thermocouples can then be supplied with a suitable high temperature “hot section” sheath and insulating materials long enough to reach a cooler zone in the furnace or reactor. At this point, a brazed transition can be made to a less expensive thermocouple or compensating material with Inconel 600 or stainless-steel sheath. This eventually comes down as a cost saver for the end customer!

What distinguishes Kamet’s thermocouples from other similar products available in the market?

We typically concentrate on extreme temperatures, which we define as those above 1200°C and under challenging conditions. Below these temperatures, we are selling our mineral insulated thermocouple cables to temperature sensor manufacturers in Europe. However, when temperatures exceed 1200°C, the use of exotic protective sheaths and specialized thermocouple alloys becomes necessary. Moreover, these thermocouples often require additional calibration, X-ray, and leak tests.

Kamet has a profound knowledge of these temperatures and these environments, no matter if it is an oxidizing, inert, reducing or vacuum atmosphere. Thanks to our expertise in materials science and the properties of exotic materials, in collaboration with our manufacturer, ARi Industries, we guarantee the best possible thermocouples for their specific applications. Additionally, we have our own production process for mineral insulated cable, allowing us to manage the entire process—from manufacturing the MI cable to producing the custom thermocouples—all under one roof.

Could you discuss any recent advancements in thermocouple technology that Kamet has pioneered or integrated into its product line?

Our manufacturer ARi has been in the temperature sensing and heating industry since the early 1950s. ARi was among the first pioneering companies to manufacture mineral insulated cables (MI Cables) to improve product performance and reliability. AerOpak and AerOrod are their trademarks for Thermocouple and Heater cables respectively. 

AerOpaks and AerOrods remain at the heart of Kamet’s products and, to this day, they continue to refine and improve that technology.  ARi also has a patent portfolio from wire wound hot junction of Type C & D thermocouples to a more robust mounting for an RTD element and a method of making non-circular cross sectional shape MI Cables.

Could you discuss how you tailor your thermocouples to meet the specific needs of industries such as aerospace or nuclear power, where extreme temperatures are common?

We customize our thermocouples to meet the specific needs of each application. For instance, in the aerospace industry, there is frequently a requirement for AMS2750 calibration, which mandates very strict tolerances on allowed deviation (Type R & S: ±1.8°C or ±0.1%, Type B: ±1.8°C or ±0.25%). In such cases, we ensure that our thermocouples adhere to these standards.

For nuclear applications, hafnium oxide insulation is often necessary due to its properties related to radiation. This type of insulation helps prevent the distortion of signals by radiation from the application.

Another critical factor is the choice of sheath material for the thermocouple. Some thermocouples are exposed to extremely high temperatures combined with specific atmospheric conditions. We therefore first gather as much information as possible from the customer about temperatures/application/industrial requirements/ atmosphere/presence of graphite/etc. before we commence with an offer.

What are some challenges in the thermocouple industry today, and how is Kamet addressing these through its products or services?

One of the main ongoing challenges in the industry is deciding which thermocouple should be used and in what specific environment. Especially for the higher temperatures over 1200°C, it is still difficult to decide which sheath material enhances the lifetime of a thermocouple. Also, when things get really complicated, for example when part of the process is in an oxidizing atmosphere up to 300°C but part of it would also be in a reducing environment where elevated temperatures are present. These applications demand knowledge about materials science as well as knowledge about the application.

Furthermore, as in many industries, supply chain disruptions remain a challenge to this day. To minimize the potential impact, we improved our communication with ARi and work ever closer with our existing vendors.We locate and test raw materials from other suppliers, we apply different designs and we also create new ones using raw materials on hand to make similar products. Hence, there is constant internal communications between us and ARi, and between ARi and their Supply Chaing Planner/Buyer and Product Managers. 

Finally, thermocouples' application environments and requirements continue to get demanding. So, ARi has to constantly find novel solutions via search of new materials, R&D and expanding their product Catalogs.

How does the relationship between Kamet and ARi Industries streamline the process from R&D to production for custom thermocouple solutions?

High precision temperature measurements start with the quality of raw materials used to make AerOpaks and Thermocouples. At ARi they take pride in using only the best materials to make their products. All of ARi’s raw material vendors and their products are subject to rigorous testing.

What role does customer feedback play in the continuous improvement of your thermocouple products?

The role of the customer is crucial for improvement, especially since every application demands its own customized solution. When atmospheric conditions of the application deviate from the depicted situation, it could have an effect on the thermocouple’s behavior. Therefore, customer feedback is very important to further improve our high temperature thermocouples.

How does Kamet support its customers with after-sales service and technical support?

We have a strong customer-focused approach to ensure our clients are engaged at every stage to minimize potential issues. Our process typically begins with an initial discussion with the customer about the challenges they are facing. It is only after we have come up with a customized solution that we provide a quotation. After the quotation phase, when we are awarded with an order, we proceed to create a drawing for customer approval . After the drawing is approved by the client, we typically start production.

Furthermore, our thermocouples are always supplied with 3.1 and calibration reports. If needed, we also deliver extra documentation, such as Xray, helium leak test reports, heat treating and special calibration traceable to NIST.

For after-sales support, we ensure that all our thermocouples are fully traceable. Additionally, for special projects, we arrange discussions between our ARi engineers and the customer to review test results and explore further improvements to our thermocouples. Furthermore, we always provide our thermocouples with warranties.

About Joep van den Brink

Joep is a passionate business development manager with about 9 years of relevant work experience within the industry (e.g. research institutes, aerospace, furnace manufacturing). In those nine years, he has been focused on high temperature applications (>1200°C) in demanding environments. Joep's expertise lies in steering project collaborations between Kamet's technical engineers and clients to develop a customized solution for special applications.

About ARi Industries

ARi Industries has been a pioneer in manufacturing mineral insulated cable to enhance product performance and reliability since its foundation in 1952. Now a leader in the industry, ARi offers a range of metal-sheathed, mineral insulated thermocouple cables, including custom solutions tailored for specific temperature, environmental, and process requirements. All standard AerOpak® cables feature high-purity MgO insulation and meet ASTM E-230 accuracy standards, with extensive inventories maintained for prompt availability. 

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.

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