{"id":17297,"date":"2023-10-03T14:43:40","date_gmt":"2023-10-03T19:43:40","guid":{"rendered":"https:\/\/blog.wika.com\/us\/\/?p=17297"},"modified":"2025-06-11T14:44:49","modified_gmt":"2025-06-11T19:44:49","slug":"how-butter-pad-affects-tubeskin-thermocouple-accuracy","status":"publish","type":"post","link":"https:\/\/blog.wika.com\/us\/products\/temperature-products\/how-butter-pad-affects-tubeskin-thermocouple-accuracy\/","title":{"rendered":"How Butter-Pad Affects Tubeskin Thermocouple Accuracy"},"content":{"rendered":"

A butter-pad allows refineries to weld new thermocouples onto it rather than directly on the bare furnace tube, as repeated welding damages the tube\u2019s integrity. However, using this weld overlay affects the accuracy of temperature readings. WIKA conducted a series of IR scans, CFD simulations, and tests to quantify the temperature deviations caused by using a butter-pad with tubeskin thermocouples.<\/strong><\/p>\n

Temperature monitoring is essential to the efficient operation of fired heaters. Accurate temperature readings allow refineries to operate with furnace tubes very close to the creep, and to minimize fouling and coking inside those tubes.<\/p>\n

Tubeskin Thermocouples, Welding Issues, and Butter-Pads<\/strong><\/h2>\n

Thermocouples are accurate, long-lasting temperature sensors. However, because tubeskin thermocouples (TSTCs) are subjected to extreme temperatures, their reliability is limited to a few turnaround cycles, after which they should be replaced. Herein lies the problem:<\/p>\n

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  1. TSTCs are typically welded onto the tube surface.<\/li>\n
  2. Replacement TSTCs need to be installed near the failed TSTCs\u2019 existing location.<\/li>\n
  3. The metallurgy of certain tubes does not allow for welding after extended use.<\/li>\n<\/ol>\n

    Therefore, refineries are limited in their ability to weld new thermocouples directly onto bare tubes when old thermocouples fail.<\/p>\n

    One of the ways to overcome the furnace tube\u2019s metallurgical limitations is with a butter-pad. This is a predefined thickness of weld material installed on the tube surface. The new TSTC is then mounted on this weld overlay rather than on the bare tube, thereby avoiding any issues with tube integrity or requiring extensive post-weld heat treatment (PWHT).<\/p>\n

    However, using a butter-pad has its own issues. We wanted to understand how much this extra layer of metal impacted temperature measurement accuracy.<\/p>\n

    Methodology: Testing the accuracy of TSTCs installed on a butter-pad<\/strong><\/h2>\n

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    Radially (longitudinal) installed butter-pad<\/p><\/div>\n \n

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    Circumferentially (transversal) installed butter-pad<\/p><\/div>\n <\/p>\n

    The variables of this project:<\/p>\n